Left Anterior Descending Coronary Artery Dose-Sparing Effects of Volumetric Modulated Arc Therapy in Patients Ineligible for Deep-Inspiration Breath-Hold in Left Breast Radiation Therapy

Abstract

Deep-inspiration breath-hold (DIBH) is a widely used and highly efficient technique of adjuvant left breast radiotherapy (RT), associated with lower radiation exposure to the left anterior descending artery (LAD). This technique involves patient training and coaching and high level of compliance is required. Hence, DIBH cannot be performed in some patients with left-sided breast cancer and free-breathing (FB) tangential RT is usually used. Volumetric modulated arc therapy (VMAT) can achieve highly conformal dose distributions and reduces treatment time. The aim of our study was to evaluate whether the patients who are ineligible for DIBH will benefit from free-breathing volumetric modulated arc therapy (FB-VMAT). Twenty patients with left-sided breast cancer underwent computed tomography simulation and images were obtained in both FB and DIBH. Ten patients were ineligible for DIBH and in this group FB-VMAT plans were generated. In FB and DIBH plans 42.72 Gy in 16 fractions was prescribed to breast tissue with 10.0 Gy boost in 4 fractions to the tumor bed. In FB-VMAT group simultaneous integrated boost planning was performed and 54.0 Gy in 20 fractions was prescribed. Treatment plans (DIBH, FB and FB-VMAT) were compared using various parameters, including mean heart dose, mean and maximal LAD dose, mean ipsilateral lung dose, percentage of ipsilateral lung receiving 20 Gy (Lung V20), mean contralateral lung dose and mean contralateral breast dose. Statistical analysis was performed using one-way ANOVA and with post-hoc Tukey test. Mean heart dose was significantly lower in DIBH plans (1.96 Gy, p<0.001) compared to FB (7.05 Gy) and FB-VMAT plans (6.99 Gy). Mean LAD doses for DIBH, FB and FB-VMAT plans were 10.61 Gy, 35.71 Gy and 20.15 Gy (p < 0.001) and maximal LAD doses were 33.64 Gy, 45.59 Gy and 35.20 Gy (p<0.001), respectively. Mean ipsilateral lung dose was significantly higher in FB-VMAT plans (11.32 Gy, p=0.006) compared to FB (7.72 Gy) and DIBH (8.49 Gy) plans while no significant difference was noted for Lung V20 (15.74 Gy, 15.42 Gy and 14.91 Gy, respectively; p=0.956). Mean contralateral lung dose was significantly higher in FB-VMAT plans (3.31 Gy, p<0.001) compared to FB (0.31 Gy) and DIBH (0.28 Gy) plans. Mean contralateral breast dose was also significantly higher in FB-VMAT plans (2.65 Gy, p<0.001) compared to FB (0.47 Gy) and DIBH (0.43 Gy) plans. Compared to the FB plans, the FB-VMAT plans allowed significant dose sparing in LAD in terms of both mean and maximal dose. However, mean heart dose reduction was achieved only in DIBH plans. In addition, VMAT-FB plans resulted in significantly higher mean doses for both ipsi- and contralateral lung and contralateral breast which may be attributed to a higher whole-body exposure to leakage radiation described in this technique. This trade-off should be considered before implementation of VMAT-FB treatment planning in patients ineligible for DIBH.