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SU‐F‐T‐69: Correction Model of NIPAM Gel and Presage for Electron and Proton PDD Measurement
Author(s) -
Lin C,
Chao T,
Lin C,
Nien H,
Tu P,
Yueh C,
Wu C
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 - 10.1118/1.4956204
Subject(s) - proton , electron , materials science , ion , range (aeronautics) , analytical chemistry (journal) , optics , physics , chemistry , nuclear physics , chromatography , quantum mechanics , composite material
Purpose: The current standard equipment for proton PDD measurement is multilayer‐parallel‐ion‐chamber. Disadvantage of multilayer‐parallel‐ion‐chamber is expensive and complexity manipulation. NIPAM‐gel and Presage are options for PDD measurement. Due to different stopping power, the result of NIPAM‐gel and Presage need to be corrected. This study aims to create a correction model for NIPAM‐gel and Presage PDD measurement. Methods: Standard water based PDD profiles of electron 6MeV, 12MeV, and proton 90MeV were acquired. Electron PDD profile after 1cm thickness of NIPAM‐gel added on the top of water was measured. Electron PDD profile with extra 1cm thickness of solid water, PTW RW3, was measured. The distance shift among standard PDD, NIPAM‐gel PDD, and solid water PDD at R50% was compared and water equivalent thickness correction factor (WET) was calculated. Similar process was repeated. WETs for electron with Presage, proton with NIPAM‐gel, and proton with Presage were calculated. PDD profiles of electron and proton with NIPAM‐gel and Presage columns were corrected with each WET. The corrected profiles were compared with standard profiles. Results: WET for electron 12MeV with NIPAM‐gel was 1.135, and 1.034 for electron 12Mev with Presage. After correction, PDD profile matched to the standard profile at the fall‐off range well. The difference at R50% was 0.26mm shallower and 0.39mm deeper. The same WET was used to correct electron 6MeV profile. Energy independence of electron WET was observed. The difference at R50% was 0.17mm deeper for NIPAM‐gel and 0.54mm deeper for Presage. WET for proton 90MeV with NIPAM‐gel was 1.056. The difference at R50% was 0.37 deeper. Quenching effect at Bragg peak was revealed. The underestimated dose percentage at Bragg peak was 27%. Conclusion: This correction model can be used to modify PDD profile with depth error within 1mm. With this correction model, NIPAM‐gel and Presage can be practical at PDD profile measurement.