Premium
SU‐FF‐T‐269: Dosimetric Properties of Scattered Photon Subsources Within a Source Model for Different Initial Electron Energies
Author(s) -
Fix M,
Keall P,
Siebers J
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1997998
Subject(s) - monte carlo method , photon , dosimetry , physics , histogram , electron , beam (structure) , intensity (physics) , computational physics , scaling , absorbed dose , radiation , nuclear medicine , atomic physics , nuclear physics , optics , mathematics , statistics , medicine , geometry , artificial intelligence , computer science , image (mathematics)
Purpose: Histogram‐based Monte Carlo (MC) source models for dose calculations in radiotherapy require methods to scale input data so as to match measured accelerator output. A previous study showed that the photon beam characteristics remain constant when the radial intensity distribution of the initial electron beam varies, but changes for different mean initial electron energies Ē e . This work investigates the dosimetric properties of scattered photon subsources for different Ē e striking the target and evaluates the scaling needed for those subsources to match dose distributions resulted for different Ē e . Method and Materials: Test scenarios were performed for 6‐MV beams using Ē e = 5, 6.2 and 7 MeV and for 18‐MV beams using 17, 18, and 19 MeV. Histogram distributions for a previously developed MC source model were created based on phase‐space data for these beams. 3D‐dose distributions for a 10×10‐cm 2 field at SSDs 50, 100 and 200‐cm and a 30×30‐cm 2 field at SSD 100‐cm were calculated in water using different subsource combinations. The dose distributions are normalized to the same integral dose for the depth dose curve of the 10×10 cm 2 field at SSD 100 and compared based upon dose differences. Results: When scattered photon subsources associated with the 5‐MeV simulation were used with the 7‐MeV target subsource, <0.4% differences were found compared with using all the 7‐MeV subsources in all cases studied. Differences were reduced to <0.2% when using the 6.2‐MeV scattered subsources with the 7‐MeV target subsource and were <0.2% when using either 17‐ or 18‐MeV scatter subsources with the 19‐MeV target subsource for 18‐MV beams. Conclusion: These results suggest that apart from scaling the scattered subsource intensity, only the target subsource distributions need to be changed to adjust the histogram‐based source model to dosimetrically match accelerator outputs due to Ē e changes. Supported by Philips Medical Systems and ACS‐grant IRG‐73‐001‐28.