Is there a preferred IMRT technique for left-breast irradiation?

Abstract

Not all clinics have breath-hold radiotherapy available for left-breast irradiation. However intensity-modulated radiotherapy (IMRT) has also been advocated as a means of lowering heart doses. There is currently no large-scale, long-term follow-up data after breast IMRT and, since dose distributions may differ from classic tangent-based radiotherapy, caution is needed to avoid unexpected worsening of the late toxicity profile. We compared four IMRT techniques for free-breathing left-breast irradiation. Consistent with the aforementioned concerns, our goal in planning was to prioritize organ at risk (OAR) sparing in a way that mimicked tangent-based radiotherapy. Ten simultaneous integrated boost treatment plans (PTVelective = 15 × 2.67 Gy; PTVboost = 15 × 3.35 Gy) were created using 1) hybrid-IMRT (H-IMRT), 2) full IMRT (F-IMRT), and 3) volumetric-modulated arc therapy with two partial arcs (2ARC) and 4) six partial arcs (6ARC). Reduction in OAR mean and low dose was prioritized. End-points included OAR sparing (e.g., heart, left anterior descending artery [LAD+3 mm], lungs, and contralateral breast) and PTV coverage/dose homogeneity. Under these conditions we found the following: 1) H-IMRT provided the best mean and low dose OAR sparing, PTVelective coverage (mean V95% = 98%), PTVboost coverage (V95% = 98%), and PTV homogeneity. However, it delivered most intermediate-high dose to the heart, LAD+3 mm and ipsilateral lung; 2) 6ARC had the best intermediate-high dose sparing, followed by F-IMRT, but this was at the expense of more dose in the contralateral lung and breast and worse PTV coverage (PTVelective mean V95% = 96%/97% and PTVboost mean V95% = 91%/96% for 6ARC/F-IMRT). When trying to spare mean and low dose to OARs, the preferred IMRT technique for left-breast irradiation without breath-hold was H-IMRT. This is currently the standard solution in our institution for left-breast radiotherapy under free-breathing and breath-hold conditions.

Figure 1

Planning target volume (PTV) and organ‐at‐risk structures $(\text{LAD}=\text{left anterior descending coronary artery})$.

Figure 2

Typical beam/arc arrangements for the various techniques used in this study. The planning target volume (PTV) of the breast is outlined with a medial boost (shaded): (a) Hybrid IMRT (H‐IMRT); (b) Full IMRT (F‐IMRT); (c) 2 Arc RapidArc (2ARC); (d) 6 Arc RapidArc (6ARC).

Figure 3

Mean dose‐volume histograms for planning target volume (PTV) and organs at risk averaged over all patients: (a) ${\text{PTV}}_{\text{boost}}$; (b) ${\text{PTV}}_{\text{elective}}$; (c) heart; (d) $\text{LAD}+3\hspace{0.17em}\text{mm}$; (e) ipsilateral lung; (f) contralateral lung; (g) contralateral breast.