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Scatter fractions from linear accelerators with x‐ray energies from 6 to 24 MV
Author(s) -
Taylor Paula L.,
Rodgers James E.,
Shobe Jileen
Publication year - 1999
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 - 10.1118/1.598670
Subject(s) - monte carlo method , imaging phantom , electromagnetic shielding , linear particle accelerator , physics , scattering , computational physics , range (aeronautics) , dosimetry , beam (structure) , nist , optics , nuclear medicine , materials science , mathematics , statistics , medicine , quantum mechanics , composite material , natural language processing , computer science
Computation of shielding requirements for a linear accelerator must take into account the amount of radiation scattered from the patient to areas outside the primary beam. Currently, the most frequently used data are from NCRP 49 that only includes data for x‐ray energies up to 6 MV and angles from 30° to 135°. In this work we have determined by Monte Carlo simulation the scattered fractions of dose for a wide range of energies and angles of clinical significance including 6, 10, 18, and 24 MV and scattering angles from 10° to 150°. Calculations were made for a 400 cm 2circular field size impinging onto a spherical phantom. Scattered fractions of dose were determined at 1 m from the phantom. Angles from 10° to 30° are of concern for higher energies where the scatter is primarily in the forward direction. An error in scatter fraction may result in too little secondary shielding near the junction with the primary barrier. The Monte Carlo code ITS (Version 3.0) developed at Sandia National Laboratory and NIST was used to simulate scatter from the patient to the barrier. Of significance was the variation of calculated scattered dose with depth of measurement within the barrier indicating that accurate values may be difficult to obtain. Mean energies of scatter x‐ray spectra are presented.