VMAT techniques for lymph node-positive left sided breast cancer

Abstract

Purpose: To investigate the plan quality of two different volumetric modulated arc therapy (VMAT) techniques for lymph node-positive left-sided breast cancer. Methods: Two VMAT plans were generated for 10 lymph node-positive left-sided breast cancer patients: one plan using one single segment of a full rotation, typically an arc segment of 230° (1s-VMAT); and a second plan consisting of 2 small tangential arc segments of about 50° (2s-VMAT).For plan comparison, various dose and dose volume metrics (Dmean, D98%, D2% for target volumes, D2%, Dmean and Vx% for organs at risk (OAR)) were evaluated. Results: Both techniques fulfilled both clinical target dose and OAR goals. 1s-VMAT achieved a slightly better homogeneity and better target coverage (D2%=54.2±0.7Gy, D98%=30.3±1.8Gy) compared to 2s-VMAT (D2%=55.0±1.1Gy, D98%=29.9±1.7Gy). For geometrical reasons, OAR sparing was noticeable but not significant better using 2s-VMAT, particularly heart and contralateral breast. The heart received a mean dose of 4.4±0.8Gy using 1s-VMAT and 3.3±1.0Gy using 2s-VMAT; the contralateral breast received 1.5±0.3Gy and 0.9±0.3Gy, respectively. Conclusions: A VMAT technique based on two small tangential arc segments enables improved OAR sparing, the differences between the two techniques in target coverage and homogeneity are minor. Patient age and -anatomy must be considered for each individual case when deciding which technique to be used.