Non-coplanar Butterfly VMAT and Deep Inspiration Breath Hold for Mediastinal Lymphoma: Do We Need Both?

Abstract

Reducing doses to organs at risk (OAR) is an important goal when treating mediastinal lymphoma in young individuals. Volumetric modulated arc therapy (VMAT) improves target coverage & heart sparing but at the expense of low-dose bath to lungs and breasts. Butterfly VMAT (B-VMAT) uses non-co-planar partial arc VMAT, limiting doses to lungs and breasts, but heart sparing may be reduced. In addition, deep inspiration breath hold (DIBH) has been shown to reduce lung and heart doses. The aim of this planning study was to assess the dosimetric benefit of B-VMAT compared to full arc VMAT and also to investigate any added benefit of adding DIBH to either technique. Forty plans for 13 consecutive patients (age: 22-59, 6 females) with mediastinal lymphoma were compared. A free-breathing (FB) scan was acquired for all patients. Two VMAT plans were produced: two full arcs and B-VMAT. The B-VMAT used double 600 partial anterior & posterior arcs and 2 craniocaudal 60° anterior arcs. Seven of these patients also had a DIBH scan and additional VMAT and B-VMAT plans were produced. Plans were optimized to achieve comparable planning target volume (PTV) coverage. Dose to lungs, heart, spinal cord, esophagus, and female breasts were reduced as much as possible. Mean PTV coverage and doses to OARs were compared and differences were tested for statistical significance with Wilcoxon signed-rank test. Results are shown in Table 1. For the FB plans, the Mean Lung Dose (MLD) decreased by 11% and lung V5 reduced by 26% when using B-VMAT. V20 did however increase by 13%. No significant difference was seen in the heart dose between the two techniques. Breast V4 was significantly reduced by 62%. DIBH had more effect on reducing MLD than B-VMAT and the combination of the two techniques was additive. The DIBH B-VMAT plans showed significant reduction in both high and low dose to the lung when compared with FB plans, as well as a significant reduction in mean and high dose to the heart and breast V4. B-VMAT reduces low-dose bath to lungs and female breast with minimal effect on heart sparing and a small increase in lung V20. The benefits of DIBH and B-VMAT are additive and result in maximum sparing of lungs, heart and breasts.Tabled 1Abstract 132; Table 1 *Superscript indicates techniques with which a comparison provides a statistically significant differenceAll patients (13)FB + DIBH cohort (7)*VMATB-VMATP value1:VMAT & FB2:BVMAT & FB3:VMAT & DIBH4:BVMAT & DIBHPTV V95% (%)97.897.90.38298.298.098.198.1MLD (Gy)7.66.80.0056.92,3,46.21,3,44.91,2,44.41,2,3Lung V20 (%)12.714.40.04612.22,3,413.41,3,46.11,2,47.71,2,3Lung V5 (%)43.331.90.00138.42,428.51,431.8421.31,2,3Heart mean dose (Gy)5.65.90.0554.03,44.23,42.81,23.01,2Heart V30 (%)5.65.20.2353.53,43.33,41.61,21.91,2Heart V15 (%)15.115.70.1249.8310.536.51,2,47.13Breast V10 (%)3.33.54.34.43.32.7Breast V4 (%)20.07.718.68.419.26.9 Open table in a new tab