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Sci‐Thur AM: YIS – 04: Stopping power‐to‐Cherenkov power ratios and beam quality specification for clinical Cherenkov emission dosimetry of electrons: beam‐specific effects and experimental validation
Author(s) -
Zlateva Yana,
Seuntjens Jan,
El Naqa Issam
Publication year - 2016
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 - 10.1118/1.4961754
Subject(s) - truebeam , cherenkov radiation , dosimetry , physics , beam (structure) , linear particle accelerator , monte carlo method , optics , laser beam quality , nuclear physics , computational physics , nuclear medicine , laser , mathematics , detector , statistics , medicine , laser beams
Purpose: To advance towards clinical Cherenkov emission (CE)‐based dosimetry by investigating beam‐specific effects on Monte Carlo‐calculated electron‐beam stopping power‐to‐CE power ratios (SCRs), addressing electron beam quality specification in terms of CE, and validating simulations with measurements. Methods: The EGSnrc user code SPRRZnrc, used to calculate Spencer‐Attix stopping‐power ratios, was modified to instead calculate SCRs. SCRs were calculated for 6‐ to 22‐MeV clinical electron beams from Varian TrueBeam, Clinac 21EX, and Clinac 2100C/D accelerators. Experiments were performed with a 20‐MeV electron beam from a Varian TrueBeam accelerator, using a diffraction grating spectrometer with optical fiber input and a cooled back‐illuminated CCD. A fluorophore was dissolved in the water to remove CE signal anisotropy. Results: It was found that angular spread of the incident beam has little effect on the SCR (≤ 0.3% at d max ), while both the electron spectrum and photon contamination increase the SCR at shallow depths and decrease it at large depths. A universal data fit of R 50 in terms of C 50 (50% CE depth) revealed a strong linear dependence (R 2 > 0.9999). The SCR was fit with a Burns‐type equation (R 2 = 0.9974, NRMSD = 0.5%). Below‐threshold incident radiation was found to have minimal effect on beam quality specification (< 0.1%). Experiments and simulations were in good agreement. Conclusions: Our findings confirm the feasibility of the proposed CE dosimetry method, contingent on computation of SCRs from additional accelerators and on further experimental validation. This work constitutes an important step towards clinical high‐resolution out‐of‐beam CE dosimetry.