Single fraction radiotherapy is efficacious: a further analysis of the Dutch Bone Metastasis Study controlling for the influence of retreatment.

Purpose: The Dutch Bone Metastasis Study on the effect on painful bone metastases of 8 Gy single fraction (SF) vs. 24 Gy in multiple fractions (MF) showed 24% retreatment after SF vs. 6% after MF (p < 0.001). The purpose of the present study was to evaluate factors influencing retreatment and its effect on response.
Methods and Materials: The database on all randomized patients was reanalyzed with separately calculated responses to initial treatment and retreatment.
Results: Response to initial treatment was 71% after SF vs. 73% after MF (p = 0.84). Retreatment raised response to 75% for SF; MF remained unaltered (p = 0.54). The response status after initial treatment did not predict occurrence of retreatment: 35% SF vs. 8% MF nonresponders and 22% SF vs. 10% MF patients with progressive pain were retreated. Logistic regression analyses showed the randomization arm and the pain score before retreatment to significantly predict retreatment (p < 0.001). Retreatment for nonresponders was successful in 66% SF vs. 33% MF patients (p = 0.13). Retreatment for progression was successful in 70% SF vs. 57% MF patients (p = 0.24).
Conclusions: With or without the effect of retreatment, SF and MF radiotherapy provided equal palliation for painful bone metastases. Irrespective of response to initial treatment, physicians were more willing to retreat after a single fraction. Overall, retreatment was effective in 63% of retreated patients.