Three-dimensional photon dosimetry: a comparison of treatment of the intact breast in the supine and prone position.

PURPOSE

To compare the adequacy of target coverage, dose homogeneity, and volume of normal tissue irradiated in treatment of the intact breast in the supine and prone position.

METHODS AND MATERIALS

Fifteen patients with early breast cancer who presented for treatment to the intact breast after excisional biopsy were studied. A specially designed device was used for the prone setup to displace the contralateral breast away from the tangential field borders. Treatment planning computed tomography was performed for each patient in both the supine and prone positions. Dosimetric data were obtained in both positions and isodose distributions were calculated for each patient in both positions.

RESULTS

The volume of breast receiving greater than 5% of the prescribed dose was significantly less in the prone position. Medial wedges were either not used or their angles were reduced for all patients in the prone position compared with the supine position. The average volume of lung receiving >10 Gy and >20 Gy was significantly less in the prone positions. The volume of heart irradiated at critical dose levels did not vary consistently in the prone and supine positions. The integral dose delivered to the contralateral breast was not significantly different.

CONCLUSION

Treatment of the intact breast in the prone position may result in improved dose homogeneity within the target volume as well as sparing of normal lung compared with treatment in the conventional supine position.