Applications of asymmetric collimation on linear accelerators

Frequency of use of asymmetric collimation (AC) at an academic radiation oncology center equipped with AC-capable linear accelerators was determined, and the type of use was cataloged. Records of patients beginning radiation treatment at U.C. Davis Cancer Center within a 3-month period (3/1/92 to 5/31/92) were reviewed. Forty-seven percent of 102 patients and 56% of 123 courses of treatment involved AC. Six common uses of AC were identified: beam-split field matching, planned boosts, other field size changes, adjustments to match divergent fields, matchline feathering, and opposed tangential fields. This study demonstrates that asymmetric collimation is a useful and powerful clinical treatment tool with widespread applications to radiation therapy.