Pergamon Int. J. Radiation Oncology Biol. Phys., Vol. 30, No. 3, pp. 707-714, 1994 Copyright 0 I994 Elsevier Science Ltd Printed in the USA. All rights reserved 0360-3016/94 $6.00 + .oO 0360-3016(94)00277-O ?? Technical Innovations and Notes A MULTILEAF COLLIMATOR FIELD PRESCRIPTION PREPARATION SYSTEM FOR CONVENTIONAL RADIOTHERAPY M. N. Du, PH.D., C. X. Yu, D.Sc., M. SYMONS, C.ENG., D. YAN, D.Sc., R. TAYLOR, M.Sc., R. C. MATTER, M.D., G. GUSTAFSON, M.D., A. MARTINEZ, M.D. AND J. W. WONG, PH.D. Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073 Purpose: The purpose of this work is to develop a prescription preparation system for efficient field shaping using aeaf collimator that can be used in community settings as well as research institutions. The efficiency advantage of the computer-controlled multileaf collimator, over cerrobend blocks, to shape radiation fields has been shown in conformal treatments, which typically require complete volumetric computerized tomographic data for three-dimensional radiation treatment planning-a utility not readily available to the genera1 community. As a result, most patients today are treated with conventional radiation therapy. Therefore, we believe that it is very important to fully use the same efficiency advantage of multileaf collimator as a block replacement in conventional practice. Methods and Material: The multileaf collimator prescription preparation systems developed by us acquires pre- scriDtion images from different sources, including film scanner, and radiation treatment planning systems. The multileaf collimator angle and leaf positions are set from the desired field contour defined on the prescription image, by minimizing the area discrepancies. Interactive graphical tools include manual adjustment of collimator angle and leaf positions, and definition of portions of the field edges that require maximal conformation. Data files of the final leaf positions are transferred to the multileaf collimator controller via a dedicated communication link. Results: We have implemented the field prescription preparation system and a network model for integrating the zf collimator and other radiotherapy modalities for routine treatments. For routine plan evaluation, isodose contours measured with film in solid water phantom at prescription depth are overlaid on the prescription image. Preliminary study indicates that the efficiency advantage of the MLC over cerrobend blocks in conformal therapy also holds true for conventional treatments. Conclusion: Our model of computer-controlled prescription, evaluation, and treatment using multileaf collimators can be effectively implemented in both community settings and research institutions. The resultant increase in treatment efficiency and accuracy is now available for conventional radiotherapy. Multileaf collimator, MLC, Radiation field shaping. INTRODUCIION The desire to improve local tumor control has spurred many efforts to develop models of computer-controlled treatment delivery for conformal therapy (4). A common key element of these models is a computer-controlled multileaf collimator (MLC) in place of cerrobend blocks. So far the use of MLC has been mostly related to the implementation of conformal therapy, although the MLC also provides an opportunity to enhance efficiency in conventional treatments. Since most patients in research institutions and all patients in community hospitals are still treated with the conventional approaches. We believe that it is equally important to manifest the potential ben- efit of MLC for conventional therapy. Multileaf collimator-shaped radiation fields have, in general, stepped edges and shape restrictions, contrasting with the arbitrarily smooth ones defined by cerrobend blocks. This inherent limitation of MLC introduces some change in the concept of beam collimation, that is, the radiation field collimated by an MLC does not necessarily coincide with the target area prescribed by a physician and only an “optimal” field is achievable. Here, and here- after in this work, “target area” stands for “desired irra- diated area in the prescription plane.” Associated with the use of a computer-controlled MLC is the need to translate field prescriptions (from simulation films or treatment planning systems) into optimized MLC set-ups. In other words, a system that derives optimized MLC leaf positions for a prescribed target area is required. Although Reprint requests to: M. N. Du, Ph.D. work with the MLC in our clinic. Special thanks go to A. Frazier, Acknowledgements-We gratefully acknowledge the support C. Mullins, and D. Germilhac. from Philips Medical System, N.A., and the many people who Accepted for publication 6 May 1994. 707