The effect of body contouring on the dose distribution delivered with volumetric‐modulated arc therapy technique

The purpose of the study was to investigate the dosimetric effect defining the body structure with various Hounsfield unit (HU) threshold values on the dose distributions of volumetric‐modulated arc therapy (VMAT) plans. Twenty patients with prostate cancer and twenty patients with head and neck (H&N) cancer were retrospectively selected. For each patient, the body structure was redefined with HU threshold values of [Formula: see text] , [Formula: see text] , [Formula: see text] , and [Formula: see text]. For each patient, dose‐volumetric parameters with those body structures were calculated using identical VMAT plans. The differences in dose‐volumetric parameters due to the varied HU threshold values were calculated. For the prostate boost target volume, the maximum dose, mean dose, [Formula: see text] , and [Formula: see text] with [Formula: see text] were higher than those with [Formula: see text] by approximately 0.7% ([Formula: see text]). For H&N target volumes, the changes in [Formula: see text] of the targets receiving 67.5 Gy, 54 Gy, and 48 Gy between [Formula: see text] and [Formula: see text] were [Formula: see text] , [Formula: see text] , and [Formula: see text] , respectively ([Formula: see text]). The differences were larger for H&N VMAT plans than for prostate VMAT plans due to the inclusion of an immobilization device in the irradiated region in H&N cases. To apply all attenuating materials to dose calculation, the body structure would be defined with [Formula: see text]. Otherwise, systematic error of about 1%, resulting in underdosage of the target volume, can occur. PACS number: 87.55.ne