A novel 675.2 nm diode laser densitometer for use with GafChromic films

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].