A linear relationship for the LET-dependence of Gafchromic EBT3 film in spot-scanning proton therapy.

A linear relationship for the LET-dependence of Gafchromic EBT3 film in spot-scanning proton therapy. Phys Med Biol. 2019 Jan 23;: Authors: Anderson SE, Grams MP, Wan Chan Tseung H, Furutani KM, Beltran CJ Abstract Radiochromic film is a valuable dosimetric tool, primarily due to its sub-millimeter spatial resolution. For accurate proton dosimetry, the dependence of film response on linear energy transfer must be characterized and calibrated. In this work, we characterized film under-response, or "quenching," as a function of dose-weighted linear energy transfer (LETd) in several proton fields and established a simple, linear relationship with LETd. 
 
 We performed measurements as a function of depth in a PMMA phantom irradiated by a spot-scanning proton beam. The fields had energies of 71.3 MeV, 71.3 MeV with filter, and 159.9 MeV. At each depth (measurements taken in depth step sizes of 0.5-1 mm in the Bragg peak), we measured dose with a PTW Markus ion chamber and EBT3 radiochromic film. EBT3 under-response was characterized by the ratio of dose measured with film to that with ion chamber. LETd values for our experimental setup were calculated using in-house clinical Monte Carlo code. Measured film under-response increased with LETd, from approximately 10% under-response for LETd = 5 keV/μm to approximately 20% for LETd = 8 keV/μm. The under-response for all measurements was plotted versus LETd. A linear fit to ...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research