A novel approach for the adsorption of iodine-125 on silver wire as matrix for brachytherapy source for the treatment of eye and prostate cancer

Monte Carlo Study on Dose Distributions Around 192Ir, 169Yb, and 125I Brachytherapy Sources Using EGSnrc-based egs_brachy User-code

Introduction

As per the recommendations of the American Association of Physicists in Medicine Task Group 43, Monte Carlo (MC) investigators should reproduce previously published dose distributions whenever new features of the code are explored. The purpose of the present study is to benchmark the TG-43 dosimetric parameters calculated using the new MC user-code egs_brachy of EGSnrc code system for three different radionuclides 192Ir, 169Yb, and 125I which represent high-, intermediate-, and low-energy sources, respectively.

Materials and Methods

Brachytherapy sources investigated in this study are high-dose rate (HDR) 192Ir VariSource (Model VS2000), 169Yb HDR (Model 4140), and 125I -low-dose-rate (LDR) (Model OcuProsta). The TG-43 dosimetric parameters such as air-kerma strength, S k, dose rate constant, Λ, radial dose function, g(r) and anisotropy function, F(r,θ) and two-dimensional (2D) absorbed dose rate data (along-away table) are calculated in a cylindrical water phantom of mass density 0.998 g/cm3 using the MC code egs_brachy. Dimensions of phantom considered for 192Ir VS2000 and 169Yb sources are 80 cm diameter ×80 cm height, whereas for 125I OcuProsta source, 30 cm diameter ×30 cm height cylindrical water phantom is considered for MC calculations.

Results

The dosimetric parameters calculated using egs_brachy are compared against the values published in the literature. The calculated values of dose rate constants from this study agree with the published values within statistical uncertainties for all investigated sources. Good agreement is found between the egs_brachy calculated radial dose functions, g(r), anisotropy functions, and 2D dose rate data with the published values (within 2%) for the same phantom dimensions. For 192Ir VS2000 source, difference of about 28% is observed in g(r) value at 18 cm from the source which is due to differences in the phantom dimensions.

Conclusion

The study validates TG-43 dose parameters calculated using egs_brachy for 192Ir, 169Yb, and 125I brachytherapy sources with the values published in the literature.

Highly efficient method for production of radioactive silver seed cores for brachytherapy

A simple and highly efficient (shorter reaction time and almost no rework) method for production of iodine based radioactive silver seed cores for brachytherapy is described. The method allows almost quantitative deposition of iodine-131 on dozens of silver substrates at once, with even distribution of activity per core and insignificant amounts of liquid and solid radioactive wastes, allowing the fabrication of cheaper radioactive iodine seeds for brachytherapy.

Brachytherapy of intra ocular tumors using 'BARC I-125 Ocu-Prosta seeds': an Indian experience

Aim:

To report our experience of brachytherapy using ‘BARC I-125 Ocu-Prosta seeds’ for the management of intraocular tumors with regard to tumor control, globe preservation visual outcome, and patient survival at Sankara Nethralaya, Chennai, India between September 2003 and May 2011.

Materials and Methods:

We reviewed records of 35 eyes of 35 patients who underwent ophthalmic brachytherapy between September 2003 and May 2011. Twenty-one cases had choroidal melanoma, nine had childhood retinoblastoma, two had adult-onset retinoblastoma, and there were one case each of vasoproliferative tumor, retinal angioma, and ciliary body melanoma. Brachytherapy was administered using a 15- or 20-mm gold plaque with or without a notch. Brachytherapy was the primary treatment modality in all tumors other than retinoblastoma, wherein brachytherapy was done post chemoreduction for residual tumor.

Results:

For choroidal melanomas, the mean radiation dose was 68.69 ± 15.07 (range, 47.72-94.2) Gy. The eye salvage rate was 13/20 (65%) and tumor control rate was 16/20 (80%) at an average follow-up of 24.43 ± 24.75 (range, 1.5-87.98) months. For retinoblastoma, the mean dose was 45.85 ± 3.90 (range, 39.51-50.92) Gy. The eye salvage rate and tumor control rate was 5/6 (83.3%) at an average follow-up of 38.36 ± 31.33 (range, 4.14-97.78) months. All eyes with retinoblastoma needed additional focal therapy for tumor control and eye salvage.

Conclusion:

The results of this retrospective study confirms that the use of ‘BARC I-125 Ocu-Prosta seeds’ in episcleral plaques to treat intraocular tumors offers a viable option for the management of intraocular cancers.

Indigenous (125)I brachytherapy source for the management of intraocular melanomas in India

Episcleral plaque brachytherapy using (125)I seed is a viable option for the management of intraocular cancer with minimal invasiveness and surgical complications. This article describes the fabrication of (125)I seeds and initial experience on their use for the management of intraocular choroidal melanomas. The process of (125)I seed fabrication includes immobilization of (125)I into palladium-coated silver wires, its encapsulation in titanium capsules using Nd: YAG laser and quality control to assure safety. Plaque preparation consists of the assignment of seeds to slots on the plaque to achieve a desired dose rate distribution. The clinical study reported here includes the retrospective review of 9 eyes of 9 patients who underwent ophthalmic brachytherapy between May 2008 and June 2011. The average apical diameter before brachytherapy was 7.6 mm and the average largest basal diameter was 12.1 mm, which reduced to 3.3 and 7.2 mm, respectively, after the procedure at an average follow-up of 24 months. Patients in our studies experienced good local tumor control. The results of this study represent a significant step forward in the management of intraocular tumors in India.

Preparation of 57Co point sources for the performance evaluation of nuclear imaging instruments

This paper describes the utility of electrodeposition method to prepare (57)Co point sources. A description of the electrolytic cell, the process of (57)Co electrodeposition, encapsulation and quality control of the sealed (57)Co sources is presented. Sources containing ~3.7-4.81 MBq (0.10-0.13 mCi) of (57)Co were prepared, encapsulated in miniature titanium capsules and subjected to quality control tests to ensure compliance with regulatory requirements. The encapsulated (57)Co sources prepared by the reported procedure were found to be effective in routine performance evaluation of nuclear medicine instruments.

A novel and facile approach for the preparation of 133Ba source core, encapsulation and quality evaluation

This paper describes a facile and effective method to prepare 133Ba source exploiting the intrinsic properties of the anodized titanium to electro-deposit 133Ba from an aqueous solution. The process consists of anodization of Ti rod [4.8 mm (∅)  ×  10 mm (l)] to create a reactive surface to permit cathodic electrodeposition of 133Ba from an aqueous solution. The factors that influence the electrodeposition of 133Ba onto the anodized titanium substrate were identified and a careful control has been exercised to ensure optimum deposition of 133Ba activity onto the substrate. The morphology of the electrodeposited samples were examined by SEM and EDS analyses. Sources containing ∼ 3.7–11.1 MBq (0.1–0.3 mCi) 133Ba were prepared, encapsulated successfully in titanium capsules and subjected to quality control tests to ensure compliance with mandatory regulatory safety requirements.

Development of a 125I source for its application in bone densitometry

This paper describes a method for the preparation of (125)I sources for their use in bone densitometer. The process consists of preparation of silver pellets of size ∼2.5 mm (ϕ) × 0.6 mm (l) by 'Cold die compaction technique', palladium coating of the silver pellets, adsorption of (125)I on the palladium coated silver pellets and encapsulation source matrix in a titanium capsule [ 3 mm (ϕ) × 10 mm(l)] using Nd:YAG laser. The texture and morphology of the source matrix were examined by SEM and EDS analyses. Encapsulated sources containing (125)I activity up to ∼1.85 GBq (50 mCi) were prepared. Quality control tests that were necessary before application were performed and gave satisfactory results.

Development of a (147)Pm source for beta-backscatter thickness gauge applications

This paper describes a method for the preparation of (147)Pm sources, utilized in the determination of graphite coating thickness on the inner surface of the zircaloy cladding tube of nuclear fuels. (147)Pm was adsorbed on a limited surface area [1.5mm (ϕ)×2mm (l)] of a cylindrical aluminum rod [1.5mm (ϕ)×10mm (l)]. In brief, the selected tip area [1.5mm (ϕ)×2mm (l)] was anodized at a current density of 15mA/cm(2) at 15°C in 3M·H(2)SO(4) for 2h followed by immersion of this area in 10μL of (147)Pm solution containing 37MBq (1mCi) of activity at pH 6.0 for 24h. The radioactive area was subsequently covered with a thin layer of Polymethyl Methacrylate (PMMA) to prevent leaching of (147)Pm from the source. The quantity of incorporated (147)Pm activity was assayed in a calibrated ion chamber. Quality control tests were carried out to ensure nonleachability, uniform distribution of activity and stability of the sources.

Development of a spherical (125)i-brachytherapy seed for its application in the treatment of eye and prostate cancer

Palladium-coated silver beads of 0.5 mm (phi) were used to adsorb (125)I, encapsulated inside a titanium capsule by an Nd:YAG laser, for use as a brachytherapy source. Experimental conditions, such as feed activity, carrier concentration, and reaction time, were optimized for the maximum adsorption of (125)I. Uniform distribution of radioactivity on the source core was ascertained by the autoradiography technique. Leachability of (125)I was found to be <0.01%. The dose-rate constant of the new source was estimated to be 1.045 cGyh(-1)U(-1). This newly developed source could be an alternative to other (125)I sources.

Studies on the production and quality assurance of miniature 125I radioactive sources suitable for treatment of ocular and prostate cancers

(125)I sources were prepared by adsorption of (125)I on palladium-coated silver wires. The effect of reducing agent on percentage adsorption of (125)I was studied and the amount of adsorbed activity on source core was studied by repeated adsorption cycles. The activity per source in the sources produced from the same batch varied with coefficient of variation (i.e. the ratio of standard deviation to mean multiplied by 100) less than 10%. The unencapsulated source exhibited low leachability (< 0.01%). The laser parameters were optimized to obtain quality welds with negligible leak rate. The sources were laser-encapsulated in titanium capsules of 0.8 mm (OD) x 4.5mm (l). The release of radioactivity from encapsulated sources in an immersion test at 50 degrees C for 5 h was <5 nCi (185 Bq). The surface contamination on the sealed capsules was found to be<0.05 nCi or 1.85 Bq per source. The sources were used in the treatment of a child having retinoblastoma.

Regional Radiochemotherapy Using In Situ Hydrogel

PURPOSE

To evaluate the feasibility of regional radiochemotherapy of mammary tumors using in situ hydrogel loaded with cisplatin (CDDP) and rhenium-188 ((188)Re).

METHODS

Sodium alginate (SA) and calcium chloride were used to create a hydrogel for delivery of CDDP and (188)Re. In vitro studies were performed to evaluate cytotoxic effects of (188)Re-hydrogel and sustained-release ability of the CDDP-hydrogel. Tumor-bearing rats were injected with (188)Re-hydrogel (0.5-1 mCi/rat), (188)Re-perrhenate (0.5-1 mCi/rat, intratumoral, I.T.), CDDP-hydrogel (3 mg/kg), and (188)Re-hydrogel loaded with CDDP (3 mg/kg body weight, 0.5-1 mCi/rat), respectively, and groups receiving (188)Re were imaged at 24 and 48 h postinjection. Tumor volume, body weight, imaging, and kidney function were assessed as required for each group.

RESULTS

Successful formation of the hydrogel was demonstrated by cytotoxic effects of (188)Re-hydrogel and slow release of CDDP-hydrogel in vitro. Tumor volume measurements showed significant delay in tumor growth in treated vs. control groups with minimal variation in normal kidney function for the CDDP-hydrogel group. Scintigraphic images indicated localization of (188)Re-hydrogel in the tumor site up to 48 h postinjection.

CONCLUSIONS

Our data demonstrate the feasibility of using hydrogel for delivery of chemotherapeutics and radiation locally. This technique may have applications involving other contrast modalities as well as treatment in cases where tumors are inoperable.

Comparison of methods for preparation of 125I brachytherapy source cores for the treatment of eye cancer

Two procedures for fixing the 125I activity on different matrices were explored. In the first method, anodic deposition of 125I on silver wire was used. In the second, 125I was adsorbed as iodate (IO3-) on alumina microspheres by using a solid-solution interface technique. While the 125I uptake was approximately 84% on the silver wires by electrodeposition method, the microspheres showed approximately 97% by the solid-solution interface technique. The low leachable (0.05%) wires, and comparatively high leachable (approximately 4%) spheres were trial encapsulated and laser welded. The encapsulated sources were measured for source strength and were found to be suitable for the treatment of eye cancer.