Imaging And Radiation Oncology Core Research Articles

Validation of Acuros for total body irradiation at extended distance.

Standardized and accurately reported doses are essential in conventional total body irradiation (TBI), especially lung doses. This study evaluates the accuracy of the Acuros algorithm in predicting doses for extended-distance TBI. Measurements and calculations were done with both 6 and 18 MV. Tissue Maximum Ratio (TMR), output and off axis ratios (OAR) were measured at 200 and 500cm source to detector distance and compared to Acuros calculated values. Two end-to-end tests were carried out, one with an in-house phantom (solid water and Styrofoam) with inserted ion chambers and the other was with the Imaging and Radiation Oncology Core (IROC) TBI anthropomorphic phantom equipped with TLDs. The end-to-end test was done for 6 and 18 MV both with and without lung blocks. The source to midplane distance for both phantoms were at 518 and 508cm respectively. Lung blocks were placed at the phantom surface and a beam spoiler was positioned 30cm from the surface of the phantoms as per our clinical set up. The agreement between measured and calculated TMR, output and off axis ratios for both 6 and 18 MV were within 2%. Ion chamber measurements in both the Styrofoam and solid water for both energies carried out with and without lung blocks were within 2% of calculated values. TLD measured doses for both 6 and 18 MV in the IROC phantom were within 5% of calculated doses which is within the uncertainty of the TLD measurement. The results indicate that the clinical beam model for Acuros 16.1 commissioned at standard clinical distances is capable of calculating doses accurately at extended distances up to 500cm.

Chromatic bleaching and fractionation effects on optically stimulated luminescent dosimeter reuse

AbstractBackgroundOptically stimulated luminescent dosimeters (OSLDs) can be bleached and reused, but questions remain about the effects of repeated bleaching and fractionation schedules on OSLD performance.PurposeThe aim of this study was to investigate how light sources with different wavelengths and different fractionation schemes affect the performance of reused OSLDs.MethodsOSLDs (N = 240) were irradiated on a cobalt‐60 beam in different step sizes until they reached an accumulated dose of 50 Gy. Between irradiations they were bleached using light sources of different wavelengths: the Imaging and Radiation Oncology Core (IROC) bleaching system (our control); monochromatic red, green, yellow, and blue lights; and a polychromatic white light. Sensitivity and linearity‐based correction factors were determined as a function of dose step‐size. The rate of signal removal from different light sources was characterized by sampling these OSLDs at various time points during their bleaching process. Relative doses were calculated according to the American Association of Physicists in Medicine Task Group‐191. Signal repopulation was investigated by irradiating OSLDs (N = 300) to various delivered doses of 2, 10, 20, 30, 40, and 50 Gy in a single fraction, bleached with one of the colors, and read over time. Fractionation effects were evaluated by irradiating OSLDs up to 30 Gy in different size steps. After reading, the OSLDs were bleached following IROC protocol. OSLDs (N = 40) received irradiations in 5, 10, 15, 30 Gy fractions until they had an accumulated dose of 30 Gy; The sensitivity response of these OSLDs was compared with reference OSLDs that had no accumulated dose.ResultsLight sources with polychromatic spectrums (IROC and white) bleached OSLDs faster than did sources with monochromatic spectra. Polychromatic light sources (white light and IROC system) provided the greatest dose stability for OSLDs that had larger amounts of accumulated dose. Signal repopulation was related to the choice of bleaching light source, timing of bleaching, and amount of accumulated dose. Changes to relative dosimetry were more pronounced in OSLDs that received larger fractions. At 5‐Gy fractions and above, all OSLDs had heightened sensitivity, with OSLDs exposed to 30‐Gy fractions being 6.4% more sensitive than reference dosimeters.ConclusionsThe choice of bleaching light plays a role in how fast an OSLD is bleached and how much accumulated dose an OSLD can be exposed to while maintaining stable signal sensitivity. We have expanded upon investigations into signal repopulation to show that bleaching light plays a role in the migration of deep traps to dosimetric traps after bleaching. Our research concludes that the bleaching light source and fractionation need to be considered when reusing OSLD.

OSLD nanoDot characterization for carbon radiotherapy dosimetry

Objective. This study characterized optically-stimulated luminescent dosimeter (OSLD) nanoDots for use in a therapeutic carbon beam using the Imaging and Radiation Oncology Core (IROC) framework for remote output verification. Approach. The absorbed dose correction factors for OSLD (fading, linearity, beam quality, angularity, and depletion), as defined by AAPM TG 191, were characterized for carbon beams. For the various correction factors, the effect of linear energy transfer (LET) was examined by characterizing in both a low and high LET setting. Main results. Fading was not statistically different between reference photons and carbon, nor between low and high LET beams; thus, the standard IROC-defined exponential function could be used to characterize fading. Dose linearity was characterized with a linear fit; while low and high LET carbon linearity was different, these differences were small and could be rolled into the uncertainty budget if using a single linearity correction. A linear fit between beam quality and dose-averaged LET was determined. The OSLD response at various angles of incidence was not statistically different, thus a correction factor need not be applied. There was a difference in depletion between low and high LET irradiations in a primary carbon beam, but this difference was small over the standard five readings. The largest uncertainty associated with the use of OSLDs in carbon was because of the k Q correction factor, with an uncertainty of 6.0%. The overall uncertainty budget was 6.3% for standard irradiation conditions. Significance. OSLD nanoDot response was characterized in a therapeutic carbon beam. The uncertainty was larger than for traditional photon applications. These findings enable the use of OSLDs for carbon absorbed dose measurements, but with less accuracy than conventional OSLD audit programs.

TEAM participation in the irradiation of IROC phantoms for cooperative group clinical trials

The participation of radiation oncology team members in the irradiation of Imaging and Radiation Oncology Core (IROC) phantom for cooperative group clinical trials is essential to comply with the latest quality management philosophy. Medical dosimetrists are expected to develop treatment plans for the irradiation of IROC phantoms. For advanced treatment techniques, such as three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT), the irradiation of the IROC phantoms serves as quality audit. If successful, the irradiation processes demonstrate that the institution has the knowledge of the protocol, and has the appropriate equipment to comply with the protocol requirements. This article describes three IROC phantoms used for credentialing external beam photon beam therapy, delivered using conventional medical linear accelerators, to the medical dosimetry community. Guidance and strategies for the development of treatment plans are discussed. Our institutional irradiation of the three IROC phantoms, delivered using the Truebeam medical linear accelerator, resulted in consistent dose accuracy to within ±1%. The participation of the team members may reduce the overall published failing rate stated to be about one-third of all participating institutions.

Multi-institution single geometry plan complexity characteristics based on IROC phantoms.

Clinical intensity modulated radiation therapy plans have been described using various complexity metrics to help identify problematic radiotherapy plans. Most previous studies related to the quantification of plan complexity and their utility have relied on institution-specific plans which can be highly variable depending on the machines, planning techniques, delivery modalities, and measurement devices used. In this work, 1723 plans treating one of only four standardized geometries were simultaneously analyzed to investigate how radiation plan complexity metrics vary across four different sets of common objectives. To assess the treatment plan complexity characteristics of plans developed for Imaging and Radiation Oncology Core (IROC) phantoms. Specifically, to understand the variability in plan complexity between institutions for a common plan objective, and to evaluate how various complexity metrics differentiate relevant groups of plans. 1723 plans treating one of four standardized IROC phantom geometries representing four different anatomical sites of treatment were analyzed. For each plan, 22 MLC-descriptive plan complexity metrics were calculated, and principal component analysis (PCA) was applied to the 22 metrics in order to evaluate differences in plan complexity between groups. Across all metrics, pairwise comparisons of the IROC phantom data were made for the following classifications of the data: anatomical phantom treated, treatment planning system (TPS), and the combination of MLC model and treatment planning system. An objective k-means clustering algorithm was also applied to the data to determine if any meaningful distinctions could be made between different subgroups. The IROC phantom database was also compared to a clinical database from the University of Wisconsin-Madison (UW) which included plans treating the same four anatomical sites as the IROC phantoms using a TrueBeam™ STx and Pinnacle3 TPS. The IROC head and neck and spine plans were distinct from the prostate and lung plans based on comparison of the 22 metrics. All IROC phantom plan group complexity metric distributions were highly variable despite all plans being designed for identical geometries and plan objectives. The clusters determined by the k-means algorithm further supported that the IROC head and neck and spine plans involved similar amounts of complexity and were largely distinct from the prostate and lung plans, but no further distinctions could be made. Plan complexity in the head and neck and spine IROC phantom plans were similar to the complexity encountered in the UW clinical plans. There is substantial variability in plan complexity between institutions when planning for the same objective. For each IROC anatomical phantom treated, the magnitude of variability in plan complexity between institutions is similar to the variability in plan complexity encountered within a single institution database containing several hundred unique clinical plans treating corresponding anatomies in actual patients.

Optimized scoring of end-to-end dosimetry audits for passive motion management – A simulation study using the IROC thorax phantom

Dosimetry audits for passive motion management require dynamically-acquired measurements in a moving phantom to be compared to statically calculated planned doses. This study aimed to characterise the relationship between planning and delivery errors, and the measured dose in the Imaging and Radiation Oncology Core (IROC) thorax phantom, to assess different audit scoring approaches. Treatment plans were created using a 4DCT scan of the IROC phantom, equipped with film and thermoluminescent dosimeters (TLDs). Plans were created on the average intensity projection from all bins. Three levels of aperture complexity were explored: dynamic conformal arcs (DCAT), low-, and high-complexity volumetric modulated arcs (VMATLo, VMATHi). Simulated-measured doses were generated by modelling motion using isocenter shifts. Various errors were introduced including incorrect setup position and target delineation. Simulated-measured film doses were scored using gamma analysis and compared within specific regions of interest (ROIs) as well as the entire film plane. Positional offsets were estimated based on isodoses on the film planes, and point doses within TLD contours were compared. Motion-induced differences between planned and simulated-measured doses were evident even without introduced errors Gamma passing rates within target-centred ROIs correlated well with error-induced dose differences, while whole film passing rates did not. Isodose-based setup position measurements demonstrated high sensitivity to errors. Simulated point doses at TLD locations yielded erratic responses to introduced errors. ROI gamma analysis demonstrated enhanced sensitivity to simulated errors compared to whole film analysis. Gamma results may be further contextualized by other metrics such as setup position or maximum gamma.

The Status and Challenges for Prostate Stereotactic Body Radiation Therapy Treatments in United States Proton Therapy Centers: An NRG Oncology Practice Survey

PurposeTo report the current practice pattern of the proton stereotactic body radiation therapy (SBRT) for prostate treatments. Materials and MethodsA survey was designed to inquire about the practice of proton SBRT treatment for prostate cancer. The survey was distributed to all 30 proton therapy centers in the United States that participate in the National Clinical Trial Network in February, 2023. The survey focused on usage, patient selection criteria, prescriptions, target contours, dose constraints, treatment plan optimization and evaluation methods, patient-specific QA, and image-guided radiation therapy (IGRT) methods. ResultsWe received responses from 25 centers (83% participation). Only 8 respondent proton centers (32%) reported performing SBRT of the prostate. The remaining 17 centers cited 3 primary reasons for not offering this treatment: no clinical need, lack of volumetric imaging, and/or lack of clinical evidence. Only 1 center cited the reduction in overall reimbursement as a concern for not offering prostate SBRT. Several common practices among the 8 centers offering SBRT for the prostate were noted, such as using Hydrogel spacers, fiducial markers, and magnetic resonance imaging (MRI) for target delineation. Most proton centers (87.5%) utilized pencil beam scanning (PBS) delivery and completed Imaging and Radiation Oncology Core (IROC) phantom credentialing. Treatment planning typically used parallel opposed lateral beams, and consistent parameters for setup and range uncertainties were used for plan optimization and robustness evaluation. Measurements-based patient-specific QA, beam delivery every other day, fiducial contours for IGRT, and total doses of 35 to 40 GyRBE were consistent across all centers. However, there was no consensus on the risk levels for patient selection. ConclusionProstate SBRT is used in about 1/3 of proton centers in the US. There was a significant consistency in practices among proton centers treating with proton SBRT. It is possible that the adoption of proton SBRT may become more common if proton SBRT is more commonly offered in clinical trials.

Performance of Positron Emission Tomography at Diagnosis and Response Assessment in Low and Intermediate-Risk Nodular Lymphocyte Predominant Hodgkin Lymphoma

Background: Nodular lymphocyte predominant Hodgkin lymphoma (nLPHL) has different histology, clinical presentation, and outcomes than classical Hodgkin Lymphoma (cHL). Positron Emission Tomography (PET) plays an important role in staging and response assessment in cHL, but little is published about the use of PET to guide treatment in nLPHL. A better understanding of the clinical significance of PET response in nLPHL is critical for incorporating PET into prospective trials. Methods: Children's Oncology Group study AHOD03P1 (NCT00107198) enrolled patients with low-risk nLPHL and AHOD0031 (NCT00025259) enrolled patients with intermediate-risk cHL and nLPHL <22 years of age. AHOD03P1 patients with stage IA and >1 lymph node or stage IIA nLPHL were treated with 3 cycles of doxorubicin, vincristine, prednisone, and cyclophosphamide (AV-PC) chemotherapy, given every 21 days. Patients with a complete response (CR) based on anatomic response and qualitative reading (<mediastinal blood pool) of negative PET on central review did not receive radiation therapy while patients with <CR received 21-Gy involved field radiation therapy (IFRT). AHOD0031 patients with stages IB, IAE, IIB, IIAE, IIIA, IVA with or without bulk disease, and IA or IIA with bulk disease received 2 cycles of doxorubicin, bleomycin, vincristine, etoposide, prednisone and cyclophosphamide (ABVE-PC) followed by response evaluation. Slow early responders were randomized to an additional 2 cycles of ABVE-PC with or without 2 cycles of dexamethasone, etoposide, cisplatin and cytarabine (DECA) and all received IFRT. Rapid early responders (RERs) received 2 additional cycles of ABVE-PC. RERs with CR were randomized to IFRT or no further therapy. RER/non-CRs were non-randomly assigned to IFRT. PET scans from both trials available in the Imaging and Radiation Oncology Core (IROC) were retrospectively reviewed and assigned a score of 1-5 on the Deauville 5-point scale (5PS). Patients who did not have evaluable imaging due to either scans not performed, on CD-ROM and inaccessible, or poor quality, were excluded from this analysis. Three-year event-free survival (EFS) was analyzed by 5PS at end of therapy using the Kaplan Meier method. Results: AHOD03P1 enrolled 135 patients with low-risk nLPHL who received chemotherapy and AHOD0031 enrolled 96 patients with intermediate-risk nLPHL. PET imaging available for review at diagnosis in 99 low-risk patients, 92% 5PS=5, and 55 intermediate-risk patients, 98% 5PS=5. Median age 13.4 years (range 16.5), 84.9% male, 29.9% Stage I, 49.8% Stage II, 18.6% Stage III, and 1.7% Stage IV. After 3 cycles of chemotherapy, 106 low-risk patients had available PET scans, 5PS 1 n=50, 5PS 2 n=35, 5PS 3 n=11, 5PS 4 n=7, and 5PS 5 n=3. Three-year EFS for patients with end of chemotherapy 5PS was: 5PS 1 89.9% (95% CI 77.3-95.7%), 5PS 2 97.1% (95% CI 81.4-99.6%), 5PS 3 90.9% (95% CI 50.8-98.7%), 5PS 4 28.6% (95% CI 1.0-71.1%), 5PS 5 66.7% (95% CI 5.4-94.5%) p=0.0081. When categorized as PET negative (5PS 1-3) and PET positive (5PS 4-5), 3-year EFS was 92.6% (95% CI 85.2-96.4%) for PET negative and 45.0% (95% CI 10.6-75.3%) for PET positive patients, p=0.0036 (Figure 1A). Forty-nine intermediate-risk patients had available PET scans after 2 cycles of chemotherapy, 5PS 1 n=9, 5PS 2 n=26, 5PS 3 n=10, 5PS 4 n=3, and 5PS 5 n=1. Three-year EFS by interim response was: 5PS 1 88.9% (95% CI 43.3-98.4%), 5PS 2 96.0% (95% CI 74.8-99.4%), 5PS 3 100%, 5PS 4 100%, 5PS 5 0%, p<0.0001. Thirty-six patients had available PET scans after 4 cycles of chemotherapy, 5PS 1 n=20, 5PS 2 n=11, 5PS 3 n=3, 5PS 4 n=1, and 5PS 5 n=1. Three-year EFS by response after 4 cycles of chemotherapy: 5PS 1 95.0% (95% CI 69.5-99.3%), 5PS 2 100%, 5PS 3 100%, 5PS 4 100%, 5PS 5 0% p<0.0001. When divided into PET negative (5PS 1-3) and PET positive (5PS 4-5), 3-year EFS 97.0% (95% CI 80.4-99.6%) for PET negative and 50.0% (95% CI 0.6-91.0%) for PET positive patients after 4 cycles of chemotherapy, p=0.1449 (Figure 1B). Conclusions: At diagnosis, low and intermediate-risk nLPHL lesions are almost always PET avid with 5PS=5. PET response following 3 cycles of AV-PC chemotherapy is highly predictive of outcome in pediatric patients with low-risk nLPHL when considering 5PS=3 as PET negative. Intermediate-risk patients with negative PET following ABVE-PC achieved excellent outcomes. Whether PET maintains prognostic significance in patients with nLPHL treated with rituximab needs to be studied.

AAPMWGDCAB Report 372:A joint AAPM, ESTRO, ABG, and ABS report oncommissioning of model-based dose calculation algorithms in brachytherapy.

The introduction of model-based dose calculation algorithms (MBDCAs) in brachytherapy provides an opportunity for a more accurate dose calculation and opens the possibility for novel, innovative treatment modalities. The joint AAPM, ESTRO, and ABG Task Group 186 (TG-186) report provided guidance to early adopters. However, the commissioning aspect of these algorithms was described only in general terms with no quantitative goals. This report, from the Working Group on Model-Based Dose Calculation Algorithms in Brachytherapy, introduced a field-tested approach to MBDCA commissioning. It is based on a set of well-characterized test cases for which reference Monte Carlo (MC) and vendor-specific MBDCA dose distributions are available in a Digital Imaging and Communications in Medicine-Radiotherapy (DICOM-RT) format to the clinical users. The key elements of the TG-186 commissioning workflow are now described in detail, and quantitative goals are provided. This approach leverages the well-known Brachytherapy Source Registry jointly managed by the AAPM and the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center (with associated links at ESTRO) to provide open access to test cases as well as step-by-step user guides. While the current report is limited to the two most widely commercially available MBDCAs and only for 192 Ir-based afterloading brachytherapy at this time, this report establishes a general framework that can easily be extended to other brachytherapy MBDCAs and brachytherapy sources. The AAPM, ESTRO, ABG, and ABS recommend that clinical medical physicists implement the workflow presented in this report to validate both the basic and the advanced dose calculation features of their commercial MBDCAs. Recommendations are also given to vendors to integrate advanced analysis tools into their brachytherapy treatment planning system to facilitate extensive dose comparisons. The use of the test cases for research and educational purposes is further encouraged.

17th International Conference on Malignant Lymphoma, Palazzo dei Congressi, Lugano, Switzerland, 13 - 17 June, 2023.

Introduction: Outcomes for high-risk pediatric and adolescent and young adult (AYA) classic Hodgkin lymphoma (cHL) improved substantially with the addition of brentuximab vedotin (Bv) to AVEPC (adriamycin, vincristine, etoposide, prednisone, cyclophosphamide) chemotherapy. As patients with stage IV disease have poor outcomes, we evaluated the prognostic implications of sites contributing to stage IV disease. Methods: On AHOD1331 (NCT02166463), patients age 2–21 years with high-risk cHL (stage IIB with bulk, IIIB, IVA, and IVB) were randomized to 5 cycles of AB (bleomycin)VE-PC versus Bv-AVE-PC, and consolidative radiotherapy based on interim response and large mediastinal adenopathy at diagnosis. Patients with stage IV disease, as determined by protocol defined and centrally reviewed PET-CT, were identified. Stage IV was defined as disseminated involvement of ≥1 extralymphatic organ or tissues (with or without lymph node involvement) or isolated extralymphatic organ involvement with distant nodal involvement. E-lesions were distinguished from sites of stage IV involvement in the lung, but any liver and/or bone marrow involvement, regardless of contiguity, was considered stage IV. Central review was performed to confirm institutional classification of stage, upstaging 33 patients to stage IV and downstaging 17 among the 353 enrolled and stratified as Stage IV by the institution. Baseline characteristics and progression-free survival (PFS) were compared by pattern of metastatic involvement (lung only, bone only, bone marrow only, or multi-site, defined as >1 site of involvement). Results: 369 patients (median age 15 years, range 3–22) with stage IV disease treated on AHOD1331 were included, of which 183 (50%) were treated with ABVE-PC and 186 (50%) with Bv-AVE-PC. Patterns of disease included: isolated involvement of lung (185; 50%); bone marrow (5; 1%); or bone (8; 2%), and 171 (46%) had multi-site involvement. B symptoms were present in 80% and 88% with bone marrow or bone involvement respectively, 50% of those with lung, and 57% with multi-site disease. The 3 year-PFS (95% CI) by site of involvement was: 88.0% (82.3, 91.9) for lung, 100% for isolated bone marrow or bone, and 82.5% (75.8, 87.5) for multi-site (p = 0.21). Bv-AVE-PC significantly improved PFS among stage IV patients compared to ABVE-PC (3-year PFS 90.2% vs. 81.5%, p = 0.01). Among those with isolated lung involvement, there was a non-significant increased PFS with Bv (3-year PFS 91.2% vs. 84.7%, p = 0.16), while those with multi-site metastatic disease experienced significantly improved PFS with Bv (3 year-PFS 88.1% vs. 77.1%, p = 0.05). Conclusions: Among pediatric and AYA patients with stage IV cHL, PFS was notably improved with Bv among patients with multi-site metastatic involvement. These results will help guide future efforts to understand strategies to improve outcomes among children with stage IV disease. The research was funded by: Supported in part by grants from the National Institutes of Health (U10CA098543, U10CA180899, and U10CA180886; all to the Children’s Oncology Group), the Quality Assurance Review Center (U10CA29511), Imaging and Radiology Oncology Core Rhode Island (U24CA180803), and St. Baldrick’s Foundation (to the Children’s Oncology Group) Keywords: Hodgkin lymphoma, molecular targeted therapies, Lymphoid Cancers - Other No conflicts of interests pertinent to the abstract.

Characterizing the interplay of treatment parameters and complexity and their impact on performance on an IROC IMRT phantom using machine learning

Aim of the StudyTo elucidate the important factors and their interplay that drive performance on IMRT phantoms from the Imaging and Radiation Oncology Core (IROC). MethodsIROC’s IMRT head and neck phantom contains two targets and an organ at risk. Point and 2D dose are measured by TLDs and film, respectively. 1,542 irradiations between 2012–2020 were retrospectively analyzed based on output parameters, complexity metrics, and treatment parameters. Univariate analysis compared parameters based on pass/fail, and random forest modeling was used to predict output parameters and determine the underlying importance of the variables. ResultsThe average phantom pass rate was 92% and has not significantly improved over time. The step-and-shoot irradiation technique had significantly lower pass rates that significantly affected other treatment parameters’ pass rates. The complexity of plans has significantly increased with time, and all aperture-based complexity metrics (except MCS) were associated with the probability of failure. Random forest-based prediction of failure had an accuracy of 98% on held-out test data not used in model training. While complexity metrics were the most important contributors, the specific metric depended on the set of treatment parameters used during the irradiation. ConclusionWith the prevalence of errors in radiotherapy, understanding which parameters affect treatment delivery is vital to improve patient treatment. Complexity metrics were strongly predictive of irradiation failure; however, they are dependent on the specific treatment parameters. In addition, the use of one complexity metric is insufficient to monitor all aspects of the treatment plan.

Quality Assurance in Clinical Trials Requiring Radiation Therapy in Sub-Saharan Africa

Given the increasing availability of radiation therapy in sub-Saharan Africa, clinical trials that include radiation therapy are likely to grow. Ensuring appropriate delivery of radiation therapy through rigorous quality assurance is an important component of clinical trial execution. We reviewed the process for credentialing radiation therapy sites and radiation therapy quality assurance through the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center for AIDS Malignancy Consortium (AMC)-081, a multicenter study of cisplatin and radiation therapy for women with locally advanced cervical cancer living with HIV, conducted by the AIDS Malignancy Consortium at 2 sites in South Africa and Zimbabwe. Women living with HIV with newly diagnosed stage IB2, IIA (>4 cm), IIB-IVA cervical carcinoma (per the 2009 International Federation of Gynecology and Obstetrics [FIGO] staging classifications) were enrolled in AMC-081. They received 3-dimensional conformal external beam radiation therapy (EBRT) to the pelvis (41.4-45 Gy) using a linear accelerator, high-dose-rate brachytherapy (6-9 Gy to point A with each fraction and up to 4 fractions), and concurrent weekly cisplatin (40 mg/m2). IROC reviewed EBRT and brachytherapy quality assurance records after treatment. All of the 38 women enrolled in AMC-081 received ±5% of the protocol-specified prescribed dose of EBRT. Geometry of brachytherapy applicator placement was scored as per protocol in all implants. Doses to points A and B, International Commission on Radiation Units and Measurements (ICRU) bladder, or ICRU rectum required correction by IROC in >50% of the implants. In the final evaluation, 58% of participants (n=22) were treated per protocol, 40% (n=15) had minor protocol deviations, and 3% (n=1) had major protocol deviations. No records were received within 60 days of treatment completion as requested in the protocol. Major radiation therapy deviations were low, but timely submission of radiation therapy data did not occur. Future studies, especially those that include specialized radiation therapy techniques such as stereotactic or intensity-modulated radiation therapy, will require pathways to ensure timely and adequate quality assurance.

Lung SBRT credentialing in the Canadian OCOG-LUSTRE randomized trial

PurposeTo report on the Stereotactic Body Radiation Therapy (SBRT) credentialing experience during the Phase III Ontario Clinical Oncology Group (OCOG) LUSTRE trial for stage I non-small cell lung cancer. MethodsThree credentialing requirements were required in this process: (a) An institutional technical survey; (b) IROC (Imaging and Radiation Oncology Core) thoracic phantom end-to-end test; and (c) Contouring and completion of standardized test cases using SBRT for one central and one peripheral lung cancer, compared against the host institution as the standard. The main hypotheses were that unacceptable variation would exist particularly in OAR definition across all centres, and that institutions with limited experience in SBRT would be more likely to violate per-protocol guidelines. ResultsFifteen Canadian centres participated of which 8 were new, and 7 were previously established (≥2 years SBRT experience), and all successfully completed surveys and IROC phantom testing. Of 30 SBRT test plans, 10 required replanning due to major deviations, with no differences in violations between new and established centres (p = 0.61). Mean contouring errors were highest for brachial plexus in the central (C) case (12.55 ± 6.62 mm), and vessels in the peripheral (P) case (13.01 ± 12.55 mm), with the proximal bronchial tree (PBT) (2.82 ± 0.78 C, 3.27 ± 1.06 P) as another variable structure. Mean dice coefficients were lowest for plexus (0.37 ± 0.2 C, 0.37 ± 0.14 P), PBT (0.77 ± 0.06 C, 0.75 ± 0.09 P), vessels (0.69 ± 0.29 C, 0.64 ± 0.31 P), and esophagus (0.74 ± 0.04 C, 0.76 ± 0.04 P). All plans passed per-protocol planning target volume (PTV) coverage and maximum/volumetric organs-at-risk constraints, although variations existed in dose gradients within and outside the target. ConclusionsClear differences exist in both contouring and planning with lung SBRT, regardless of centre experience. Such an exercise is important for studies that rely on high precision radiotherapy, and to ensure that implications on trial quality and outcomes are as optimal as possible.

The current status and shortcomings of stereotactic radiosurgery.

BackgroundStereotactic radiosurgery (SRS) is a common treatment for intracranial lesions. This work explores the state of SRS treatment delivery to characterize current treatment accuracy based on treatment parameters.MethodsNCI clinical trials involving SRS rely on an end-to-end treatment delivery on a patient surrogate (credentialing phantom) from the Imaging and Radiation Oncology Core (IROC) to test their treatment accuracy. The results of 1072 SRS phantom irradiations between 2012 and 2020 were retrospectively analyzed. Univariate analysis and random forest models were used to associate irradiation conditions with phantom performance. The following categories were evaluated in terms of how they predicted outcomes: year of irradiation, TPS algorithm, machine model, energy, and delivered field size.ResultsOverall, only 84.6% of irradiations have met the IROC/NCI acceptability criteria. Pass rate has remained constant over time, while dose calculation accuracy has slightly improved. Dose calculation algorithm (P < .001), collimator (P = .024), and field size (P < .001) were statistically significant predictors of pass/fail. Specifically, pencil beam algorithms and cone collimators were more likely to be associated with failing phantom results. Random forest modeling identified the size of the field as the most important factor for passing or failing followed by algorithm.ConclusionConstant throughout this retrospective study, approximately 15% of institutions fail to meet IROC/NCI standards for SRS treatment. In current clinical practice, this is particularly associated with smaller fields that yielded less accurate results. There is ongoing need to improve small field dosimetry, beam modeling, and QA to ensure high treatment quality, patient safety, and optimal clinical trials.

Quality assurance in radiation oncology.

The Children's Oncology Group (COG) has a strong quality assurance (QA) program managed by the Imaging and Radiation Oncology Core (IROC). This program consists of credentialing centers and providing real-time management of each case for protocol compliant target definition and radiation delivery. In the International Society of Pediatric Oncology (SIOP), the lack of an available, reliable online data platform has been a challenge and the European Society for Paediatric Oncology (SIOPE) quality and excellence in radiotherapy and imaging for children and adolescents with cancer across Europe in clinical trials (QUARTET) program currently provides QA review for prospective clinical trials. The COG and SIOP are fully committed to a QA program that ensures uniform execution of protocol treatments and provides validity of the clinical data used for analysis.

Geographic Access to Radiation Therapy in the United States

Prior literature describes an association between the distance to radiation facilities and the receipt of radiation therapy (RT). However, the current distribution of RT facilities in the US is not well established. A comprehensive inventory of US RT facilities was last assessed in 2005, based on data from state regulatory agencies and international dosimetric quality assurance bodies. We updated this database to characterize population-level measures of geographic access to RT in the US and analyze changes over the past 15 years. We compiled data from state regulatory agencies regarding the location of facilities that deliver RT for human medical treatment in 2018-2020. Data was also abstracted from the databases of two independent peer review organizations (Radiation Dosimetry Services (RDS) and the Imaging and Radiation Oncology Core (IROC)) that provide nationwide dosimetry auditing for radiation therapy units. Addresses were geocoded using the Google Maps Platform API and mapped and analyzed with Geographic Information Services (GIS) software. Latitude and longitude coordinates were rounded to two decimal places to create pseudo-unique identifiers of RT treatment sites, allowing for comparison across time. Geographic access was characterized by assessing the Euclidian (straight-line) distance between county centroids and RT facilities. Populations were assigned to each county to estimate the impact of facility changes at the population level. In 2020, a total of 2,332 US RT facilities were reported compared to 1,987 in 2005, representing a 17% growth in facilities over nearly 15 years. 33% (662/1987) of sites in the prior dataset did not exist in the updated dataset based on geolocation with latitude and longitude coordinates alone. 25.6% of county centroids are currently located within 12.5 miles of a RT facility, while 16.9% are located farther than 50 miles away. Based on population attribution to county centroids, nearly 70% of the US population lives within 12.5 miles of an RT facility (up from 65% in 2005). As far as the authors are aware, this represents the most comprehensive and detailed modern dataset characterizing geographic access to RT facilities in the United States. Based on a 50-mile threshold, 4.5% of the US population has limited geographic access to radiation therapy. 1/3 of sites demonstrated geographic turnover over time, representing facility closures, movement, or methodological differences in data capture. Although a national pattern of expansion and redistribution of RT facilities is evident, these trends have preferentially improved access for people already living near RT facilities, suggesting disparities in geographic access may worsen without intervention.Abstract 203; TablePercent of US population within a given range, based on centroid attributionYear20052018Population attributed to a county centroid located within:50 miles94.6%95.5%25 miles83.8%86.4%12.5 miles65.4%69.6% Open table in a new tab

NCI support for pediatric radiation therapy: Past, present, and future.

NCI support for pediatric radiation therapy: Past, present, and future.

Sensitivity of IROC phantom performance to radiotherapy treatment planning system beam modeling parameters based on community-driven data.

PurposeTreatment planning system (TPS) dose calculations have previously been shown to be sensitive to modeling errors, especially when treating with complex strategies like intensity‐modulated radiation therapy (IMRT). This work investigates the dosimetric impact of several dosimetric and nondosimetric beam modeling parameters, based on their distribution in the radiotherapy community, in two commercial TPSs in order to understand the realistic potential for dose deviations and their clinical effects.Methods and materialsBeam models representing standard 120‐leaf Varian Clinac‐type machines were developed in Eclipse 13.5 (AAA algorithm) and RayStation 9A (v8.99, collapsed‐cone algorithm) based upon median values of dosimetric measurements from Imaging and Radiation Oncology Core (IROC) Houston site visit data and community beam modeling parameter survey data in order to represent a baseline linear accelerator. Five clinically acceptable treatment plans (three IMRT, two VMAT) were developed for the IROC head and neck phantom. Dose distributions for each plan were recalculated after individually modifying parameters of interest (e.g., MLC transmission, percent depth doses [PDDs], and output factors) according to the 2.5th to 97.5th percentiles of community survey and machine performance data to encompass the realistic extent of variance in the radiotherapy community. The resultant dose distributions were evaluated by examining relative changes in average dose for thermoluminescent dosimeter (TLD) locations across the two target volumes and organ at risk (OAR). Interplay was also examined for parameters generating changes in target dose greater than 1%.ResultsFor Eclipse, dose calculations were sensitive to changes in the dosimetric leaf gap (DLG), which resulted in differences from −5% to +3% to the targets relative to the baseline beam model. Modifying the MLC transmission factor introduced differences up to ± 1%. For RayStation, parameters determining MLC behaviors likewise contributed substantially; the MLC offset introduced changes in dose from −4% to +7%, and the MLC transmission caused changes of −4% to +2%. Among the dosimetric qualities examined, changes in PDD implementation resulted in the most substantial changes, but these were only up to ±1%. Other dosimetric factors had <1% impact on dose accuracy. Interplay between impactful parameters was found to be minimal.ConclusionFactors related to the modeling of the MLC, particularly relating to the leaf offset, can cause clinically significant changes in the calculated dose for IMRT and VMAT plans. This should be of concern to the radiotherapy community because the clinical effects of poor TPS commissioning were based on reported data from clinically implemented beam models. These results further reinforce that dose errors caused by poor TPS calculations are often involved in IROC phantom failures.

A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds.

The purpose of this study was to investigate the feasibility of using fused deposition modeling (FDM) three-dimensional (3D) printer to generate radiation compensators for high-resolution (~1mm) intensity-modulated radiation therapy (IMRT) for small animal radiation treatment. We propose a novel method incorporating 3D-printed compensator molds filled with NaI powder. The inverse planning module of the computational environment for radiotherapy research (CERR) software was adapted to simulate the XRAD-225Cx irradiator, both geometry and kV beam quality (the latter using a phase space file provided for XRAD-225Cx). A nine-field IMRT treatment was created for a scaled-down version of the imaging and radiation oncology core (IROC) Head and Neck IMRT credentialing test, recreated on a 2.2-cm-diameter cylindrical phantom. Optimized fluence maps comprising nine fields and a total of 2564 beamlets were calculated at resolution of 1.25×1.25mm2 . A hollow compensator mold was created (using in-house software and algorithm) for each field using 3D printing with polylactic acid (PLA) filaments. The molds were then packed with sodium iodide powder (NaI, measured density ρNaI =2.062g/cm3 ). The mounted compensator mold thickness was limited to 13.8mm due to clearance issues with couch collision. At treatment delivery, each compensator was manually mounted to a customized block tray attached to the reference 40×40mm2 collimator. Compensator reproducibility among three repeated 3D-printed molds was measured with Radiochromic EBT2 film. The two-dimensional (2D) dose distributions of the nine fields were compared to calculated 2D doses from CERR using gamma comparisons with distance-to-agreement criteria of 0.5-0.25mm and dose difference criteria of 3-5%. Good reproducibility of 3D-printed compensator manufacture was observed with mean error of ±0.024Gy and relative dose error of ±4.2% within the modulated part of the beam. Within the limit of 13.8mm compensator height, a maximum radiation blocking efficiency of 91.5% was achieved. Per field, about 45.5g of NaI powder was used. Gamma analysis on each of the nine delivered IMRT fields using radiochromic films resulted in eight of nine treatment fields with >90% pass rate with 5%/0.5mm tolerances. However, low gamma passing rate of 49-66% (3%/0.25mm to 5%/0.5mm) was noted in one field, attributed to fabrication errors resulting in over-filling the mold. The nine-field treatment plan was delivered in under 30min with no mechanical or collisional issues. We show the feasibility of high spatial resolution IMRT treatment on a small animal irradiator utilizing 3D-printed compensator shells packed with NaI powder. Using the PLA mold with NaI powder was attractive due to the ease of 3D printing a PLA mold at high geometric resolution and the well-balanced attenuation properties of NaI powders that prevented the mold from becoming too bulky. IMRT fields with 1.25-mm resolution are capable with significant fluence modulation with relative dose accuracy of ±4.2%.

Dose calculation errors as a component of failing IROC lung and spine phantom irradiations.

Between July 2013 and August 2019, 22% of the imaging and radiation oncology core (IROC) spine, and 15% of the moving lung phantom irradiations have failed to meet established acceptability criteria. The spine phantom simulates a highly modulated stereotactic body radiation therapy (SBRT) case, whereas the lung phantom represents a low-to-none modulation moving target case. In this study, we assessed the contribution of dose calculation errors to these phantom results and evaluated their effects on failure rates. We evaluated dose calculation errors by comparing the calculation accuracy of various institutions' treatment planning systems (TPSs) vs IROC-Houston's previously established independent dose recalculation system (DRS). Each calculation was compared with the measured dose actually delivered to the phantom; cases in which the recalculation was more accurate were interpreted as a deficiency in the institution's TPS. A total of 258 phantom irradiation plans (172 lung and 86 spine) were recomputed. Overall, the DRS performed better than the TPSs in 47% of the spine phantom cases. However, the DRS was more accurate in 93% of failing spine phantom cases (with an average improvement of 2.35%), indicating a deficiency in the institution's treatment planning system. Deficiencies in dose calculation accounted for 60% of the overall discrepancy between measured and planned doses among spine phantoms. In contrast, lung phantom DRS calculations were more accurate in only 35% and 42% of all and failing lung phantom cases respectively, indicating that dose calculation errors were not substantially present. These errors accounted for only 30% of the overall discrepancy between measured and planned doses. Dose calculation errors are common and substantial in IROC spine phantom irradiations, highlighting a major failure mode in this phantom and in clinical treatment management of these cases. In contrast, dose calculation accuracy had only a minimal contribution to failing lung phantom results, indicating that other failure modes drive problems with this phantom and similar clinical treatments.