Computation of the electron beam quality $k_{{\rm Q,Q}_0}$ factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE

TL;DR

This study calculates the electron beam quality correction factors for three specific ionization chambers using Monte Carlo simulations, providing data crucial for accurate dosimetry in radiotherapy.

Contribution

It introduces detailed Monte Carlo calculations of $k_{Q,Q_0}$ factors for NE2571, NE2571A, and NE2581A chambers across various electron beam qualities, filling a gap in dosimetric data.

Findings

$k_{Q,Q_0}$ factors agree with previous EGSnrc calculations for NE2571.

Monoenergetic beam results differ slightly from clinical beam results, especially at low and high $R_{50}$ values.

NE2571A factors are systematically ~0.5% lower than NE2571.

Abstract

The quality correction factor $k_{Q,Q_{0}}$ for electron beams was calculated for three thimble ionization chambers, namely, NE2571, NE2571A and NE2581A. The Monte Carlo code PENELOPE was used to estimate the overall correction factor $f_{\rm c,Q}$ of these chambers for electron beams with nominal energies ranging between 6 and 22 MeV, corresponding to a Varian Clinac 2100 C/D. A $^{60}$Co beam was used as reference quality ${\rm Q}_0$. Also eight monoenergetic electron beams reproducing the quality index $R_{50}$ of the Clinac beams were considered. The $k_{Q,Q_{0}}$ factors were calculated as the ratio between $f_{\rm c,Q}$ and $f_{{\rm c,Q}_0}$. Those obtained for the NE2571 ionization chamber show a nice agreement with those calculated by Muir and Rogers with EGSnrc. As it occurred to other ionization chambers analyzed in previous works, the $k_{{\rm Q,Q}_0}$ factors found for the monoenergetic beams are larger (smaller) than those corresponding to the Clinac beams at low (high) $R_{50}$ values, the differences being slightly above $0.5\%$. Finally, the $k_{{\rm Q,Q}_0}$ factors obtained in the case of the NE2571A chamber are systematically ~0.5% below those of its predecessor chamber, the NE2571.