Reproducibility Of Patient Setup Research Articles

Organ sparing treatment for penile cancer using a 3D-printed high-dose-rate brachytherapy applicator

PURPOSEWe present a case study of the treatment of localized squamous cell carcinoma on the glans penis with a custom-fabricated high-dose-rate (HDR) brachytherapy applicator. METHODS AND MATERIALSA cylindrically shaped applicator was fabricated with eight embedded channels suitable for standard plastic brachytherapy catheters. An additional custom silicone bolus/sleeve was designed to be used with the 3D-printed applicator to provide an additional offset from the source to skin to reduce the surface dose and for patient comfort. RESULTSThe patient (recurrent cT1a penile cancer) underwent CT simulation, and the brachytherapy plan was created with a nominal prescription dose of 40 Gy in 10 fractions given bidaily to the surface, and 35 Gy at 5 mm depth. Dose coverage to the clinical target volume was 94% (D90). Most fractions were treated with only 5-10 min of setup time. Follow up visits up to 1 year showed no evidence of disease with no significant changes in urinary and sexual function and limited cosmetic detriment to the patient. CONCLUSIONSPatient-specific organ-sparing HDR plesiotherapy using 3D printing technology can provide reliable and reproducible patient setup and may be effective in achieving disease control for superficial penile cancer, although preserving patient quality of life.

To Assess the Effect of BMI on Patient Setup Reproducibility in Hypofractionation of Breast Cancer to Establish an Imaging Protocol

Objectives: To analyze the setup accuracy among patients treated for breast cancer with hypofractionation radiation therapy (HFRT) regimen (five fractions instead of 15-16 fractions in standard regimen) and predict the necessity of performing the setup imaging in the 4th and 5th fractions as a function of setup accuracy in the first three fractions. Methods: This retrospective study reviewed setup displacements in each direction (lateral, longitudinal, and vertical) for 51 women with breast cancer treated with HFRT at the Radiation Therapy Unit between September 2020 and May 2022. Besides the five fractions (#1– # 5), the mean setup error was computed for the first three fractions (AVG-III) for each direction. Setup accuracy rates were computed for each direction and fraction as the percentage of fractions with setup error ≤ 0.5 cm. The correlations of #1, #2, #3, and AVG-III setup errors and their value in indicating #4 and #5 setup error and accuracy were analyzed using Pearson's coefficient and Receiver Operating Characteristics (ROC) curve, respectively. Furthermore, the effect of body mass index (BMI) on setup reproducibility was analyzed using logistic regression Result: The mean (SD) age of the participants was 54.41 (11.46) years. There was a high percentage of overweight (25.5%) and obese (53.0%). The mean setup error was 0.05) and #5 (r = -0.128–0.254; p>0.05) within any of the first three fractions or AVG-III, in any of the directions. In the ROC curve, only #5 accuracy was indicated by #3 in the longitudinal direction (AUC=0.89, p=0.025). BMI was only associated with inaccurate setup for fraction #3 in the lateral direction, in a positive relationship (OR=1.15, 95% CI = 1.01–1.30; p=0.031). Conclusion: Setup accuracy in the first fractions of HFRT does not predict accuracy in the two last fractions nor is predicted by the patient’s BMI. Consequently, women with breast cancer treated with HFRT require daily imaging for optimal setup before each radiotherapy fraction.

Dose coverage and breath-hold analysis of breast cancer patients treated with surface-guided radiotherapy

BackgroundSurface-guided radiotherapy (SGRT) is used to ensure a reproducible patient set-up and for intra-fraction motion monitoring. The arm position of breast cancer patients is important, since this is related to the position of the surrounding lymph nodes. The aim of the study was to investigate the set-up accuracy of the arm of patients positioned using SGRT. Moreover, the actual delivered dose was investigated and an extensive breath-hold analysis was performed.Methods84 patients who received local or locoregional breast radiation therapy were positioned and monitored using SGRT. The accuracy of the arm position, represented by the clavicle position, was studied on the anterior–posterior kV-image. To investigate the effect of changes in anatomy and patient set-up, the actual delivered dose was calculated on cone-beam CT-scans (CBCT). A deformable registration of the CT to the CBCT was applied to deform the structures of the CT onto the CBCT. The minimum dose in percentage of the prescribed dose that was received by 98% of different CTV volumes (D98) was determined. An extensive breath-hold analysis was performed and definitions for relevant parameters were given.ResultsThe arm position of 77 out of 84 patients in total was successful, based on the clavicle rotation. The mean clavicle rotation was 0.4° (± 2.0°). For 89.8% of the patients who were irradiated on the whole-breast D98 was larger than 95% of the prescribed dose (D98 > 95%). D98 > 95% applied for 70.8% of the patients irradiated on the chest wall. Concerning the lymph node CTVs, D98 > 95% for at least 95% of the patients. The breath-hold analysis showed a mean residual setup error of − 0.015 (± 0.90), − 0.18 (± 0.82), − 0.58 (± 1.1) mm in vertical, lateral, and longitudinal direction, respectively. The reproducibility and stability of the breath-hold was good, with median 0.60 mm (95% confidence interval (CI) [0.66–0.71] mm) and 0.20 mm (95% CI 0.21–0.23] mm), respectively.ConclusionsUsing SGRT we were able to position breast cancer patients successfully, with focus on the arm position. The actual delivered dose calculated on the CBCT was adequate and no relation between clavicle rotation and actual delivered dose was found. Moreover, breath-hold analysis showed a good reproducibility and stability of the breath-hold.Trial registration CCMO register NL69214.028.19.

Retrospective Analysis of Replan Frequency and Causes in Esophageal Cancer Patients Treated with Spot Scanned Proton Therapy

<h3>Purpose/Objective(s)</h3> For patients with esophageal cancer treated with intensity-modulated proton therapy (IMPT) at our institution, weekly verification CT scans are obtained to ensure that the plan is still acceptable. If unacceptable deviations from the intended dose are observed, replanning is performed. This study aims to investigate the frequency and causes of replans to determine the appropriate frequency of performing verification scans. <h3>Materials/Methods</h3> Data from a cohort of 205 esophageal cancer patients treated with IMPT between 2015 and 2020 were retrospectively analyzed. Patients were typically positioned head first supine with arms up in a vacuum immobilization device, and a four-dimensional CT (4DCT) simulation scan was obtained. The typical prescription was 50 Gy in 25 fractions over 5 weeks, with contours delineated as per consensus guidelines. For tumor motion ≤ 10 mm, patients were treated free-breathing with isolayer repainting, while for motion > 10 mm, gating was also added. Two posterior oblique beams were typically used, and single field optimization was performed. Robust optimization was utilized with 5-mm translational perturbations and 3% range uncertainty, with dose evaluation, also performed on the extreme respiratory phases. Weekly 4DCT verification scans in treatment position were acquired. Rigid image registration to the original planning CT image set was performed, and the care team reviewed the recalculated dose distributions to determine the need for replan. CTV (V95%) % was selected as a metric to compare the difference in target volume dose between verification scans that did [CTV_replan (V95%) %], versus did not [CTV_no-replan (V95%) %], lead to a replan. <h3>Results</h3> The primary tumor location was upper/middle esophagus (16%) or lower/gastroesophageal junction (83%). 21 patients (10%) required replanning, including 3 patients with 2 replans. Replans occurred during the 1^st (20%), 2^nd (33%), 3^rd (20%), or 4^th (25%) weeks of treatment. Primary reasons for replanning were a superior shift of the diaphragm baseline position affecting the range of the beams entering near this interface (46%), changes in tumor size or position (17%), new or resolving pleural effusion affecting the range of beams (13%), changes in stomach filling affecting the target geometry (13%), and patient setup reproducibility issues (13%). The average value of CTV_no-replan (V95%) % = 98% ± 3% vs. CTV_replan (V95%) % = 96% ± 1%. The modest size of this difference suggests that other factors, including poor fidelity of rigid CTV contours, also contribute to clinical decision-making. <h3>Conclusion</h3> In this large cohort of patients with esophageal cancer treated with robustly planned IMPT, the rate of adaptive replanning was 10% and resulted from 5 discrete changes as described above. Every other week frequency of verification scans should be considered.

Streaking artifact reduction for CBCT-based synthetic CT generation in adaptive radiotherapy.

Cone-beam computed tomography (CBCT) is widely used for daily image guidance in radiation therapy, enhancing the reproducibility of patient setup. However, its application in adaptive radiotherapy (ART) is limited by many imaging artifacts and inaccurate Hounsfield units (HUs). The correction of CBCT image is necessary and of great value for CBCT-based ART. To explore the synthetic CT (sCT) generation from CBCT images of thorax and abdomen patients, which usually surfer from serious artifacts duo to organ state changes. In this study, a streaking artifact reduction network (SARN) is proposed to reduce artifacts and combine with cycleGAN to generate high-quality sCT images from CBCT and achieve an accurate dose calculation. The proposed SARN was trained in a self-supervised manner. Artifact-CT images were generated from planning CT by random deformation and projection replacement, and SARN was trained based on paired artifact-CT and CT images. The planning CT and CBCT images of 260 patients with cancer, including 120 thoracic and 140 abdominal CT scans, were used to train and evaluate neural networks. The CBCT images of another 12 patients in late treatment fractions, which contained large anatomy changes, were also tested by trained models. The trained models include commonly used U-Net, cycleGAN, attention-gated cycleGAN (cycAT), and cascade models combined SARN with cycleGAN or cycAT. The generated sCT images were compared in terms of image quality and dose calculation accuracy. The sCT images generated by SARN combined with cycleGAN and cycAT showed the best image quality, removed the most artifacts, and retained the normal anatomical structure. The SARN+cycleGAN performed best in streaking artifacts removal with the maximum percent integrity uniformity (PIUm ) of 91.0% and minimum standard deviation (SD) of 35.4 HU for delineated artifact regions among all models. The mean absolute error (MAE) of CBCT images in the thorax and abdomen were 71.6 and 55.2 HU, respectively, using planning CT images after deformable registration as ground truth. Compared with CBCT, the thoracic and abdominal sCT images generated by each model had significantly improved image quality with smaller MAE (p < 0.05). The SARN+cycAT obtained the minimum MAEs of 42.5 HU in the thorax while SARN+cycleGAN got the minimum MAEs of 32.0 HU in the abdomen. The sCT generated by U-Net had a remarkably lower anatomical structure accuracy compared with the other models. The thoracic and abdominal sCT images generated by SARN+cycleGAN showed optimal dose calculation accuracy with gamma passing rates (2 mm/2%) of 98.2% and 96.9%, respectively. The proposed SARN can reduce serious streaking artifacts in CBCT images. The SARN combined with cycleGAN can generate high-quality sCT images with fewer artifacts, high-accuracy HU values, and accurate anatomical structures, thus providing reliable dose calculation in ART.

Feasibility of surface guided radiotherapy for patient positioning in breast radiotherapy versus conventional tattoo-based setups- a systematic review.

BackgroundTraditionally tattoos are used for patient setup in radiotherapy. However they may pose challenges for the radiotherapists to achieve precise patient alignment, and serve as a permanent visual reminder of the patient’s diagnosis and often challenging cancer journey. The psychological impact of tattoos has been recognized in recent years. The increasing complexity of treatment techniques and the utilization of hypofractionated regimes, requires an enhanced level of accuracy and safety. Surface guided radiotherapy (SGRT) enables improvements in the accuracy and reproducibility of patient isocentric and postural alignment, enhanced efficiency, and safety in breast radiotherapy.PurposeThe aim of this review was to compare the accuracy and reproducibility of SGRT to conventional tattoo-based setups in free-breathing breast radiotherapy and to determine if SGRT can reduce the frequency of routine image guided radiotherapy (IGRT).Materials and MethodsA systematic literature review was performed as per PRISMA guidelines. Papers identified through PubMed, Embase, Web of Science and Google Scholar database searches between 2010 and 2021, were critically appraised. Systematic, random, mean residual errors and 3D vector shifts as determined by IGRT verification were analysed.ResultsA review of 13 full papers suggests SGRT improves the accuracy and reproducibility of patient setup in breast radiotherapy with consistent reductions in the residual errors. There appears to be a good correlation between SGRT setups and radiographic imaging. The frequency of IGRT and the corresponding dose could potentially be reduced. Additionally, SGRT improves treatment efficiency.ConclusionSGRT appears to have improved the accuracy and reproducibility of patient setup and treatment efficiency of breast radiotherapy compared to conventional tattoo/laser-based method, with the potential to reduce the frequency of routine IGRT. The reliance on tattoos in breast radiotherapy are likely to become obsolete with positive implications for both patients and clinical practice.

Multi-jet fusion for additive manufacturing of radiotherapy immobilization devices: Effects of color, thickness, and orientation on surface dose and tensile strength.

Immobilization devices are used to obtain reproducible patient setup during radiotherapy treatment, improving accuracy, and reducing damage to surrounding healthy tissue. Additive manufacturing is emerging as a viable method for manufacturing and personalizing such devices. The goal of this study was to investigate the dosimetric and mechanical properties of a recent additive technology called multi‐jet fusion (MJF) for radiotherapy applications, including the ability for this process to produce full color parts. Skin dose testing included 50 samples with dimensions 100 mm × 100 mm with five different thicknesses (1 mm, 2 mm, 3 mm, 4 mm, and 5 mm) and grouped into colored (cyan, magenta, yellow, and black (CMYK) additives) and non‐colored (white) samples. Results using a 6 MV beam found that surface dose readings were predominantly independent of the colored additives. However, for an 18 MV beam, the additives affected the surface dose, with black recording significantly lower surface dose readings compare to other colors. The accompanying tensile testing of 175 samples designed to ASTM D638 type I standards found that the black agent resulted in the lowest ultimate tensile strength (UTS) for each thickness of 1–5 mm. It was also found that the print orientation had influence on the skin dose and mechanical properties of the samples. When all data were combined and analyzed using a multiple‐criteria decision‐making technique, magenta was found to offer the best balance between high UTS and low surface dose across different thicknesses and orientations, making it an optimal choice for immobilization devices. This is the first study to consider the use of color MJF for radiotherapy immobilization devices, and suggests that color additives can affect both dosimetry and mechanical performance. This is important as industrial additive technologies like MJF become increasingly adopted in the health and medical sectors.

Radiotherapy in oncological emergencies: fast-track treatment planning

Background and purposeTo report on our clinical experience with a newly implemented workflow for radiotherapy (RT) emergency treatments, which allows for a fast treatment application outside the regular working-hours, and its clinical applicability.MethodsTreatment planning of 18 emergency RT patients was carried out using diagnostic computed tomography (CT) without a dedicated RT simulation CT. The cone-beam CT (CBCT) deviations of the first RT treatment were analyzed regarding setup accuracy. Furthermore, feasibility of the “fast-track” workflow was evaluated with respect to dose deviations caused by different Hounsfield unit (HU) to relative electron density (rED) calibrations and RT treatment couch surface shapes via 3D gamma index analysis of exemplary treatment plans. The dosimetric uncertainty introduced by different CT calibrations was quantified.ResultsMean patient setup vs. CBCT isocenter deviations were (0.49 ± 0.44) cm (x), (2.68 ± 1.63) cm (y) and (1.80 ± 1.06) cm (z) for lateral, longitudinal and vertical directions, respectively. Three out of four dose comparisons between the emergency RT plan calculated on the diagnostic CT and the same plan calculated on the treatment planning CT showed clinically acceptable gamma passing rates, when correcting for surface artifacts. The maximum difference of rED was 0.054, while most parts of the CT calibration curves coincided well.ConclusionIn an emergency RT setting, the use of diagnostic CT data for treatment planning might be time-saving and was shown to be suitable for many cases, considering reproducibility of patient setup, accuracy of initial patient setup and accuracy of dose-calculation.

A comparative evaluation of two head and neck immobilization devices using verification film for head and neck cancer patients receiving radiation therapy at Ocean Road Cancer Institute (ORCI) aero-digestive tract

Background: Accurate and reproducible patient positioning is fundamental to the success of fractionated radiotherapy. To achieve accurate daily treatment delivery, various immobilization devices are used in radiotherapy departments. At ORCI the mostly used immobilization devices for radiotherapy treatment of head and neck cancer patients are thermoplastic mask and LS-2000. However, the effectiveness and accuracy of these immobilization devices in daily set-up is not known. This study was performed to evaluate accuracy and reproducibility of patient setup for both thermoplastic mask and LS-2000 devices, during irradiation of head and neck tumors.

Reproducibility of patient setup in the seated treatment position: A novel treatment chair design.

Radiotherapy in a seated position may be indicated for patients who are unable to lie on the treatment couch for the duration of treatment, in scenarios where a seated treatment position provides superior anatomical positioning and dose distributions, or for a low‐cost system designed using a fixed treatment beam and rotating seated patient. In this study, we report a novel treatment chair that was constructed to allow for three‐dimensional imaging and treatment delivery while ensuring robust immobilization, providing reproducibility equivalent to that in the traditional supine position. Five patients undergoing radiation treatment for head‐and‐neck cancers were enrolled and were setup in the chair, with immobilization devices created, and then imaged with orthogonal X‐rays in a scenario that mimicked radiation treatments (without treatment delivery). Six subregions of the acquired images were rigidly registered to evaluate intra‐ and interfraction displacement and chair construction. Displacements under conditions of simulated image guidance were acquired by first registering one subregion; the residual displacement of other subregions was then measured. Additionally, we administered a patient questionnaire to gain patient feedback and assess comparison to the supine position. Average inter‐ and intrafraction displacements of all subregions in the seated position were less than 2 and 3 mm, respectively. When image guidance was simulated, L‐R and A‐P interfraction displacements were reduced by an average of 1 mm, providing setup of comparable quality to supine setups. The enrolled patients, who had no indication for a seated treatment position, reported no preference in the seated or the supine position. The novel chair design provides acceptable inter‐ and intrafraction displacement, with reproducibility equivalent to that reported for patients in the supine position. Patient feedback will be incorporated in the refinement of the chair, facilitating treatment of head‐and‐neck cancer in patients who are unable to lie for the duration of treatment or for use in an economical fixed‐beam setup.

PUB110 Clinical Results of an EPID-Based In-vivo Dosimetry for Lung Cancer Radiation Therapy

In-vivo dose verification is a step of quality assurance to ensure that the dose delivered during treatment agrees with the prescribed. This work reports the in-vivo dosimetry (IVD) results obtained with SOFTDISO (Best Medical Italy). SOFTDISO was developed by National Institute of Nuclear Physics and Catholic University of Sacred Heart (Rome). The software reconstructs in quasi-real time the dose at isocenter (Diso) from the transit signal acquired by the EPID and the comparison between EPIDs of every fractions. For each beam and fraction, the R ratios between Diso in 3D-CRT plans for lung targets and the dose (2 Gy/fraction) calculated by the treatment planning system Diso,TPS (Oncentra) were computed. The acceptance criteria was 0.95≤R≤1.05. The γ-analysis (DD=5%; Dd=5mm) between EPIDs to test the beam delivery reproducibility with the Pγ<1>90% and γmean<0.5 was performed. Fourteen patients with lung cancer were treated with 6 MV photon beams delivered by an Elekta Synergy Agility. The pass criteria was Δd equal to the mean distance Δr (mm) along x, y, z directions, accepted in the patient set-up reproducibility. The IVD test were performed twice weekly when the CBCT wasn't acquired. The IVD supplied 682 tests. The tests off-tolerance were >13% for R, >35% for Pγ<1 and >16% for γmean. For each patient the Rmean value was within the tolerance level. As regards Pγ<1 and γmean, 70% and 86% of patients had values within the tolerance, respectively. These values were obtained considering set-up errors and morphological changes (tumor reduction, atelectasis and/or air). Results of an EPID-based in-vivo dosimetry for lung cancer treatments are in tolerance for the dose at the isocenter (Rvalue). The γ-analysis suffer from some restrictions due to morphological changes that affect the results. The SOFTDISO real-time analysis allows to daily investigate the dose delivery.

SU‐F‐J‐34: Automatic Target‐Based Patient Positioning Framework for Image‐Guided Radiotherapy in Prostate Cancer Treatment

Purpose:Current image‐guided radiotherapy (IGRT) procedure is bonebased patient positioning, followed by subjective manual correction using cone beam computed tomography (CBCT). This procedure might cause the misalignment of the patient positioning. Automatic target‐based patient positioning systems achieve the better reproducibility of patient setup. Our aim of this study was to develop an automatic target‐based patient positioning framework for IGRT with CBCT images in prostate cancer treatment.Methods:Seventy‐three CBCT images of 10 patients and 24 planning CT images with digital imaging and communications in medicine for radiotherapy (DICOM‐RT) structures were used for this study. Our proposed framework started from the generation of probabilistic atlases of bone and prostate from 24 planning CT images and prostate contours, which were made in the treatment planning. Next, the gray‐scale histograms of CBCT values within CTV regions in the planning CT images were obtained as the occurrence probability of the CBCT values. Then, CBCT images were registered to the atlases using a rigid registration with mutual information. Finally, prostate regions were estimated by applying the Bayesian inference to CBCT images with the probabilistic atlases and CBCT value occurrence probability. The proposed framework was evaluated by calculating the Euclidean distance of errors between two centroids of prostate regions determined by our method and ground truths of manual delineations by a radiation oncologist and a medical physicist on CBCT images for 10 patients.Results:The average Euclidean distance between the centroids of extracted prostate regions determined by our proposed method and ground truths was 4.4 mm. The average errors for each direction were 1.8 mm in anteroposterior direction, 0.6 mm in lateral direction and 2.1 mm in craniocaudal direction.Conclusion:Our proposed framework based on probabilistic atlases and Bayesian inference might be feasible to automatically determine prostate regions on CBCT images.

Site-specific tolerance tables and indexing device to improve patient setup reproducibility.

While the implementation of tools such as image‐guidance and immobilization devices have helped to prevent geometric misses in radiation therapy, many treatments remain prone to error if these items are not available, not utilized for every fraction, or are misused. The purpose of this project is to design a set of site‐specific treatment tolerance tables to be applied to the treatment couch for use in a record and verify (R&V) system that will insure accurate patient setup with minimal workflow interruption. This project also called for the construction of a simple indexing device to help insure reproducible patient setup for patients that could not be indexed with existing equipment. The tolerance tables were created by retrospective analysis on a total of 66 patients and 1,308 treatments, separating them into five categories based on disease site: lung, head and neck (H&N), breast, pelvis, and abdomen. Couch parameter tolerance tables were designed to encompass 95% of treatments, and were generated by calculating the standard deviation of couch vertical, longitudinal, and lateral values using the first day of treatment as a baseline. We also investigated an alternative method for generating the couch tolerances by updating the baseline values when patient position was verified with image guidance. This was done in order to adapt the tolerances to any gradual changes in patient setup that would not correspond with a mistreatment. The tolerance tables and customizable indexing device were then implemented for a trial period in order to determine the feasibility of the system. During this trial period we collected data from 1,054 fractions from 65 patients. We then analyzed the number of treatments that would have been out of tolerance, as well as whether or not the tolerances or setup techniques should be adjusted. When the couch baseline values were updated with every imaging fraction, the average rate of tolerance violations was 10% for the lung, H&N, abdomen, and pelvis treatments. Using the indexing device, tolerances for patients with pelvic disease decreased (e.g., from 5.3 cm to 4.3 cm longitudinally). Unfortunately, the results from breast patients were highly variable due to the complexity of the setup technique, making the couch an inadequate surrogate for measuring setup accuracy. In summary, we have developed a method to turn the treatment couch parameters within the R&V system into a useful alert tool, which can be implemented at other institutions, in order to identify potential errors in patient setup.PACS numbers: 87.53Kn, 87.55.kh, 87.55.ne, 87.55.km, 87.55K‐, 87.55.Qr

Efficacy and workload analysis of a fixed vertical couch position technique and a fixed-action-level protocol in whole-breast radiotherapy.

Quantification of the setup errors is vital to define appropriate setup margins preventing geographical misses. The no‐action–level (NAL) correction protocol reduces the systematic setup errors and, hence, the setup margins. The manual entry of the setup corrections in the record‐and‐verify software, however, increases the susceptibility of the NAL protocol to human errors. Moreover, the impact of the skin mobility on the anteroposterior patient setup reproducibility in whole‐breast radiotherapy (WBRT) is unknown. In this study, we therefore investigated the potential of fixed vertical couch position‐based patient setup in WBRT. The possibility to introduce a threshold for correction of the systematic setup errors was also explored. We measured the anteroposterior, mediolateral, and superior–inferior setup errors during fractions 1–12 and weekly thereafter with tangential angled single modality paired imaging. These setup data were used to simulate the residual setup errors of the NAL protocol, the fixed vertical couch position protocol, and the fixed‐action–level protocol with different correction thresholds. Population statistics of the setup errors of 20 breast cancer patients and 20 breast cancer patients with additional regional lymph node (LN) irradiation were calculated to determine the setup margins of each off‐line correction protocol. Our data showed the potential of the fixed vertical couch position protocol to restrict the systematic and random anteroposterior residual setup errors to 1.8 mm and 2.2 mm, respectively. Compared to the NAL protocol, a correction threshold of 2.5 mm reduced the frequency of mediolateral and superior–inferior setup corrections with 40% and 63%, respectively. The implementation of the correction threshold did not deteriorate the accuracy of the off‐line setup correction compared to the NAL protocol. The combination of the fixed vertical couch position protocol, for correction of the anteroposterior setup error, and the fixed‐action–level protocol with 2.5 mm correction threshold, for correction of the mediolateral and the superior–inferior setup errors, was proved to provide adequate and comparable patient setup accuracy in WBRT and WBRT with additional LN irradiation.PACS numbers: 87.53.Kn, 87.57.‐s

Evaluation of Set-up Accuracy for Frame-based and Frameless Lung Stereotactic Body Radiation Therapy

The purpose of this study was to evaluate the set up accuracy using stereotactic body frame and frameless immobilizer for lung stereotactic body radiation therapy (SBRT). For total 40 lung cancer patients treated by SBRT, 20 patients using stereotactic body frame and other 20 patients using frameless immobilizer were separately enrolled in each group. The setup errors of each group depending on the immobilization methods were compared and analyzed. All patients received the dose of 48∼60 Gy for 4 or 5 fractions. Before each treatment, a patient was first localized to the treatment isocenter using room laser s, and further aligned with a series of image guidance procedures; orthogonal kV radiographs, cone-beam CT, o rthogonal fluoroscopy. The couch shifts during these procedures were recorded and analyzed for systematic and random errors of each group. Student t-test was performed to evaluate significant difference depending on the immobilization methods. The setup reproducibility was further analyzed using F-test with the random errors excluding the systematic setup errors. In addition, the ITV-PTV margin for each group was calculated. The setup errors for SBF were 0.05±0.25 cm in vertical direction, 0.20±0.38 cm in longitudinal direction, and 0.02±0.30 cm in lateral direction, respectively. However the setup errors for frameless immobilizer showed a significant increase of -0.24±0.25 cm in vertical direction while similar results of 0.06±0.34 cm, −0.02±0.25 cm in longitudinal and lateral directions. ITV-PTV margins for SBF were 0.67 cm (vertical), 0.99 cm (longitudinal), and 0.83 cm (lateral), respectively. On the other hand, ITV-PTV margins for Frameless immobilizer were 0.75 cm (vertical), 0.96 cm (longitudinal), and 0.72 cm (lateral), indicating less than 1 mm difference for all directions. In conclusion, stereotactic body frame improves reproducibility of patient setup, resulted in 0.1∼0.2 cm in both vertical and longitudinal directions. However the improvements are not substantial in clinic considering the effort and time consumption required for SBF setup.

SU‐E‐T‐426: Dose Delivery Accuracy in Breast Field Junction for Free Breath and Deep Inspiration Breath Hold Techniques

Purpose:The purpose of this work was to verify the accuracy of the dose distribution along the field junction in a half beam irradiation technique for breast cancer patients receiving radiation to the breast or chest wall (CW) and the supraclavicular LN region for both free breathing and deep inspiration breath hold (DIBH) technique.Methods:We performed in vivo measurements for nine breast cancer patients receiving radiation to the breast/CW and to the supraclavicular LN region. Six patients were treated to the left breast/CW using DIBH technique and three patients were treated to the right breast/CW in free breath. We used five microMOSFET dosimeters: three located along the field junction, one located 1 cm above the junction and the fifth microMOSFET located 1 cm below the junction. We performed consecutive measurements over several days for each patient and compared the measurements to the TPS calculation (Eclipse, Varian™).Results:The calculated and measured doses along the junction were 0.97±0.08 Gy and 1.02±0.14 Gy, respectively. Above the junction calculated and measured doses were 0.91±0.08 Gy and 0.98±0.09 Gy respectively, and below the junction calculated and measured doses were 1.70±0.15 Gy and 1.61±0.09 Gy, respectively. All differences were not statistically significant. When comparing calculated and measured doses for DIBH patients only, there was still no statistically significant difference between values for all dosimeter locations. Analysis was done using the Mann‐Whitney Rank‐Sum Test.Conclusion:We found excellent correlation between calculated doses from the TPS and measured skin doses at the junction of several half beam fields. Even for the DIBH technique, where there is more potential for variance due to depth of breath, there is no over or underdose along the field junction. This correlation validates the TPS, as well an accurate, reproducible patient setup.

Monte Carlo modeling and image-guidance in particle therapy

Monte Carlo modeling and image-guidance in particle therapy

A Cooperatively Controlled Robot for Ultrasound Monitoring of Radiation Therapy.

Image-guided radiation therapy (IGRT) involves two main procedures, performed in different rooms on different days: (1) treatment planning in the simulator room on the first day, and (2) radiotherapy in the linear accelerator room over multiple subsequent days. Both the simulator and the linear accelerator include CT imaging capabilities, which enables both treatment planning and reproducible patient setup, but does not provide good soft tissue contrast or allow monitoring of the target during treatment. We propose a cooperatively-controlled robot to reproducibly position an ultrasound (US) probe on the patient during simulation and treatment, thereby improving soft tissue visualization and allowing real-time monitoring of the target. A key goal of the robotic system is to produce consistent tissue deformations for both CT and US imaging, which simplifies registration of these two modalities. This paper presents the robotic system design and describes a novel control algorithm that employs virtual springs to implement guidance virtual fixtures during "hands on" cooperative control.

Reproducibility of target coverage in stereotactic spot scanning proton lung irradiation under high frequency jet ventilation

PurposeTo investigate scanned-beam proton dose distribution reproducibility in the lung under high frequency jet ventilation (HFJV). Materials and methodsFor 11 patients (12 lesions), treated with single-fraction photon stereotactic radiosurgery under HFJV, scanned-beam proton plans were prepared with the TRiP98 treatment planning system using 2, 3–4 and 5–7 beams. The planning objective was to deliver at least 95% of the prescription of 33Gy (RBE) to 98% of the PTV. Plans were subsequently recomputed on localization CT scans. Additionally, for selected cases, the effects of range uncertainties were investigated. ResultsMedian GTV V98% was 98.7% in the original 2-field plans and 93.7% in their recomputation (p=0.039). The respective values were 99.0% and 98.0% (p=0.039) for the 3–4-field plans and 100.0% and 99.6% (p=0.125) for the 5–7-field plans. CT calibration uncertainties of ±3.5% led to a GTV V98% reduction below 1.5 percentual points in most cases and reaching 3 percentual points for 2-field plans with beam undershoot. ConclusionsThrough jet ventilation, reproducible tumor fixation for proton radiotherapy of lung lesions is achievable, ensuring excellent target coverage in most cases. In few cases, non-optimal patient setup reproducibility induced density changes across beam entrance channels, leading to dosimetric deterioration between planning and delivery.

Tatouage invisible : un avantage cosmétique pour les patientes en cours de radiothérapie mammaire

Traditionally tattoos are used for patient setup in radiotherapy. However they may pose challenges for the radiotherapists to achieve precise patient alignment, and serve as a permanent visual reminder of the patient’s diagnosis and often challenging cancer journey. The psychological impact of tattoos has been recognized in recent years. The increasing complexity of treatment techniques and the utilization of hypofractionated regimes, requires an enhanced level of accuracy and safety. Surface guided radiotherapy (SGRT) enables improvements in the accuracy and reproducibility of patient isocentric and postural alignment, enhanced efficiency, and safety in breast radiotherapy.The aim of this review was to compare the accuracy and reproducibility of SGRT to conventional tattoo-based setups in free-breathing breast radiotherapy and to determine if SGRT can reduce the frequency of routine image guided radiotherapy (IGRT).A systematic literature review was performed as per PRISMA guidelines. Papers identified through PubMed, Embase, Web of Science and Google Scholar database searches between 2010 and 2021, were critically appraised. Systematic, random, mean residual errors and 3D vector shifts as determined by IGRT verification were analysed.A review of 13 full papers suggests SGRT improves the accuracy and reproducibility of patient setup in breast radiotherapy with consistent reductions in the residual errors. There appears to be a good correlation between SGRT setups and radiographic imaging. The frequency of IGRT and the corresponding dose could potentially be reduced. Additionally, SGRT improves treatment efficiency.SGRT appears to have improved the accuracy and reproducibility of patient setup and treatment efficiency of breast radiotherapy compared to conventional tattoo/laser-based method, with the potential to reduce the frequency of routine IGRT. The reliance on tattoos in breast radiotherapy are likely to become obsolete with positive implications for both patients and clinical practice.