A 2-day course of high-dose stereotactic body radiotherapy (SBRT) doubles the complete pain response for patients with painful spinal metastases in comparison with conventional palliative radiotherapy. It is also safe and nondestabilizing, conclude researchers reporting a phase 3 Canadian trial.
“Conventional radiation has historically not achieved high rates of complete response to pain or long-term local control,” commented lead author Arjun Sahgal, MD. “So many years ago, we started building on the idea of using high-dose stereotactic body radiation for the spine.”
Sahgal, who is professor and deputy chief of radiation oncology at Sunnybrook Health Sciences Center, the University of Toronto, Ontario, Canada, explained that his team came up with a plan to use SBRT with 24 Gy in two fractions. This involves only two consecutive treatments, which is very convenient for patients. Conventional radiation requires five or more sessions.
“Now we have shown a doubling of the complete response rate to pain at 3 and 6 months compared with conventional palliative radiation, and patients appreciate fewer treatment sessions, too, so we are helping our patients financially,” Shagal told Medscape Medical News.
He presented the new results during the virtual annual meeting of the American Society for Radiation Oncology (ASTRO).
Patients enrolled in this trial had de novo painful spinal metastases with three or fewer consecutive metastatically involved spinal segments arising from a primary tumor causing pain that was scored at least 2 on the Brief Pain Inventory.
The median baseline worst pain score was 5 in a range of 2 to 10. The median total spinal instability and neoplasia score (SINS) was 7 in a range of 3 to 12, Sahgal noted. “The primary endpoint was complete pain response rate at 3 months,” Sahgal told a press briefing held within the context of the virtual meeting.
Patients were randomly assigned to receive either SBRT with 24 Gy delivered in two fractions over 2 consecutive days or conventional palliative radiotherapy with 20 Gy delivered in five fractions.
Initially, the trial was launched as a phase 2 study, but once investigators could demonstrate that accrual was possible, they converted the trial into a phase 3 study, Sahgal noted.
A total of 114 patients were enrolled in the SBRT arm; 115 patients were enrolled in the conventional radiotherapy arm. All were included in the intent-to-treat analysis. “We found that at 3 months, the complete response rate was 35% in the SBRT arm and 14% in the conventional radiation arm, and the difference was statistically significant,” Sahgal reported.
The complete response rate was sustained at 6 months. It remained at 32% in the SBRT arm and 16% in the conventional radiotherapy arm. There was also a reduction in the total SINS score at 6 months that favored the SBRT arm.
Adjusted for age, sex, performance status, primary cancer, and total baseline SINS, SBRT was almost 3.5-fold more likely to result in a complete pain response rate at 3 months and was about 2.5-fold more likely to yield the same response at 6 months