SBRT Doubles Pain Response Over Usual RT in Spinal Metastases

Pam Harrison

October 29, 2020

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 compared with conventional radiotherapy ― "which was highly significant at both endpoints," Sahgal noted.

However, there was no difference between treatment groups in either radiation site–specific progression free survival or overall survival. After 3 months, 92% of patients in the SBRT arm and 86% of patients in the conventional radiotherapy arm were cancer free at the treated site, whereas at 6 months, 75% and 69%, respecrtively, were cancer free at the treatment site.

As for adverse events, 17% of patients who received conventional palliative radiotherapy developed a vertebral compression fracture following treatment, compared with 11% of SBRT-treated patients, but the risk for adverse events of grade 2 or higher was essentially the same in both treatment arms.

Importantly, those treated with the SBRT protocol reported a better quality of life than those treated with five fractions of conventional radiotherapy. "Patients are dealing with metastatic disease. Now they have to come to the hospital for another treatment, and the financial burden of coming to the hospital is not inconsiderable," Sahgal said.

"So patients appreciate fewer treatment sessions, and even if it costs our department more, because treatment with SBRT needs so much more planning and resources, we are helping our patients financially, and this is going to push our departments to say, even if it costs more for us to do, SBRT is better for our patients," he said.

Special Advantage

Commenting on the study, session moderator Sue Yom, MD, PhD, professor of radiation oncology, otolaryngology–head and neck surgery, University of California, San Francisco, reminded the press that with SBRT, very high doses can be delivered very safely to precise areas of the body with a small number of treatments. "This has obvious advantages over conventional radiation therapy," she noted, "and may be especially an advantage now in the midst of the COVID pandemic, as it reduces the risk [for viral exposure] to patients and hospital personnel," she said.

With this study, the additional resources and expense involved in offering SBRT in comparison with conventional radiotherapy appear to be justified, Yom said. "The increased dose that was given in only two fractions of SBRT produced results that allowed significantly more patients to achieve complete pain relief than patients who got conventional treatment with five fractions to the same site," Yom reaffirmed.

"And the rate of complete resolution of the spinal tumors at 6 months was also superior with SBRT, so the oncologic benefits with SBRT vs conventional radiation are also better," she said. Yom also felt that the quality-of-life surveys that were filled out by patients during the study — not reported during the press briefing but alluded to by Sahgal during his interview with Medscape Medical News — were also quite revealing.

"It's easy to dismiss any difference between two and five treatments as not being significant, but there was a real quantifiable difference between two and five treatments in terms of patients' quality of life," she noted.

"So being able to have fewer treatments is significant to patients, and that significance buttresses this study's importance," she said.

The study was supported by the Canadian Clinical Trials Group. Sahgal reports receiving research grants from Elekta AB, Varian, and BrainLAB as well as honoraria from Elekta AB, Varian, BrainLAB, and Accuray. He has also served as a consultant for Varian, AbbVie, and Roche and on the advisory board for Viecure.

American Society for Radiation Oncology (ASTRO) 2020 Annual Meeting: Abstract LBA-2, presented October 26, 2020.

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