P177] 3D Rapid manufacturing bolus vs commercial bolus – Skin dose comparison

Abstract

Purpose Most of the breast treatments uses a megavoltage photon beams. This kind of energy exhibits a skin-sparing effect that is a concern in some stages of both breast conservative and post-mastectomy irradiation. To overwhelm this effect a bolus material is placed on the skin. However, when using commercial non-customized bolus, small air gaps can occur in certain regions of the treatment area where the bolus cannot establish the perfect match with the irregular skin of the patient, altering locally the expected skin dose. The objective of this study is to verify the improvement in the breast radiotherapy treatment using a customized bolus produced by 3D rapid manufacturing (3D-RM) techniques, and compare it with the commercial ones. Measurement of the surface dose and comparisons with the doses calculated by the Treatment Planning System (TPS) were also performed. Methods The customized 3D rapid manufactured bolus was prepared for an anthropomorphic female phantom breast area. 3D-CRT treatment plans for right breast were performed on CT scans of the phantom both with the customized and commercial bolus. The skin dose was measured in 5 points on the phantom breast surface using a MOSFET-based system. Results A better fitting to the surface of the phantom was observed for the customized bolus, reducing the air gaps and improving the daily positioning on the irregular breast surfaces. The average differences between calculated and measured doses in the customized and commercial bolus ranged from 2 to 10%. However, the highest dose difference (approximately 10%) was observed for the commercial bolus. Conclusions The 3D rapid manufactured bolus can reduce the uncertainty in the daily positioning and help to overcome the dose discrepancy due to unwanted air gaps affecting breast cancer radiation therapy. With the commercial bolus a higher dose difference relatively to TPS was observed. The skin dose increase is observed in the same proportion for both boluses.