Validation of an in vivo transit dosimetry algorithm using Monte Carlo simulations and ionization chamber measurements.

PURPOSE: Transit dosimetry is a safety tool based on the transit images acquired during treatment. Forward-projection transit dosimetry software, as PerFRACTION, compares the transit images acquired with an expected image calculated from the DICOM plan, the CT, and the structure set. This work aims to validate PerFRACTION expected transit dose using PRIMO Monte Carlo simulations and ionization chamber measurements, and propose a methodology based on MPPG5a report. METHODS: The validation process was divided into three groups of tests according to MPPG5a: basic dose validation, IMRT dose validation, and heterogeneity correction validation. For the basic dose validation, the fields used were the nine fields needed to calibrate PerFRACTION and three jaws-defined. For the IMRT dose validation, seven sweeping gaps fields, the MLC transmission and 29 IMRT fields from 10 breast treatment plans were measured. For the heterogeneity validation, the transit dose of these fields was studied using three phantoms: 10 , 30 , and a 3 cm cork slab placed between 10 cm of solid water. The PerFRACTION expected doses were compared with PRIMO Monte Carlo simulation results and ionization chamber measurements. RESULTS: Using the 10 cm solid water phantom, for the basic validation fields, the root mean square (RMS) of the difference between PerFRACTION and PRIMO simulations was 0.6%. In the IMRT fields, the RMS of the difference was 1.2%. When comparing respect ionization chamber measurements, the RMS of the difference was 1.0% both for the basic and the IMRT validation. The average passing rate with a γ(2%/2 mm, TH = 20%) criterion between PRIMO dose distribution and PerFRACTION expected dose was 96.0% ± 5.8%. CONCLUSION: We validated PerFRACTION calculated transit dose with PRIMO Monte Carlo and ionization chamber measurements adapting the methodology of the MMPG5a report. The methodology presented can be applied to validate other forward-projection transit dosimetry software.

Per-fraction planning to enhance optimization degrees of freedom compared to the conventional single-plan approach.

Objective. In conventional radiotherapy, a single treatment plan is generated pre-treatment, and delivered in daily fractions. In this study, we propose to generate different treatment plans for all fractions ('Per-fraction' planning) to reduce cumulative organs at risk (OAR) doses. Per-fraction planning was compared to the 'Conventional' single-plan approach for non-coplanar 4 × 9.5 Gy prostate stereotactic body radiation therapy (SBRT).Approach. An in-house application for fully automated, non-coplanar multi-criterial treatment planning with integrated beam angle and fluence optimization was used for plan generations. For the Conventional approach, a single 12-beam non-coplanar IMRT plan with individualized beam angles was generated for each of the 20 included patients. In Per-fraction planning, four fraction plans were generated for each patient. For each fraction, a different set of patient-specific 12-beam configurations could be automatically selected. Per-fraction plans were sequentially generated by adding dose to already generated fraction plan(s). For each fraction, the cumulative- and fraction dose were simultaneously optimized, allowing some minor constraint violations in fraction doses, but not in cumulative.Main results. In the Per-fraction approach, on average 32.9 ± 3.1 [29;39] unique beams per patient were used. PTV doses in the separate Per-fraction plans were acceptable and highly similar to those in Conventional plans, while also fulfilling all OAR hard constraints. When comparing total cumulative doses, Per-fraction planning showed improved bladder sparing for all patients with reductions in Dmean of 22.6% (p= 0.0001) and in D1cc of 2.0% (p= 0.0001), reductions in patient volumes receiving 30% and 50% of the prescribed dose of 54.7% and 6.3%, respectively, and a 3.1% lower rectum Dmean (p= 0.007). Rectum D1cc was 4.1% higher (p= 0.0001) and Urethra dose was similar.Significance. In this proof-of-concept paper, Per-fraction planning resulted in several dose improvements in healthy tissues compared to the Conventional single-plan approach, for similar PTV dose. By keeping the number of beams per fraction the same as in Conventional planning, reported dosimetric improvements could be obtained without increase in fraction durations. Further research is needed to explore the full potential of the Per-fraction planning approach.

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

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

Validation of Three-dimensional Electronic Portal Imaging Device-based PerFRACTION™ Software for Patient-Specific Quality Assurance.

PURPOSE: PerFRACTION™ is a three-dimensional (3D) in vivo electronic portal imaging device-based dosimetry software. To validate the software, three phantoms with different inserts (2D array, ionization chamber, and inhomogeneity materials) were constructed to evaluate point dose and fluence map. MATERIALS AND METHODS: Phantoms underwent independent computed tomography simulation for planning and received repetitive fractions of volumetric modulated arc therapy, simulating prostate treatment. Fluence and absolute point dose measurements, PerFRACTION™ reconstructed doses, and the dose predictions of the planning system were compared. RESULTS: There was concordance between ionization chamber and PerFRACTION™ 3D absolute point dose measurements. Close agreement was also obtained between X- and Y-axis dose profiles with PerFRACTION™ calculated doses, MapCHECK measured doses, and planning system predicted doses. Setup shifts significantly influenced 2D gamma passing rates in PerFRACTION™ software. CONCLUSIONS: PerFRACTION™ appears reliable and valid under experimental conditions in air and with phantoms.

The exploration of improving perfraction dose by 3DCRT / 肿瘤研究与临床

Objective To evaluate the feasibility of increasing the perfraction dose in treatment of neoplasms by 3DCRT (three- dimention confornial radiation therapy). Methods From May 1998 to June 2002, the radiation therapy plans of 300 out- cranial neoplasms patients were analysed retrospectively, including 143 patients with chest neoplasms and 157 patients with abdomen neoplasms. The PTV was 7.0 ~ 1 478 cm3, major PTV was encircled by 90 % isodose curve, minor 95 % PTV were encircled by 80 % isodose curve. Prescription dose was 90 % reference point dose, perfraction dose was 5 ~ 10 Gy, a majority of dose was 6 ~ 8 Gy, period of treatment was 5 ~ 15 days with an interval of 0 ~ 1 day. The general dose was given to radical cure dose or appeasement dose. The biological effect increased 10 % ~ 30 %. Results All treatment plans were accomplished and there were not complication which reduced patients' QOL. Conclusions 1.Owing to the f factor, increasing dose of perfraction, shortening general period of treatment and improving radiative biological effect were possible during the 3DCRT. 2. It was suggested that the larger out- cranial neoplasms should be treated by 3DCRT firstly, but precise plan, precise design and precise treatment can not intensely be pursued because of the limit of knowledge. 3. During the 3DCRT for out- cranial neoplasms, 2 ~ 3 times routine radiation therapy dose was secure, credible and effective according to different purpose.