OBJECTIVE Stereotactic radiosurgery (SRS) is a well-established treatment for brain arteriovenous malformations (bAVMs). However, data on radiation-induced neoplasms (RINs) following SRS in patients with bAVMs remain limited. In this study, authors aimed to evaluate the incidence of newly developed intracranial RINs following SRS for bAVMs. METHODS The authors retrospectively analyzed anonymized data for patients who underwent SRS for bAVMs between 1990 and 2019 at 18 Gamma Knife centers in Japan. Patients with fewer than 3 years of radiological follow-up, prior radiotherapy, or genetic tumor predisposition were excluded. Newly developed tumors were classified as in field (within the 2-Gy isodose line) or out of field. Annual incidence rates were calculated based on total patient-years of follow-up. RESULTS During a median radiological follow-up of 100 months, new intracranial tumors developed in 12 (0.27%) of the 4376 patients included in the study. In-field malignant tumors occurred in 5 patients (0.11%), with a median latency of 13.3 years. Out-of-field tumors were observed in 7 patients (0.16%), including malignant (n = 3) and benign (n = 4) neoplasms, with a median latency of 17.4 years. The cumulative incidence of in-field tumors at 10, 15, and 20 years was 0.08%, 0.16%, and 0.16%, respectively. The corresponding incidence of out-of-field tumors was 0.11%, 0.11%, and 0.58%, respectively. In terms of tumor histology, the cumulative incidence of new intracranial brain tumors at 10, 15, and 20 years was 0.15%, 0.24%, and 0.40% for malignant tumors and 0.03%, 0.03%, and 0.34% for nonmalignant tumors, respectively. Across 43,950.3 patient-years of radiological follow-up, the overall annual incidence was 0.027%, increasing from 0.005% within 5 years to 0.046% after 5 years. The annual incidence of in-field tumors was 0.011% (0% within and 0.021% after 5 years) and 0.016% for out-of-field tumors (0.005% within and 0.025% after 5 years). Malignant tumors had an annual incidence of 0.018% (0.005% within and 0.030% after 5 years), whereas benign tumors occurred only out of field with an annual incidence of 0.009% (0% within and 0.017% after 5 years). CONCLUSIONS The incidence of radiation-induced malignancies after SRS for bAVMs is extremely low but potentially fatal. Although the current risk is acceptable compared to the mortality associated with microsurgical resection, the possibility of late-onset malignancies, especially in younger patients, warrants caution. As more patients are treated and follow-up periods become extended, this risk may increase. Therefore, long-term surveillance is essential for accurately assessing and managing the potential for RINs over time.
Hasegawa et al. (Thu,) studied this question.