A standard dosimetry procedure for¹⁹²Ir sources used for endovascular brachytherapy

Abstract

The experimental dosimetry of a high dose rate (HDR) 192Ir source used for the brachytherapy of peripheral vessels is reported. The direct determination of the reference air kerma rate Kr agrees, within the experimental uncertainty, with the results obtained by a well ionization chamber calibrated at the NIST and the manufacturer's certification. A highly sensitive (HS) radiochromic film (RCF), that presents only one active layer, was used for the source dosimetry in a water phantom. The adopted experimental set-up, with the source in its catheter positioned on the RCF plane, seems to have given better accuracy of the RCF optical density measurements. The agreement between the measurement of the dose rate constant DKr (10 mm, pi/2) and the literature data confirmed the coherence of the HS RCF calibration obtained by the kerma in air measurements. The RCF measurements supplied dosimetric information about the dose to water per reference air kerma rate D(r, theta)/Kr along the source transverse bisector axis, the radial dose function g(r) and the anisotropy function F(r, theta). The value D(2 mm, pi/2)/Kr = 22.4 +/- 1.2 cGy h(-1)/(microGy h(-1)) is supplied with a dose uncertainty that is essentially due to the indeterminacy of the source position in the catheter. The data of the radial and anisotropy functions have been compared with Monte Carlo determinations reported in the literature.

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

“…IVBT is different from conventional HDR brachytherapy for cancer treatment because of the closer proximity (within millimeters) of the IVBT prescription point(s) relative to the radioactive sources, and the very steep dose gradients (more than 50% in 1 mm) at the distances of interest which are as close as 0.5 mm 345,346 . RCF has emerged as the mainstay experimental measurement tool that can meet the challenge of accurate IVBT dosimetry and also verify MC simulations 14,109,347 . RCF (HD‐810, MD‐55, and HS models) can be used to study heterogeneity effects (calcium, stent, gold marker, air pockets, and guide wire) for IVBT sources 2,8,110,150 .…”

“…During this period, HS and XR film models were also introduced and are detailed in the literature. 2,3,5,[14][15][16][17][18][19][20] By the early 2000s several limitations of the original GafChromic films for radiotherapy dosimetry had become apparent. These included the relatively low sensitivity of the products, their lack of uniformity, the limitation on film size and its high cost.…”

“…Remote afterloading HDR sources: Remote afterloading HDR brachytherapy is a well-established treatment modality in radiation therapy. 319 RCF measurement of dosimetric characteristics in water or water equivalent solid phantoms have been reported for 192 Ir 14,138,146,328,329 , and 60 Co. 330,331 Based on the measured dose distributions, TG-43 dosimetric parameters 149 can be generated. 14,138,329,331 Dosimetric measurements of HDR sources in various applicators and catheters have been reported.…”

Gafchromic film dosimetry of a new HDR brachytherapy source

“…In recent years, many attempts have been made to perform the dosimetry of ${\hspace{0.17em}}^{192}\text{Ir}$‐HDR brachytherapy sources using radiochromic films (RCFs) 5 , 6 , 7 , 8 , 9 . Piermattei et al (5) performed experimental dosimetry of the MicroSelectron HDR ${\hspace{0.17em}}^{192}\text{Ir}$ source model 080950 (Elekta AB, Stockholm, Sweden), used for the brachytherapy of peripheral vessels in a water phantom with high sensitivity (HS) RCF.…”

“…Piermattei et al (5) performed experimental dosimetry of the MicroSelectron HDR ${\hspace{0.17em}}^{192}\text{Ir}$ source model 080950 (Elekta AB, Stockholm, Sweden), used for the brachytherapy of peripheral vessels in a water phantom with high sensitivity (HS) RCF. They reported the dose rate constant, Λ, of the ${\hspace{0.17em}}^{192}\text{Ir}$‐HDR source to be $1.11\pm 0.02\%\hspace{0.17em}{\text{cGyh}}^{-1}{\mathrm{normalU}}^{-1}$.…”