Background: The purpose of this study was to assess the feasibility of deep inspiration breath-hold (DIBH)based volumetric modulated arc therapy (VMAT) for locally advanced left sided breast cancer patients undergoingradical mastectomy. DIBH immobilizes the tumor bed providing dosimetric benefits over free breathing (FB).Materials and
Methods: Ten left sided post mastectomy patients were immobilized in a supine position withboth the arms lifted above the head on a hemi-body vaclock. Two thermoplastic masks were prepared for eachpatient, one for normal free breathing and a second made with breath-hold to maintain reproducibility. DIBH CTscans were performed in the prospective mode of the Varian real time position management (RPM) system. Theplanning target volume (PTV) included the left chest wall and supraclavicular nodes and PTV prescription dosewas 5000cGy in 25 fractions. DIBH-3DCRT planning was performed with the single iso-centre technique usinga 6MV photon beam and the field-in-field technique. VMAT plans for FB and DIBH contained two partial arcs(179o-300oCCW/CW). Dose volume histograms of PTV and OAR’s were analyzed for DIBH-VMAT, FB-VMATand DIBH-3DCRT. In DIBH mode daily orthogonal (0o and 90o) KV images were taken to determine the setupvariability and weekly twice CBCT to verify gating threshold level reproducibility.
Results: DIBH-VMAT reducedthe lung and heart dose compared to FB-VMAT, while maintaining similar PTV coverage. The mean heart V30Gywas 2.3% ±2.7, 5.1% ±3.2 and 3.3% ±7.2 and for left lung V20Gy was 18.57% ±2.9, 21.7% ±3.9 and 23.5% ±5.1 forDIBH-VMAT, FB-VMAT and DIBH-3DCRT respectively.
Conclusions: DIBH-VMAT significantly reduced theheart and lung dose for left side chest wall patients compared to FB-VMAT. PTV conformity index, homogeneityindex, ipsilateral lung dose and heart dose were better for DIBH-VMAT compared to DIBH-3DCRT. However,contralateral lung and breast volumes exposed to low doses were increased with DIBH-VMAT.