Intensity modulation for breast treatment using static multi-leaf collimators

Purpose: To achieve more uniform dose distributions in breast cancer treatm ent using multiple sets of multi-leaf collimator (IMLC) defined fields. Dos e uniformity for many breast cancer patients can be significantly improved by using two or more sets of portals and the "hot" regions of a traditional treatment can be significantly reduced. Methods and Materials: Patients for breast cancer treatment are immobilized with alpha cradle in the traditional arm-up position and have a CT scan in the treatment position. The target volume is delineated on the 5-mm thick CT slices that are obtained from the Lower neck to well below the breast ta rget volume, Medial and lateral tangential fields at conventional gantry an gles are designed with the aid of digitally reconstructed radiographs (DRRs ), The MLC, without collimator rotation, is used to shape the field to spar e as much lung as possible. The wedges and relative weights of the beams ar e optimized to provide the best dose uniformity. For the patients with larg e dose inhomogeneity, a second set of fields is designed. The weight of the original set of fields is reduced (usually to similar to 90%) so that the "original hot" regions receive the prescription dose; the second set of fie lds delivers a supplemental dose to the "cold" region, typically similar to 10% of the total dose. The second set of fields has the same beam paramete rs but "treat" only the part of breast tissue that is "cool," Presently, th e design of the reduced field is an iterative process. The process can be e xtended to more than two sets of pedals to obtain the desired dose uniformi ty. Results: With 3D planning and multiple MLC fields, dose uniformity in the t reatment of breast patients was improved from 7%-22% to similar to 7%-15%. The volume receiving these high doses decreased significantly and shifted f rom the lung to the target. By keeping the gantry angles and wedges the sam e for the multiple fields, treatments can be delivered quickly and reliably . The internal mammary nodes (IM) can also be treated without including sig nificant amount of lung or heart in the field. Conclusion: Dose uniformity can be significantly improved by using this int ensity modulation technique to treat certain breast patients. With these st atic MLC fields creating the intensity modulation, the dose uniformity to t he breast can be significantly improved and the hot region in lung reduced. There is no increase in setup complexity. The small increase in treatment time is insignificant. (C) 2000 Elsevier Science Inc.