PLANNING, DELIVERY, AND QUALITY ASSURANCE OF INTENSITY-MODULATED RADIOTHERAPY USING DYNAMIC MULTILEAF COLLIMATOR - A STRATEGY FOR LARGE-SCALE IMPLEMENTATION FOR THE TREATMENT OF CARCINOMA OF THE PROSTATE

Purpose: To improve the local control of patients with adenocarcinoma of the prostate we have implemented intensity modulated radiation ther apy (IMRT) to deliver a prescribed dose of 81 Gy. This method is based on inverse planning and the use of dynamic multileaf collimators (DML C). Because IMRT is a new modality, a major emphasis was on the qualit y assurance of each component of the process and on patient safety. In this article we describe in detail our procedures and quality assuran ce program. Methods and Materials: Using an inverse algorithm, we have developed a treatment plan consisting five intensity-modulated(IM) ph oton fields that are delivered with DMIC. In the planning stage, the p lanner specifies the number of beams and their directions, and the des ired doses for the target, the normal organs and the ''overlap'' regio ns. Then, the inverse algorithm designs intensity profiles that best m eet the specified criteria. A second algorithm determines the leaf mot ion that would produce the designed intensity pattern and produces a D MLC file as input to the MLC control computer. Our quality assurance p rogram for the planning and treatment delivery process includes the fo llowing components: 1) verification of the DMLC field boundary on loca lization pod film, 2) verification that the leaf motion of the DMLC fi le produces the planned dose distribution (with an independent calcula tion), 3) comparison of dose distribution produced by DMLC in a flat p hantom with that calculated by the treatment planning computer for the same experimental condition, 4) comparison of the planned leaf motion s with that implemented for the treatment (as recorded on the MLC log files), 5) confirmation of the initial and final positions of the MLC for each field by a record-and-verify system, and 6) in vivo dose meas urements. Results: Using a five-field IMRT plan we have customized dos e distribution to conform to and deliver 81 Gy to the PTV. In addition , in the overlap regions between the PTV and the rectum, and between t he PTV and the bladder, the dose is kept within the tolerance of the r espective organs. Our QA checks show acceptable agreement between the planned and the implemented leaf motions. Correspondingly, film and TL D dosimetry indicates that doses delivered agrees with the planned dos e to within 2%. As of September 15, 1996, we have treated eight patien ts to 81 Gy with IMRT. Conclusion: For complex planning problems where the surrounding normal tissues place severe constraints on the prescr iption dose, IMRT provides a powerful and efficient solution. Given a comprehensive and rigorous quality-assurance program, the intensity-mo dulated fields can be efficaciously and accurately delivered using DML C. IMRT treatment is now ready for routine implementation on a large s cale in our clinic. (C) 1997 Elsevier Science Inc.