Left-sided breast cancer loco-regional radiotherapy with deep inspiration breath-hold: Does volumetric-modulated arc radiotherapy reduce heart dose further compared with tangential intensity-modulated radiotherapy?

INTRODUCTION: Left-sided breast cancer radiotherapy has been associated with an increase in cardiac mortality. This study investigated the potential heart-sparing effect of volumetric-modulated arc radiotherapy (VMAT). We compared VMAT to tangential intensity-modulated radiotherapy (t-IMRT) in the loco-regional treatment of left-sided breast cancer, including internal mammary nodal irradiation, based on deep inspiration breath-hold (DIBH) and free-breathing (FB).

METHODS: Radiotherapy for 15 patients was re-planned. Four plans were compared: t-IMRT-DIBH; VMAT-DIBH; t-IMRT-FB; VMAT-FB. Prescribed dose was 50 Gy in 25 fractions. T-IMRT plans were generated using tangentially orientated fields. VMAT plans were generated using two partial arcs (average arc 190°).

RESULTS: Mean heart dose (MHD) was 5 ± 2.4 Gy, 5.7 ± 1.4 Gy, 9.7 ± 3.3 Gy and 8.1 ± 2.0 Gy for t-IMRT-DIBH, VMAT-DIBH, IMRT-FB and VMAT-FB respectively. The difference in MHD between IMRT-DIBH and VMAT-DIBH was not significant (P = 0.14). VMAT-DIBH significantly spared the volume of heart irradiated to doses of 20 Gy and above (p < 0.05), however, resulted in a significantly higher V5 Gy (P < 0.001), compared to t-IMRT-DIBH. VMAT-DIBH resulted in higher combined lung mean (11 ± 0.8 Gy vs. 8.8 ± 1.1 Gy, P < 0.001) and higher contralateral breast mean dose (5 ± 1 Gy vs. 1.6 ± 1.2 Gy, P < 0.001) compared with t-IMRT-DIBH.

CONCLUSIONS: On average, there was no significant difference in MHD between VMAT-DIBH and t-IMRT-DIBH. However, VMAT-DIBH was found to benefit a select group of patients. For patients in whom the MHD was >6.3 Gy with t-IMRT-DIBH, the use of VMAT-DIBH resulted in a benefit in reducing the MHD.