Comparing brass mesh to tissue equivalent bolus materials for volumetric modulated arc therapy chest wall irradiation.

Abstract

To compare the superficial dose when using brass mesh bolus (BMB), no bolus, or 3mm tissue-equivalent bolus with a pseudo-flash volumetric modulated arc therapy (VMAT) breast treatment planning technique. Two different beam arrangements for right-sided irradiation and one beam arrangement for bilateral irradiation were planned on an inhomogeneous thorax phantom in accordance with our clinical practice for VMAT postmastectomy radiotherapy (PMRT). Plans were optimized using pseudo-flash and representative critical organ optimization structures were used to shape the dose. Plans were delivered without bolus, with 3mm tissue-equivalent bolus (TEB), or with one-layer BMB. Optically stimulated luminescence dosimeter (OSLD) and radiochromic film measurements were taken and analyzed to determine the superficial dose in each case and the relative enhancement from the no bolus delivery. Superficial dose measured with OSLDs was found to be 76.4±4.5%, 103.0±6.1%, and 98.1±5.8% of prescription for no physical bolus (NB), TEB, and BMB, respectively. Superficial dose was observed to increase from lateral to medial points when measured with film. However, the relative increase in superficial dose from NB was consistent across the profile with an increase of 43±2.1% and 34±3.3% of prescription for TEB and BMB, respectively. The results are in good agreement with expectations from the literature and the experience with tangential radiotherapy. Three millimeter TEB and one-layer BMB were shown to provide similar enhancement to the superficial dose compared to delivery without bolus. BMB, which does not significantly affect dose at depth and is more conformal to the patient surface, is an acceptable alternative to 3mm TEB for chest wall PMRT patients treated with pseudo-flash PMRT.