CT Simulation Research Articles

MSS02 Presentation Time: 3:50 PM: Feasibility of 3D-Printed Endorectal High Dose Rate Brachytherapy Applicator: A Single Patient Case Report

<h3>Purpose</h3> Endorectal brachytherapy is an effective treatment for select patients with rectal cancer, particularly in re-irradiation cases. In the United States, this technique is underutilized. Herein we describe, to our knowledge, the first report of a previously irradiated rectal cancer patient treated with a 3D-printed Endorectal High Dose Rate Brachytherapy Applicator. <h3>Materials and Methods</h3> A 64 year old morbidly obese female who was previously irradiated for endometrial cancer in 2009 presented with newly diagnosed uT3N0, MRI T2N0 rectal adenocarcinoma. Previous radiation records were no longer available other than a treatment summary identifying a total dose of 50.4 Gy in 28 fractions was delivered to the pelvis. Total neoadjuvant therapy was recommended with a watch and wait approach given surgical difficulties in a morbidly obese woman previously irradiated. The mass began 3 cm from the anal verge, extended nearly 5 cm superiorly, and circumferentially involved less than 50% of the rectal lumen. Fiducial markers were placed in the 4 cardinal directions. A 2.5 cm diameter, 18 cm length, 13 multichannel applicator (1 central channel, and 12 outer channels 5mm from cylinder surface) design was designed in <i>Autodesk Fusion 360</i> to ensure adequate coverage (see figure 1). 3D printing was achieved with a FormLabs 3 printer using Surgical Guide V1 resin. [JF1] The applicator was placed on the first day of treatment at CT simulation. The patient was placed in the prone position with the applicator inserted in the rectum. Treatment was delivered in 4 consecutive daily fractions of 6.5 Gy for a total of 26 Gy. <h3>Results</h3> The CTV volume was 19.8 cc and maximum tumor depth was 13 mm. Tumor coverage was excellent with a V200 of 6%, V150 of 23%, V100 of 70%, D90 of 83%. Target coverage was sacrificed to reduce the V200, given unknown previous radiation fields. The bladder D2cc dose was 5.4 Gy[JD2] [MS3] . The patient had complete resolution of rectal bleeding by the 4^th fraction. She reported no acute toxicities. At the time of this report, the patient is 1 month post brachytherapy with no reported toxicities with significantly easier bowel movements and continues to have no bleeding. <h3>Conclusion</h3> To our knowledge, this is the first reported 3D printed Endorectal High Dose Rate Brachytherapy Applicator used in clinical practice. In this case, the patient had early response with no adverse events. We believe 3D printing is a useful tool for Brachytherapists, and a feasible treatment option for rectal cancer patients.

GPP02 Presentation Time: 8:10 AM: Evaluating the Relationship Between Vaginal Apex ``Dog Ears'' and Patterns of Recurrence in Endometrial Cancer Following Adjuvant Image Guided Vaginal Cuff Brachytherapy

<h3>Purpose</h3> The vaginal cuff is a common site of tumor recurrence following surgery for endometrial cancer, and adjuvant vaginal cuff brachytherapy (VCB) is indicated to reduce the risk of local recurrence. Following hysterectomy, many patients have redundant tissue at the lateral apex of the vaginal cuff ("dog ears"). This extra tissue may extend irregularly beyond the typical cylindrical dose distribution of radiation delivered during single channel VCB and it is hypothesized that they are a potential site of local treatment failure even after VCB. The effects of the presence and size of vaginal cuff "dog ears" on tumor recurrence is not yet fully understood. The aim of this study is to evaluate the prevalence and size of extra tissue at the vaginal apex, and whether these factors predict disease recurrence in patients treated with adjuvant VCB for endometrial cancer. <h3>Materials and Methods</h3> We retrospectively reviewed the medical records of 219 patients with early-stage endometrial cancer treated with image-guided single channel VCB at our institution from 2012 - 2021 with available brachytherapy planning CT simulation images. "Dog ears" were defined as the presence of additional soft tissue extending at least 10 mm from the apex of the vaginal cuff perpendicular to the surface of the brachytherapy applicator as defined on a coronal or axial CT simulation. Patient characteristics and outcomes including stage, size and laterality of dog ears, presence of air gaps, and patterns of failure were collected. Vaginal cuff recurrence (VCR) failure free survival was calculated from time of first brachytherapy to VCR and was estimated by the product limit method of Kaplan and Meier. Fisher's exact test was used to compare categorical variables and a multivariate logistic regression model was developed to evaluate the association of overall treatment failure with various factors of interest. <h3>Results</h3> We found that 57.5% of patients (n = 126) met our criteria for having "dog ears," which, on average, extended 23.8 mm (SD = 6.4) from the brachytherapy applicator. In total, 13 patients (5.9%) developed a VCR, 12 (5.5%) developed a regional recurrence, and 16 (7.3%) developed distant recurrence. There was no statistically significant difference in VCRs between patients with dog ears and those without dog ears (7.1% vs 4.3%, p=0.56). The various surgical approaches (abdominal, laparoscopic, transvaginal) did not have an increased propensity to result in dog ears (p=0.74). The 3-year probability of VCR failure-free survival is 86%. On multivariate analysis (MVA), no factors predicted for overall treatment failure including the presence of dog ears, maximum dimension of dog ears, FIGO stage, presence of air gaps at the applicator surface on post insertion CT images, or brachytherapy duration. There was a trend toward increased risk of recurrence with higher grade histology on MVA (p=0.0805). <h3>Conclusions</h3> In this investigation of a single institution experience with single-channel image-guided VCB, the presence of "dog ears" at the vaginal apex is prevalent; however, VCR remains low with distant metastases being the predominant site of failure. While dog ears appear to have little impact on overall recurrence patterns, these may be a factor to consider when planning adjuvant brachytherapy including choosing alternate applicators.

GSOR2 Presentation Time: 9:05 AM: Implementation of Hybrid Intracavitary and Interstitial Brachytherapy for Cervical Cancer in a Freestanding Clinic

<h3>Purpose</h3> Radiation therapy for locally-advanced cervical cancer consists of external beam radiation therapy and brachytherapy. While the recent introduction of image-guided brachytherapy and hybrid intracavitary and interstitial brachytherapy treatments (HBT) may potentially improve clinical outcomes, current literature describes the procedure requiring significant resources (such as general anesthesia, conscious sedation, and MRI-based treatment planning). With increases in treatment time and patient movements, there is greater potential for positional changes of the applicator and neighboring organs at risk (OAR), which can alter dosimetry. Furthermore, these resources might not be universally available to all radiation oncology centers that perform intracavitary cervical brachytherapy, potentially limiting the widespread implementation of HBT. Here we describe our experience with CT-guided interstitial needle placement in a typical freestanding outpatient setting, with an emphasis on minimization of patient movement and treatment duration. <h3>Materials and Methods</h3> All patients that were treated with HBT from June 2018 to May 2020 were included in this series. Initially, patients were taken to the operating room, for an exam under anesthesia and Smit sleeve placement by the radiation oncologist. The patients were determined to need interstitial brachytherapy either by exam under anesthesia, due to anatomy and tumor extent, or after the first brachytherapy treatment, due to dosimetry. All tandem, ovoid and needle insertions and HDR treatments were performed in a freestanding clinic, on the CT simulator table. The patients were treated using minimal sedation (oral lorazepam and oxycodone/acetaminophen). An indwelling urinary catheter was inserted into the bladder. The tandem and ovoids (Elekta) were inserted in the patient, and a vaginal balloon was substituted for packing. Multiple CT scans were performed while advancing the interstitial needles, the bladder was filled with 180 cc of diluted contrast, and a final CT scan was taken for planning purposes. The patients were shifted from the CT table to a surgical bed (single shift), and then transported to the treatment room while treatment planning was performed using Oncentra (Elekta) treatment planning software. After the treatment plan was approved, the bladder was refilled to 180 cc and treatment was delivered using a microSelectron HDR afterloader (Elekta). The applicator was removed and the patient was examined for bleeding. If any vaginal bleeding occurred, vaginal packing was inserted with pressure applied. Time stamps and clinical data were collected during each procedure. <h3>Results</h3> Sixty-three patients underwent placement of a total of 244 interstitial implants. The median time for the entire procedure, from the time of patient entry into the CT simulation room to exit of the HDR treatment room, was 70.0 minutes (mean 70.3, range 54-100). The median time after tandem and ovoid insertion to complete interstitial needle insertion was 9.0 minutes (mean 9.8, range 4-24), using median 2 needles (mean 1.93, range 1-3) and median 3 CT scans (mean 2.63, range 1-4). Bleeding occurred in 22.1% (54/244) of implants, which resolved after median 3 minutes (mean 3.33, range 1-8) of vaginal packing with pressure. All patients (100%) required only one total shift, from the CT table to the mobile surgical bed. <h3>Conclusions</h3> In our series, the interstitial insertion portion of the HBT added 9 minutes, with an overall procedure time of 70 minutes (including insertion, planning, treatment and removal). There was an acceptable bleeding rate which quickly resolved with vaginal packing and pressure. Combining intracavitary and interstitial implants using a hybrid applicator appears to be feasible, efficient and safe in an outpatient freestanding clinic. Further studies aimed at evaluating long-term toxicities and tumor control are warranted.

Friday, June 17, 20224:00 PM - 5:00 PM MSPP01 Presentation Time: 4:00 PM: A Feasibility Study on Utilizing Cadaveric Models at a Network of Brachytherapy Research and Training Centers to Encourage Development and Widespread Use of Novel Robotic Bladder Cancer Brachytherapy Techniques

<h3>Purpose</h3> This feasibility study outlines a proof-of-concept model – the Houston Methodist Institute for Technology, Innovation & Education (MITIE) – for the use of cadaveric models at research centers to encourage development and training of novel robotic brachytherapy techniques, thereby expediting the incorporation of brachytherapy into the standard of care for muscle-invasive bladder cancer (MIBC). <h3>Materials and Methods</h3> Catheter insertion sites were marked on a male cadaver, and the da Vinci Surgical System(R) (Intuitive Surgical, Inc., Sunnyvale, CA) was docked. A modified catheter-needle system was assembled since pre-assembled bladder-specific catheter-needle systems are not compatible with all brachytherapy afterloaders. Closed-end catheters were inserted into 17-gauge curved needles. The first catheter was placed into the right lateral hypogastric abdominal wall, through the bladder dome wall, and out the opposing side. A single plane implant was completed with 1 cm spacing with the two other catheters (Figure 1a). Catheters were secured with nylon retaining buttons (Figure 1b). A CT simulation scan confirmed placement and a plan was developed for simulated brachytherapy delivery (Figure 1c). <h3>Results</h3> Cadaveric models enable physicians to develop new brachytherapy procedures in a controlled and simulated surgical environment without affecting operative time. Physicians can gain familiarity with the procedure and practice alterations to surgical equipment, including the catheter-needle system, which may prevent complications peri- and postoperatively. The proof-of-concept trial in MITIE shows how research and training centers can serve as incubators for the development of brachytherapy techniques. With a network of these centers, experts across the country can collaborate to test new techniques on cadaveric models and accelerate developments in bladder brachytherapy. This network would provide training opportunities for physicians, especially residents, which can familiarize physicians with brachytherapy techniques, promoting their use and providing clinical data to support these techniques as a new standard of care. Currently, institutes like MITIE are limited in number, necessitating travel and coordination of attending and resident physicians' schedules. Although an expanded network of these institutes would alleviate this issue, these training centers are associated with high operating costs, including the acquisition costs and high turnover rate required of cadaveric training models. Therefore, cost may impede scalability and must be considered alongside the benefits of establishing a widespread network of research and training programs for brachytherapy. <h3>Conclusions</h3> Robotic brachytherapy is a rarely utilized, minimally invasive treatment modality for MIBC. Innovation-focused facilities with cadaveric models can provide simulated surgical environments for the research, development, and training of robotic brachytherapy techniques and applicators, accelerating the acceptance of brachytherapy as the standard of care for MIBC.

Carbon-Ion Therapy Patient-Specific QA: Preliminary Results Derived Using 3D Polymer Gel Dosimetry in Anthropomorphic Inhomogeneous Geometry

<h3>Purpose/Objective(s)</h3> Improved conformity in carbon-ion radiation therapy (CIRT) with respect to photon RT comes at the cost of a potential reduced delivery robustness due to patient setup uncertainties, approximations in dose calculations and carbon-ion range uncertainties. This work presents preliminary results of a study aiming to address these challenges using 3D polymer gel dosimetry in anthropomorphic and inhomogeneous geometry. <h3>Materials/Methods</h3> All irradiations were performed at a synchrotron facility, in one of the treatment rooms equipped with a horizontal fixed beam line and pencil beam scanning (PBS) modality. For basic dosimetric characterization, carbon pristine Bragg peaks (BP) (ranges 30, 70, 90 mm in water) and a spread-out BP (SOBP) (range 115 mm and modulation 40 mm) were delivered on a cylindrical PMMA container filled with VIPAR polymer gel. An anthropomorphic phantom equipped with a cylindrical polymer gel insert was used for the irradiation of a pseudo-clinical CIRT plan, following all the steps of the standard clinical workflow, from simulation CT to irradiation. Two contralateral beams were optimized with a TPS (v.8b) to deliver 15 Gy (RBE) on a target located approximately at the center of the brain, in proximity of critical OARs such as brainstem and optical pathways. The phantom was then MRI scanned post-irradiation to retrieve the irradiated brain volume in 3D. The measured irradiated volume was compared against corresponding TPS derived data. <h3>Results</h3> Carbon-ion range was spatially verified with an accuracy of < 1 mm. For both the pristine BP and the SOBP irradiations. A significant deviation of the polymer gels' response on high-LET has been observed, as expected from previous studies with proton irradiations. For the pseudo-clinical treatment plan, a qualitative comparison between doses measured in polymer gels, against the corresponding TPS calculations, revealed a satisfying geometric accuracy of dose delivery in 3D, thus showing a high 3D geometrical accuracy of dose delivery in a typical standard clinical workflow. <h3>Conclusion</h3> In this work, we showed that patient-specific 3D polymer gel dosimetry is applicable to CIRT, as a valid tool to evaluate dosimetric and spatial plan accuracy in the clinical environment. As expected, the LET dependence of polymer gel's response, especially in the high-LET region, poses severe limitations for accurate dose measurements. Nevertheless, the proposed methodology is a promising efficient and safe clinical way for verifying such a complex RT technique.

Performance evaluation of online motion synchronizing systems for patient-specific respiratory movements with helical tomotherapy

Background and purpose. The introduction of online motion synchronizing system on helical tomotherapy paves way for robust motion tracking. A recent upgrade launches modifications on both hardware and software of the kV tracking system. An evaluation on the kV subsystems, prior (Version1) and post upgrade (Version2), was performed to compare tracking accuracy by means of fiducial tracking error and resulted root-mean-square (RMS). Impacts influenced by various patient-specific breathing pattern regularities and target movements were also investigated to refine motion tracking error estimations upon future selection of possible candidates. Materials and methods. Respiratory patterns from twenty-five lung cases were imported individually into a commercial dynamic platform model. Situating a phantom implanted with gold fiducial markers on the platform, superior-inferior (SI) movements of corresponding targets were simulated. Each case was delivered via an identical treatment plan in Version1 and was repeated in Version2. Motion tracking accuracy, by means of discrepancies between subsystem predicted model and raw data motion recorded in patient CT simulation, was analyzed statistically. Wilcoxon signed ranked test was employed to evaluate the difference in tracking error range between the two versions. Statistical model was fitted to inspect the dependence of internal target movement towards fiducial tracking errors. Results. A small difference of ±1 mm was exhibited in 99% of fiducial tracking errors for all cases experimented under both versions. RMS errors were all below 0.5 mm. Version2 demonstrated a greater extremity in fiducial tracking error (p = 0.04). A positive correlation was depicted between internal target amplitudes and 95% interval of fiducial tracking errors (p < 0.02). Overall, irregular respiratory patterns tended to have greater fiducial tracking errors. Conclusions. The excellent tracking performance in both kV subsystem versions offers motion compensations benefits, yet Version1 outperformed Version2 in fiducial tracking accuracy. It is noticeable that greater magnitude in internal target movement and irregular breathing patterns yield greater tracking error.

From Alpha to Omicron: A Radiation Oncology Network's Biocontainment-Based COVID-19 Experience

PurposeTo develop the safest possible environment for treating urgent patients with COVID-19 requiring radiation, we describe the unique construction of negative air pressure computed tomography simulator and linear accelerator treatment vaults in addition to screening, delay, and treatment protocols and their evolution over the course of the COVID-19 pandemic. Methods and MaterialsConstruction of large high-efficiency particulate air filter air-flow systems into existing ductwork in computed tomography simulator rooms and photon and proton treatment vaults was completed to create negative-pressure rooms. An asymptomatic COVID-19 screening protocol was implemented for all patients before initiation of treatment. Patients could undergo simulation and/or treatment in the biocontainment environments according to a predefined priority scale and protocol. Patients treated under the COVID-19 protocol from June 2020 to January 2022 were retrospectively reviewed. ResultsNegative air-flow environments were created across a regional network, including a multi-gantry proton therapy unit. In total, 6525 patients were treated from June 2020 through January 2022 across 5 separate centers. The majority of patients with COVID-19 had radiation treatment deferred when deemed safe. A total of 42 patients with COVID-19, who were at highest risk of an adverse outcome should there be a radiation delay, were treated under the COVID-19 biocontainment protocol in contrast to those who were placed on treatment break. For 61.9% of patients, these safety measures mitigated an extended break during treatment. The majority of patients (64.3%) were treated with curative intent. The median number of biocontainment sessions required by each patient was 6 (range, 1-15) before COVID-19 clearance and resumption of treatment in a normal air-flow environment. ConclusionsConstructing negative-pressure environments and developing a COVID-19 biocontainment treatment protocol allowed for the safe treatment of urgent radiation oncology patients with COVID-19 within our department and strengthens future biopreparedness. These biocontainment units set a high standard of safety in radiation oncology during the current or for any future infectious outbreak.

Left Anterior Descending Coronary Artery Radiation Dose Association with All-Cause Mortality in NRG Oncology Trial RTOG 0617

Left Anterior Descending Coronary Artery Radiation Dose Association with All-Cause Mortality in NRG Oncology Trial RTOG 0617

Development and Implementation of an Evidence-Based Pregnancy Screening Protocol in an Academic Radiation Oncology Department

<h3>Purpose/Objective(s)</h3> National guidelines give broad recommendations for which patients should be screened and timing of screening. Previous survey of ASTRO member institutions indicated that approximately 30% of centers did not have a clear pregnancy screening protocol. In this department, screening was done on the basis of individual physician clinical judgement. The purpose of this project is to develop an institutional protocol that defined patient criteria and timing for pre-radiation pregnancy screening in patients and to compare rates of screening before and after policy implementation. <h3>Materials/Methods</h3> A review of both radiation oncology and OB/GYN literature was performed with attention to risks of radiation to the fetus, current pregnancy screening protocols, and women at risk for pregnancy. Our institutional protocol defined the "at risk" population as female patients age 12-50 with intact reproductive organs. Contraceptive use was not considered an exclusion from screening. Screening would not be required for boost simulations or replans. Screening had to be performed within 30 days of CT simulation. Our policy was implemented 10/1/21. All CT simulations from 1/1/18-9/30/21 were reviewed. The medical record of patients meeting screening criteria was reviewed in further detail to establish the baseline screening rate. The medical records of patients meeting screening criteria from 10/1/21-1/31/22 was reviewed to establish an adherence rate after implementation. <h3>Results</h3> From 1/1/18-9/30/21, a total of 5,107 CT simulations were performed. Of these, 414 were performed on women age 12-50. 49 had prior removal of reproductive organs. This left 365 women as the baseline population. Screening occurred per the newly developed protocol in 189 of these women (51.8%.) There was one positive test. Retesting was negative, and the patient proceeded with treatment. An additional 64 patients underwent screening deviating from our current protocol. This included testing within 3 months but greater than 1 month from the date of CT simulation as well as screening after the date of simulation but prior treatment initiation. 112 of 365 women did not have documented pregnancy screening prior to CT and treatment initiation (30.6%). After the implementation of the screening protocol on 10/1/21, a total of 403 patients underwent CT simulation through 1/31/21. Of these, 34 were women age 12-50. 7 had prior removal of reproductive organs. Of the remaining 27 patients, 25 underwent screening per protocol (92.5%). One patient was 49 years old and refused testing. The other was tested before the initiation of therapy. <h3>Conclusion</h3> Our conclusion is implementation of a pregnancy screening protocol in an academic medical center radiation oncology department improved the screening rate for women at risk for pregnancy prior to radiation treatment planning. The use of a standardized policy eliminates inter-provider variation and improves patient safety.

Prompt Pain Relief from Bone Metastases: The Virtual Simulation Program

<h3>Purpose/Objective(s)</h3> Patients commonly present to radiation oncology with painful bone metastases. A major bottleneck in delaying treatment of these patients is scheduling a separate CT simulation appointment. We implemented an alternative radiation planning workflow, which utilized a pre-existing diagnostic CT scan "virtual simulation" in lieu of acquiring an additional CT simulation scan. We hypothesized this would significantly decrease the time interval between initial consultation and treatment start date. <h3>Materials/Methods</h3> Patients meeting strict criteria were selected for virtual simulation. This included only those with painful bone metastases in the thorax/abdomen/pelvis/upper femur who would be treated with palliative intent using standard AP/PA or opposed lateral fields. A recent (within 30 days) diagnostic CT scan clearly visualizing the target volume and surrounding anatomy was required for treatment planning and for daily IGRT treatment purposes. Descriptive statistics were used to analyze time from consultation to start of treatment in virtual versus in-person simulation patients. Before and after the virtual simulation study period, surveys were administered to all stakeholders (physicians, nurses, dosimetrists, physicists, and radiation therapists) to assess staff satisfaction of virtual simulation workflow using a Likert scale. Staff were surveyed on their stress levels, how rushed they felt, and overall level of satisfaction. A 1–5-point scale was used with higher numbers indicating worse outcomes such as increased stress, being more rushed, and less satisfaction. <h3>Results</h3> 24 patients were palliatively treated for painful bone metastases as part of this pilot virtual simulation project from May 2021 to January 2022. Median number of fractions for all courses was one fraction. A reference group of 40 patients palliatively treated with in-person CT simulation from February 2021 to July 2021 was also retrospectively reviewed. Median time from consult to start of treatment for in-person CT simulation patients was 167 hours (6.96 days). In comparison, median time from consult to start of treatment for virtual simulation patients was 71 hours (2.96 days). Median duration of treatment itself was 12 minutes for virtual simulation patients versus 9 minutes for in-person simulation patients. 20 surveys were collected prior to the virtual simulation while 15 surveys were collected after the time period. For virtual versus in-person workflows, staff felt less rushed (2.5 vs. 2.8), less stressed (2.0 vs. 2.5), and more satisfied overall (1.86 vs. 2.76). <h3>Conclusion</h3> The virtual simulation program decreased time from consult to start of treatment for patients requiring urgent palliative radiotherapy for painful bone metastases by 57.5% (6.96 vs. 2.96 days). The alternative virtual workflow did not decrease overall staff satisfaction.

Detection of Kidney Impairment Using Correlation of CT Number and ADC

<h3>Purpose/Objective(s)</h3> It has been reported that a correlation exists between the mean apparent diffusion coefficient (ADC) measured from MRI and the mean CT number (CTN) in kidney. This correlation can be interpreted as both ADC and CTN reflect extracellular volume (ECV) ratio. This study aims to investigate the correlation of ADC and estimated glomerular filtration ratio (eGFR) and the use of ADC-CTN correlation to detect kidney impairment. <h3>Materials/Methods</h3> Data acquired for radiation therapy (RT) planning of twenty-two patients with abdominal/pelvic cancers were analyzed retrospectively in two groups. Group I included sixteen patients with no history of severe kidney disease and Group II had six patients having apparent issues including kidney stones, chronic disease, or tumor on kidney. CT images were acquired during CT simulation using a scanner at 120 kVp and the ADC maps were derived from the diffusion weighted imaging (DWI) acquired immediately before the first fraction of MRI guided RT using a 1.5T MR-Linac approximately 3 weeks following CT simulation. Left and right kidneys excluding renal pelvis were contoured on both the ADC and CT images. The mean values of the ADC and CTN from the voxels within the contours were analyzed using linear regression. The eGFR was calculated based on serum creatinine level measured on the same day as DWI. The correlation between eGFR and mean ADC value of left and right kidneys was evaluated with Pearson test. The linear regression fit was used to correct the ADC values to eliminate the filtration effect to show the ECV effect only. <h3>Results</h3> The CTN and ADC over the Group I patients had an average 29.3 HU and 2.00 µm/s² ranging from 23.0 HU to 38.2 HU and 1.79 µm/s² to 2.16 µm/s², respectively. The eGFR of all patients ranged from 40 to 129 mL/min/1.73 sqm, and had a moderate correlation to ADC (coefficient=0.46, p=0.04). Using the linear fit of ADC-eGFR data, the ADC values were corrected by extrapolating their corresponding eGFR to 0. This correction did not alter the strong correlation between the ADC and CTN (Pearson coefficient = -0.83 with and -0.84 without correction, p<0.0001) but dropped the line of linear fit by 0.2 µm/s². There was no significant difference in eGFR, CTN, or ADC between Group I and II. However, almost all patients in Group II (5 out of 6) had one kidney data residing within the +/- 0.15 µm/s² region of fit line while the other one fell out of the region as an outlier, identified as the actual problematic kidney in the medical record (4 of 5). In two cases kidney stones were not found when the images were taken but in 6-12 months posteriorly. <h3>Conclusion</h3> Our study showed that eGFR affected ADC in a minor way and would not change the strong negative correlation between ADC and CTN. Impaired kidneys tend to fall out of the ADC-CTN correlation line as outliers, which were not identified using eGFR, CTN, or ADC alone. These results indicate that ADC-CTN correlation is a new sensitive method to detect kidney impairment and has a potential application in monitoring radiation toxicity.

Improved Cone-Beam Reconstruction Using a Prior Breathing Motion Model

<h3>Purpose/Objective(s)</h3> To demonstrate whether incorporating a pre-measured breathing motion model into algebraic cone-beam CT (CBCT) reconstruction could improve daily target imaging for radiotherapy delivery of lung tumors. <h3>Materials/Methods</h3> We employed our clinic's 5DCT simulation technique to generate the breathing motion model. 5DCT provides a voxel-by-voxel representation of breathing motion as a function of breathing amplitude and rate, and the motion model was used to characterize the breathing motion during CBCT acquisition. We acquired CBCT projections before treatment and simultaneously acquired a breathing amplitude signal using a respiratory bellows. The 5DCT reference image was registered to the CBCT geometry using a rigid registration of the spine. To enable the use of the 5DCT motion model on the CBCT data, a correspondence between the simulation and CBCT surrogates needed to be made. The breathing surrogates of the simulation were correlated with the CBCT using the diaphragm shadow in the CBCT projections and the 5DCT reference image deformed using the motion model. By adjusting the 5DCT model breathing amplitude, the diaphragm shadow moved until the CBCT projection and 5DCT diaphragm shadows overlapped, yielding the correspondence between the two surrogates such that the 5DCT motion model could be directly applied to the CBCT reconstruction. To reconstruct the CBCT image, we modified the motion-compensated simultaneous algebraic reconstruction technique (MC-SART) by introducing the aligned and scaled 5DCT motion model parameters. The modified MC-SART compared the raw projections to corresponding model-generated projections with various levels of binning. To quantify the 5DCT model's ability to describe the breathing motion during the CBCT, we reconstructed the CBCT dividing the breathing amplitude into 1, 2, 4 and 8 bins. We examined the corresponding sharpness of the diaphragm to see if the diaphragm boundary continuously sharpened with increasing bins. <h3>Results</h3> We found that the diaphragm appeared most blurred when only 1 amplitude bin was used, appearing sharper as bins were added. At 8 bins, the diaphragm boundary was only 2 voxels, consistent with typical breath-hold CT reconstruction. This demonstrated that the motion model from the CT simulation could quantitatively track breathing motion during the CBCT. However, while the diaphragm appeared sharper, the reconstructed images with increasing bins also had poorer image contrast. <h3>Conclusion</h3> We have shown that using a previously determined breathing motion model with algebraic reconstruction can improve image sharpness. We will expand the current study to more patients and fractions and develop techniques to improve image contrast. However, since the purpose of this approach will be to localize lung tumors and characterize their motion at the treatment table, the image contrast may be sufficient. We will also compare our approach to published 4DCT approaches to determine if ours better manages irregular breathing.

Impact of a Patient Tracking Dashboard on the Timeliness for Chart Check in a Community-Based Radiation Oncology Department

<h3>Purpose/Objective(s)</h3> One of the cornerstones for the safe delivery of radiation treatment is the chart check completed by the radiation therapist. It is recommended that the therapists have adequate time to complete this check. We set an institutional quality improvement goal for non-urgent cases to be ready for chart check at least one day prior to the verification day/first fraction. We report the impact of a patient-tracking dashboard to improve this quality metric at our community-based radiation oncology department. <h3>Materials/Methods</h3> We constructed a custom patient tracking dashboard within Microsoft Teams. Patients were added to the dashboard during CT simulation along with other information including physician, radiation technique, planned start date, and step in the planning process. Dashboard was available to all members of the department, updated daily and reviewed during morning huddle. The dashboard was then piloted at one of four departments in the health system starting in January 2021. Charts that were completed and ready for review at least 1 day prior to the start date were considered "on-time". Those that were deemed "urgent" were excluded from this quality metric. All other charts, which were ready for final check on the same day of treatment, were considered "late". We evaluated the impact of the dashboard pilot on on-time percentage. All comparisons are made using chi square analysis. <h3>Results</h3> The study period covered 16 months and 398 patients, including 4 months prior to the dashboard pilot (n=84, 09/2020–12/2020) and 12 months following (n=314, 01/2021–12/2021). As expected, there was no difference in the percent of patients considered urgent before and following the pilot (22.6% vs. 17.5%, <i>p</i>=NS). There was a significant improvement in the on-time percentage following the dashboard pilot (60.0% vs. 94.9%, <i>p</i><0.0001). On-time performance was also analyzed at the other radiation oncology departments in the health system, which were subject to the same quality improvement goals but were not part of the pilot (n=1,217). No difference was found in the on-time percentage over the same study period (84.9% vs. 84.2%, p=NS). On-time percentage was significantly higher with the pilot than in the departments which had not yet implemented (94.9% vs. 84.2%, <i>p</i><0.0001). <h3>Conclusion</h3> We found that the pilot implementation of a patient tracking dashboard significantly increased the percentage of patients meeting our quality goal of having charts available for check at least one day prior to start of treatment from 60.0% to 94.9%. The dashboard was easily built internally and implemented without any additional investment. We found that this approach was well received and helped promote safety and efficiency, especially during the pandemic when the department experienced staffing shortages and cross-coverage. We hope to expand use of the dashboard across the system and potentially to other aspects of the care continuum for cancer patients.

Prospective Pilot Study to Measure Baseline Anxiety prior to Radiotherapy after Standard Education at Consultation

<h3>Purpose/Objective(s)</h3> Pre-operative patient education has been shown to reduce patient anxiety and increase patient medical comprehension. This prospective pilot study hypothesized that patient anxiety related to the radiotherapy treatment process would be elevated after receiving traditional radiation educational materials and counseling at the time of initial consultation. <h3>Materials/Methods</h3> Patients with non-metastatic cancer receiving definitive or adjuvant radiotherapy at three suburban radiation therapy clinics affiliated with an academic medical center completed a 34-question survey. The survey included questions on demographics, the Spielberger State-Trait Anxiety Inventory short-form (STAI-S-6), a modified radiotherapy Amsterdam preoperative anxiety and information scale (mRT-APAIS), and radiotherapy knowledge. Patients also provided qualitative responses. Surveys were administered prior to the patient's CT-simulation scan. Descriptive statistics were performed. <h3>Results</h3> 22 patients were enrolled in this prospective pilot study. 19 (86%) patients were female. The median age was 66 (range: 38-80). 14 (64%) patients were white, 7 (32%) black, and 1 (4%) American Indian/Alaskan Native. 6 (27%) patients received a high school degree or GED, 10 (46%) obtained a 2-year degree and 5 (22%) received a 4-year degree or higher. 16 (73%) patients had breast cancer with the others having lung, brain, gastrointestinal, gynecologic, or other malignancies. The median STAI-S-6 score was 43.3 [IQR: 36.7 - 46.7] and the median mRT-APAIS score was 18 [IQR: 14.8 – 20.0]. 68% of patients were "anxious" by STAI-S-6 (score ≥ 40) and 77% by mRT-APAIS (score ≥ 12). Patients reported low levels of knowledge related to radiotherapy set-up (41%), immobilization (41%), x-ray use (64%), and sensation (tactile 41%, auditory: 59%). <h3>Conclusion</h3> A majority of patients reported anxiety related to the radiotherapy treatment process prior to CT simulation. These findings suggest an educational intervention at the time of consultation may be beneficial to reduce patient anxiety and increase patient knowledge related to the radiotherapy treatment process. Accrual is ongoing in this prospective pilot study. Future research directions include a phase 3 multi-institutional stepped-wedge clinical trial to investigate the impact of a novel patient education tool such as the Communicating the External Beam Radiotherapy Experience (CEBRE) discussion guide used during initial consultation to reduce patient anxiety and increase patient knowledge about radiotherapy.

An Essential Treatment Pattern of Lung Cancer: Magnetic Resonance-Guided Stereotactic Body Radiotherapy

<h3>Purpose/Objective(s)</h3> Stereotactic body radiation therapy (SBRT) has emerged as an important treatment for non-resectable lung cancer. MR-Linac can offer superior soft-tissue contrast, have the ability to visualize cancer physiology and daily on-table treatment adaptation. Obviously combined SBRT with MR-Linac holds the promise to improve the accuracy of radiotherapy and reduce the toxicity of organs-at-risk (OAR). However, data on treatment effect and patient acceptance is still limited. <h3>Materials/Methods</h3> Between July 2019 and October 2021,14 patients with lung cancer were treated with an MRI-Linac guided SBRT, of them, 6 in left upper lobe, 1 in left lower lobe, 2 in right upper lobe and 5 in right lower lobe. The CT simulation used a Siemens big-bore CT scanner (syngo CT VA62A) for all patients. All patients were treated with step and shoot intensity modulated radiotherapy (IMRT). The online plan was created while the patient was on the treatment table and based on the online MRI images; pre-treatment CT was deformably registered to the online MRI to obtain position error. All patients used adapt to position (ATP) workflow. The curative effect and adverse reactions in the process of treatment need to be paid close attention to, and the adverse reactions should be treated and recorded in time. <h3>Results</h3> Fourteen patients (with n=2 metastases; n=12 primary tumor) received MR-guided SBRT. Median prescribed does was 60Gy(range:54Gy-70Gy) and median planning target volume was 28.8cc (range:11.1-93.4cc). Two patients occurred grade I bone marrow suppression and two occurred grade II bone marrow suppression. One patient occurred grade I gastrointestinal toxicity. No patient occurred grade III or higher toxicity. Only one patient developed left lung recurrence and left hilar lymph node metastasis ten months after treatment, one patient was not re-examined, and others were controlled locally. <h3>Conclusion</h3> In summary, MR-guided SBRT of lung cancer is well-effective and well-accepted. The results are promising that it holds with prominent local control and mild adverse events. The influence of magnetic field on dosimetry remains to be studied. The relevant work is also conducted.

Implementation of Data-Driven Timelines and Visual Guidance Tools to Improve Radiation Oncology Task Completion: “Plan Readiness”

<h3>Purpose/Objective(s)</h3> The time between physician treatment plan approval and patient treatment initiation is often too short in our current Radiation Oncology practice. This reflects inconsistencies in the timeframe of task completion between CT simulation and treatment plan approval, the first and last steps in a complex, multi-step planning workflow in Radiation Oncology. This poses challenges in terms of the QA and plan checks needed prior to treatment initiation, with potential implications for patient safety. Our goal was to implement a sustainable and clear departmental process that would increase the percentage of plans approved by the attending Radiation Oncologist 1 full business day prior to treatment start for all non-urgent patients. Secondary goals included a reduction in last-minute patient delays and improvement in team member engagement and satisfaction. <h3>Materials/Methods</h3> We established realistic timelines for each task from simulation to treatment initiation, while setting a cutoff time for implementing patient appointment delay when expectations were not met. Treatment site, technique, and complexity-specific timelines were built by our team based on 4 major factors: 1) Clinical Urgency, 2) Task Complexity, 3) Evaluation of "task completion" data from a large cohort of previously treated patients, and 4) Interviews with all team members involved in the treatment planning process. These timelines were generated in a visual task management tool, and were linked as serial or parallel to keep the entire team on schedule for each patient. Prior to implementation, appropriate departmental meetings were held to discuss these changes, with extensive team member feedback utilized to generate the new policy. Timelines were generated that ranged from 5 to 12 working days, with clear goals and guidelines for each involved team member regarding their task(s). Our overarching goal, termed "Plan Readiness", was to achieve an electronically approved treatment plan 1 full working day prior to treatment start for > 90% of our patients. Appropriate exclusions were made for emergencies and special/new procedures in the department. <h3>Results</h3> For the 5 months prior to implementation, our baseline data demonstrated that 71% of plans were electronically approved in our treatment planning system greater than 24 hours prior to treatment start. After implementation of our new "Plan Readiness" process in March 2021, we have been able to stay above 90% pass rate, with a cumulative average of 94.6% over an ongoing 10-month timeframe. <h3>Conclusion</h3> The design and execution of data-driven timelines and visual guidance tools, combined with a team-based approach of communication and open feedback, has resulted in preliminary favorable outcomes in achieving timely "Plan Readiness" in our relatively large, hospital-based Department of Radiation Oncology. Future directions include the use of analytics software and automated data collection to perform more robust assessments.

Verification Studies Confirm Reproducibility of Post-Hysterectomy Pelvic Proton Radiotherapy

<h3>Purpose/Objective(s)</h3> Post-hysterectomy radiotherapy (RT) is associated with urinary, gastrointestinal, and hematologic toxicity. Concern for organ and target motion has limited exploration of proton RT as a tool to reduce toxicity. Attention to planning and treatment delivery is paramount given sensitivity of protons to small changes in soft tissue in the beam path. We sought to evaluate the consistency of target coverage and organ at risk (OAR) sparing in post-hysterectomy proton RT. <h3>Materials/Methods</h3> The first 10 patients treated with proton RT on an institutional prospective non-randomized trial of proton post-hysterectomy RT for endometrial cancer were included. CT simulation was performed with pelvic immobilization and a rectal balloon, which was also used for treatment. Full and empty bladder and IV contrast scans were obtained. Clinical target volumes (CTV) included the vaginal cuff, proximal 3 cm of vagina, and pelvic lymph nodes to the level of L4/L5. Prescription was 45 Gy (relative biological effectiveness (RBE) 1.1) in 25 fractions. Planning was multi-field optimization with two posterior oblique beams and a posterior beam. Plans were evaluated for robustness to ensure CTV coverage in worst case scenarios of ±5 mm isocenter shifts in x, y, and z directions and ±5% range uncertainty. A variable RBE calculation assuming a linear relationship between RBE and linear energy transfer was used to evaluate for target coverage and increased RBE within OARs. If needed, the plan was modified to limit hot spots without compromising coverage in the calculation with uniform 1.1 RBE. Patients underwent weekly CT-on-rails verification scans. Target coverage and dose to OARs were assessed at each verification and replanning was done if target coverage or OAR constraints did not meet original planning objectives. <h3>Results</h3> The first patient on the study required replan after first verification due to excess air in the rectum at simulation and verification, resulting in rectum V30Gy 90% and V40Gy 81%. After replan, subsequent verifications met objectives. Subsequent patients were planned with air in the rectum or bowel accounted for by evaluation of plans with air overridden to HU = -300 to -450 and HU = 0. Target coverage met acceptable planning parameters in all cases (Table 1). There was no statistical difference in bladder mean, V30Gy, and V45Gy; sigmoid V45Gy; rectum mean, V30Gy, and V40Gy; and small bowel V40% and V45Gy. All patients were successfully treated with protons for all planned fractions. <h3>Conclusion</h3> Proton post-hysterectomy pelvic RT with robust optimization is feasible, reproducible, and associated with appropriate target coverage and acceptable dose to organs at risk as assessed with weekly verification scans.

Therapeutic optimization in head and neck radiotherapy planning: Advocacy for 18FDG PET-CT in treatment condition

The necessity to perform 18FDG PET-CT both for initial tumour staging and for target volume delineation in head and neck cancers seems well established. The aim of the present study is to advocate the place and role of 18FDG PET-CT acquired in planning treatment position (18FDG PET-CT/RT). Between March 2018 and July 2019, 22 patients with a squamous cell head and neck carcinoma treated by EBRT were included in the analysis. All these consecutive patients had a 18FDG PET-CT/RT. Three GTV volumes were defined. First, "GTV 40%" corresponded to 40% of SUVmax. "Visual GTV" was defined as the tumor volume obtained from the PET the nuclear medicine physician interpreted. The radiation oncologist used the medical record, clinical anatomy, CT simulation and 18FDG PET-CT/RT data ("GTV40%" and "visual GTV") to draw the GTV. Mean GTVs and mean "GTVs40%" were significantly different (P<0.001) with an intraclass index of 0.734. Mean "GTV40%" and mean "visual GTVs" were also significantly different (P<0.001) with an intraclass index of 0.72. Conversely, the difference between mean GTVs and mean "visual GTVs" were not significant (P=0.11) with an intraclass index of 0.91. Mean DICE between "GTVs40%" and GTV was 0.7 (ranging from 0.2 to 0.9). The mean intersection between GTVs and "visual GTVs" volumes was 0.8 (ranging from 0.4 to 1). The difference between DICES was significant (P=0.015), "visual GTV"/GTV DICE was the smallest. 18FDG PET-CT/RT definitely remains the imaging modality that individualized/customized head and neck cancer treatment needs.

Comparison of Diagnostic PET and 4D CT-Based Tumor Delineation for Oligometastatic Lung Tumors

<h3>Purpose/Objective(s)</h3> Stereotactic body raiation therapy (SBRT) is increasingly used to treat oligometastatic tumors. To account for internal motion, 4D-CT is commonly used for lung SBRT. Biology-guided radiotherapy (BgRT) is an emerging concept that may allow for reduction of treatment volumes using positron emission tomography (PET) signal guidance. Benchtop testing of BgRT technology suggests target delineation on a single respiratory phase with 5 mm biology-guided margin may be sufficient, however this has not been clinically validated. We tested our hypothesis that PET-based tumor delineation would result in smaller target volumes than 4D-CT. <h3>Materials/Methods</h3> We retrospectively reviewed a single-institution lung radiotherapy database to identify patients with oligometastatic lung tumors treated with ablative doses of biologically effective dose (BED10) >=100 Gy. We included patients treated from 2015-2020 with a diagnostic PET performed within 30 days of CT simulation. Tumors were contoured on the diagnostic PET using an auto-threshold of 40% of the lesion SUVmax, followed by manual editing to include CT-based tumor accounting for possible PET signal misregistration. A 5 mm isotropic expansion was applied to generate the planning target volume (PTV). We compared these to existing 4D CT-based tumor volumes accounting for internal motion and their associated PTVs. <h3>Results</h3> Of 102 patients with oligometastatic lung tumors, we included 13 patients with 15 lung tumors. There were 7 female and 6 male patients, with a median age of 72 (range 52 – 89) at the time of treatment. Primary tumor types included 4 colorectal, 2 head and neck, 1 non-small cell lung cancer, 1 melanoma, and 5 other cancer types. Patients were treated to 50 to 54 Gy in 3 to 5 fractions. Median time from diagnostic PET scan to CT simulation was 17 days (range 0 – 27). Median lesion diameter was 1.2 cm (IQR 0.9 – 1.7) with median SUVmax of 5.4 (IQR 4.0 – 7.7). Diagnostic PET-based tumor contours had a median volume of 2.5 cc (IQR 1.7 – 3.1 cc), whereas 4D CT-based tumor contours had a median volume of 3.0 cc (IQR 2.4 – 9.9 cc). Diagnostic PET-based PTV had a median volume of 10.4 cc (IQR 8.4 – 12.6 cc), whereas 4D CT-based PTV had a median volume of 11.8 cc (IQR 10.8 – 31.5). <h3>Conclusion</h3> Diagnostic PET-based tumor delineation resulted in smaller tumor and planning target volumes compared to 4D-based tumor delineation. This data will serve as a benchmark for future research focusing on imaging modality concordance and clinical impact of reduced biology-guided margins in BgRT for oligometastatic patients undergoing lung SBRT.

From Alpha to Omicron: A Tertiary Care Hospital-Based Radiation Oncology Network's COVID-19 Response Experience

Purpose/Objective(s)The COVID-19 pandemic completely altered access to medical care, severely limiting or halting outpatient procedures over long periods of time. However, it was clear that radiation therapy needed to remain available to patients. We implemented asymptomatic testing algorithms and constructed negative air pressure CT simulator and treatment rooms within our tertiary care hospital-based Radiation Oncology network to accommodate the safe treatment of patients affected by the COVID-19 pandemic.Materials/MethodsOur Radiation Oncology department undertook dedicated construction to convert select CT simulator rooms and treatment vaults into negative pressure environments, including one CT simulator room and photon-based linear accelerator treatment vault at the main campus in 5/2020; and one CT simulator room, two photon-based linear accelerator vaults, and a single proton therapy gantry between two regional campuses in 12/2021. From 5/18/20 to 9/7/21, an asymptomatic screening protocol was implemented for all patients prior to initiation of radiation therapy. Patients with COVID-19 infection and Persons Under Investigation (PUIs) could undergo simulation and/or treatment in the newly constructed biocontainment environments at the discretion of the treating physician with guidance from a predefined priority scale. A biocontainment treatment protocol delineated specific roles within a treatment team of one Nursing Safety Officer, one Direct Contact Radiation Therapist, and one Indirect Contact Radiation Therapist. Safety drills were performed to establish and practice safe pathways for escorting patients directly from their car to the treatment room, and vice versa, for the last treatment slot(s) of the day. Patients who were treated under COVID-19 protocol from 6/2020 to 1/2022 were chart reviewed to assess utilization of our newly constructed and developed biocontainment resources.ResultsA total of 6,525 patients were treated from 6/2020 through 1/2022 across our 5 campuses. During this time, 42 patients were treated under the COVID-19 biocontainment protocol. All but 3 had documented personal COVID-19 positivity, while the others were designated as PUI, typically for COVID-positive household contacts. For 61.9% of patients, these safety measures mitigated the need for extended breaks during treatment courses that had already been initiated. The majority (64.3%) of patients were being treated with curative intent, while 10 patients (23.8%) were treated as a result of an inpatient palliative consult. A third (35.7%) were transferred from a regional campus to the main campus for management prior to expansion of biocontainment resources. The median number of biocontainment sessions required by each patient was 6 (range: 1-15).ConclusionThe construction of negative pressure environments and development of a COVID-19 biocontainment protocol have helped to mitigate the impact of the pandemic on our patients and to maximize efforts in protecting our staff.