Dosimetric impact of interplay effect on a volumetric modulated arc therapy (VMAT) stereotactic lung (SBRT) delivery: Validation using a 6D motion platform and 3D dosimeter

Abstract

Purpose/Objective(s) The aim of the study is to use a system to quantify the differences between calculated and measured doses in the presence of motion with treatment using 1 versus 2 partial arcs. Materials/Methods The 6D Hexamotion platform (ScandiDos®) was developed in order to make 3D delta4® dosimeter dynamic. It is able to simulate the 4D movement of the Clinical Target Volume (CTV) according to the respiratory cycle of a patient obtained from a 4DCT. The study was conducted on treatment plans generated from 5 patients treated with VMAT SBRT technique. Indeed, at first five treatment plans (2arcs) irradiated with own 4D movement of the CTV and a second time: 10 treatment plans (1 arc) irradiated with the same 4D movement with 200 and 400 MU/min. They were compared with those irradiated without movement. In addition to confirm the results, plans with 1 arc (400 MU/min) were also delivered with a sinusoidal motion pattern with peak to peak amplitudes of 1, 1.5 and 2 cm and target period of 4 s. Results Plans with one and two arcs irradiated without movement gave similar results (localV (3% 3 mm) = 99.8 ± 0.4%). Analysis of the plans, an arc (400 MU/min and 200 MU/min) and two arcs (400 MU/min) irradiated with tumor specific movement, we show that there is no significant differences (localV (3% 3 mm) = 95.3 ± 5.7%). The passing rate at 3% 3 mm threshold criteria was 99.3 ± 0.3%, 91.4 ± 3.2%, 80.3 ± 7% with respectively 1, 1.5 and 2 cm peak to peak sinusoidal motion in the superior-inferior (SI). Conclusion Dosimetry measurements using 3D dosimeter and Hexamotion6D platform indicate that VMAT plans can be accurately delivered and that interplay effect is not significant for target amplitudes less than or equal to 1 cm. The interplay effect is low because of the larger averaging effect associated with increased dose per fraction (1000 cGy) delivered during at least 90 breathing cycles. The aim of the study is to use a system to quantify the differences between calculated and measured doses in the presence of motion with treatment using 1 versus 2 partial arcs. The 6D Hexamotion platform (ScandiDos®) was developed in order to make 3D delta4® dosimeter dynamic. It is able to simulate the 4D movement of the Clinical Target Volume (CTV) according to the respiratory cycle of a patient obtained from a 4DCT. The study was conducted on treatment plans generated from 5 patients treated with VMAT SBRT technique. Indeed, at first five treatment plans (2arcs) irradiated with own 4D movement of the CTV and a second time: 10 treatment plans (1 arc) irradiated with the same 4D movement with 200 and 400 MU/min. They were compared with those irradiated without movement. In addition to confirm the results, plans with 1 arc (400 MU/min) were also delivered with a sinusoidal motion pattern with peak to peak amplitudes of 1, 1.5 and 2 cm and target period of 4 s. Plans with one and two arcs irradiated without movement gave similar results (localV (3% 3 mm) = 99.8 ± 0.4%). Analysis of the plans, an arc (400 MU/min and 200 MU/min) and two arcs (400 MU/min) irradiated with tumor specific movement, we show that there is no significant differences (localV (3% 3 mm) = 95.3 ± 5.7%). The passing rate at 3% 3 mm threshold criteria was 99.3 ± 0.3%, 91.4 ± 3.2%, 80.3 ± 7% with respectively 1, 1.5 and 2 cm peak to peak sinusoidal motion in the superior-inferior (SI). Dosimetry measurements using 3D dosimeter and Hexamotion6D platform indicate that VMAT plans can be accurately delivered and that interplay effect is not significant for target amplitudes less than or equal to 1 cm. The interplay effect is low because of the larger averaging effect associated with increased dose per fraction (1000 cGy) delivered during at least 90 breathing cycles.