The Impact of Contouring the Axillary Lymph Nodal Levels on Achieving Adequate Doses during Tangential Chestwall Irradiation

Background: Breast cancer accounts for 15% of all new cancer cases in the Philippines for both sexes and 8% of all cancer deaths. Adjuvant radiation therapy is an essential part of treatment for breast cancer. A radiation dose of 50.4 Gy is delivered via tangential fields to the chestwall and direct antero-posterior field to the ipsilateral supraclavicular area to ensure adequate radiation treatment particularly to the axillary nodal areas. Contouring and delineating axillary nodal areas after CT simulation and planning ensures that these areas receive the adequate amount of radiation dose. However, this practice is not widely used. This study aims to compare the radiation doses after contouring with the actual doses received by breast cancer patients.

Methods: A review of CT planning scans of post-mastectomy patients was done. Axillary nodal areas were contoured by a single radiation oncologist and confirmed by two consultants following the Radiation Treatment Oncology Group guidelines for breast cancer. The mean doses were compiled and calculated.

Results: A total of 79 patients were included for review. Thirty-three (42%) patients were underdosed at axillary node level 1, 36 (46%) patients at axillary node level II and 10 (13%) at axillary node level III.

Conclusion: Contouring axillary nodal areas I, II and III in all axial CT slices is very much necessary to ensure that these target volumes are given adequate doses of at least 45 Gy for levels I and II and III. This matters as well in the decision to do a posterior axillary boost, which effectively raises the doses of the axillary nodal areas to adequate levels.