Accelerated partial breast irradiation (APBI): are breath-hold and volumetric radiation therapy techniques useful?

In a selective group of patients accelerated partial breast irradiation (APBI) might be applied after conservative breast surgery to reduce the amount of irradiated healthy tissue. The role of volumetric modulated arc therapy (VMAT) and voluntary moderately deep inspiration breath-hold (vmDIBH) techniques in further reducing irradiated healthy--especially heart--tissue is investigated.

For 37 partial breast planning target volumes (PTVs), three-dimensional conformal radiotherapy (3D-CRT) (3-5 coplanar or non-coplanar 6 and/or 10 MV beams) and VMAT (two partial 6 MV arcs) plans were made on CTs acquired in free-breathing (FB) and/or in vmDIBH. Dose-volume parameters for the PTV, heart, lungs, and breasts were compared.

Better dose conformity was achieved with VMAT compared to 3D-CRT (conformity index 1.24±0.09 vs. 1.49±0.20). Non-PTV ipsilateral breast receiving ≥50% of the prescribed dose was on average reduced by 28% in VMAT plans compared to 3D-CRT plans. Mean heart dose (MHD) reduced from 2.0 (0.1-5.1) Gy in 3D-CRT(FB) to 0.6 (0.1-1.6) Gy in VMAT(vmDIBH). VMAT is beneficial for MHD reduction if MHD with 3D-CRT exceeds 0.5Gy. Cardiac dose reduction as a result of VMAT increases with increasing initial MHD, and adding vmDIBH reduces the cardiac dose further. Mean dose to the ipsilateral lung decreased from 3.7 (0.7-8.7) to 1.8 (0.5-4.0) Gy with VMAT(vmDIBH) compared to 3D-CRT(FB). VMAT resulted in a slight increase in the contralateral breast dose (DMean) always remaining <1.9 Gy).

For APBI patients, VMAT improves PTV dose conformity and delivers lower doses to the ipsilateral breast and lung compared to 3D-CRT. This goes at the cost of a slight but acceptable increase of the contralateral breast dose. VMAT reduces cardiac dose if MHD exceeds 0.5 Gy for 3D-CRT. Adding vmDIBH results in a further reduction of heart and ipsilateral lung dose.