Abstract
Purpose: To study the effect of vaccum bag, body positioning system and accelerator treatment couch on the dosimetry of lungcancerradiotherapy. Methods: Ten patients with central lungcancer treated with radiotherapywere enrolled in this study, using Varian Eclipse treatment planning system delineated three different regions of dose calculation on CTimages of each patient. Only the contours of patients' surface were delineated on the first group CTimages; contours of vaccum bag and body positioning system were added on the second group CTimages;then contours of accelerator treatment couch were added on the third group CTimages. Same plans were designed on each patient's three group CTimages respectively, and named plan1, plan2, plan3. The dose of target and organs at risk and the number of MUs were analyzed. Results: The maximum, minimum, mean dose to target and the target volume receiving prescription dose have no statistically significant differences among three group plans.No statistically significant differences were observed in the maximum dose of spinal cord between plan1 and the other plans. Compared with plan2, the maximum dose of spinal cord increased 3% in plan3(p=0.008). No statistically significant differences were observed in the mean dose of heart and ipsilateral lung among three plans.For the volume receiving more than 20 Gy (V20) of ipsilateral lung,plan3 and plan1 showed the highest and lowest values respectively, significant differences were observed between any two plans. Compare to plan1, the plan2 and plan3 statistically significantly increased the maximum, minimum and mean dose of subcutaneous 5mm and 10mm regions of the patients' back, and the plan3 performed more obviously. Compared to plan1, the MUs of plan2 and plan3 increased 2% and 5% respectively(p<0.005). Conclusions: Vaccum bag, body positioning system and accelerator treatment couch would affect the dose of radiotherapy plans, we should consider these factors when designing plans, and correct the dose if necessary.
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