Computation of the electron beam quality [Formula: see text] factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE.

The quality correction factor [Formula: see text] 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 of these chambers for electron beams with nominal energies ranging between 6 and 22MeV, corresponding to a Varian Clinac 2100 C/D. A Co beam was used as reference quality Q. Also eight monoenergetic electron beams reproducing the quality index R of the Clinac beams were considered. The [Formula: see text] factors were calculated as the ratio between f and [Formula: see text] . 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 [Formula: see text] factors found for the monoenergetic beams are larger (smaller) than those corresponding to the Clinac beams at low (high) R values, the differences being slightly above 0.5%. Finally, the [Formula: see text] factors obtained in the case of the NE2571A chamber are systematically ∼0.5% below those of its predecessor chamber, the NE2571.