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SU‐FF‐T‐188: Correlation Between in Vivo Electron Diodes Response and Nominal Surface Dose for Broad Electron Beams
Author(s) -
Li T,
Tong S,
Su M,
Grant D,
Torres C,
Kim T,
Chu K
Publication year - 2005
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 - 10.1118/1.1997890
Subject(s) - diode , ionization chamber , electron , physics , cathode ray , optics , dosimeter , calibration , atomic physics , beam (structure) , nuclear medicine , ion , nuclear physics , optoelectronics , radiation , ionization , medicine , quantum mechanics
Purpose: To establish correlation between in vivo diodes response and nominal surface dose Ds for broad electron beams, thus simplifying the calibration process for electron diodes. Method and Materials: The nominal surface dose Ds defined by TG25 was extracted from electron PDD data that were measured by cylindrical ion chamber (RK chamber, Scanditronix‐Wellhofer) on a Varian 2100C Linac at 100 cm SSD. Cone factors were measured using ion chamber (Capintec PR‐06) at d max . A QED p‐type electron diode with Model 1131 dosimeter (Sun Nuclear Corp.) was calibrated to the dose at d max for 9 MeV electron beam at 100 cm SSD using 10×10 cone. Diode readings using this calibration factor were then obtained with 10×10 cone and 15×15 cone for 6, 9, 12, 16 and 20 MeV electron beams delivering 200 MUs. The same diode was then re‐calibrated to the dose at d max for 12 MeV electron beam. The above measurements were repeated with 10×10 cone and 25×25 cone to reconfirm our hypothesis. Results: The diode readings were first divided by cone factors, and then the corrected readings were plotted against nominal skin dose. For diodes calibrated by 9 MeV electrons, the correlation coefficient R‐squared value were 0.9954 and 0.9796 for 10×10 cone and 15×15 cone respectively. For diodes calibrated by 12 MeV electrons, the R‐squared value were 0.9967 and 0.9980 for 10×10 cone and 25×25 cone respectively. Conclusion: The correlation between in vivo p‐type diode response and nominal surface dose Ds for broad electron beams has been empirically established and confirmed. The diode response corrected by cone factor demonstrated a clear correlation with nominal surface dose Ds. This correlation can significantly simplify the electron diode calibration process. It can also be potentially used to monitor relative skin dose along with d max dose at the same time.