Feasibility study of FLUKA Monte Carlo simulation for a beta-emitting brachytherapy source: dosimetric parameters of 142Pr glass seed

Surface dose rate variations in planar and curved geometries of 106Ru/106Rh plaque sources for ocular tumors

PURPOSE

Investigation of surface dose rate variation with respect to the source configuration of ¹⁰⁶Ru/¹⁰⁶Rh eye plaque. To explore an alternate way to determine activity of brachytherapy plaques.

METHODS

The surface dose rates of ¹⁰⁶Ru/¹⁰⁶Rh plaque developed indigenously were measured by extrapolation chamber. To rule out possibility of any error in the activity distribution and quantity, same source was used in two different configurations namely planar and curved. EBT3 Gafchromic film was used for determination of uniformity in activity. Monte Carlo-based Codes EGSnrc and FLUKA were used to calculate dose rate in tissue, percentage depth dose and for determination of activity. Parameters and correction factors were estimated using simulations.

RESULTS

The measured reference absorbed dose rates for planar and curved ¹⁰⁶Ru/¹⁰⁶Rh eye plaques are found to be 589 ± 29 mGy/h and 560 ± 28 mGy/h, respectively. The difference in the reference absorbed dose rate of curved eye plaque is about ~5% as compared to planar configuration. The FLUKA-calculated dose values are almost independent of cavity length of the extrapolation chamber for both eye plaques. The FLUKA-based dose rates per μCi ¹⁰⁶Ru/¹⁰⁶Rh are about 17.28 ± 0.08 mGy/h and 16.48 ± 0.06 mGy/h, respectively for planar and curved eye plaques which match well with the measurements. The calculated activities for planar and curved eye plaques are 34.08 μCi and 33.98 μCi, respectively.

CONCLUSIONS

Surface dose rates for a prototype ¹⁰⁶Ru/¹⁰⁶Rh eye plaque with different configurations were estimated using simulations and measured experimentally. An alternate way to determine activity of beta-gamma brachytherapy plaque has been proposed.

Evaluation of influential correction factors applicable for absolute beta dosimetry of 85Kr, 90Sr-90Y and 106Ru-106Rh beta emitters

Extrapolation ionization chamber is normally used for absolute measurement of absorbed dose to tissue and in standardization of beta particle emitting sources in particular. However, in this technique, several correction factors are applied to the measured ionization current to evaluate the true value of the dose to the tissue from beta radiation. These correction factors are described in ISO 6980-2:2004. Out of these, ion recombination correction factor (k_sat) and ambient air density correction factor (k_ad) are evaluated experimentally during measurement of ionization current. Other significant correction factors are backscatter correction factor (k_ba), correction factor for perturbation in electron spectrum due to ionization chamber side wall scatter (k_pe), correction factor for difference in attenuation of beta spectrum due to change in ambience condition (k_abs) and correction factor for radial non-uniformity of dose inside detector volume (k_ra). Experimental evaluation of correction factors k_ba, k_pe and k_abs are not easily achievable. In the present work four significant correction factors k_ba, k_pe, k_abs and k_ra are derived theoretically by Monte Carlo particle transport simulation. These correction factors are evaluated for beta emission spectrum of ⁸⁵Kr, ⁹⁰Sr-⁹⁰Y and ¹⁰⁶Ru-¹⁰⁶Rh radioactive sources.