In this article we compare the accuracy of a diode laser densitometer emitt
ing 675.2 nm to that of a commercial He-Ne laser densitometer emitting 632.
8 nm for GafChromic MD-55 film readout. A Leksell gamma unit (AB Elekta Sto
ckholm, Sweden) Model B with a 14 and 8 mm collimator at the same isocenter
(combined 11 mm collimator) was used to irradiate GafChromic MD-55 films.
Dose response curves, dose cross profile and FWHM were measured with a cust
om-designed diode laser scanning device, emitting light at 675.2 nm. The sa
me data were recorded with a commercial He-Ne laser densitometer (PTW FIPS
Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements wer
e compared to dose cross profiles of a radiosurgery dose planning program (
GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He-Ne laser den
sitometer, the custom-designed diode laser scanning device showed better ag
reement with the calculated dose cross profile. For two axes, the full widt
h half maxima (FWHM) of the diode laser scanning device was within 0.1 mm d
eviation compared to the data calculated by the dose planning program. The
FWHM of the commercial He-Ne laser densitometer was less accurate (1.6 and
2.1 mm deviation). Our data show that a diode laser scanning device using a
Light source emitting 675.2 nm increases the accuracy of a GafChromic MD-5
5 film readout. This greater accuracy may be related to the diode laser mea
suring the optical density close to maximum absorption of the GafChromic fi
lm MD-55 (671-675 nm). (C) 1999 American Association of Physicists in Medic
ine. [S0094-2405(99)00305-3].