Korean J Med Phys.  2009 Jun;20(2):97-105.

Study on Absorbed Dose Determination of Electron Beam Quality for Cross-calibration with Plane-parallel Ionization Chamber

• Rah JE
• Shin DO
• Park SH
• Jeong H
• Hwang UJ
• Ahn SH
• Lim YK
• Kim DW
• Yoon M
• Shin DH
• Lee SB
• Suh TS
• Park SY

Abstract

Absorbed dose to water based protocols recommended that plane-parallel chambers be calibrated against calibrated cylindrical chambers in a high energy electron beam with R50>7 g/cm2 (E> or =16 MeV). However, such high-energy electron beams are not available at all radiotherapy centers. In this study, we are compared the absorbed dose to water determined according to cross-calibration method in a high energy electron beam of 16 MeV and in electron beam energies of 12 MeV below the cross-calibration quality remark. Absorbed dose were performed for PTW 30013, Wellhofer FC65G Farmer type cylindrical chamber and for PTW 34001, Wellhofer PPC40 Roos type plane-parallel chamber. The cylindrical and the plane-parallel chamber to be calibrated are compared by alternately positioning each at reference depth, zref=0.6R50-0.1 in water phantom. The DW of plane-parallel chamber are derived using across-calibration method at high-energy electron beams of 16, 20 MeV. Then a good agreement is obtained the DW of plane-parallel chamber in 12 MeV. The agreement between 20 MeV and 12 MeV are within 0.2% for IAEA TRS-398.

Keyword

Electron beam; Absorbed dose to water calibration coefficient; Plane-parallel ionization chamber; Cross-calibration; Beam quality

MeSH Terms

Electrons
Water
Water