SU-E-T-116: Dosimetry On Beam Modeling at the Small Field for Stereotactic Radiosurgery

Abstract

Purpose: Beam modeling performed based on the results of the present study, measuring the amount of radiation from a variety of small field of radiation measurement equipment beam modeling is based on the results of clinical practice, such as stereotactic radiosurgery and radiation therapy planning system applied to the treatment plan of each radiation dose distribution is to compare and analyze. Methods: A RapidArc medical linear accelerator was used with norminal 6 and 15 MV photon beam energies in this study. The small beams were generated that field sizes were 1×1, 2×2, 3×3 cm2 and reference field size was 10×10 cm2 to compare small field. We were generated the beam modeling and performed the automatic modeling with adjusted the mean and standard deviation of energy with the spectrum modeling base on the generated the PDD of the beam model. And, we were the lateral profile modeling by using adjusted each horn factor, effect source size, jaw transmission factor, MLC transmission factor, softening factor. Results: In this study, the edge detector measured a narrower penumbra width than the other detectors for small field sizes. For the 20–80% penumbra, the penumbra width measured with the ion chamber was approximately two times wider than the penumbra measured with the edge detector in all cases. The CC13 measured a penumbra width that was 25% wider for all field sizes. We found that the PDD measured with film had some signal fluctuation at the buildup region(6 MV: 1.5 cm, 15 MV: 2.9 cm) for the smallest field size when compared to the standard ionization chamber. Conclusion: The edge detector showed a greater suitability for small field dosimetry than the other detectors tested. We compared the detectors and evaluated the beam modeling results that as they have relatively large volumes, significant discrepancies could occur during the small field dosimetry.