Abstract
PurposeTo verify the accuracy of volumetric arc therapy (VMAT) using the RapidArc™ device when switching patients from one single linear accelerator (linac) to a paired energy and mechanics "twin" linac without reoptimization of the original treatment plan.Patients and MethodsFour centers using 8 linacs were involved in this study. Seventy-four patients previously treated with the 6MV photon RapidArc™ technique were selected for analysis, using 242 measurements. In each institution, all patients were planned on linac A, and their plans were verified both on linac A and on the twin linac B. Verifications were done using the amorphous silicium electronic portal imager (EPID) of the linacs and were analyzed with the EpiQa software (Epidos, Bratislavia, Slovakia). The gamma index formalism was used for validation with a double threshold of 3 % and 3 mm with a measurement resolution of 0.39 mm/pixel, and a smoothed resolution of approximately 2.5 mm.ResultsThe number of points passing the gamma criteria between the measured and computed doses was 94.79 ± 2.57 % for linac A and 94.61 ± 2.46 % for linac B. Concerning the smoothed measurement analysis, 98.67 ± 1.26 % and 98.59 ± 1.20 % points passing the threshold were obtained for linacs A and B, respectively.The difference between the 2 dose matrices acquired on the EPID was very small, with 99.92 ± 0.06 % of the points passing the criteria.ConclusionFor linacs sharing the same mechanical and energy parameters, this study tends to indicate that patients may be safely switched from treatment with one linac to treatment with its twin linac using the same VMAT plan.
Highlights
New radiotherapy techniques aiming at improving target coverage and protection of organs-at-risk have emerged in the last decade
For linacs sharing the same mechanical and energy parameters, this study tends to indicate that patients may be safely switched from treatment with one linac to treatment with its twin linac using the same volumetric arc therapy (VMAT) plan
Intensity-modulated radiation therapy (IMRT) improved dosimetric results compared with 3-dimensional conformal radiotherapy (3D-CRT) by modulating the beam intensity for static gantry angles [1,2,3,4]
Summary
New radiotherapy techniques aiming at improving target coverage and protection of organs-at-risk have emerged in the last decade. Intensity-modulated radiation therapy (IMRT) improved dosimetric results compared with 3-dimensional conformal radiotherapy (3D-CRT) by modulating the beam intensity for static gantry angles [1,2,3,4]. The resulting treatment plan is often more complex than that of the standard IMRT, which raises the question of the feasibility of switching a patient treated with a VMAT plan computed for a specific linac to a “twin” linac e.g. in case of repair or maintenance. While it has been shown possible for 3DCRT and standard IMRT, no data is available regarding this possibility with VMAT. We conducted a study in Fenoglietto et al Radiation Oncology (2016) 11:2 order to compare the accuracy of the actual patients’ VMAT plans optimized for a specific linac to the same plans when radiotherapy is delivered on a “twin” linac
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