RESUMEN
This work evaluates experimentally the dose enhancement factor (DEF) and dose sparing factor (DSF) due to radiation self-shielding, produced by Gd infused in tumor phantom irradiated with brachytherapy HDR 192Ir source by Gafchromic EBT3 dosimeter. The phantom was made of a set of solid water slabs (30 × 30 × 1.0) cm3 and three acrylic slabs of (30 × 30 × 0.5) cm3 machined to contain in the central axis acrylics vials of (1 × 1 × 5) cm3. The first and second acrylic vials were filled with an identical Gd solution of 0, 10 and 20 mg/ml, simulating Gd-doped and undoped tumor, and the third vial was filled in all the measurement only with water, representing an organ at risk. Additional solid water slabs were used to complete a phantom of (30 × 30 × 16) cm3. In the phantom center an acrylic slab was machined to introduce the 2.5 mm flexible guide tube of GammaMed plus iX equipment and positioning the 192Ir source in the phantom central part. EBT3 fragments of (0.9 × 4) cm2 were placed on the inner edge of the second and third vials to measure dose enhancement and dose sparing simultaneously. Phantom CT images were acquired for planning and to prescribe a dose of 6.0 Gy at 2.0 cm of the source, achieving an isodose curve of 44.5% at 3.0 cm (positions of the EBT3 films). Additionally, Monte Carlo simulation of the identical experimental setup was implemented to compare measurement values. The results showed the feasibility of measuring a DEF of 1.15 ± 0.05 in 20 mg/ml of Gd concentration consistent with the Monte Carlo DEF of 1.112 ± 0.005 for the same concentration. DEF value for concentration of 10 mg/ml would not be detected (1.00 ± 0.04) by an expected under measurement of the EBT3 films associated with the non-detection of photoelectrons and Auger electrons of very low energy that cannot reach the radiosensitive substrate.
Asunto(s)
Braquiterapia/métodos , Gadolinio/análisis , Radioisótopos de Iridio/administración & dosificación , Neoplasias/radioterapia , Dosímetros de Radiación , Simulación por Computador , Humanos , Fantasmas de Imagen , Dosificación RadioterapéuticaRESUMEN
In this work, the benefits in terms of dose enhancement and dose sparing via radiation shielding are evaluated, for a combined irradiation scheme with sources of 241Am and tumor-infused with Gd agents, regarding conventional 192Ir treatment. Monte Carlo simulations using PENELOPE code were implemented for endocavitary brachytherapy geometries, configuring a pelvis phantom of 15 cm radius and 30 cm length. Inside, it was defined cylindrical tumor phantoms of 2 cm radius and 4 cm-6 cm length (simulating initial stages) as well as tumors of extensive volume (2.5 and 3.0 cm radius) and difficult coverage. Tumor phantoms were doped with 68 mM and 138 mM of Gd in order to assess the effects of enhancement and protection based on the concentration and emission energy of the isotope. Obtained results for the first tumor group, shown the feasibility of achieving dose enhancements of 94.3%-117% and 160%-194% for 68 mM and 138 mM of Gd infused into the tumor and irradiation with 241Am, respectively. Similarly, reduced dose enhancements of 3.5-5.7% y 8.9%-11.2% for 68 mM and 138 mM of Gd are attained with 192Ir. In terms of dose sparing outer the tumor, the radiation shielding and dose enhancement allowed a higher reduction in the dose by 241Am of 17%-24% for 68 mM and 21%-32% for 138 mM of Gd, and non-negligible dose sparing are produced too by 192Ir of 2% and 5% for the same concentration of Gd. For the second tumors group, the combined use of 241Am and Gd agents simultaneously allowed to improve coverage and reduce the healthy tissue dose, showing the obtained results the possibility of achieving coverage of 95% of the prescribed dose in 100% of tumor volume together with dose sparing factor of 6-21% reduction in isodose of the studied point and dose enhancements of 75%-158% at the prescription point.
Asunto(s)
Americio/administración & dosificación , Braquiterapia/métodos , Gadolinio/administración & dosificación , Neoplasias/radioterapia , Dosificación Radioterapéutica , Humanos , Método de Montecarlo , Fantasmas de ImagenRESUMEN
This work reports the experimental development of an integral Gd-infused dosimeter suitable for Gd dose enhancement assessment along with Monte Carlo simulations applied to determine the dose enhancement by radioactive and X-ray sources of interest in conventional and electronic brachytherapy. In this context, capability to elaborate a stable and reliable Gd-infused dosimeter was the first goal aimed at direct and accurate measurements of dose enhancement due to Gd presence. Dose-response was characterized for standard and Gd-infused PAGAT polymer gel dosimeters by means of optical transmission/absorbance. The developed Gd-infused PAGAT dosimeters demonstrated to be stable presenting similar dose-response as standard PAGAT within a linear trend up to 13â¯Gy along with good post-irradiation readout stability verified at 24 and 48â¯h. Additionally, dose enhancement was evaluated for Gd-infused PAGAT dosimeters by means of Monte Carlo (PENELOPE) simulations considering scenarios for isotopic and X-ray generator sources. The obtained results demonstrated the feasibility of obtaining a maximum enhancement around of (14⯱â¯1)% for 192Ir source and an average enhancement of (70⯱â¯13)% for 241Am. However, dose enhancement up to (267⯱â¯18)% may be achieved if suitable filtering is added to the 241Am source. On the other hand, optimized X-ray spectra may attain dose enhancements up to (253⯱â¯22) %, which constitutes a promising future alternative for replacing radioactive sources by implementing electronic brachytherapy achieving high dose levels.