AAPM MEDICAL PHYSICS PRACTICE GUIDELINE 2.b.: Commissioning and quality assurance of X-ray-based image-guided radiotherapy systems.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.

Control of growth of vestibular schwannomas with low-dose Gamma Knife surgery.

OBJECT: The treatment of solitary vestibular schwannomas by performing Gamma Knife surgery is well established. It has been reported that decreasing the surface dose reduces patient morbidity, especially facial weakness and numbness. The authors of this retrospective study examine patient data from a single center to determine if low-dose (< or = 14 Gy) GKS controls tumor growth as effectively as higher doses (> 14 Gy). METHODS: Based on the formula for ellipsoid volumes, the tumor volumes were calculated using measurements from MR images obtained at follow up in patients treated at the authors' center. Follow-up data were available in 159 patients with a mean age of 59.5 +/- 14.2 years at treatment. Fifty-six percent of the patients were women and 53.5% of the tumors were located on the right side of the brain. The mean tumor volume was 3.3 +/- 4.3 cm3 with 10% of the tumors having volumes larger than 8 cm3. After GKS, smaller tumors (> or = 40% decrease in volume) were observed in 44.8% of patients treated with a low dose and in 48.8% treated with a high dose. Enlarged tumors (> or = 40% increase in volume) were seen in 5.2% of the patients receiving a low dose and 2.3% of those receiving a high dose. These differences were not statistically significant. Patients who had been followed up for longer than 5 years after treatment had median residual volumes of only 28.2% of the starting volume in the low-dose group and 26% in the high-dose group. This difference was statistically not significant. CONCLUSIONS: No statistically significant differences were observed between tumors given low-dose radiation treatment and those given high-dose radiation treatment.