Modified simultaneous integrated boost radiotherapy for unresectable locally advanced breast cancer: preliminary results of a prospective clinical trial.

Background: The purpose of this study was to evaluate the effect of modified simultaneous integrated boost (SIB) radiotherapy for patients with extensive breast cancer.

Patients And Methods: Patients with macroscopic tumor and histologically proven adenocarcinoma of the breast were enrolled in the study. Patients were included whether they had or did not have previous surgery, chemotherapy, hormone therapy, or molecular targeted therapy; patients with past history of thoracic radiotherapy were excluded. Under conditions of not exceeding the tolerance dose for normal tissue, irradiation to the tumor was increased to the maximum possible extent using the modified SIB technique.

Results: Three breast cancer patients were treated with the modified SIB technique. All patients were diagnosed as T4b (median maximum diameter of the tumor: 16 cm; range, 15.5-22 cm), and all patients exhibited symptoms because of the extremely large tumor. The median total dose to the part of tumor tissue was 128.8 Gy (range, 110-140 Gy). Total dose to normal tissue was < 72 Gy in all patients. Although large tumors were radio-resistant, it was macroscopically confirmed that all tumors eventually disappeared. Although skin defects persisted because of tumor disappearance, there were no Grade ≥ 3 toxicities due to radiotherapy.

Conclusion: Although much care is required in delivering extremely high doses of radiotherapy to the tumor, modified SIB radiotherapy was shown to be effective against extremely large tumors that could not be controlled using conventional radiotherapy. In future, an increase in the number of study patients and establishment of the technique will be required.