Out-of-field Dose for Scanned and Scattered Proton Beams
- Proton Therapy, Inc. Colton, CA 92324 (United States)
The dose delivered outside of the primary field to non-target tissues is of concern in all types of radiotherapy. For a given radiation type, this dose is dependent upon the delivery technique. Proton beams may be spread laterally to cover the target volume using scattering foils or magnetic scanning. Although scattered beams always use apertures or multi-leaf collimators to limit the radiation to normal tissues, scanning beams may or may not use them. A direct comparison of out-of-field dose for different proton delivery techniques has been thwarted because no institution had, as of April 2008, used multiple delivery techniques and comparisons have had to make extrapolations from measurements or calculations made using different field sizes, ranges, modulations, collimator-to-skin distances, and collimator materials. In this study, the Monte Carlo program MCNPX was used to simulate the dose deposited outside of the primary field for scattered/collimated (STC), scanned/collimated (SNC), and scanned/uncollimated (SNU) beams that have the same field size and penetration depth within a simulated patient. The out-of-field doses ranged from 10{sup -2} to 10{sup -7} of the prescribed dose. The ratio of STC to SNU dose varied from 2 to 420 depending upon the depth and distance off-axis while the SNC to SNU dose varied from 1.2 to 140. As the out-of-field doses are very small for all beam delivery techniques, decisions regarding which technique is appropriate for a given patient or facility should be based upon the magnitude of the out-of-field dose per unit prescribed dose and other issues rather than the ratio of doses for the different beam delivery techniques.
- OSTI ID:
- 21289571
- Journal Information:
- AIP Conference Proceedings, Vol. 1099, Issue 1; Conference: CAARI 2008: 12. international conference on application of accelerators in research and industry, Fort Worth, TX (United States), 10-15 Aug 2008; Other Information: DOI: 10.1063/1.3120072; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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