Comparison of prone versus supine position for whole breast radiotherapy following breast conservation: A dosimetric study

ABSTRACT Background: Long-term morbidity of breast radiotherapy, particularly due to the dose received by the heart and lungs is a cause for concern. Prone positioning for treatment has reported benefits with regard to acute and late toxicities with no detrimental effect on efficacy, especially for patients with large and pendulous breasts. This dosimetric study was aimed at assessing the dose conformity and homogeneity to a defined breast PTV and doses received by structures such as the heart, lungs, and contralateral breast using 3DCRT plans generated in supine and prone positions. The study was approved by the Institutional Review Board. Methods: The computed tomography (CT) image data sets of 41 consecutive women with large breasts who had undergone breast conservation surgery for pT1/T2, N0 cancer, and underwent dual CT imaging (in supine and prone positions) for planning whole breast radiotherapy were used for this comparative analysis. The various dosimetric parameters were calculated for the target volumes and organs-at-risk (OARs) and compared for both positions. Results: Among the 41 patients, 32 had left-sided cancer. The mean of breast PTV dose and homogeneity index were better for the prone position. The mean conformity index was comparable for both positions. The PTV V95%, V98%, and V100% of the prescribed dose were significantly better in the supine position; however, the V107% was comparable for both positions. The mean dose, V20, V12, and V5 of the ipsilateral lung were better in the prone position. The mean heart dose was comparable for both supine and prone positions. The V5 (%) of the heart was significantly lower for the prone position. The mean contralateral breast dose and low-dose radiation to normal tissue were significantly worse for the prone position. Based on individual dosimetric parameters, 26 patients had superior plans in the prone position. Conclusion: Prone breast radiotherapy is capable of producing improved normal tissue sparing with no detriment to target volume coverage in appropriately selected patients with large/pendulous breasts. Strict standard operating procedures with regard to simulation, planning, and treatment execution should be in place to ensure accuracy and daily reproducibility to achieve maximum benefit from this labor-intensive process.