Outcome evaluation of the Response to SBRT

Local control was defined as the absence of tumor growth in the treated adrenal gland. Response evaluation was most often planned three months after the end of SBRT and repeated every three or four months, usually for the two first years, and consisted of a clinical evaluation and imaging (CT, MRI or PET scan), at the physician’s discretion. Local relapse assessments were conducted centrally by the coordinating center overseeing the study. If imaging reports did not indicate adrenal progression, they were reviewed by an experienced radiation oncologist. In cases of uncertainty, a radiologist reviewed the images. This process was carried out for each surveillance imaging until an adrenal relapse was documented. The assessments for relapse were based on established criteria, namely Response Evaluation Criteria In Solid Tumors (RECIST) [8], the immune RESIST [9], and the PET Response Criteria in Solid Tumors PERCIST [10].

PFS was defined as the time from the first day of the radiotherapy to any in- or out-of-field disease progression or mortality. If the patient was treated for bilateral metastases at separate times, the date of the first day of the first SBRT was considered.

OS was calculated from the end of radiotherapy to either the date of death from any cause or the date of the last follow-up examination. To evaluate the effects of different treatment protocols with various fraction sizes and total doses for the PTV, a BED was used in a linear-quadratic model using an α/β ratio of 10 for the tumor, in accordance with standard practice.