Impact of range shifter material on proton pencil beam spot characteristics. Issue 3 (25th February 2015)

• Record Type: Journal Article
• Authors: Shen, Jiajian; Liu, Wei; Anand, Aman; Stoker, Joshua B.; Ding, Xiaoning; Fatyga, Mirek; Herman, Michael G.; Bues, Martin
• Is Part Of: Medical physics. Volume 42:Issue 3(2015)
• Page Start: 1335
• Page End: 1340
• Publication Date: 2015-02-25
• Subjects: polymers -- proton beams -- radiation therapy -- waxes; Therapeutic applications, including brachytherapy; Radiation therapy -- Compositions of oils, fats or waxes; Compositions of derivatives thereof -- Animal or vegetable oils, fats, fatty substances or waxes; Fatty acids therefrom; Detergents; Candles; range shifter material -- proton pencil beam -- spot size -- scattering -- bolus; Protons -- Materials properties -- Optical microcavities -- Monte Carlo methods -- Proton therapy -- Materials analysis -- Multiple scattering -- Dosimetry -- Cancer; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4908208
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: To quantitatively investigate the effect of range shifter materials on single‐spot characteristics of a proton pencil beam. Methods: An analytic approximation for multiple Coulomb scattering ("differential Moliere" formula) was adopted to calculate spot sizes of proton spot scanning beams impinging on a range shifter. The calculations cover a range of delivery parameters: six range shifter materials (acrylonitrile butadiene styrene, Lexan, Lucite, polyethylene, polystyrene, and wax) and water as reference material, proton beam energies ranging from 75 to 200 MeV, range shifter thicknesses of 4.5 and 7.0 g/cm 2, and range shifter positions from 5 to 50 cm. The analytic method was validated by comparing calculation results with the measurements reported in the literature. Results: Relative to a water‐equivalent reference, the spot size distal to a wax or polyethylene range shifter is 15% smaller, while the spot size distal to a range shifter made of Lexan or Lucite is about 6% smaller. The relative spot size variations are nearly independent of beam energy and range shifter thickness and decrease with smaller air gaps. Conclusions: Among the six material investigated, wax and polyethylene are desirable range shifter materials when the spot size is kept small. Lexan and Lucite are the desirable range shifter materials when the scattering power is kept similar to water.