Background: Total scalp irradiation presents technical and dosimetric challenges. While reports suggest that HyperArc, a new stereotactic radiosurgery planning technique applied to non-coplanar volumetric-modulated arc therapy (VMAT) technique, is associated with high conformity and rapid dose fall-off, the performance of HyperArc for total scalp irradiation has not been explored. The current study aimed to compare the dosimetric performance of HyperArc plans with those of non-coplanar VMAT plans in angiosarcoma of the scalp. Methods: Ten patients with angiosarcoma of the scalp were included in this study. The performance of three different plans administered using TrueBeam Edge were compared: non-coplanar VMAT using flattening filter (FF) beams (VMAT-FF), HyperArc using FF beams (HyperArc-FF), and HyperArc using flattening filter free (FFF) beams (HyperArc-FFF). The dose distribution, dosimetric parameters, and dosimetric accuracy for each of these plans were evaluated. Results: The three plans showed no statistically significant differences in target volume coverage, conformity, and homogeneity. The HyperArc-FF and HyperArc-FFF plans provided significantly lower mean brain doses (12.63 ± 3.31 Gy and 12.71 ± 3.40 Gy) than did the VMAT-FF plans (17.11 ± 5.25 Gy). There were almost no differences in sparing the organs at risk between the HyperArc-FF and HyperArc-FFF plans. The HyperArc-FF and HyperArc-FFF plans provided a shorter beam-on time than did the VMAT-FF plan. The 3%/2 mm gamma test pass rates were above 95% for all three plans. Conclusions: Our results suggest that the HyperArc plan can be potentially used for radiation therapy of target regions with large and complicated shapes, such as the scalp, and that there are no advantages of using FFF beams.
Background/Aim: The aim of this study was to evaluate the mechanical performance and the effect on dose distribution and deliverability of volumetric modulated arc therapy (VMAT) plans for prostate cancer created with the commercial knowledge-based planning (KBP) system (RapidPlan™). Materials and Methods: Three institutions, A, B, and C were enrolled in this study. Each institution established and trained a KBP model with their own cases. CT data and structures for 45 patients at institution B were utilized to validate the dose-volume parameters (D 2(%) , D 95(%), and D 98(%) for target, and V 50(%) , V 75(%), and V 90(%) for rectum and bladder), and the following mechanical performance parameters and gamma passing rates of each KBP model: leaf sequence variability (LSV), aperture area variability (AAV), total monitor unit (MU), modulation complexity score for VMAT (MCSv), MU/control point (CP), aperture area (AA)/CP, and MU×AA/CP. Results: Significant differences (p<0.01) in dosimetric parameters such as D 2 and D 98 for target and V 50 , V 75, and V 90 for bladder were observed among the three institutions. The means and standard deviations of MCSv were 0.31±0.03, 0.29±0.02, and 0.32±0.03, and the angles of maximum and minimum MU×AA/CP were 269˚and 13˚, 269˚and 13˚, and 273˚and 153˚at institutions A, B, and C, respectively. The mean gamma passing rate (1%/1 mm.) was >95% for all cases in each institution. Dose distribution and mechanical performance significantly differed between the three models. Conclusion: Each KBP model had different dose distributions and mechanical performance but could create an acceptable plan for deliverability regardless of mechanical performance.Volumetric modulated arc therapy (VMAT) is an intensitymodulated technique delivered with dynamic gantry motion, while varying multi leaf collimators (MLC), dose rates, and gantry speeds (1) and can be used to create a steep dose gradient and complement dose distribution (2). It utilizes inverse planning to improve target conformity and organ at risk (OAR) sparing (3) and has often been used for prostate and head and neck cancer (4, 5). However, one of the disadvantages of VMAT is that the plan quality, such as target coverage and OAR sparing, depends on the planner's skill and experience or institution's plan policy during optimization (6, 7).VMAT plans require more complex parameters related to treatment equipment such as gantry, linear accelerator, and MLC than conformal plans; therefore, it is recommended that patient-specific quality assurance (QA) be performed prior to initiating treatment to ensure deliverability. Complexity is associated with gantry speed, MU and sequence and aperture of MLC, which we defined as 687 This article is freely accessible online.
Objective Dosimetric potential of knowledge‐based RapidPlan planning model trained with HyperArc plans (Model‐HA) for brain metastases has not been reported. We developed a Model‐HA and compared its performance with that of clinical volumetric modulated arc therapy (VMAT) plans. Methods From 67 clinical stereotactic radiosurgery (SRS) HyperArc plans for brain metastases, 47 plans were used to build and train a Model‐HA. The other 20 clinical HyperArc plans were recalculated in RapidPlan system with Model‐HA. The model performance was validated with the 20 plans by comparing dosimetric parameters for normal brain tissue between clinical plans and model‐generated plans. The 20 clinical conventional VMAT‐based SRS or stereotactic radiotherapy plans (CL‐VMAT) were reoptimized with Model‐HA (RP) and HyperArc system (HA), respectively. The dosimetric parameters were compared among three plans (CL‐VMAT vs. RP vs. HA) in terms of planning target volume (PTV), normal brain excluding PTVs (Brain − PTV), brainstem, chiasm, and both optic nerves. Results In model validation, the optimization performance of Model‐HA was comparable to that of HyperArc system. In comparison to CL‐VMAT, there were no significant differences among three plans with respect to PTV coverage ( p > 0.17) and maximum dose for brainstem, chiasm, and optic nerves ( p > 0.40). RP provided significantly lower V 20 Gy , V 12 Gy , and V 4 Gy for Brain − PTV than CL‐VMAT ( p < 0.01). Conclusion The Model‐HA has the potential to significantly reduce the normal brain dose of the original VMAT plans for brain metastases.
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