ESTRO 2024 Congress Report

An interesting presentation from Emma Dunne debated the role of stereotactic body radiotherapy (SBRT) as a standard-of-care (SOC) for spine bone metastases (BM). The speaker emphasised that SBRT could already be considered the SOC in several oligometastatic diseases as she reported the recommendations contained in several international guidelines. However, the big open debate regards painful BM. On one hand, the guidelines of 2022 from the ESTRO guidelines committee do not support the routine use of SBRT in patients with BM because of pain response; while on the other hand, the ESTRO practical guidelines of 2024 seem to support its use in appropriately selected cases.

Analysis of the different trials shows that there have been several overlapping studies, the majority of which were of small, non-randomised, mixed populations of spinal and non-spinal BM, not powered for superiority. The higher evidence level in this regard has been provided by the SC.24 and Radiation Therapy Oncology Group (RTOG) 0631 trials.

The phase II/III SC.24 trial involved randomisation of 229 patients 1:1 to 24Gy/two fractions versus 20Gy/five fractions. Up to three spinal BMs with spinal instability neoplastic score (SINS) of ≤12 could have been treated. The primary end-point was three months of pain complete response (CR). After SBRT, a 21% absolute CR increase was reported, which persisted at six months and with no spine destabilising effect. The RTOG 0631 trial was a superiority trial that involved randomisation of 339 patients 2:1 to 16-18Gy/one fraction or 8Gy/one fraction, and the primary end-point was three months of pain response. The study was negative; it showed a higher pain response in the standard arm (41% versus 60%; p=0.01) with no quality of life or vertebral fracture differences between the two arms. The only factor that influenced pain response was performance status (PS).

Regarding the details of the trials, the RTOG 0631 included significantly more patients with PS2 in the stereotactic radiosurgery arm (22% versus 10%), while the PS was balanced in the SC.24 trial. In fact, patients with higher PSs showed less compliance across time versus PS 0/1 patients. A second factor was stability evaluation. While during the SC.24, vertebral instability was systematically evaluated, RTOG 0631 was developed before the use of SINS. Therefore, the initial high pain score may have had a mechanical pain component, which ultimately did not respond to radiation. Lastly, 55% of patients in the RTOG 0631 trial received 16Gy, which has a lower BED10 (41.6Gy) compared with the 18Gy (50.4Gy) and 24Gy/two fractions (BED 52.8Gy) of the SC.24 trial. Higher radiotherapy dose improves not only local control but also durable pain response, as shown in the randomised phase II trial of Guckenberber et al. (48.5Gy/10 fractions or 40Gy/five fractions versus conventional external beam radiation therapy of 30Gy/10 fractions or 20Gy/five fractions).

Ultimately, the use of SBRT might provide an indirect cost saving as the number of retreatments and interventions are reduced due to the higher response rate and durable pain control, especially in patients with long life expectancies. In conclusion, SBRT might be considered for use in selected patients with mechanically stable but painful metastases.

Luca Nicosia

IRCCS Sacro Cuore Don Calabria Cancer Care Center

Negrar, Verona, Italy

Member of the ESTRO SBRT Focus Group