ESTRO 2024 - Abstract Book

S506

Clinical - Breast

ESTRO 2024

correlated to MHD and mLAD, heart volume and lung volume were correlated (lung inversely) with MHD, mLAD and MLAD dose.

Right sided patients

Larger breast volumes were associated with increased MHD, mLAD and MLAD. Lung volume did not show a strong relationship with heart dose variable (p=0.024) and therefore a multivariate analysis was not performed. The following formulas specifies the univariate linear regression-fitting model for MHD (a), mLAD (b) and MLAD (c):

a) MHD (Gy) =0.881 + (0.531 x breast volume)

b) mLAD (Gy) = 0.860 + (0.443 x breast volume)

c) MLAD (Gy) =1.100 + (0.323 x breast volume)

Left sided patients

Breast volume resulted highly related only to MHD in univariate analysis, not in multivariate analysis. Heart volume and lung volume resulted significantly related to MHD and mLAD dose in both univariate and multivariate analysis. Lung volume only was the best predictor of increased MLADdose. The following specifies the multiple linear regression fitting model of MHD (a) and mLAD dose (b)

1. MHD (Gy) = 1.705 + (0.208 x breast volume) + (0.312 x heart volume) - (0.411 x lung volume) 2. mLAD dose (Gy) = 6.528 + (0.281 x heart volume) - (0.565 x lung volume)

The following equation specifies the linear regression fitting model of MLADdose

1. MLAD dose (Gy) = 22.812 - (0.639 x lung volume)

Conclusion:

In this study we observed an increase of heart and LAD doses in larger breasted patients undergoing breast only radiotherapy. In right sided patients breast volume resulted the only predictor of increased heart dose and LAD dose. Even if the absolute increase of doses was limited, given the low doses of heart dosimetry in these patients, the role of breast volume is certain and should be further evaluated also in patients undergoing regional nodal irradiation when VMAT planning is used. This can be of particular relevance since in right sided patients deep inspiration breath hold (DIBH) is not routinely used.

Keywords: Breast cancer, VMAT, heart dose

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Proffered Paper

Cardiac safety of ultra-Hypofractionated RT in the HYPORT Adjuvant randomized trial (NCT03788213)