Fractionation of palliative radiotherapy in metastatic breast cancer: Selection and survival.

Abstract

201 Background: Various schedules of palliative radiotherapy (pRT) are prescribed for metastatic breast cancer (MBC) patients. Length of treatment can vary from a single day to three weeks. Single fraction pRT provides similar pain relief vs. multi-fraction pRT for bone metastases, but retreatment rates are higher. In the era of targeted and hormonal therapy, patients with MBC can survive many years after their initial diagnosis. We investigated whether patients with MBC who were prescribed single fraction pRT had poorer prognoses and experienced shorter survival than patients who were prescribed multi-fraction pRT. Methods: Patients at a single institution with MBC underwent pRT, with fractionation schedules including 8 Gy in 1 fraction (fx), 20 Gy in 5 fx, 30 Gy in 10 fx, 37.5 Gy in 15 fx between 2001-2015. 392 treatments were prescribed (109/241/29/13 in each regimen as above). Date of death was obtained from medical records, Social Security Death Index, or published obituaries. Patients who were alive or whose date of death could not be determined were censored at the date of their last encounter. Survival was calculated from the start of treatment to the date of death or censorship. Results: Patients treated with 37.5 Gy in 15 fx (MS 20 months, p = 0.002) or 30 Gy in 10 fx (MS 22 months, p = 0.03) experienced longer survival than patients treated with 8 Gy in 1 fx (MS 8 months). There was no significant survival difference between patients treated with 20 Gy in 5 fx (MS 18 months, p = 0.49) and patients treated with 8 Gy in 1 fx. There was no significant survival difference between patients treated by the three multi-fractionation schedules. Conclusions: MBC patients who were prescribed 37.5 Gy and 30 Gy lived longer than patients who were prescribed 8 Gy of pRT. No statistically significant difference was found between patients who were prescribed 20 Gy compared to 8 Gy, possibly due to the lower number of patients who received these regimens. Single fraction pRT was more likely to be prescribed to patients who would ultimately have shorter survival. More research is needed, ideally across multiple institutions, to explore the correlation between physician estimation of patient survival and selection of pRT regimen for patients with MBC.