A MULTILEAF COLLIMATOR FIELD PRESCRIPTION PREPARATION SYSTEM FOR CONVENTIONAL RADIOTHERAPY

Purpose: The purpose of this work is to develop a prescription prepara tion system for efficient field shaping using a multileaf collimator t hat can be used in community settings as well as research institutions . The efficiency advantage of the computer-controlled multileaf collim ator, over cerrobend blocks, to shape radiation fields has been shown in conformal treatments, which typically require complete volumetric c omputerized tomographic data for three-dimensional radiation treatment planning-a utility not readily available to the general 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 repl acement in conventional practice. Methods and Material: The multileaf collimator prescription preparation systems developed by us acquires p rescription 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 t he prescription image, by minimizing the area discrepancies. Interacti ve graphical tools include manual adjustment of collimator angle and l eaf positions, and definition of portions of the field edges that requ ire maximal conformation. Data files of the final leaf positions are t ransferred to the multileaf collimator controller via a dedicated comm unication link. Results: We have implemented the field prescription pr eparation system and a network model for integrating the multileaf col limator 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 i mage. Preliminary study indicates that the efficiency advantage of the MLC over cerrobend blocks in conformal therapy also holds true for co nventional treatments. Conclusion: Our model of computer-controlled pr escription, evaluation, and treatment using multileaf collimators can be effectively implemented in both community settings and research ins titutions. The resultant increase in treatment efficiency and accuracy is now available for conventional radiotherapy.