Superficial doses in breast cancer radiotherapy using conventional and IMRT techniques: a film-based phantom study

Abstract

Background and purpose: Superficial doses in radiotherapy are affected by the treatment technique. The implications for breast cancer treatments were evaluated.

Material and methods: Four treatment techniques relevant for breast cancer irradiation were evaluated; tangential standard, tangential IMRT, 7-field IMRT (arc-like field arrangement) and hybrid IMRT (an IMRT plan mixed with non-modulated fields). Only 6MV photons were used. GafChromic EBT film was used for dose measurements at the surface, in the skin (0-5mm depth) and in the superficial parts of CTV (5-10mm depth) of an anthropomorphic thorax phantom.

Results: Only small differences in superficial doses were observed between tangential standard and tangential IMRT. Compared to the tangential standard plan, the surface and skin doses were reduced with the 7-field IMRT plan, on average by 20% and 5%, respectively, while hybrid IMRT reduced the surface and skin doses medially (by 44% and 8%, respectively) and increased the surface and skin dose laterally (by 40% and 15%, respectively). Minimum superficial CTV doses varied between regions, but were mainly between 90% and 95% of the target dose for all plans, only the hybrid IMRT plan resulted in a region with minimum dose below 90%.

Conclusions: Compared to tangential irradiation, skin sparing was achieved by the 7-field IMRT plan. The minimum dose in the superficial parts of the CTV was below 95% of the target dose for all plans investigated.