Wide dynamic dose range of VIPAR polymer gel dosimetry

Abstract

In this work the extent of the linear dose response and the dynamic dose range of N-vinylpyrrolidone-argon based (VIPAR) polymer gels were investigated. VIPAR gels were irradiated using a 6 MV linear accelerator up to 60 Gy and a Nucletron microSelectron 192Ir HDR brachytherapy source to much higher doses to cover a dose range of two orders of magnitude. They were then MR scanned at 1.5 T to obtain T2-maps. VIPAR gel measurements obtained from the two irradiation regimes were calibrated against ion chamber measurements and dose calculations derived using the AAPM TG-43 protocol respectively. A satisfying agreement between the calibration results derived using the 6 MV x-rays and the 192Ir source was found for doses up to 60 Gy, implying that the response of the VIPAR gels is independent of photon energy and dose rate. A linear R2 dose response up to approximately 40 Gy and a dynamic dose range up to at least approximately 250 Gy were observed. VIPAR gel dose measurements derived using the monoexponentially fitted brachytherapy calibration data were found to be quite accurate.

Water equivalence of polymer gel dosimeters

“…The polymer gel called BANG-1 (Bis Acrylamide Nitrogen Gelatin) (Maryanski et al, 1994;Michael et al, 2000), PAG (Poly Acrylamide Gelatin) (Maryanski et al, 1993(Maryanski et al, , 1994 contains acrylamide as a monomer and BANG-2 (Bis Acrylic acid Nitrogen Gelatin) (Maryanski et al, 1996a,b) contains acrylic acid as a monomer. These monomers are highly toxic, so the researchers replaced these monomers with less toxic monomers like N-vinyl pyrolidone in VIPAR (N-Vinyl Pyrolidone ARgon gel) (Kipouros et al, 2001;Pappas et al, 1999) and poly (ethylene glycol) diacrylate in PABIG (Poly (ethylene glycol) diAcrylate, BIS, Gelatin) (Sandilos et al, 2004) gel. Even though these monomers are less toxic, all these gel dosimeters have to be prepared in the hypoxic condition.…”

Mechanical and dose delivery accuracy evaluation in radiosurgery using polymer gels

“…Both gel formulations exhibit comparable dose sensitivity and a wide linear dose‐response region extending up to about 40 Gy. ( 6 , 13 ) The VIPAR gel also features an increased dynamic dose range of dose response (up to about 250 Gy) at the expense, however, of dose resolution in the low‐dose region (13) …”

“…1, was derived for each of the manufactured gel batches using the $\mathrm{R}{2}_{\text{NET}}$ values of the corresponding brachytherapy irradiated samples (13) : $\begin{array}{l}left\mathrm{R}{2}_{\text{NET}}(\mathrm{D})=\text{aD}=(0.079\pm 0.006)\hspace{0.17em}\mathrm{D},r^2=0.994\hspace{0.17em}\text{for}\hspace{0.17em}\text{PABIG}\hspace{0.17em}\text{gels}\hfill \\ left{\text{R2}}_{\text{NET}}(\mathrm{D})=\text{aD}=(0.074\pm 0.004)\hspace{0.17em}\mathrm{D},r^2=0.994\hspace{0.17em}\text{for}\hspace{0.17em}\text{VIPAR}\hspace{0.17em}\text{gels}\hfill \end{array}$ …”

The effective atomic number of dosimetric gels

“…BANG (bisacrylamide nitrogen gelatine) has been commercialised with multiple formulations, such as BANG-1 33 that is made with powdered acrylamide and BANG-2 6, 36 that uses acrylic acid as a monomer with sodium hydroxide to alter the pH. Other gels of reduced toxicity exist, such as PABIG (polyethylene glycol diacrylate bis gelatine) 37 and VIPAR (N-vinyl pyrolidone argon gel) [38][39][40] . Fong et al developed a normoxic gel dosimeter, MAGIC (methacrylic acid, ascorbic acid in gelatine initiated by copper), which does not require an oxygen-free environment to be prepared 41 .…”