Abstract P5-14-15: Discovery and validation of simple heart measurements to screen patients who will benefit from deep inspiration breath hold for left breast irradiation
Authors: Carlson R , Hiemstra K , Pearson S , Qiu X , Xu W , Fyles A , Chung C 
Published: August 2014

Abstract
Purpose:
Deep inspiration breath hold (DIBH) using active breath control in left-sided breast irradiation (RT) can significantly reduce radiation dose to heart and coronary arteries in selected patients. At our institution, a cutoff of V50% &gt;10cc is currently used to identify patients who require DIBH. This dose-volume cutoff requires generation of a radiation plan in order to select patients. The purpose of this study was to identify simple 2-D measurements of the heart at the time of CT simulation that can help screen patients for DIBH in order to streamline the process for left-sided breast RT.
Methods:
This study evaluated CT simulation scans from 50 left-sided breast cancer patients treated with tangent RT alone, where 50% of patients were treated with DIBH. On each CT dataset, a tangential line was drawn between the medial and lateral tattoos. The following heart measurements were recorded by a blinded observer at 2, 3, 4, and 5 cm below the tattoos: (1) maximal heart distance (MHD) perpendicular to this line and (2) heart length (HL) along this line. Predictive models were created using two strategies; (1) step wise approach utilizing the most significant factor and (2) principle component analysis. Using C-statistics, 3 cutoffs with the highest correlations with heart dose were determined from the model. These cutoffs were validated in a cohort of 100 consecutive patients treated from Jan-May 2012.
Results:
Data from 49 patients in the derivation cohort were analyzable. The HL at 2 cm had the strongest correlation with V50 (R2 = 0.45; p &lt;0.0001). Other values that were associated with V50 were HL at 3 cm (R2 = 0.37; p = &lt;0.0001), MHD at 2cm (R2 = 0.25; p = 0.0003), MHD at 3 cm (R2 = 0.23; p = 0.0006) and HL at 4 cm (R2 = 0.17, p = 0.0035). The predictive model using HL at 2 cm gave an adjusted R2 = 0.4385 (P&lt;0.0001). Adding other variables into the predictive model did not improve the adjusted R2. The following 3 cutoffs for HL at 2 cm with respective (sensitivity; specificity) were identified: 3.92 cm (0.955; 0.48), 7.65 cm (0.32; 0.48), and 6.5 cm (0.5; 0.8). In the validation cohort, 22/100 had V50% &gt; 10 cc. Validation of the 3 derived cutoffs for HL at 2 cm yielded the following sensitivities and specificities: 1.0 and 0.28 for 3.92 cm; 0.53 and 0.93 for 7.65 cm; 0.58 and 0.69 for 6.5 cm. Positive predictive value (PPV) and negative predictive value (NPV) were as follows: 3.92 cm (PPV = 0.25; NPV = 1.00). 7.65 cm (PPV = 0.63; NPV = 0.89), and 6.5cm (PPV = 0.30; NPV = 0.87).
Conclusions:
A simple 2-D heart measurement, heart length at 2 cm below the tattoos, had moderate correlation with the irradiated heart volume. Although HL at 2 cm did not have both high specificity and sensitivity to predict who would benefit from DIBH, cut-offs could be selected to maximize sensitivity (3.92 cm for sensitivity 1.0) or specificity (7.65 cm for specificity 0.93). For example, in departments that routinely acquire both free-breathing and DIBH CT simulation scans for all left-sided patients, a cutoff of 3.92cm would minimize the number of unnecessary DIBH scans.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-14-15.