Dosimetric Effects on skin of supine Immobilization Device in Intensity Modulated Radiation Therapy for breast cancer: a retrospective study

Abstract

BackgroundBreast immobilization devices are commonly used in supine breast radiotherapy while the dose perturbation effect is often overlooked in Intensity Modulated Radiation Therapy for breast cancer (BC). This study is to assess the dosimetric effect of supine immobilization devices on skin with a commercial treatment planning system.Methods40 women with BC were divided into four groups according to the type of primary surgery, group A and B corresponding to patients with left and right BC after radical mastectomy, received a radiotherapy of 50 Gy in 25 fractions, group C and D corresponding to patients with left and right BC after breast-conservation surgery, received a prescription of 40.05 Gy in15 fractions and tumor bed simultaneous integrated boost to 45 Gy. A 0.2 cm thick skin contour and two sets of body contours were outlined for each patient. Dose calculations were conducted for the two sets of contours using the same plan, the dose difference was assessed by comparing the dose-volume histogram parameter results and by plan subtraction.ResultsThe supine immobilization devices for BC caused a significantly increase in the skin dose which may finally lead to skin toxicity. The mean dose increased by approximately 0.5 Gy and 0.45 Gy in left (group A) and right (group B) BC after radical mastectomy, 2.7 Gy and 3.25 Gy in left (group C) and right (group D) BC after BCS; corresponding to group A, B, C, D, the V10 of skin increased1.27%,1.83%, 1.36%, 2.88% ; the V20 of skin increased 0.85%, 1.87%, 2.76%, 4.86%; the V30 of skin increased 1.3%, 1.24%, 10.58%, 11.91%; the V40 of skin increased 1.29%, 0.65%, 10%, 10.51%. The dose encompassing of planning target volume, as well as the HI and CI, showed little distinction between plan- and plan+.ConclusionThe supine immobilization devices significantly increased the dose of skin, especially for patients with BCS. The immobilization devices should be included in the external contour to account for the dose attenuation and skin dose increment.Trial registrationThis is a retrospectively study and it has no intervention on human health care, so this study was not registered.