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

다국어 초록 (Multilingual Abstract)

<P>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 −180(<SUB>Body180</SUB>), −350(<SUB>Body350</SUB>), −700(<SUB>Body700</SUB>), and −980(<SUB>Body980</SUB>). 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, <SUB>D95%</SUB>, and <SUB>D5%</SUB> with <SUB>Body180</SUB> were higher than those with <SUB>Body980</SUB> by approximately 0.7% (p<0.001). For H&N target volumes, the changes in <SUB>D95%</SUB> of the targets receiving 67.5 Gy, 54 Gy, and 48 Gy between <SUB>Body180</SUB> and <SUB>Body980</SUB> were −1.2%, −0.9%, and −1.2%, respectively (p<0.001). 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 −980 HU. Otherwise, systematic error of about 1%, resulting in underdosage of the target volume, can occur.</P><P>PACS number: 87.55.ne</P>