SU-E-P-24: Essential Parameters of the IORT Electron Beam Must Be Revised

Abstract

Purpose: The treatment of tumors with intraoperative electron beam radiotherapy is getting speed in recent years due to presence of smaller, cheaper IORT machines. Beam quality of such machines is lower than that of the standard heavy equipment. Characterization of the electron beam in reliable and adequate way is a very important task. Both time and radiation exposure need to be take in consideration. We discuss here adequateness of the commonly used beam characterization parameters for such beams. Methods: Water tank system was used to measure beam profiles of the IORT machineMobetron for several different units. Results were compared and differences analyzed. MATLABcalculations were used to analyze properties and predict desired profiles Results: Authors analyzed parameters commonly used to characterize beam quality and came to the conclusion that they are inadequate for providing safety and efficiency in modern world IORT accelerators. Both depth and spacial beam characteristics work well either with beams wider than 10 cm, or extremely flat beams produced by monoenergetic beams with multi-leaf collimators.Characteristics of the narrow electron beam produced by small linac differ a lot from ones of conventional linac with bending magnet and need to be redefined. Conclusion: Authors propose and defend method of electron beam characterization while commissioning based on real life experience. Further investigation might lead to rewriting commonly accepted TG25/51 protocols to reflect reality and increase safety and reliability of the results.