The relative response of NE2561 and NE2611A ionization chambers in megavoltage x-ray beams

Abstract

The relative energy response of NE2561 and NE261 IA ionization chambers to megavoltage photon beams from the ARPANSA linac indicates significant differences between these two types of chamber. In 16 MV beams of TPR20(10) 0.779, differences of about 2% are observed. The results are expressed as ratios KQ of the beam quality correction factors kQ, where the kQ factor for each type of chamber is the ratio of the absorbed dose to water calibration factor ND, at the x-ray quality Q to that at 60Co. These results have implications for the use of generic kQ factors in dosimetry protocols and suggest that NE2561 and NE2611A ionization chambers cannot be assumed to be identical.

Measured and Monte Carlo calculated kQ factors: Accuracy and comparison

“…The change was made because of radiation damage causing cracks in the POM of the NE2561. Boas et al 21 reported that the relative responses of the NE2561 and NE2611 chambers differ by about 2%. However, follow-up measurements did not yield any difference in response at the 0.5% level.…”

A comparison of Australian and Canadian calibration coefficients for air kerma and absorbed dose to water for60Co γ radiation

“…The five correction factors, k i , are summarized in Allisy-Roberts et al 19 and their values and uncertainties are given in table 3.…”

“…These chambers are very similar, apart from design of the stem and the use of Delrin R (NE 2561) or aluminium (NE 2611A) for the chamber cap-retaining nut. The two chamber types are assumed to be equivalent in 60 Co radiation, although this may not be the case in other radiation beams 19 .…”