Background The dose perturbation effect of immobilization devices is often overlooked in intensity-modulated radiation therapy (IMRT) for breast cancer (BC). This retrospective study assessed the dosimetric effects of supine immobilization devices on the skin using a commercial treatment planning system. Methods Forty women with BC were divided into four groups according to the type of primary surgery: groups A and B included patients with left and right BC, respectively, who received 50 Gy radiotherapy in 25 fractions after radical mastectomy, while groups C and D included patients with left and right BC, respectively, who received breast-conservation surgery (BCS) and 40.05 Gy in 15 fractions as well as a 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 differences were assessed by comparing the dose-volume histogram parameter results and by plan subtraction. Results The supine immobilization devices for BC resulted in significantly increased skin doses, which may ultimately lead to skin toxicity. The mean dose increased by approximately 0.5 and 0.45 Gy in groups A and B after radical mastectomy and by 2.7 and 3.25 Gy in groups C and D after BCS; in groups A–D, the percentages of total normal skin volume receiving equal to or greater than 5 Gy (V5) increased by 0.54, 1.15, 2.67, and 1.94%, respectively, while the V10 increased by 1.27, 1.83, 1.36, and 2.88%; the V20 by 0.85, 1.87, 2.76, and 4.86%; the V30 by 1.3, 1.24, 10.58, and 11.91%; and the V40 by 1.29, 0.65, 10, and 10.51%. The dose encompassing the planning target volume and other organs at risk, showed little distinction between IMRT plans without and with consideration of immobilization devices. Conclusions The supine immobilization devices significantly increased the dose to the skin, especially for patients with BCS. Thus, immobilization devices should be included in the external contour to account for dose attenuation and skin dose increment. Trial registration This study does not report on interventions in human health care.

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.

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