Guided Radiation Therapy Research Articles

Ablative radiotherapy for colorectal liver metastases and intrahepatic cholangiocarcinoma

The role of radiation therapy in the management of liver cancers, both primary and metastatic, has changed drastically over the past several decades. Although conventional radiation was limited by technology, the advent of advanced image-guided radiotherapy and the rise in evidence for and popularity of stereotactic body radiotherapy have expanded the indications for radiation in these two distinct disease types. Magnetic resonance imaging–guided radiation therapy, daily online adaptive radiotherapy, and proton radiotherapy are some of many modern radiotherapy techniques that allow for increasingly efficacious treatment of intrahepatic disease while simultaneously allowing for increased normal tissue sparing, including sparing of the normal liver and the radiosensitive luminal gastrointestinal tract. Modern radiation therapy should be considered along with approaches such as surgical resection and radiofrequency ablation for the management of liver cancers of diverse histologies. Herein we describe the use of modern radiotherapy in two example settings, colorectal liver metastases and intrahepatic cholangiocarcinoma, and how external beam radiotherapy provides options within multidisciplinary discussions to elect optimal patient-specific treatments.

Assessment of organ and size-specific effective doses from cone beam CT (CBCT) in image-guided radiotherapy (IGRT) based on body mass index (BMI)

The ability of radiation therapy to deliver radiation doses accurately to tumour targets, while sparing normal tissues, has advanced remarkably over recent decades. A development that has been key to achieving this improvement has been the application of image-guidance that facilitates more precise delivery of the prescribed dose to the treatment site. A recent international survey showed that kV cone beam CT (CBCT) is the imaging modality used most widely for image guided radiation therapy (IGRT) procedures. However, IGRT will deliver additional radiation doses to patients that should be considered. The aims of this study were to (1) estimate organ and size-specific effective doses resulting from kV-CBCT chest and pelvis scans based on body mass index (BMI) of the patient, and (2) investigate the influence of patient size on imaging dose. A validated Monte Carlo model developed with BEAMnrc/EGSnrc was employed to simulate kV spectra generated by Varian on-board imaging (OBI) system. Organ and size-specific effective doses were assessed for adult phantoms in the National Cancer Institute (NCI) phantom library using DOSXYZnrc/EGSnrc code. The library has been reconstructed from images of CT patients, and contains 100 male and 93 female phantoms of a wide range of sizes. The phantoms were grouped into six categories based on body mass index (BMI) as classified by the world health organization. For all sizes, average doses to organs that lay fully or partially inside the field of the chest and pelvic scans were in the range of (0.20–3.06 mGy/100 mAs) and (0.17–4.47 mGy/100 mAs), and size-specific effective doses were (0.63 – 1.78 mSv/100 mAs) and (0.30 – 1.17 mSv/100 mAs), respectively. Patient size played a significant role in determining the imaging doses resulting from both scans. In general, organ and effective doses of chest and pelvic scans of thin patients were about 2–3 times larger than those of obese patients, with the impact of patient size on pelvis doses being slightly higher than on chest ones. Results of this study suggests that patient size should be taken into consideration when estimation and optimization of the imaging doses resulting from CBCT. Although development of patient size-specific CBCT protocols is a practical approach that can account for patient size, it has not been implemented worldwide. Results from this investigation might be used as a simple approach to obtain an estimation of the imaging doses for patients of various sizes based on BMI.

First treatments for Lattice stereotactic body radiation therapy using magnetic resonance image guided radiation therapy

Two abdominal patients were treated with Lattice stereotactic body radiation therapy (SBRT) using magnetic resonance guided radiation therapy (MRgRT). This is one of the first reported treatments of Lattice SBRT with the use of MRgRT. A description of the treatment approach and planning considerations were incorporated into this report. MRgRT Lattice SBRT delivered similar planning quality metrics to established dosimetric parameters for Lattice SBRT. Increased signal intensity were seen in the MRI treatments for one of the patients during the course of treatment.

Strategy for automatic ultrasound (US) probe positioning in robot-assisted ultrasound guided radiation therapy

Objective. As part of image-guided radiotherapy, ultrasound-guided radiotherapy is currently already in use and under investigation for robot assisted systems Ipsen 2021. It promises a real-time tumor localization during irradiation (intrafractional) without extra dose. The ultrasound probe is held and guided by a robot. However, there is a lack of basic safety mechanisms and interaction strategies to enable a safe clinical procedure. In this study we investigate potential positioning strategies with safety mechanisms for a safe robot-human-interaction. Approach. A compact setup of ultrasound device, lightweight robot, tracking camera, force sensor and control computer were integrated in a software application to represent a potential USgRT setup. For the realization of a clinical procedure, positioning strategies for the ultrasound head with the help of the robot were developed, implemented, and tested. In addition, basic safety mechanisms for the robot have been implemented, using the integrated force sensor, and have been tested by intentional collisions. Main results. Various positioning methods from manual guidance to completely automated procedures were tested. Robot-guided methods achieved higher positioning accuracy and were faster in execution compared to conventional hand-guided methods. The developed safety mechanisms worked as intended and the detected collision force were below 20 N. Significance. The study demonstrates the feasibility of a new approach for safe robotic ultrasound imaging, with a focus on abdominal usage (liver, prostate, kidney). The safety measures applied here can be extended to other human-robot interactions and present the basic for further studies in medical applications.

Factors Affecting Implementation of Radiological Protection Aspects of Imaging in Radiotherapy

Dramatic improvements in radiotherapy equipment have allowed radiation fields to be conformed to tumours for more accurate treatment. Successful delivery often requires imaging at every treatment fraction, a method known as image guided radiation therapy (IGRT). But increased X-ray imaging exposes patients to doses that carry risks of inducing second cancers in normal tissues. Therefore, reductions in high-dose treatment margins achieved with IGRT must be balanced against detriments from greater imaging doses. ICRP Task Group 116 has been set up to prepare guidance on radiological protection aspects of IGRT. Factors affecting the optimization of radiological protection are the modalities used, the frequency of imaging, the image acquisition parameters influencing image quality and radiation dose, and the volume of normal tissue included in the images. The Task Group has undertaken two projects: (1) a snapshot survey of radiotherapy imaging practices across six continents, which has shown that use of kV cone beam CT (CBCT) increases with Human Development Index for the country; and (2) a project looking at ways for measuring CBCT doses that could be applied more widely. The results highlight the need for raising awareness of imaging doses, and development of the dose quantities displayed on imaging equipment used in radiotherapy.

Mesorectal motion evaluation in rectal cancer MR-guided radiotherapy: an exploratory study to quantify treatment margins

BackgroundMesorectal motion (MM) is a source of uncertainty during neoadjuvant chemoradiotherapy (nCRT) delivery for locally advanced rectal cancer (LARC). Previously published experiences using cone-beam computed tomography imaging have already described significant movement. Aim of this analysis is to assess inter-fraction MM using the higher tissue contrast provided by hybrid magnetic resonance imaging (MRI) in LARC patients (pts) treated with MRI guided radiation therapy (MRgRT).MethodsThe total mesorectum, its superior (Msup), middle (Mmid) and lower (Mlow) regions were contoured on the positioning MRIs acquired on simulation day and on each treatment day. Six PTVs were obtained adding 0.5, 0.7, 1, 1.3, 1.5 and 2 cm margin to the whole mesorectum, starting from the simulation MRI. Margins including 95% of the mesorectal structures during whole treatment in 95% of patients (pts) were considered adequate.ResultsA total number of 312 fractions of 12 consecutive pts was retrospectively analyzed. The different mesorectum regions show specific motion variability. In particular, Msup shows larger variability in left, right and anterior directions, while the Mlow in caudal and posterior ones. The anterior margin is significantly larger in the Msup than in the other regions.ConclusionDifferent mesorectal regions move differently throughout the radiotherapy treatment, with the largest MM in the Msup anterior direction. Asymmetrical margins are recommended.

Lung-heart toxicity in a randomized clinical trial of hypofractionated image guided radiation therapy for breast cancer.

TomoBreast hypothesized that hypofractionated 15 fractions/3 weeks image-guided radiation therapy (H-IGRT) can reduce lung-heart toxicity, as compared with normofractionated 25-33 fractions/5-7 weeks conventional radiation therapy (CRT). In a single center 123 women with stage I-II operated breast cancer were randomized to receive CRT (N=64) or H-IGRT (N=59). The primary endpoint used a composite four-items measure of the time to 10% alteration in any of patient-reported outcomes, physician clinical evaluation, echocardiography or lung function tests, analyzed by intention-to-treat. At 12 years median follow-up, overall and disease-free survivals between randomized arms were comparable, while survival time free from alteration significantly improved with H-IGRT which showed a gain of restricted mean survival time of 1.46 years over CRT, P=0.041. The finding establishes TomoBreast as a proof-of-concept that hypofractionated image-guided radiation-therapy can improve the sparing of lung-heart function in breast cancer adjuvant therapy without loss in disease-free survival. Hypofractionation is advantageous, conditional on using an advanced radiation technique. Multicenter validation may be warranted. https://clinicaltrials.gov/ct2/show/NCT00459628. Registered 12 April 2007.

Assessing the impact of adaptations to the clinical workflow in radiotherapy using transit in vivo dosimetry.

Currently in-vivo dosimetry (IVD) is primarily used to identify individual patient errors in radiotherapy. This study investigated possible correlations of observed trends in transit IVD results, with adaptations to the clinical workflow, aiming to demonstrate the possibility of using the bulk data for continuous quality improvement. In total 84,100 transit IVD measurements were analyzed of all patients treated between 2018 and 2022, divided into four yearly periods. Failed measurements (FM) were divided per pathology and into four categories of causes of failure: technical, planning and positioning problems, and anatomic changes. The number of FM due to patient related problems gradually decreased from 9.5% to 6.6%, 6.1% and 5.6% over the study period. FM attributed to positioning problems decreased from 10.0% to 4.9% in boost breast cancer patients after introduction of extra imaging, from 9.1% to 3.9% in Head&Neck patients following education of radiation therapists on positioning of patients' shoulders, from 6.1% to 2.8% in breast cancer patients after introduction of ultrahypofractionated breast radiotherapy with daily online pre-treatment imaging and from 11.2% to 4.3% in extremities following introduction of immobilization with calculated couch parameters and a Surface Guided Radiation Therapy solution. FM related to anatomic changes decreased from 10.2% to 4.0% in rectum patients and from 6.7% to 3.3% in prostate patients following more patient education from dieticians. Our study suggests that IVD can be a powerful tool to assess the impact of adaptations to the clinical workflow and its use for continuous quality improvement.

Image Guided Radiation Therapy

Image Guided Radiation Therapy

Quality and Safety Considerations in Image Guided Radiation Therapy: An ASTRO Safety White Paper Update

PurposeThis updated report on image guided radiation therapy (IGRT) is part of a series of consensus-based white papers previously published by the American Society for Radiation Oncology addressing patient safety. Since the first white papers were published, IGRT technology and procedures have progressed significantly such that these procedures are now more commonly used. The use of IGRT has now extended beyond high-precision treatments, such as stereotactic radiosurgery and stereotactic body radiation therapy, and into routine clinical practice for many treatment techniques and anatomic sites. Therefore, quality and patient safety considerations for these techniques remain an important area of focus. Methods and MaterialsThe American Society for Radiation Oncology convened an interdisciplinary task force to assess the original IGRT white paper and update content where appropriate. Recommendations were created using a consensus-building methodology, and task force members indicated their level of agreement based on a 5-point Likert scale from “strongly agree” to “strongly disagree.” A prespecified threshold of ≥75% of raters who selected “strongly agree” or “agree” indicated consensus. SummaryThis IGRT white paper builds on the previous version and uses other guidance documents to primarily focus on processes related to quality and safety. IGRT requires an interdisciplinary team-based approach, staffed by appropriately trained specialists, as well as significant personnel resources, specialized technology, and implementation time. A thorough feasibility analysis of resources is required to achieve the clinical and technical goals and should be discussed with all personnel before undertaking new imaging techniques. A comprehensive quality-assurance program must be developed, using established guidance, to ensure IGRT is performed in a safe and effective manner. As IGRT technologies continue to improve or emerge, existing practice guidelines should be reviewed or updated regularly according to the latest American Association of Physicists in Medicine Task Group reports or guidelines. Patient safety in the application of IGRT is everyone's responsibility, and professional organizations, regulators, vendors, and end-users must demonstrate a clear commitment to working together to ensure the highest levels of safety.

Insights From Image Guided Radiation Therapy Credentialing for the NRG Oncology RTOG 1112 Liver Stereotactic Body Radiation Therapy Trial

NRG Oncology trial RTOG 1112 is a randomized phase 3 study of sorafenib with or without stereotactic body radiation therapy for locally advanced hepatocellular carcinoma. Image guided radiation therapy (IGRT) credentialing is essential for this study because of the high doses, respiratory motion, and variety of delivery technologies. This analysis presents the IGRT credentialing experience. Credentialing of volumetric IGRT requires submission of planning and localization images, planning structures, and resulting IGRT shifts for a patient treated according to the study requirements. A study reviewer uses these data to repeat the registrations and compare to the actual clinical registrations. Agreement within 5 mm was considered acceptable for credentialing. Volumetric images of 130 fractions from 42 institutions between June 2013 and January 2018 were reviewed. The median agreement between clinical registrations and study reviewer was 3 mm, with 95% of all fractions within 5 mm. A subanalysis identified a statistically significant difference between the use of low-contrast soft tissue and high-contrast surrogates (eg, implanted fiducial markers, surgical clips, metallic stents) for registration. Soft tissue and high-contrast surrogate registrations both agreed within 3 mm in 50% of fractions. However, soft tissue registrations exceeded 10 mm in 3% of fractions, while no high-contrast surrogate registrations exceeded 5 mm. The RTOG 1112 credentialing experience suggests that most institutions perform liver IGRT with sufficient accuracy to deliver stereotactic body radiation therapy safely, as assessed by expert reviewers. Both soft tissue and high-contrast surrogates appear adequate for consistent registration in most instances; however, some disagreements were observed when using soft-tissue registration targets. The use of high-contrast surrogates appears to reduce the small risk of substantial geographic miss owing to mis-registration in liver IGRT.

Assessment of incidental Findings and the Need for Alteration of Treatment Plan after Cone Beam Computer Tomography – A Descriptive Cross - sectional Study

Background: Cone beam computed tomography (CBCT) is commonly used for guidance in radiotherapy and computed tomography (CT) machines. It gives a rapid acquisition of a certain dataset involving a complete view of the area under study. CBCT has attained a great importance in the diagnosis and clinical treatment planning in dentistry in recent times. Aim and objectives: To assess the frequency of different incidental findings on CBCT and the need to alter the treatment plan after a radiological interpretation accordingly. Methods: Ninety-three CBCT reports by a single radiologist in Hamdan Bin Mohamed College of Dental Medicine were collected. Each report was analysed by a single maxillofacial radiologist, for any of the incidental findings that were recorded. These findings were broadly classified depending on their location, nature, and necessity of further intervention, alteration of treatment plan as well as patient age group and gender, and the reason for the scan. At 95% confidence intervals, statistical analysis was performed, using Chi-square test having a p value <0.05 as significant. Results: Our study findings showed that 86 CBCT was taken during the study period (2013 – 2019) showed incidental findings on the scan. A total of 66% of patients demonstrated a minimum of one type of incidental finding. Other findings including root fragments, dental abnormalities, inflammatory bone changes & non-inflammatory TMJ abnormalities were reported in 36 subjects (41.9%). Conclusions: This descriptive study concludes that approximately 66% of patients showed a minimum of one incidental finding on the CBCT scan and about 1% of these findings were instrumental in actually altering the proposed treatment plan. Therefore, it's recommended that a trained-personnel in interpretation techniques of CBCT, must report in all the images to avoid misdiagnosis.

End-to-end testing for stereotactic radiotherapy including the development of a Multi-Modality phantom

PurposeA new insert for a commercially available end-to-end test phantom was designed and in-house manufactured by 3D printing. Subsequently, the insert was tested for different stereotactic radiation therapy workflows (SRS, SBRT, FSRT, and Multimet) also in comparison to the original insert. Material and methodsWorkflows contained imaging (MR, CT), treatment planning, positioning, and irradiation. Positioning accuracy was evaluated for non-coplanar x-ray, kV- and MV-CBCT systems, as well as surface guided radiation therapy. Dosimetric accuracy of the irradiation was measured with an ionization chamber at four different linear accelerators including dynamic tumor tracking for SBRT. ResultsCT parameters of the insert were within the specification. For MR images, the new insert allowed quantitative analysis of the MR distortion. Positioning accuracy of the phantom with the new insert using the imaging systems of the different linacs was < 1 mm/degree also for MV-CBCT and a non-coplanar imaging system which caused > 3 mm deviation with the original insert. Deviation of point dose values was <3% for SRS, FSRT, and SBRT for both inserts. For the Multimet plans deviations exceeded 10% because the ionization chamber was not positioned in each metastasis, but in the center of phantom and treatment plan. ConclusionThe in-house manufactured insert performed well in all steps of four stereotactic treatment end-to-end tests. Advantages over the commercially available alternative were seen for quantitative analysis of deformation correction in MR images, applicability for non-coplanar x-ray imaging, and dynamic tumor tracking.

Ensemble learning and personalized training for the improvement of unsupervised deep learning-based synthetic CT reconstruction.

The growing adoption of magnetic resonance imaging (MRI)-guided radiation therapy (RT) platforms and a focus on MRI-only RT workflows have brought the technical challenge of synthetic computed tomography (sCT) reconstruction to the forefront. Unpaired-data deep learning-based approaches to the problem offer the attractive characteristic of not requiring paired training data, but the gap between paired- and unpaired-data results can belimiting. We present two distinct approaches aimed at improving unpaired-data sCT reconstruction results: a cascade ensemble that combines multiple models and a personalized training strategy originally designed for the paired-datasetting. Comparisons are made between the following models: (1) the paired-data fully convolutional DenseNet (FCDN), (2) the FCDN with the Intentional Deep Overfit Learning (IDOL) personalized training strategy, (3) the unpaired-data CycleGAN, (4) the CycleGAN with the IDOL training strategy, and (5) the CycleGAN as an intermediate model in a cascade ensemble approach. Evaluation of the various models over 25 total patients is carried out using a five-fold cross-validation scheme, with the patient-specific IDOL models being trained for the five patients of fold 3, chosen atrandom. In both the paired- and unpaired-data settings, adopting the IDOL training strategy led to improvements in the mean absolute error (MAE) between true CT images and sCT outputs within the body contour (mean improvement, paired- and unpaired-data approaches, respectively: 38%, 9%) and in regions of bone (52%, 5%), the peak signal-to-noise ratio (PSNR; 15%, 7%), and the structural similarity index (SSIM; 6%, <1%). The ensemble approach offered additional benefits over the IDOL approach in all three metrics (mean improvement over unpaired-data approach in fold 3; MAE: 20%; bone MAE: 16%; PSNR: 10%; SSIM: 2%), and differences in body MAE between the ensemble approach and the paired-data approach are statisticallyinsignificant. We have demonstrated that both a cascade ensemble approach and a personalized training strategy designed initially for the paired-data setting offer significant improvements in image quality metrics for the unpaired-data sCT reconstruction task. Closing the gap between paired- and unpaired-data approaches is a step toward fully enabling these powerful and attractive unpaired-dataframeworks.

WASPE Sleep Deprivation, Paired with an Optical Surface Monitoring System, Can Provide Accurate Radiation Therapy to Pediatric Patients Without the Need for Sedation

This study aimed to explore the use of a protocol for sleep deprivation, combined with a surface optical monitoring system (OSMS)-guided radiation therapy (RT) to eliminate the need for pharmaceutical sedation of pediatric patients with cancer. The study subjects were 28 children aged 0 to 3 years undergoing intensity modulated RT. Parents used the WASPE method to keep the children awake from 6:00 am to 2:00 pm on each day of RT. To compare the potential effects of sleep deprivation versus sedation on treatment, the first 16 patients tested were alternately sleep deprived 1 day and given sedatives the next day for the duration of the RT. In all cases, RT was delivered under the real-time guidance of an OSMS. Twenty-seven of 28 children successfully completed 343 fractions of OSMS-guided RT. The 5-mm threshold for intrafractional motion was exceeded, and treatment was interrupted for patient repositioning during 13 sessions (sleep deprivation: 10 of 253 fractions; sedation: 3 of 90 fractions). Among the first 16 patients, no significant differences in inter- or intrafractional errors were noted on cone beam computed tomography scanning, except for an intrafractional error in the vertical direction for the 8th patient (P=.046). No significant difference in intrafractional errors measured by OSMS was found between the sleep-deprivation and sedation groups, except for 1 in the lateral direction for the 4th patient (P=.042) and 1 in the vertical direction for the 7th patient (P=.05). No differences were found in complete blood counts between the sleep-deprivation and sedation groups. In all, 36 of 52 parents surveyed (69%) preferred sleep deprivation, and only 3 parents (6%) preferred sedatives. The use of a sleep-deprivation protocol with OSMS guidance allows for accurate delivery of RT to children aged 0 to 3 years without the need for sedation and without jeopardizing target coverage. This approach may be useful for children who are resistant to or cannot tolerate sedatives.

Magnetic Resonance-Guided Adaptive Radiation Therapy for Prostate Cancer: The First Results from the MOMENTUM study—An International Registry for the Evidence-Based Introduction of Magnetic Resonance-Guided Adaptive Radiation Therapy

Magnetic resonance (MR)-guided radiation therapy (MRgRT) is a new technique for treatment of localized prostate cancer (PCa). We report the 12-month outcomes for the first PCa patients treated within an international consortium (the MOMENTUM study) on a 1.5T MR-Linac system with ultrahypofractionated radiation therapy. Patients treated with 5×7.25 Gy were identified. Prostate specific antigen-level, physician-reported toxicity (Common Terminology Criteria for Adverse Events [CTCAE]), and patient-reported outcomes (Quality of Life Questionnaire PR25 and Quality of Life Questionnaire C30 questionnaires) were recorded at baseline and at 3, 6, and 12 months of follow-up (FU). Pairwise comparative statistics were conducted to compare outcomes between baseline and FU. The study included 425 patients with localized PCa (11.4% low, 82.0% intermediate, and 6.6% high-risk), and 365, 313, and 186 patients reached 3-, 6-, and 12-months FU, respectively. Median prostate specific antigen level declined significantly to 1.2 ng/mL and 0.1 ng/mL at 12 months FU for the nonandrogen deprivation therapy (ADT) and ADT group, respectively. The peak of genitourinary and gastrointestinal CTCAE toxicity was reported at 3 months FU, with 18.7% and 1.7% grade ≥2, respectively. The QLQ-PR25 questionnaire outcomes showed significant deterioration in urinary domain score at all FU moments, from 8.3 (interquartile range [IQR], 4.1-16.6) at baseline to 12.4 (IQR, 8.3-24.8; P=.005) at 3 months, 12.4 (IQR, 8.3-20.8; P=.018;) at 6 months, and 12.4 (IQR, 8.3-20.8; P=.001) at 12 months. For the non-ADT group, physician- and patient-reported erectile function worsened significantly between baseline and 12 months FU. Ultrahypofractionated MR-guided radiation therapy for localized PCa using a 1.5T MR-Linac is effective and safe. The peak of CTCAE genitourinary and gastrointestinal toxicity was reported at 3 months FU. Furthermore, for patients without ADT, a significant increase in CTCAE erectile dysfunction was reported at 12 months FU. These data are useful for educating patients on expected outcomes and informing study design of future comparative-effectiveness studies.

Online Adaptive Radiation Therapy and Opportunity Cost

Changes in patient anatomy and tumor geometry pose a challenge to ensuring consistent target coverage and organ-at-risk sparing; online adaptive radiation therapy (ART) accounts for these interfractional changes by facilitating replanning before each treatment. This project explored the opportunity cost of computed tomography (CT)-based online ART by evaluating time and human resource requirements. Time-driven activity-based costing (TDABC) was employed to determine the cost of this time to assess if the dosimetric benefit is worthwhile. CT-based online ART was recently employed at our institution and has been used to treat pelvic disease sites (prostate, prostate bed, prostate with nodal coverage, bladder, rectum); data points from all adaptively treated patients (415 fractions) were used. Time taken for each adaptive fraction before treatment, which at our facility is best represented by the duration between 2 cone beam CT scans, was used as a broadly applicable and transferable metric, representing the additional time required for ART on top of standard image guided radiation therapy. Dosimetric effect was also considered by taking the difference of planning target volume V100% for the scheduled and adapted plans. Using recently validated TDABC at this facility, the per fraction cost of ART was determined, reflecting the added cost of ART on top of image guided radiation therapy. A median time of 15.97 (interquartile range, 13.23-18.83) additional minutes was required for each adaptive fraction. TDABC demonstrated an average minimum cost per adapted fraction of $103.58. Dosimetric differences between V100% of the scheduled versus adapted plan showed a mean dosimetric difference of 15.8%. Although online ART decreases the uncertainty of anatomic shifts, each adaptive fraction requires more staff time, delaying completion of other tasks and increasing resource utilization. Although toxicity benefits require further studies, the implementation of progressively complex radiation therapy technologies, like ART, requires consideration of the time and human resource requirements and subsequent opportunity cost.

Safety and Efficacy of Stereotactic MRI-Guided Adaptive Radiation Therapy for Localized Kidney Cancer

<h3>Purpose/Objective(s)</h3> To assess the safety, feasibility as well as short term oncologic and renal functional outcomes of stereotactic MRI guided adaptive radiotherapy (SMART) for localized kidney cancer. <h3>Materials/Methods</h3> Single institution experience of patients undergoing MRI guided radiation therapy with daily plan adaptation for localized kidney cancer from 2020-2021. Patients were treated to a dose of 4000cGy over 5 fractions utilizing a 0.35T MR-Linac. Prior to each fraction, a pre-treatment MRI was obtained to allow for re-contouring of tumor and organs-at-risk. Patients were treated using an MR guided gated breath hold technique. Adverse events were classified according to the <i>Common Terminology Criteria for Adverse Events</i> (CTCAE) guideline version 5.0. <h3>Results</h3> Our cohort includes 12 patients with median age 75 years, median tumor diameter 4.75 cm, and median RENAL Nephrometry score 7. In terms of staging, 5 were cT1a, 5 were cT1b, 1 was cT2a, and 1 was cT3a. In total, 67.7% of patients had baseline Stage III CKD or worse renal function, and median Charlson Comorbidity index was 8. Histologic subtypes were 58.3% RCC and 25% papillary RCC. There was a total of 11 adverse events (AE) within 90 days: 10 were grade 1 for fatigue, nausea, vomiting, and diarrhea; there was one grade 2 AE for nausea (Table 1). No grade 3 or higher events were observed. The median baseline eGFR was 56.5 mL/min/1.73m², with median change in eGFR of -10 mL/min/1.73m² and the median change in tumor diameter was -0.5 cm at 7.5 months of follow-up, with no local or distant progression. No SMART-related hospital admissions occurred (Figure 1). <h3>Conclusion</h3> SMART is a treatment option for localized RCC that is associated with minimal toxicity, limited decline in renal function, and high rates of local tumor control. For patients who are not surgical candidates, SMART may be an effective therapy for localized kidney cancer.

Cost of Care Related to Treatment of Bone Metastases: Real World Data from a National Health Insurance Provider

<h3>Purpose/Objective(s)</h3> Bone metastases are a common occurrence in patients with advanced stage malignancy, often impacting quality of life. Radiation has been, and remains, a highly effective modality for the treatment of symptomatic bone metastases. Various radiation fractionation schemes and techniques exist and are used across the United States in these patients. The cost of care presumably varies significantly based on those factors (technique and number of fractions). We accessed payer claims data from a health insurance provider in Pennsylvania, Delaware, and West Virginia to help determine the actual cost of care for patients with bone metastases treated with radiation. <h3>Materials/Methods</h3> This study was a secondary data analysis of medical claims data using a retrospective design among insured members in Pennsylvania, Delaware, and West Virginia with an ICD-10 code of C79.51 and history of radiation therapy billed under that code from 1/1/2016 to 9/30/2021. Patients were grouped by age, sex, and geographical region. Number of claims and total cost of care were tabulated by year. We also examined which radiation technique was used (intensity modulated radiation therapy (IMRT) vs. 3D conformal radiotherapy (3D CRT) vs. complex isodose plan) based on CPT codes. Lastly, we looked at the use of image guided radiation therapy (IGRT) over that same time period, again using CPT codes. <h3>Results</h3> We identified 29,201 patients treated with radiation for diagnosis code C79.51 between 2016 and 2021. The median number of claims per year was 4,866 (2,744-6,000). Fifty-one percent of patients were male (13,676). The majority of patients (79%) resided in Pennsylvania. The median total cost of care related to ICD-10 C79.51 was $181,918,217 ($163,672,315-$183,565,407). The median number of claims for those years was 95,024 (89,870-101,449). The number of claims per patient varied from 2.3-5.0 and 3.5-10.2 for isodose complex treatment and IMRT, respectively. Most patients were treated using isodose complex technique or 3D CRT (combined 80-90%) with a relatively even split. The use of IMRT remained relatively stable over the timeframe (5-15%). The use of IGRT increased over time, with highest number of claims for IGRT being 2020 (458 claims) (median 266, range: 183-458). The median cost per year for all care related to ICD10 C79.51 was $10,887,581, $7,274,264, and $1,902,141 for patients treated with 3D CRT, IMRT, and isodose complex, respectively. <h3>Conclusion</h3> Radiation remains a widely used technique for the palliation of bone metastases. The cost of care related to its use are significant. The use of IGRT increased over time, with no obvious impact on overall cost of care. The use of IMRT remained low for bone metastases, with an associated increase in cost of care. The overall cost of care remained lowest for those patients treated with isodose complex treatment.

The Feasibility of Biologically Guided Radiation Therapy Implemented in a Small-Animal Radiation Therapy Platform Integrated with Quad-Modal On-Board Imaging

<h3>Purpose/Objective(s)</h3> Unparallel evolution between clinical radiation therapy (RT) paradigms and preclinical RT techniques, especially in biologically guided RT, has posed a challenge to completely validate the benefits and pitfalls of novel RT techniques prior to their translation to bedside practices. In this study, we firstly investigated the feasibility of biologically guided RT implemented within a small animal radiation therapy (SART) platform, with quad-modal on-board positron emission tomography (PET), single-photon emission computed tomography (SPECT), spectral CT, and cone-beam computed tomography (CBCT) imaging integrated, in a Monte Carlo model as a proof-of-concept. <h3>Materials/Methods</h3> The SART platform with quad-modal imaging guidance was modeled by using a planning tool. A preclinical biologically guided RT workflow with quad-modal imaging guidance was designed, in which image-guided RT and emission-guided radiation therapy (EGRT) can be implemented. To demonstrate the potential of contrast-enhanced spectral CT used in biologically guided RT for simultaneously guiding dose prescription based on tracer uptakes and dose calculation based on underlying tissue electron densities in the platform, iodine uptake fractions and virtual non-contrast electron densities in the Kidney1 inserts within a simulated phantom, mixed with an iodine contrast agent at electron fractions of 0.02 and 0.03, were decomposed quantitatively by using the Bayesian eigen tissue decomposition method and the maximum a posterior (MAP) estimation. To demonstrate EGRT implemented in the platform, the preliminary algorithm of EGRT was illustrated by introducing a 2-mm setup error to a target in the simulated phantom. The dose calculation was implemented after the set of binary micro-multileaf collimator (bmMLC) configurations was determined. The dose distributions delivered by EGRT were compared to that delivered by the conventional RT method with three treatment beams with and without setup error. <h3>Results</h3> For the Kidney1 insert with an iodine contrast agent fraction of 0.02, the average relative errors in the iodine contrast agent fraction and the underlying electron density estimated were 0.64% and 0.95%, respectively. In EGRT, the simulations resulted in 4339 and 5197 beamlet responses in an exemplary dose slice delivery with and without the 2-mm setup error, respectively. Compared to the conventional RT method, EGRT scheme introduced into the SART platform was validated to be more robust to setup errors while providing improved tumor targeting and a lesser dose burden on normal tissues during the treatment beam delivery in preclinical RT setting. <h3>Conclusion</h3> The results demonstrated the successful implementation of biologically guided RT within the SART platform with quad-model imaging guidance. With the comprehensive image- and emission-guided RT schemes integrated, this novel SART platform affords one-stop preclinical RT studies.