Douglas Kondziolka, MD
In a retrospective cohort study reported in The Lancet Oncology, Douglas Kondziolka, MD, of NYU Langone Health System, and colleagues found that patients undergoing Gamma Knife stereotactic radiosurgery for nonmalignant neurosurgical conditions did not appear to be at long-term increased risk of radiation-associated secondary intracranial malignancy or malignant transformation.
The study involved data from 4,905 eligible patients who had Gamma Knife stereotactic radiosurgery between August 1987 and December 2011 at five radiosurgery centers (one in Czech Republic, one in Spain, three in the United States). Patients had to have received no prior radiotherapy and had to have minimum follow-up time of 5 years. Gamma Knife radiosurgery was performed for arteriovenous malformation; trigeminal neuralgia; or benign intracranial tumors. Stereotactic radiosurgery–associated intracranial malignancy, including malignant transformation of a benign lesion or development of radiation-associated secondary intracranial cancer, was defined as occurring within the 2-Gy isodose line.
Risk of Malignancy
Median follow-up was 8.1 years. A total of 2 (0.0006%) of 3,251 patients with benign tumors were diagnosed with suspected malignant transformation and 1 (0.0002%) of 4,905 patients was considered to have radiosurgery-associated intracranial malignancy; these figures yielded an incidence of 6.87 per 100,000 patient-years for malignant transformation and 2.26 per 100,000 patient-years for radiosurgery-associated intracranial malignancy.
The overall incidence of radiosurgery-associated malignancy of 6.80 per 100,000 patient-years (cumulative incidence of 0.00045% over 10 years) was similar to risk of developing a malignant central nervous system tumor in the general population of the United States and some European countries, according to estimates from the Central Brain Tumor Registry of the United States and the International Agency for Research on Cancer Global Cancer statistics.
The investigators concluded, “These data show that the estimated risk of an intracranial secondary malignancy or malignant transformation of a benign tumour in patients treated with stereotactic radiosurgery remains low at long-term follow-up.…”