Impact on pulmonary function in a randomized trial of single and multi-fraction stereotactic body radiotherapy (SBRT) for pulmonary oligometastatic disease, an analysis of TROG 13.01 (SAFRON II)

Background[Anonymized] was a phase 2 multicentre trial comparing single fraction and multi-fraction SBRT. Patients with 1-3 peripheral pulmonary oligometastases were randomized 1:1 between 28Gy in 1 fraction and 48Gy in 4 fractions. There were no differences between arms in efficacy or toxicity. We performed an analysis to assess changes in pulmonary function tests (PFTs) between arms over time and assessed the impact of the number and total volume of targets on PFT change over time.MethodsA linear mixed model was used to describe the PFTs by treatment arm over time. The effect of number and volume of targets on PFTs at 6 and 12 months was assessed by a simple linear model.ResultsNinety patients were randomised; 87 were treated for 133 pulmonary oligometastases. Forty-four were randomised to the SF arm and 43 to the MF arm. There were no differences in absolute or relative PFT measures of forced expiratory volume in 1 second (FEV1),diffusing capacity of the lungs for carbon monoxide (DLCO) or Forced Vital Capacity (FVC) between the two arms. At 12 months, there was a reduction in absolute DLCO from baseline (−1.7ml/min/mmHg, [95%CI: −2.5; −1.0]), relative DLCO (−5.5% [−8.4;-2.6]),absolute FEV1 (−0.17L [−0.23;-0.11]) and absolute FVC (-0.20L [−0.27;-0.13]). In patients with multiple pulmonary targets, increase in target number (per lesion) was associated with a reduction in the absolute FEV1 at 6 months of −0.10L [−0.18; −0.03] (p = 0.007),FEV1 at 12 months −0.10L [−0.20; −0.01] (p = 0.04), FVC at 6 months of −0.11L [−0.20; −0.03] (p = 0.014), FVC at 24 months −0.13L [−0.25; −0.01] (p = 0.036) Reduction in FEV1 was also seen per 10ml increase in PTV at 12 months −0.03L [−0.06; −0.00] (p = 0.036). Number of targets and PTV were not associated with DLCO.ConclusionTreating multiple targets resulted in increased loss of FEV1 and FVC but not DLCO. There were no significant differences in PFT decline between SF and MF SBRT.