Dosimetric effects of prone immobilization devices on skin in intensity-modulated radiation therapy for gynecologic cancer: a retrospective study

The dose perturbation effect of immobilization devices is often overlooked in intensity-modulated radiation therapy (IMRT) for gynecologic cancer. This retrospective study assessed the dosimetric effects of a prone immobilization device combined with a belly board (PIDBB) on the skin.

We recruited 63 women with gynecologic cancer undergoing postoperative IMRT at our institute. A 0.3 cm thick skin contour and body contours with or without PIDBB system were outlined for each patient. Dose calculations were performed for the two sets of contours using the same plan, named Plan₋ and Plan₊, respectively. The accuracy of calculated doses was verified by gafchromic EBT3 film and anthropomorphic phantom.

The V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of skin increased by 56.94%, 65.48%, 53.12%, 41.91%, and 1.91%, respectively. Even after excluding the effect of prescription dose coverage, the V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of skin still increased by 46.90%, 92.07%, 72.81%, 52.25%, and 18.06%, respectively. No significant differences were observed in doses to other organs at risk. The EBT3 measurements showed that the skin dose map to the anthropomorphic phantom was 23.79% higher than that calculated by the treatment planning system without the PIDBB system.

While the PIDBB system effectively reduces the low dose to small intestine, it also induces radiation attenuation, leading to a sharp increase in skin dose, particularly in patients receiving radiation in the groin and perineum area. Therefore, immobilization devices should be included in the external contour to account for dose attenuation and the increment in skin dose.

This study does not report on interventions in human health care.