CT-on-rails Research Articles

Verification of surface-guided radiation therapy (SGRT) alignment for proton breast and chest wall patients by comparison to CT-on-rails and kV-2D alignment.

Surface-guided radiation therapy (SGRT) systems have been widely installed and utilized on linear accelerators. However, the use of SGRT with proton therapy is still a newly developing field, and published reports are currently very limited. To assess the clinical application and alignment agreement of SGRT with CT-on-rails (CTOR) and kV-2D image-guided radiation therapy (IGRT) for breast treatment using proton therapy. Four patients receiving breast or chest wall treatment with proton therapy were the subjects of this study. Patient #1's IGRT modalities were a combination of kV-2D and CTOR. CTOR was the only imaging modality for patients #2 and #3, and kV-2D was the only imaging modality for patient #4. The patients' respiratory motions were assessed using a 2-min surface position recorded by the SGRT system during treatment. SGRT offsets reported after IGRT shifts were recorded for each fraction of treatment. The agreement between SGRT and either kV-2D or CTOR was evaluated. The respiratory motion amplitude was<4mm in translation and <2.0° in rotation for all patients. The mean and maximum amplitude of SGRT offsets after application of IGRT shifts were ≤(2.6mm, 1.6° ) and (6.8mm, 4.5° ) relative to kV-2D-based IGRT; ≤(3.0mm, 2.6° ) and (5.0mm, 4.7° ) relative to CTOR-based IGRT without breast tissue inflammation. For patient #3, breast inflammation was observed for the last three fractions of treatment, and the maximum SGRT offsets post CTOR shifts were up to (14.0mm, 5.2° ). Due to the overall agreement between SGRT and IGRT within reasonable tolerance, SGRT has the potential to serve as a valuable auxiliary IGRT tool for proton breast treatment and may improve the efficiency of proton breast treatment.

CT-on-Rails Utilization for Image Guidance and Plan Adaptation at a Single-Room Proton Therapy Center.

In-room CT-on-rails is a relatively rare imaging modality in proton therapy. This work evaluated the utilization of CT-on-rails (CTOR) for image guidance and plan adaptation at a single-room proton therapy center. All patients treated from the proton center beginning treatment to the current date were evaluated (May 2021 - January 2023). Patients were treated using a Mevion S250i scanning beam proton therapy system with an in-room Definition Edge CTOR. The image guidance technique utilized for each patient was evaluated (CTOR, orthogonal planar kV imaging, or both). For patients who required a new CT for plan adaptation, the use of CT images from CTOR or a new simulation CT was assessed. Of the 132 patients treated over the evaluated time period, 56.0% utilized CTOR for image guidance at some point during their treatment. 21.2% utilized CTOR as the only image guidance technique, while 34.8% utilized CTOR in combination with kV planar imaging. For 43.9% of patients, only orthogonal planar kV imaging was utilized. Head and neck treatment sites most often utilized CTOR alone as an image guidance technique, while central nervous system sites most often utilized kV planar imaging alone. Of the patients who required new CT imaging for plan adaptation, 75.0% utilized CTOR images. Some reasons for patients not being able to utilize CTOR imaging for re-planning were the need for 4DCT imaging (which was not available on the CTOR) or the need to re-make immobilization devices (such as thermoplastic masks due to becoming loose). CTOR was shown to be utilized for image guidance in the majority of patients receiving proton therapy at a single-room proton therapy center. CTOR was able to be used for plan adaptation in a large majority of patients, eliminating the need to schedule additional CT simulation appointments for these patients.

Leveraging deep learning-based segmentation and contours-driven deformable registration for dose accumulation in abdominal structures

Discrepancies between planned and delivered dose to GI structures during radiation therapy (RT) of liver cancer may hamper the prediction of treatment outcomes. The purpose of this study is to develop a streamlined workflow for dose accumulation in a treatment planning system (TPS) during liver image-guided RT and to assess its accuracy when using different deformable image registration (DIR) algorithms. Fifty-six patients with primary and metastatic liver cancer treated with external beam radiotherapy guided by daily CT-on-rails (CTOR) were retrospectively analyzed. The liver, stomach and duodenum contours were auto-segmented on all planning CTs and daily CTORs using deep-learning methods. Dose accumulation was performed for each patient using scripting functionalities of the TPS and considering three available DIR algorithms based on: (i) image intensities only; (ii) intensities + contours; (iii) a biomechanical model (contours only). Planned and accumulated doses were converted to equivalent dose in 2Gy (EQD2) and normal tissue complication probabilities (NTCP) were calculated for the stomach and duodenum. Dosimetric indexes for the normal liver, GTV, stomach and duodenum and the NTCP values were exported from the TPS for analysis of the discrepancies between planned and the different accumulated doses. Deep learning segmentation of the stomach and duodenum enabled considerable acceleration of the dose accumulation process for the 56 patients. Differences between accumulated and planned doses were analyzed considering the 3 DIR methods. For the normal liver, stomach and duodenum, the distribution of the 56 differences in maximum doses (D2%) presented a significantly higher variance when a contour-driven DIR method was used instead of the intensity only-based method. Comparing the two contour-driven DIR methods, differences in accumulated minimum doses (D98%) in the GTV were >2Gy for 15 (27%) of the patients. Considering accumulated dose instead of planned dose in standard NTCP models of the duodenum demonstrated a high sensitivity of the duodenum toxicity risk to these dose discrepancies, whereas smaller variations were observed for the stomach. This study demonstrated a successful implementation of an automatic workflow for dose accumulation during liver cancer RT in a commercial TPS. The use of contour-driven DIR methods led to larger discrepancies between planned and accumulated doses in comparison to using an intensity only based DIR method, suggesting a better capability of these approaches in estimating complex deformations of the GI organs.

Improving GI Toxicity Models Through Deep Learning-Based Segmentation and Biomechanical Model-Based Dose Accumulation

<h3>Purpose/Objective(s)</h3> Current GI toxicity models are limited by the uncertainty in the estimated delivered dose used to develop the models. The purpose of this study is to assess the benefit of harnessing deep learning and biomechanical models to improve the understanding of the dose-toxicity relationship. <h3>Materials/Methods</h3> Retrospective dose accumulation was conducted on 75 patients with primary and metastatic liver cancer treated with external beam radiotherapy guided by daily CT-on-rails (CTOR), based on a novel deformable image registration (DIR) approach that applies biomechanical model-based and intensity-based DIR inside and outside the liver, respectively. The liver was auto-segmented on all images using a clinically validated 2D deep learning model. On a sub-cohort, the combination of stomach and duodenum region of interest (GI ROI) was auto-contoured using a 3D UNet model trained independently on 102 patients. These contours were compared to physician-drawn contours on CTOR, using Dice similarity coefficient (DSC), mean distance to agreement (DTA), Hausdorff distance (HD), and planned dose metrics. Intra-observer variability was evaluated. Doses were converted to equivalent dose in 2Gy fractions (EQD2) for analysis (α/β = 3.5). Differences between planned and delivered dose were calculated, as well as GI ROI daily dose variation. Toxicity probability was calculated based on previously developed accumulated dose normal tissue complication probability (NTCP) models for duodenum and stomach. <h3>Results</h3> Average (SD) DSC, DTA, and HD between the deep learning model and physician-drawn GI ROI were 0.9 (0.1), 0.2 (0.1) cm, and 2.4 (2.2) cm; intra-observer values were 0.9 (0.0), 0.1 (0.0) cm, and 2.3 (0.8) cm, <i>P</i> > 0.1. Average differences in volume (SD), D50 (SD), and D1 (SD) between the AI model and physician-drawn contours were 25.0 (36.7) cc, 0.6 (1.1) Gy, and 0.5 (0.2) Gy; intra-observer values were 7.1 (4.5) cc, 0.2 (0.3) Gy and 0.3 (0.3) Gy, <i>P</i> > 0.1. Average planned and accumulated D1 (EQD2) to the GI ROI were 28.1 Gy and 26.6 Gy, respectively. These distributions were significantly different (<i>P</i> < 0.01), with differences ranging from 0.2 Gy to 2.9 Gy. Daily D1 to the GI ROI varied by up to 47% (average 25%). For 38% of patients, relative differences in NTCP based on planned and accumulated dose were greater than 50%. Compared to planned dose, 63% of the patients had lower NTCP with accumulated dose, and 13% had higher NTCP. <h3>Conclusion</h3> Variability between AI-based and physician-drawn stomach and duodenum segmentation was equivalent to intra-observer variability. Accumulated dose showed statistically significant differences from planned dose for the stomach and duodenum leading to meaningful differences in NTCP. The daily variability in the maximum dose varied by an average of +/- 25%, demonstrating the potential to optimize daily fractionation based on anatomical configuration of the day.

Dosimetric Uncertainties Resulting From Interfractional Anatomic Variations for Patients Receiving Pancreas Stereotactic Body Radiation Therapy and Cone Beam Computed Tomography Image Guidance

PurposeTo estimate the effects of interfractional anatomic changes on dose to organs at risk (OARs) and tumors, as measured with cone beam computed tomography (CBCT) image guidance for pancreatic stereotactic body radiation therapy. Methods and MaterialsWe evaluated 11 patients with pancreatic cancer whom were treated with stereotactic body radiation therapy (33-40 Gy in 5 fractions) using daily CT-on-rails (CTOR) image guidance immediately before treatment with breath-hold motion management. CBCT alignment was simulated in the treatment planning software by aligning the original planning CT to each fractional CTOR image set via fiducial markers. CTOR data sets were used to calculate fractional doses after alignment by applying the rigid shift of the planning CT and CTOR image sets to the planning treatment isocenter and recalculating the fractional dose. Accumulated dose to the gross tumor volume (GTV), tumor vessel interface, duodenum, small bowel, and stomach were calculated by summing the 5 fractional absolute dose-volume histograms into a single dose-volume histogram for comparison with the original planned dose. ResultsFour patients had a GTV D100% of at least 1.5 Gy less than the fractional planned value in several fractions; 4 patients had fractional underestimation of duodenum dose by 1.0 Gy per fraction. The D1.0 cm3 <35 Gy constraint was violated for at least 1 OAR in 3 patients, with either the duodenum (n = 2) or small bowel (n = 1) D1.0 cm3 being higher on the accumulated dose distribution (P = .01). D100% was significantly lower according to accumulated dose GTV (P = .01) and tumor vessel interface (P = .02), with 4 and 2 patients having accumulated D100% ≥4 Gy lower than the planned value for the GTV and tumor vessel interface, respectively. ConclusionsFor some patients, CBCT image guidance based on fiducial alignment may cause large dosimetric uncertainties for OARs and target structures, according to accumulated dose.

Implementation of an HDR brachytherapy–based breast IORT program: Initial experiences

PurposeA multidisciplinary team at our institution developed a novel method of intraoperative breast radiation therapy (precision breast intraoperative radiation therapy [PB-IORT]) that uses high-dose-rate brachytherapy with CT on-rails imaging to deliver high-dose, customized radiotherapy to patients with early-stage breast cancer. This report summarizes our program's experience developing and implementing PB-IORT. Methods and MaterialsLiterature on PB-IORT was reviewed including published articles and abstracts. To evaluate case volume, all patients with a breast cancer diagnosis who underwent breast surgery or breast radiation (2010–2017) at our academic institution were identified. Patients were stratified into pre-IORT and post-IORT eras with initiation of our PB-IORT program in October 2013. Overall trends in surgical and radiation therapy volume in each era were analyzed by linear regression. Travel distance for all surgical patients was calculated using Google Maps (Alphabet Inc.) and then compared between IORT and non-IORT patients. ResultsData from a PB-IORT Phase 1 trial found that the primary endpoints were met and that PB-IORT is feasible and safe. The direct health system's delivery costs for PB-IORT exceed those of 16-fraction whole-breast irradiation when accounting for consumable supplies (multilumen balloon applicator = $2,750 per patient). There was a significant increase in yearly growth of breast cancer surgical volume with PB-IORT. ConclusionsAccrual rates for the ongoing Phase II trial have been quicker than expected in an area where more research is needed. The rapid accrual indicates patient interest and demand for this treatment and that it is very feasible to get more data from randomized trials.

Time-Driven Activity-Based Cost Analysis of CT-Guided Intraoperative High-Dose Rate Brachytherapy Versus Whole Breast Irradiation in the Treatment of Early Stage Breast Cancer

To evaluate the health care delivery cost of single fraction CT-guided intraoperative high-dose rate brachytherapy (HDR-IORT) in early stage breast cancer using time-driven activity-based costing (TDABC). Process maps were created for each step of the radiation treatment process at our institution for early stage breast cancer. The capacity cost from consultation to completion of radiation was calculated for personnel, equipment, and consumable resource. Personnel costs were calculated using individual personnel time and salary data. Equipment costs were calculated to include cost of CT-simulation, treatment planning software, and treatment machine time. Consumable costs were limited to resources specific to the individual radiation treatment (e.g. multi-lumen balloon) of each patient and did not include diagnostic, surgical, or anesthesia costs associated with lumpectomy alone as patients treated with whole breast irradiation (WBI) incurred similar costs. Patients are treated with HDR-IORT on an ongoing prospective trial. The procedure includes lumpectomy and placement of a multi-lumen balloon applicator by the breast surgeon. Intraoperative CT on-rails is utilized for image confirmation of catheter placement, treatment planning and delivery of 12.5 Gy to 1 cm from the balloon surface. In comparison, whole breast irradiation (WBI) alone consisted of 42.56 Gy in 16 fractions, with consideration of a 4 fraction boost. The total health care cost to deliver HDR-IORT for a patient was $4,875. The total cost to deliver WBI alone was $2,832, with an additional $363 for a 4 fraction boost. Radiation oncology personnel accounted for $1,909 (39%) and $1,658 (59%) of the total IORT and WBI cost, respectively. Surgical attending physician time required an additional 30 minutes to allow for balloon placement and image-guided confirmation in the brachytherapy suite. During HDR-IORT, the anesthesia team spent an additional 315 minutes (accounting for multiple team members). Radiation oncology attending time was 16% less for HDR-IORT compared to WBI, 91 minutes versus 108 minutes respectively. Equipment cost was $216 (4%) and $1,174 (41%) for the total cost of HDR-IORT and WBI, respectively. The cost of the multi-lumen balloon applicator ($2,750 per patient) represented 56% of the total IORT cost. TDABC analysis demonstrates a higher cost of delivery for treatment with HDR-IORT compared to WBI, largely due to increased consumable costs. Our calculated total delivery cost ($4,875), which exceeds the current payment rates for other forms of breast IORT, should be considered for reimbursement decisions. These findings exemplify that a streamlined process and dedicated team can result in efficient delivery of HDR-IORT.

A robotic C-arm cone beam CT system for image-guided proton therapy: design and performance.

A ceiling-mounted robotic C-arm cone beam CT (CBCT) system was developed for use with a 190° proton gantry system and a 6-degree-of-freedom robotic patient positioner. We report on the mechanical design, system accuracy, image quality, image guidance accuracy, imaging dose, workflow, safety and collision-avoidance. The robotic CBCT system couples a rotating C-ring to the C-arm concentrically with a kV X-ray tube and a flat-panel imager mounted to the C-ring. CBCT images are acquired with flex correction and maximally 360° rotation for a 53 cm field of view. The system was designed for clinical use with three imaging locations. Anthropomorphic phantoms were imaged to evaluate the image guidance accuracy. The position accuracy and repeatability of the robotic C-arm was high (<0.5 mm), as measured with a high-accuracy laser tracker. The isocentric accuracy of the C-ring rotation was within 0.7 mm. The coincidence of CBCT imaging and radiation isocentre was better than 1 mm. The average image guidance accuracy was within 1 mm and 1° for the anthropomorphic phantoms tested. Daily volumetric imaging for proton patient positioning was specified for routine clinical practice. Our novel gantry-independent robotic CBCT system provides high-accuracy volumetric image guidance for proton therapy. Advances in knowledge: Ceiling-mounted robotic CBCT provides a viable option than CT on-rails for partial gantry and fixed-beam proton systems with the added advantage of acquiring images at the treatment isocentre.

SU‐F‐J‐107: Online Adaptive VMAT Planning Based On Deformed Dose

Purpose:Prostate treatment with volumetric‐modulated arc therapy (VMAT) in conjunction with small PTV margins, allows the dose to the rectum and bladder to be minimized, at the potential cost of prostate coverage. Coverage can be restored by online adaptive planning. Here, the deformed planning dose is used as the goal for adaptive plan optimization.Methods:9 prostate patients with CT‐on‐Rails (CTOR) imaging were replanned using Monaco (Elekta AB, Stockholm, Sweden) with 2 VMAT arcs, and 70 Gy to 95% of the PTV. A variable margin of 4–6 mm was used. The planning CT was deformably registered to each CTOR, the resulting deformation field was then applied to morph the structures and dose to the CTORs, using ADMIRE (Elekta AB, Stockholm Sweden). The deformed dose, edited contours and CTOR were imported into Monaco, and the dose referred as a guide for plan optimization. The original treatment plan was also copied to the CTOR, keeping the center of the prostate as the isocenter, to mimic the current repositioning based therapy.Results:The deformed dose guided optimization maintained the prostate coverage and the sparing of OAR. The shifted plan was unable to do both. The mean percentage volume covered by 100% isodose line increased from 96.11±2.04 to 99.74±0.10 for prostate, and 83.48±2.63 to 94.61±0.34 for PTV by adapting the deformed dose guided optimization. PTV coverage is of some interest, as there still needs to be some margin for intra‐fraction motion. Besides, the resulting lower inter‐fraction dose variation of optimized plan implied a better dose delivery consistency.Conclusion:Using the planned dose, deformed to the daily CTOR provided a successful goal for adaptive optimization, allowing reduced margins, increased OAR sparing, and maintained prostate coverage.Godley receives research grant from Elekta.

Comparison of surface matching and target matching for image-guided pelvic radiation therapy for both supine and prone patient positions.

We investigate the difference between surface matching and target matching for pelvic radiation image guidance. The uniqueness of our study is that all patients have multiple CT‐on‐rails (CTOR) scans to compare to corresponding AlignRT images. Ten patients receiving pelvic radiation were enrolled in this study. Two simulation CT scans were performed in supine and prone positions for each patient. Body surface contours were generated in treatment planning system and exported to AlignRT to serve as reference images. During treatment day, the patient was aligned to treatment isocenter with room lasers, and then scanned with both CTOR and AlignRT. Image‐guidance shifts were calculated for both modalities by comparison to the simulation CT and the differences between them were analyzed for both supine and prone positions, respectively. These procedures were performed for each patient once per week for five weeks. The difference of patient displacement between AlignRT and CTOR was analyzed. For supine position, five patients had an average difference of displacement between AlignRT and CTOR along any direction (vertical, longitudinal, and lateral) greater than 0.5 cm, and one patient greater than 1 cm. Four patients had a maximum difference greater than 1 cm. For prone position, seven patients had an average difference greater than 0.5 cm, and three patients greater than 1 cm. Nine patients had a maximum difference greater than 1 cm. The difference of displacement between AlignRT and CTOR was greater for the prone position than for the supine position. For the patients studied here, surface matching does not appear to be an advisable image‐guidance approach for pelvic radiation therapy for patients with either supine or prone position. There appears to be a potential for large alignment discrepancies (up to 2.25 cm) between surface matching and target matching.PACS number(s): 87.55.‐x

Interstitial High Dose-Rate Gynecologic Brachytherapy With In-Room CT On-Rails Imaging: Early Clinical and Dosimetric Outcomes

Interstitial High Dose-Rate Gynecologic Brachytherapy With In-Room CT On-Rails Imaging: Early Clinical and Dosimetric Outcomes

Intraoperative Breast Irradiation: CT on-rails Balloon Brachytherapy

Intraoperative Breast Irradiation: CT on-rails Balloon Brachytherapy

P13.02 * PROTON THERAPY FOR BRAIN AND SKULL BASE TUMORS AT THE NEW OPENING TRENTO FACILITY

BACKGROUND: Thanks to their distinct physical properties proton therapy (PT) offers a superior dose distribution than photon radiation therapy. For brain and skull base (SB) tumors such dose sparing can be harnessed: a) in benign tumors, to achieve long-term better quality of life and reduced risk of neurocognitive deficits as well as radiation-related malignancies by delivering standard dose level; b) in malignant tumors or malignancies with local aggressiveness, to improve local control by safe delivery of tumor dose escalation. In the following we report an overview on our facility and the neuro-oncology program. METHODS/RESULTS: The Trento facility is built on over an area that will host the new Trento Hospital so that it will be a hospital-based PT center. As opposed to most centers using PT in the past, our facility is equipped with active beam delivery employing the spot scanning technique. A cyclotron provides a library of pencil beams of variable energy (70 - 226 MeV) and spot size (σ, 3 - 7 mm). Within the center, radiation therapy is offered in two treatment rooms. To allow for 360° rotation of the beamline these rooms are equipped with two gantries. In the treatment rooms, patients are placed on a robotic treatment table offering maximal variability and flexibility for patient positioning. The rooms are also equipped with devices enabling X-ray for treatment position verification. In a second step, the rooms will be equipped with cone-beam CT (room 1) and CT on-rails (room 2). Additionally there is one room equipped with horizontal beamline and equivalent beam scanning technology dedicated to quality assurance and preclinical research. For treatment planning imaging, the center is equipped with a dedicated CT and 1.5T MR. The staff is composed by professionals that experienced in leading particle centers in Villigen (CH), Heidelberg (GER), Boston (USA), Jacksonville (USA), Philadelphia (USA). Dedicated protocols for tumors of the brain and SB, for both adults and pediatric patients will be conducted based on the previous conducted trials on PT and potential expected benefit. As mentioned above, according to different clinical aims we are going to treat both benign and malignant tumors. The former group includes pituitary adenomas, schwannoma, benign meningioma, chondrosarcoma, craniopharyngioma, ependymoma, low-grade gliomas, medulloblastoma. In a second step, a PT radiosurgery program will be implemented for some of them. The latter group includes chordoma, high-grade gliomas, and atypical-malignant meningiomas. Regardless of the tumor type patients can be accepted also for re-irradiation. CONCLUSIONS: After a dedicated planning, construction and commissioning phase, patient treatment at Trento PT center is expected for summer 2014. Based on the already demonstrated as well as further potential clinical benefit neuro-oncology represents one of the most important field of interest.

Comparative Assessment of Adaptive Radiation Therapy on Partial Bladder Cancer Treatment between CT-on-Rails (CTOR) and KV Cone Beam CT (CBCT)

Comparative Assessment of Adaptive Radiation Therapy on Partial Bladder Cancer Treatment between CT-on-Rails (CTOR) and KV Cone Beam CT (CBCT)

SU-E-J-214: Comparative Assessment On IGRT On Partial Bladder Cancer Treatment Between CT-On-Rails (CTOR) and KV Cone Beam CT (CBCT)

Purpose: Image-Guided radiation therapy(IGRT) depends on reliable online patient-specific anatomy information to address random and progressive anatomy changes. Large margins have been suggested to bladder cancer treatment due to large daily bladder anatomy variation. KV Cone beam CT(CBCT) has been used in IGRT localization prevalently; however, its lack of soft tissue contrast makes clinicians hesitate to perform daily soft tissue alignment with CBCT for partial bladder cancer treatment. This study compares the localization uncertainties of bladder cancer IGRT using CTon- Rails(CTOR) and CBCT. Methods: Three T2N0M0 bladder cancer patients (total of 66 Gy to partial bladder alone) were localized daily with either CTOR or CBCT for their entire treatment course. A total of 71 sets of CTOR and 22 sets of CBCT images were acquired and registered with original planning CT scans by radiation therapists and approved by radiation oncologists for the daily treatment. CTOR scanning entailed 2mm slice thickness, 0.98mm axial voxel size, 120kVp and 240mAs. CBCT used a half fan pelvis protocol from Varian OBI system with 2mm slice thickness, 0.98axial voxel size, 125kVp, and 680mAs. Daily localization distribution was compared. Accuracy of CTOR and CBCT on partial bladder alignment was also evaluated by comparing bladder PTV coverage. Results: 1cm all around PTV margins were used in every patient except target superior limit margin to 0mm due to bowel constraint. Daily shifts on CTOR averaged to 0.48, 0.24, 0.19 mms(SI,Lat,AP directions); CBCT averaged to 0.43, 0.09, 0.19 mms(SI,Lat,AP directions). The CTOR daily localization showed superior results of V100% of PTV(102% CTOR vs. 89% CBCT) and bowel(Dmax 69.5Gy vs. 78Gy CBCT). CTOR images showed much higher contrast on bladder PTV alignment. Conclusion: CTOR daily localization for IGRT is more dosimetrically beneficial for partial bladder cancer treatment than kV CBCT localization and provided better soft tissue PTV identification.

SU‐E‐J‐189: Credentialing of IGRT Equipment and Processes for Clinical Trials

Purpose:Current dosimetry phantoms used for clinical trial credentialing do not directly assess IGRT processes. This work evaluates a custom‐built IGRT phantom for credentialing of multiple IGRT modalities and processes.Methods:An IGRT phantom was built out of a low‐density body with two inserts. Insert A is used for the CT simulation. Insert B is used for the actual treatment. The inserts contain identical targets in different locations. Relative positions are unknown to the user. The user simulates the phantom (with insert A) as they would a patient, including marking the phantom. A treatment plan is created and sent to the treatment unit. The phantom (with insert B) is then positioned using local IGRT practice. Shifts (planned isocenter, if applicable, and final isocenter) are marked on the phantom using room lasers. The mechanical reproducibility of re‐inserting the inserts within the phantom body was tested using repeat high‐resolution CT scans. The phantom was tested at 7 centers, selected to include a wide variety of imaging equipment.Results:Mechanical reproducibility was measured as 0.5‐0.9mm, depending on the direction. Approaches tested to mark (and transfer) simulation isocenter included lasers, fiducials and reflective markers. IGRT approaches included kV imaging (Varian Trilogy, Brainlab ExacTrac), kV CT (CT‐on‐rails), kV CBCT (Varian Trilogy, Varian Truebeam, Elekta Agility) and MV CT (Tomotherapy). Users were able to successfully use this phantom for all combinations of equipment and processes. IGRT‐based shifts agreed with the truth within 0.8mm, 0.8mm and 1.9mm in the LR, AP, and SI directions, respectively.Conclusion:Based on these preliminary results, the IGRT phantom can be used for credentialing of clinical trials with an action level of 1mm in AP and LR directions, and 2mm in the SI direction, consistent with TG142. We are currently testing with additional institutions with different equipment and processes, including Cyberknife.This project was funded by the Cancer Prevention Research Institute of Texas

Comparison of Reproducibility of Manual and Automated Prostate Contouring Using Kilovoltage Cone Beam Computed Tomography and Diagnostic Quality Computed Tomography

Kilovoltage Cone-Beam Computed Tomography (kV-CBCT) images have less soft tissue contrast when compared to the diagnostic quality images obtained from a CT On-rails (CTOR) system. In addition to daily prostate localization, this volumetric data is valuable for estimation of daily dose delivery and potentially for real time planning, requiring accurate prostate contouring. Using CTOR or kV-CBCT images, we sought to quantify the reproducibility of manual and automated prostate contouring.

SU-E-J-60: Comparison of CT-On-Rails and a 3D Surface Imaging System for Image Guided Pelvic Radiation Therapy for Both Supine and Prone Patient Positions.

We investigate the feasibility of using AlignRT for pelvic radiation image guidance. The uniqueness of our study is that all patients have multiple CT-on-rails (CTOR) scans to compare corresponding AlignRT images to. Ten patients receiving pelvic radiation were enrolled in this study. Two simulation CT scans were performed in supine and prone positions for each patient. Body surface contours were generated in treatment planning system and exported to AlignRT to serve as reference images. The patient was aligned to treatment isocenter with room lasers, and then scanned with both CTOR and AlignRT in both supine and prone positions. Image guidance shifts were calculated for both modalities by comparison to the simulation CT and the differences between them were analyzed. These procedures were performed for each patient once per week for five weeks. The average and maximum difference of displacement between AlignRT and CTOR were calculated for each patient. For supine position, there are 4 patients who had the average difference of displacement between AlignRT and CTOR along any direction (vertical, longitudinal, and lateral) greater than 0.5cm, and 1 patient greater than 1cm. For prone position, there are 7 patients who had the average difference greater than 0.5cm, and 3 patients greater than 1cm. For supine position, there are 4 patients who had the maximum difference great than 1cm. For prone position, there are 9 patients who had the maximum difference greater than 1 cm. The difference of displacement between AlignRT and CTOR is greater for prone position than for supine position. AlignRT does not appear to be an advisable image guidance approach for pelvic radiation therapy for patients with either supine or prone position. There appears to be a potential for large alignment discrepancies (up to 2.25 cm) between AlignRT and CTOR.

CT On-Rails (CTOR) Characterization of Tumor Volume Rate-of-Reduction in Head Neck Squamous Cell Carcinoma Treated with IMRT Simultaneous Integrated Boost (IMRT-SIB) and Concurrent Chemotherapy

CT On-Rails (CTOR) Characterization of Tumor Volume Rate-of-Reduction in Head Neck Squamous Cell Carcinoma Treated with IMRT Simultaneous Integrated Boost (IMRT-SIB) and Concurrent Chemotherapy

SU‐E‐J‐54: Evaluation of a Toolkit for Automatic Deformable Registration and Segmentation of Treatment Images in Clinical Prostate Cancer IGRT Applications

Purpose: High quality IGRT is only practical when robust tools are available for accurate and fast deformable registration and segmentation of the treatment images. We have implemented such a toolkit for the male pelvis using a class of statistically trainable deformable models (SDMs) of anatomical structures, called medial representations (m‐reps). The aim of this study is to evaluate its capabilities and performance in clinical prostate cancer IGRT applications. Methods: An image collection for prostate cancer patients treated with IGRT using a CT‐on‐Rails (CTORs) system was studied retrospectively with this toolkit to determine the actual delivered dose throughout the treatment course. The patient‐specific planning models of the male pelvic organs, including the prostate, bladder, rectum, and femoral heads, were constructed via user‐guided autosegmentation of the planning CT. The planning CT was then automatically registered to the CTORs images via a rigid‐body, soft‐tissue‐based registration method. The planning models were then transformed into initialized treatment models to segment the CTORs images. The essential tissue‐voxel correspondence across treatment images was established by this model‐based segmentation process. The dose delivered to the same tissue elements can, therefore, be accumulated for adaptive planning and/or outcome assessment. Results: Preliminary results show that the m‐rep‐based planning image segmentations are clinically acceptable to the physicians and can be readily constructed from the planning CT with nominal user guidance. The automatic image registration with the treatment‐day image, occasionally followed by manual refinement, also considered acceptable by clinical staff. Treatment image segmentation with intrinsic tissue‐voxel correspondence used substantially less time (5 ± 1.3 minutes) in comparison to manual contouring. Conclusions: Our clinic‐oriented toolkit is effective in segmentation of treatment images of the male pelvis. Application for dose accumulation and adaptive IGRT is in progress.This work has been conducted in collaboration with Morphormics, Inc. with grant support from NCI R44 CA119571.