Purpose: To study CT determined response to external beam radiotherapy as well as influence of tumor-related factors, especially of tumor volume, on remission and to evaluate whether particular subgroups of metastases are controlled by low-dose radiotherapy.
Methods and materials: Contrast-enhanced CT scans before and after radiotherapy were analyzed.
Inclusion criteria: brain metastases treated with whole-brain radiotherapy (10 fractions of 3 Gy over 2 weeks) since 1983; no additional treatment, for example, surgery or chemotherapy; at least one follow-up CT. Three hundred thirty-six metastases from 108 patients were evaluated with regard to their volume, extent of necrosis, histology of primary tumor, and interval between radiotherapy and follow-up CT. All parameters were correlated with best local result and progression-free survival by uni- and multivariate tests. Volume-response curves were calculated.
Results: In univariate analysis local result was significantly influenced by each of the four parameters mentioned above. Complete remission was observed in 37% of metastases from small-cell carcinoma, 35% of those from breast cancer, 25% of those from squamous-cell carcinoma, and 14% of those from nonbreast adenocarcinoma. The rate was 52% for metastases <0.5 cm3 and 0% for those >10 cm3. In multivariate analysis, small volume and no necrosis were the most important prognostic factors for complete remission. Progression-free survival was influenced by best local result.
Conclusion: With radiotherapy to a total dose of 30 Gy even small metastases had a complete remission rate of 52% only. Therefore, patients should be treated with locally more effective dose and fractionation schedules when local control is the aim. However, partial remission rate was remarkable even for large and necrotic metastases. This should be considered when palliation is the aim of treatment.