ESTRO 2024 - Abstract Book

S5977

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

The aim of this study was to analyse cardiac substructures’ radiation exposure in left-sided breast cancer radiotherapy with regards to specific patient’s anatomic features.

Material/Methods:

Data of patients planned for adjuvant left-sided breast cancer radiotherapy (RT) were analysed. All patients were treated with 3D conformal hypofractionated RT, with a prescription dose of 40 Gy delivered in 15 fractions +/- an additional boost to the tumor bed. Cardiac subvolumes were delineated according to the Duane’s cardiac atlas. For each patient, the following anatomic features were assessed: contact heart (sagittal heart’s contact with the anterior chest wall), Haller index, breast size and breast index (largest distance between the medial and lateral borders of CTV breast). Dose-volume histograms were generated for the whole heart and its substructures, and statistically analysed with regards to patient’s specific anatomic features, using Pearson correlation coefficient and the linear regression analysis.

Results:

A total of 87 patients with left-sided breast cancer were included in this study. The mean heart dose (MHD) was 3.09 ranging between 1.2 and 4.92 Gy. The mean Dmax/Dmean to left anterior descending artery (LAD) and left ventricle (LV) were 30.6 Gy/11.42 Gy and 38 Gy/4.87 Gy, respectively. The V5 Gy to LV ranged between 9.1% and 78.6%, with a mean value of 27.59%. Neither the contact heart nor the Haller index were statistically correlated to heart subvolumes doses (p= 0.6; p= 0,32). The mean breast size was 478.21 (111.6-1003.3) cm3. The breast index ranged between 11.21 and 20.91 cm with a mean value of 15.9 cm. A statistically significant positive correlation was found between Dmax and Dmean to the LAD and breast size, with Pearson coefficients of 0.3 and 0.4 respectively. Dmean/Dmax to the LAD increased with increasing breast size. Nonetheless, the linear regression analysis showed a poor predictive value of the breast size with r² coefficient ≤ 0.16. The breast index was statistically correlated with doses to both LAD and LV with Pearson coefficients ≥ 0.4 (p<0.01) and r² coefficient <0.5.

Conclusion:

Our study showed a wide range of cardiac dosimetry metrics along with patients’ anatomy variability. Breast size and breast index did correlate with doses to cardiac subvolumes. Although the statistical predictive value was poor, breast volume and shape may predict heart exposure and help select patients who would benefit the most from heart sparing RT techniques. Further analysis in larger cohorts are still needed to confirm these results.

Keywords: Bilateral breast cancer;VMAT;heart sparing

1741

Proffered Paper

Simultaneous integrated boost and organ at risk constraints in the APHRODITE trial [ISRCTN16158514]