CT planning of boost irradiation in radiotherapy of breast cancer after conservative surgery.

Abstract

A study was performed to compare the accuracy of clinical treatment set-up and CT planning of boost irradiation in radiotherapy of breast cancer. Between September 1993 and October 1994, 45 women who underwent breast conserving surgery and irradiation containing a boost to the tumour bed were investigated. Prospective evaluation of CT planning of the boost was carried out. The target volume/boost field, electron energy and treatment set-up had been defined on the basis of clinical examination, initial and postsurgical mammograms by one radiotherapist. Next, a planning CT was performed in treatment position and a CT-based treatment plan was calculated according to a target volume defined by another radiotherapist. The clinical treatment set-up was imported into our computer planning system and the resulting isodose plots were compared with those from CT planning and reviewed critically. The clinically defined treatment set-up had to be modified in 80% of the patients. Most discrepancies observed were related to the size of the boost field itself and the chosen electron energy. Minor changes had to be made with respect to angle of table and gantry. Critical review of the isodose plots from both methods showed clear advantages for CT planning. Guidelines for target definition in CT planning of boost irradiation and subgroups of patients benefiting from this technique are described.