Background: To compare non-coplanar and coplanar volumetric-modulated arc therapy (VMAT) for hippocampal avoidance during whole-brain radiotherapy (HA-WBRT) using the Elekta Synergy and Pinnacle treatment planning system (TPS) according to the suggested criteria of the radiation therapy oncology group (RTOG) 0933 trial.Methods: Nine patients who underwent WBRT were selected for this retrospective study. The hippocampus was contoured, and the hippocampal avoidance regions were created using a 5-mm volumetric expansion around the hippocampus for each patient. Non-coplanar and coplanar VMAT plans were generated for each patient. All treatment plans were generated for a prescribed dose (PD) of 30 Gy in 10 fractions. Results:The average volumes of the hippocampus and hippocampal avoidance region were 2.8±0.38 and 27±2.48 cm 3 , respectively. For coplanar and non-coplanar VMAT plans, the average D 100% of the hippocampus was 8.60 Gy (range, 8.30-8.80 Gy) and 8.56 Gy (range, 8.30-8.90 Gy), respectively, and the average D max of the hippocampus was 15.29 Gy (range, 14.35-15.92 Gy) and 14.99 Gy (range, 13.80-15.83 Gy), respectively. The non-coplanar VMAT plans showed a significantly lower average D max of the lens (4.23 Gy) than did the coplanar VMAT plans (4.77 Gy). The average gamma passing rate for non-coplanar and coplanar VMAT quality assurance (QA) with criteria of 3%/3 mm were 95.4%±2.6% and 95.6%±1.6%, indicating good agreement between the calculated plan dose and the measured dose. Conclusions:We showed that the suggested criteria of the RTOG 0933 trial for the hippocampal dose can be achieved in both coplanar and non-planar VMAT plans. We performed VMAT QA for each treatment plan to verify the clinical feasibility.

Whole-brain radiotherapy (WBRT) is commonly used in patients with multiple brain metastases. Compared with conventional WBRT, hippocampal avoidance WBRT (HA-WBRT) more favorably preserves cognitive function and the quality of life. The hippocampal volume is considerably small (approximately 3.3 cm 3 ). Therefore, downsizing the leaf width of a multileaf collimator (MLC) may provide higher spatial resolution and better plan quality. Volumetric modulated arc therapy (VMAT) could simulate the half MLC leaf width through couch shifting between arcs. This study investigated changes in VMAT quality for HA-WBRT with a simulated fine MLC leaf width. Methods: We included 18 patients with brain metastasis. All target and avoidance structures were contoured by an experienced radiation oncologist. The prescribed dose was 30 Gy in 10 fractions. For each patient, three different treatment plans were generated for comparison: VMAT with couch-shift, VMAT without couch-shift, and TomoTherapy. All treatment plans fulfilled Radiation Therapy Oncology Group (RTOG) 0933 criteria for HA-WBRT. The Wilcoxon paired signed-rank test was used to compare different treatment plans. Results: VMAT with couch-shift had the better average conformity index (0.823) with statistically significant difference compared to VMAT without couch-shift (0.810). VMAT with couch-shift (0.219) had a more favorable average homogeneity index (HI) than did VMAT without couch-shift (0.230), although the difference was not significant. TomoTherapy had an optimal average HI of 0.070. In terms of the hippocampus, all three treatment plans met the RTOG 0933 criteria. VMAT with couch-shift had a lower average D max (15.2 Gy) than did VMAT without couch-shift (15.3 Gy, p = 0.071) and TomoTherapy (15.5 Gy, p = 0.133). The average D 100% of hippocampus was the same for both VMAT with and without couch-shift (8.5 Gy); however, TomoTherapy had a lower average D 100% value of 7.9 Gy. The treatment delivery time was similar between VMAT with and without couch-shift (average, 375.0 and 369.6 s, respectively). TomoTherapy required a long average delivery time of 1489.9 s. Conclusion:The plan quality of VMAT for HA-WBRT was improved by using the couch-shift technique to simulate the half MLC leaf width. However, the improvement was not statistically significant except conformity index. The downsizing This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Background: Quality assurance (QA) plays a critical role in patient safety during radiation therapy. Among various QA checks, pretreatment physics plan review is sensitive at detecting errors before beam delivery. Therefore, we aimed to assess the errors detected during pretreatment physics plan and chart review (PTPCR) through a failure mode and effects analysis (FMEA) and to evaluate the quality and effectiveness of the PTPCR performed at our clinic.Methods: Five qualified medical physicists used a single checklist to perform a total of 1,406 PTPCRs in 2019. Five major PTPCR process steps were reviewed: (I) planning parameters, (II) plan quality, (III) image parameters, (IV) MOSAIQ management, and (V) chart documents. Errors detected during the PTPCR were identified to failure modes (FMs) in each process step. A risk priority number (RPN) was assigned to each FM based on tabulated scores for the severity (S), frequency of occurrence (O), and detectability (D) of errors, each on a scale of 1 to 10. The single error rate, multiple error rate, and overall error rate were calculated to evaluate the quality of the treatment planning. The PTPCR compliance rate was used to quantify the effectiveness of the PTPCR.Results: In total, 201 errors were identified from the 1,406 plans. From the FMEA results, image parameters had the highest mean RPN, and the planning parameters had the highest RPN from the FM of skin flash. The chart documents had the highest number of FMs and highest occurrence rate, followed by MOSAIQ management and planning parameters. The average single, multiple, and overall error rates were 10.6%, 1.3%, and 11.9%, respectively. The PTPCR compliance rate was 90.3%. Conclusions:The FMEA provided a systematic and useful method for evaluating the errors detected in the PTPCR. The compliance rate could help us understand the effectiveness of our PTPCR. The FMEA results and the PTPCR compliance rate could help us improve our PTPCR to ensure the safety of treatment and the efficiency of the clinical workflow.