Abstract
The unwanted radiation transmission through the multileaf collimators could be reduced by the jaw tracking technique which is commercially available on Varian TrueBeam accelerators. On the basis of identical plans, this study aims to investigate the dosimetric impact of jaw tracking on the volumetric‐modulated arc therapy (VMAT) plans. Using Eclipse treatment planning system (TPS), 40 jaw‐tracking VMAT plans with various tumor volumes and shapes were optimized. Fixed jaw plans were created by editing the jaw coordinates of the jaw‐tracking plans while other parameters were identical. The deliverability of this artificial modification was verified using COMPASS system via three‐dimentional gamma analysis between the measurement‐based reconstruction and the TPS‐calculated dose distribution. Dosimetric parameters of dose‐volume histogram (DVH) were compared to assess the improvement of dose sparing for organs at risk (OARs) in jaw‐tracking plans. COMPASS measurements demonstrated that over 96.9% of structure volumes achieved gamma values less than 1.00 at criteria of 3 mm/3%. The reduction magnitudes of maximum and mean dose to various OARs ranged between 0.06%∼6.76%(0.04∼7.29 Gy) and 0.09%∼7.81%(0.02∼2.78 Gy), respectively, using jaw tracking, agreeing with the disparities of radiological characteristics between MLC and jaws. Jaw tracking does not change the delivery efficiency and total monitor units. The dosimetric comparison of VMAT plans with and without jaw tracking confirms the physics hypotheses that reduced transmission through tracking jaws will reduce doses to OARs without sacrificing the target dose coverage because it is meant to be covered by radiation beams going through the opening.PACS number(s): 87.55.de, 87.55.dk
Highlights
134 Wu et al.: volumetric-modulated arc therapy (VMAT) with/without jaw tracking only by multileaf collimator (MLC), the transmitted dose rate could be 0.90%–4.40% (6 MV photon) or 1.14%–7.00% (18 MV) higher than that shielded by jaws or both MLC and jaws.[5,6] These inherent differences enabled potential better sparing of organs at risk (OARs) from transmitted radiation through MLC either by manual adjustment of jaw positions,(7) or by jaw-tracking technique which continuously adjusting the main jaws to tangentially enclose the distal apertures shaped by MLC
The benefits of jaw tracking have been well assessed for intensity-modulated radiotherapy (IMRT) based on the same plan except for the jaw patterns.[8,9,10,11] bearing more variables than IMRT, such as gantry rotation speed, dose rate variety, jaw translation direction, and speed and range, any reoptimization with/without jaw tracking can change these parameters and the MLC sequences,(12) the interplan differences were not exclusively induced by the jaw tracking technique.[13,14] Alternatively, the artificial conversion from VMAT
To jaw-tracking static arc plans failed to include jaw tracking into the optimization procedure, the suboptimal plans may violate the mechanical constraints of jaws and were clinically not deliverable by the accelerators.[15] the dosimetric impact of jaw tracking has not been evaluated based on the same VMAT plans by far, which is the aim of this study
Summary
134 Wu et al.: VMAT with/without jaw tracking only by MLC, the transmitted dose rate could be 0.90%–4.40% (6 MV photon) or 1.14%–7.00% (18 MV) higher than that shielded by jaws or both MLC and jaws.[5,6] These inherent differences enabled potential better sparing of organs at risk (OARs) from transmitted radiation through MLC either by manual adjustment of jaw positions,(7) or by jaw-tracking technique which continuously adjusting the main jaws to tangentially enclose the distal apertures shaped by MLC.The benefits of jaw tracking have been well assessed for IMRT based on the same plan except for the jaw patterns.[8,9,10,11] bearing more variables than IMRT, such as gantry rotation speed, dose rate variety, jaw translation direction, and speed and range, any reoptimization with/without jaw tracking (even with the same optimization objectives) can change these parameters and the MLC sequences,(12) the interplan differences were not exclusively induced by the jaw tracking technique.[13,14] Alternatively, the artificial conversion from VMAT to jaw-tracking static arc plans failed to include jaw tracking into the optimization procedure, the suboptimal plans may violate the mechanical constraints of jaws and were clinically not deliverable by the accelerators.[15]. The dosimetric impact of jaw tracking has not been evaluated based on the same VMAT plans by far, which is the aim of this study
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