USE OF THE PRONE POSITION IN RADIATION TREATMENT FOR WOMEN WITH EARLY STAGE BREAST CANCER

Abstract Purpose: The prone position has been advocated for women with large pendulous breasts undergoing breast-conserving treatment with radiation therapy. However, there is no information in the literature regarding the coverage of the target volume with this technique. The purpose of this study was to evaluate the effectiveness of the prone treatment position in including at least the biopsy cavity with a 2-cm margin. Methods and Materials: Eleven consecutive patients who underwent CT simulation in the prone position were included in this study. Patients underwent CT simulation in the prone position using a flat platform containing an aperture for the breast to hang through in a dependent fashion. CT slices were 5-mm thick taken at 3-mm intervals. The biopsy cavity was localized and outlined on sequential CT images using the surgical clips (when present) as well as the residual seroma. A 2-cm margin was included around the biopsy cavity to define the minimal target volume (mTV). Lateral fields were used for treatment planning. The beam arrangements were considered adequate if the mTV was totally included in the lateral fields. Results: Median age of the patient population was 55 years. Bra sizes ranged from 36A–44DD. The majority of patients had mammographically detected T1 lesions. Median volume of the biopsy cavity was 48 cm 3 . Five of 11 (45%) patients underwent reexcision of the biopsy cavity, and 6 of 11 (55%) had surgical clips placed in the biopsy cavity. Overall, 8 of 11 (73%) patients did not have the entire mTV included in the lateral opposed tangential fields in the prone position. This was especially true in patients whose biopsy cavity extended down to the chest wall. There were no other clinical factors that could predict for the adequacy of coverage in the prone position. Conclusion: Special attention must be paid to the location of the surgical clips to determine the proximity of the biopsy cavity to the chest wall, or CT simulation should be performed to determine the exact location of the biopsy cavity prior to selecting patients with large pendulous breasts for treatment in the prone position.