Absolute dose determination in high-energy electron beams: Comparison of IAEA dosimetry protocols

• Main Authors: Sathiyan S, Ravikumar M
• Format: Article
• Language: English
• Published: Wolters Kluwer Medknow Publications 2008-01-01
• Series: Journal of Medical Physics
• Subjects: Absorbed dose; chamber; cross-calibration; protocol
• Online Access: http://www.jmp.org.in/article.asp?issn=0971-6203;year=2008;volume=33;issue=3;spage=108;epage=113;aulast=Sathiyan
• ISSN: 0971-6203; 1998-3913

In this study, absorbed doses were measured and compared for high-energy electrons (6, 9, 12, 16, and 20 MeV) using International Atomic Energy Agency (IAEA), Technical Reports Series No. 277 (TRS), TRS 381, and TRS 398 dosimetry protocols. Absolute dose measurements were carried out using FC65-G Farmer chamber and Nordic Association of Clinical Physicists (NACP) parallel plate chamber with DOSE1 electrometer in WP1-D water phantom for reference field size of 15 x 15 cm² at 100 cm source-to-surface distance. The results show that the difference between TRS 398 and TRS 381 was about 0.24% to 1.3% depending upon the energy, and the maximum difference between TRS 398 and TRS 277 was 1.5%. The use of cylindrical chamber in electron beam gives the maximum dose difference between the TRS 398 and TRS 277 in the order of 1.4% for energies above 10 MeV (R₅₀ > 4 g/cm² ). It was observed that the accuracy of dose estimation was better with the protocols based on the water calibration procedures, as no conversion quantities are involved for conversion of dose from air to water. The cross-calibration procedure of parallel plate chamber with high-energy electron beams is recommended as it avoids p_wall correction factor entering into the determination of k_Q,Qo .