Breast Sub-Volumes: Preliminary Results of a New Concept to Gradually decrease the Dose from the Tumor Bed to the Peripheral Breast Using Simplified IMRT

Abstract

Purpose : To gradually decrease the dose from the tumor bed to the peripheral breast volume. Methods and Materials : The whole breasts (small, medium and large) of 31 patients were divided into three sub-volumes: CTV_SIB (CTV of the simultaneous integrated boost); CTV_proximal, 3 cm expansion from the CTV_SIB across the CTV_ breast; and CTV_distal. Simplified intensity-modulated radiation technique (sIMRT) was used. Radiation therapy was delivered in 25 fractions over 5 weeks. The dose prescribed to the PTV_SIB ranged from 62, 5 Gy to 66 Gy, 50 Gy and 46 Gy to the PTV_proximal and PTV_distal respectively. The dose volume histograms (DVHs) and the dose distribution of D95% were analyzed and compared for each sub-volume. The dose-volume constraints used for the lung and the heart were V20 Gy<10%, and V10 Gy<10% respectively. Results :Between May 16 and July 27, 2013, thirty-one consecutive early breast cancer patients referred for radiation therapy were planned in order to decrease the dose delivered to the breast volume. The D95% for PTV_SIB, PTV_proximal and PTV_distal were 62.6 Gy (60.5-65.6 Gy); 49,3 Gy (47.0-51.1 Gy) and 45.5 Gy (43.2-47.3 Gy) respectively (p=0.0000). The 21 left breast plans showed no statistical significant difference in the dose received by the heart and the left lung between the conventional technique and the 3-sub-volume technique. The median dose received by the heart was 1.2 Gy lower with the 3 sub-volume technique compared with the conventional technique. Conclusion : The three breast sub-volumes irradiated with simplified intensity-modulated technique would allow for a slight but significant gradual decrease of the dose from the tumor bed to the distal breast. A long-term follow-up is required to confirm whether this dose decrease may contribute to reduce toxicities.