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

Abstract

In this article we compare the accuracy of a diode laser densitometer emitting 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 Stockholm, 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 custom-designed diode laser scanning device, emitting light at 675.2 nm. The same data were recorded with a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements were compared to dose cross profiles of a radiosurgery dose planning program (GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He-Ne laser densitometer, the custom-designed diode laser scanning device showed better agreement with the calculated dose cross profile. For two axes, the full width half maxima (FWHM) of the diode laser scanning device was within 0.1 mm deviation 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-55 film readout. This greater accuracy may be related to the diode laser measuring the optical density close to maximum absorption of the GafChromic film MD-55 (671-675 nm).

Radiochromic Film Dosimetry and its Applications in Radiotherapy

“…Light emitting diodes (LEDs) are available over a range of wavelengths from infra-red down to ultraviolet and have spectral bandwidths of approximately 30nm. A special subgroup of LEDs known as laser diodes are available at particular wavelengths and have narrower bandwidths than standard LEDs, at 1-10nm [67][68][69] FIGURE 10…”

High precision film dosimetry with GAFCHROMIC® films for quality assurance especially when using small fields

“…Several authors have discussed the dosimetry by using radiochromic films. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Niromand et al 16 reported on nearly all features and phenomena on GAFCHROMIC® films, McLaughlin 35 studied the response of these films and its use as a detector for radiosurgery 42 and Meigooni et al 10 reported on methods to improve the quality of the film dosimetry with radiochromic films. FIG.…”

Qualitätssicherung im stereotaktischen Raum

“…Radiochrome Filme sind nahezu gewebeäquivalent [23] und ihre Empfindlichkeit ist energieunabhängig [18]. Die Verfärbung der sensitiven Schicht des GAFCHROMIC™-Films durch Bestrahlung zeigt eine breite Absorptionsverteilung im Sichtbaren mit zwei Absorptionsmaxima bei 610 und 676 nm [9]. Der Film ist selbst entwickelnd, zeigt Additivität, hat eine exzellente Ortsauflösung und erlaubt absolute Dosismessungen.…”