Similar Relief From Cancer-Related Pain With Two Radiotherapy Techniques

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No difference in complete response at 1 or 3 months with 3D conformal, stereotactic body RT

by
Charles Bankhead, Senior Editor, MedPage Today
May 14, 2025 • 4 min read

Single-fraction stereotactic body radiotherapy (SBRT) failed to improve cancer-related bone pain in a randomized comparison with conventional radiation therapy (RT).

The complete response (CR) rate at 1 month improved from 25% with single-fraction conformal 3D RT (3D-CRT) to 37% with SBRT, a difference that did not achieve statistical significance. The difference between the two arms remained non-significant after 3 months of follow-up.

A per-protocol analysis showed a marginally higher CR rate at 3 months with SBRT, reported Carole Mercier, MD, of the Iridium Network in Antwerp, Belgium, and co-authors in the Journal of Clinical Oncology (JCO).

“[The study] is consistent with the literature: Conventional palliative RT works well in the short term,” the authors stated. “The initial idea that dose-escalated SBRT induces faster and earlier pain relief, as was commonly assumed when this trial was designed, is currently no longer considered valid.”

“However, the durability of the response is more of an issue now, particularly as patients with metastatic cancer have continuously improving survival rates. After 3 months, patients still alive and evaluable did have a higher complete pain response rate after SBRT than the 3D-CRT group, apparently independent of primary tumor or baseline pain score. Although not specifically powered for an analysis after 3 months, this difference seems clinically relevant and seems mainly drive by radiotherapy, although selection bias cannot be formally excluded.”

Though technically a negative study, the ROBOMET trial provided new information that supporters of both RT techniques can point to, according to the authors of an accompanying editorial.

“For patients with painful bone metastases, ROBOMET provides additional evidence that SBRT should be considered in patients with favorable prognosis, keeping in mind the limitations of physician-assessed life expectancy,” concluded Shankar Siva, PhD, MBBS, of Peter MacCallum Cancer Center in Melbourne, Australia, and colleagues. “In addition, it lends evidence to feasibility and acceptability of SBRT in a setting that can provide treatment in a timely manner.”

“On the other hand, these data are reassuring that conventional radiotherapy appears to have similar short-term palliative effects to SBRT and remains a very acceptable treatment option.”

JCO associate editor Jonathan P.S. Knisely, MD, of Weill Cornell Medicine in New York City, essentially seconded the views expressed in the editorial but from the opposite perspective of life expectancy.

“Single-fraction 8-Gy three-dimensional conformal palliative irradiation for painful bony metastases alleviates pain as rapidly as single-fraction 20-Gy SBRT and should be preferentially employed for patients with limited survival prospects,” he wrote.

Palliative RT offers effective relief from cancer-related bone pain, including pathologic fractures and spinal cord compression. Studies comparing single- and multifraction regimens have shown comparable efficacy, including a median response duration of 5 months, the authors noted in their introduction. Nonetheless, improved palliation is needed, particularly for the increasing number of long-term survivors.

3D-CRT has been standard for palliative RT but is limited in the total dose that can be delivered, the authors continued. More recently, SBRT demonstrated ability to treat bone metastases and delay or prevent systemic treatment. However, SBRT’s usefulness in patients with more widespread disease remained unclear.

Investigators in the multicenter ROBOMET trial compared dose-escalated 20-Gy single-fraction SBRT and single-fraction 8 Gy with 3D-CRT. Eligible patients were adults with painful bone metastases and an expected survival of more than 3 months. They were randomly assigned to palliative RT with the two techniques and were blinded to the assigned treatment.

The primary endpoint was CR at 1 month, defined as a score of 0 on a pain scale ranging from 0-10. The trial was statistically powered to demonstrate the superiority of SBRT versus 3D-CRT.

There were 126 patients included who were evaluable for the primary endpoint. The most common primary cancers were lung (n=40), prostate (n=30), and breast (n=26). The data showed a 12% absolute advantage favoring SBRT, but the difference failed to achieve statistical significance (P=0.25). At 3 months the CR rates were 24% with 3D-CRT and 33% with SBRT, also non-significant (P=0.32).

Investigators performed per-protocol analysis limited to 87 patients evaluable at 3 months (48 assigned to 3D-CRT, 39 to SBRT). The results showed a CR rate of 54% with SBRT versus 31% with 3D-CRT, a difference that translated into a relative risk of 1.72 in favor of SBRT, a difference that did reach statistical significance (P=0.048).

Symptomatic pain flares occurred in 27% of patients in the control arm and 18% in the experimental arm. Two patients in each group required corticosteroids for pain relief. Re-irradiation rates were 11% in the 3D-CRT arm and 2% in the SBRT group (P=0.06). Additionally, 11% of patients in the 3D-CRT arm had symptomatic skeletal events versus 3% in the SBRT group (P=0.16).

Grade 2/3 toxicity (no grade 4) occurred in 14% and 15% of the 3D-CRT and SBRT arms, respectively. One grade ≥3 fracture occurred in each group.