Prospective Assessment of Deep Inspiration Breath Hold Using 3-Dimensional Surface Tracking for Irradiation of Left-Sided Breast Cancer

Abstract

Deep inspiration breath hold (DIBH) is used to reduce dose and volume of cardiac irradiation during radiation therapy (RT) for breast cancer (BC). Patient subgroups most likely to benefit from DIBH and the effect of DIBH on treatment time remain largely unknown. We sought to identify predictors for the use of DIBH and to quantify differences in dosimetry and treatment time using a large, prospective registry of patients (pts) with BC. One hundred forty-eight pts (ages 26-81) with Stage I-IV left BC were enrolled on a prospective registry from 2011-2014. Pts with any type of breast surgery, systemic therapy and RT fields were included. All pts were deemed potential candidates for DIBH and were simulated with both free-breathing (FB) and DIBH. RT was delivered using either FB or DIBH scans based on physician assessment of tolerance, compliance, and anatomy, without formal dosimetric comparison. Alternate scans were also planned using deformable registration to include identical volumes within RT fields. DIBH pts were monitored using a real-time surface tracking system, AlignRT®. Baseline characteristics and treatment times were compared using Fisher’s exact test and Wilcoxon Rank Sum test. Coefficient of variation (CV) measured the dispersion of treatment times. Dosimetric endpoints were compared across paired DIBH and FB scans using Wilcoxon signed rank test. Linear regression was used to identify predictors for change in mean heart dose (ΔMHD) across paired scans. We treated 38 pts with FB and 110 with DIBH. FB pts were significantly older (median: 58 vs. 49.5 years; P=.002), more likely to have pre-existing heart (11% vs. 1%; P=.02) and lung disease (13% vs. 4%; P=.05), and less likely to receive chemotherapy (42% vs. 66%; P=.01) or immediate reconstruction (11% vs. 34%; P=.01) relative to DIBH pts. MHD (138 cGy vs. 256 cGy), heart V5 (3.8% vs. 8%), heart V30 (0% vs. 1.5%), mean lung dose (923 cGy vs. 992 cGy), and lung V20 (17.1% vs. 18.7%) were all significantly lower in DIBH than in paired FB plans. Of 146 evaluable pts, DIBH resulted in >20 cGy improvement in MHD in 107 (range: 22-881 cGy), neutral change in 25, and >20 cGy increase in MHD in 14 (range: 21-153 cGy). Treatment times were not significantly different between DIBH and FB pts (median 4.2 min vs. 3.8 min; P=.87), but DIBH pts had greater variability in times (P=.0002). On multivariate analysis, younger age (4.18 cGy/yr; P<.0001); higher BMI (6.06 cGy/kg/m2; P=.0018) and larger change in lung volumes (130 cGy/L; P = 0.003) were associated with greater ΔMHD. DIBH is an effective technique that improves cardiac dosimetry without significantly affecting treatment time in most pts receiving breast RT. As expected, greater inspiratory lung volumes augment the benefit in DIBH. As the benefit of DIBH was not seen in all pts, pts should be scanned with both FB and DIBH before choosing a treatment approach.