SU‐GG‐T‐179: Analysis of Electron Cutout Factor Measurements

Abstract

Purpose: To compare electron cutout factor (COF) measured with various dosimeters for different cone sizes. Method and Materials: The COFs for various electron fields were measured on a Varian‐2300EX linear accelerator at 6, 9, 12, 16 and 20 MeV. A thimble ion chamber, plane parallel chamber, thermoluminescent dosimeters (TLDs), EDR film, X Omat‐V (XV) film, GafChromic film and Thomson‐Nielsen mosfets were used to measure COFs. Each detector was placed along the beam's central axis at 100 cm from the source. Measurements were made in solid water at dmax for 6×6, 10×10 and 20×∼20 cone sizes with circular cutouts. The thimble chamber was used as the standard to compare COF measurements. The raw measurements made with the two chambers and the diodes were used to determine the COFs. Films were analyzed with RIT software and TLDs were read the next day to determine COFs. Results: Measurements for the 10×10 and 20×20 cone sizes agreed within 3.5% between all the dosimeters and the thimble chamber. Measurements made for the 6×6 cone and cutout were more than 3.5% from those made with the thimble chamber. There was better agreement for COF measurements between the mosfets, TLDs, EDR film and XV film. Conclusion: This study takes a look at the various dosimeters available at the clinic that can be used for determining electron cutout factors. For most cutout sizes, ionization chambers, mosfets, TLDs, EDR, XV and GafChromic film can be used to measure the COFs for all electron energies. For small field sizes, the use of TLDs, mosfets, and film can give more accurate COFs.