The Gamma Knife

To the Editor. —  The November 4 letter by Dr Kjellberg¹ criticizing a previous letter comparing radiosurgery using the gamma knife with proton beam therapy was itself misleading. For instance, Dr Kjellberg belittled gamma knife therapy for arteriovenous malformations by equating it to previously unsuccessful treatment by conventional cobalt teletherapy. The gamma knife is an entirely new device, using 201 separately collimated cobalt sources for a single "surgical" treatment, and its well-documented results speak for themselves.Two years after gamma knife radio-surgery, 80% of arteriovenous malformations disappeared, as judged by strict angiographic criteria that included that there not even be an early filling vein, in a 97% follow-up of 159 patients.² However, 2 years after proton beam therapy, only 22% of arteriovenous malformations disappeared angiographically in the follow-up by Kjellberg et al³ of "about" 57% of 260 patients.To justify these poorer results, Dr Kjellberg dismisses angiographic