Monte Carlo-based dosimetry of proposed bi-radionuclide (125I and 106Ru/106Rh) eye plaque: A feasibility study.

BACKGROUND: Combining the sharp dose fall off feature of beta-emitting 106Ru/106Rh radionuclide with larger penetration depth feature of photon-emitting125I radionuclide in a bi-radionuclide plaque, prescribed dose to the tumor apex can be delivered while maintaining the tumor dose uniformity and sparing the organs at risk. The potential advantages of bi-radionuclide plaque could be of interest in context of ocular brachytherapy. PURPOSE: The aim of the study is to evaluate the dosimetric advantages of a proposed bi-radionuclide plaque for two different designs, consisting of indigenous 125I seeds and 106Ru/106Rh plaque, using Monte Carlo technique. The study also explores the influence of other commercial 125I seed models and presence or absence of silastic/acrylic seed carrier on the calculated dose distributions. The study further included the calculation of depth dose distributions for the bi-radionuclide eye plaque for which experimental data are available. METHODS: The proposed bi-radionuclide plaque consists of a 1.2-mm-thick silver (Ag) spherical shell with radius of curvature of 12.5 mm, 20 µm-thick-106Ru/106Rh encapsulated between 0.2 mm Ag disk, and a 0.1-mm-thick Ag window, and water-equivalent gel containing 12 symmetrically arranged 125I seeds. Two bi-radionuclide plaque models investigated in the present study are designated as Design I and Design II. In Design I, 125I seeds are placed on the top of the plaque, while in Design II 106Ru/106Rh source is positioned on the top of the plaque. In Monte Carlo calculations, the plaque is positioned in a spherical water phantom of 30 cm diameter. RESULTS: The proposed bi-radionuclide eye plaque demonstrated superior dose distributions as compared to 125I or 106Ru plaque for tumor thicknesses ranges from 5 to 10 mm. Amongst the designs, dose at a given voxel for Design I is higher as compared to the corresponding voxel dose for Design II. This difference is attributed to the higher degree of attenuation of 125I photons in Ag as compared to beta particles. Influence of different 125I seed models on the normalized lateral dose profiles of Design I (in the absence of carrier) is negligible and within 5% on the central axis depth dose distribution as compared to the corresponding values of the plaque that has indigenous 125I seeds. In the presence of a silastic/acrylic seed carrier, the normalized central axis dose distributions of Design I are smaller by 3%-12% as compared to the corresponding values in the absence of a seed carrier. For the published bi-radionuclide plaque model, good agreement is observed between the Monte Carlo-calculated and published measured depth dose distributions for clinically relevant depths. CONCLUSION: Regardless of the type of 125I seed model utilized and whether silastic/acrylic seed carrier is present or not, Design I bi-radionuclide plaque offers superior dose distributions in terms of tumor dose uniformity, rapid dose fall off and lesser dose to nearby critical organs at risk over the Design II plaque. This shows that Design I bi-radionuclide plaque could be a promising alternative to 125I plaque for treatment of tumor sizes in the range 5 to 10 mm.

An electrochemical technique for fabrication of Mn-54 sources towards characterization of gamma counting nuclear instruments.

Long lived sealed radioactive sources are used for the energy calibration and efficiency determination of counting systems used in the nuclear sector. Using a sulphate bath, a facile electrochemical method was developed by electrodeposition of 54Mn on 5 mm (φ) stainless steel substrates for the preparation of 54Mn sources for such uses. Inactive sources prepared under suitable experimental parameters characterized by XRD revealed that manganese is deposited in oxide form. SEM and EDS analyses of electrodeposited surfaces confirmed uniform distribution of elements and the absence of fractures, flaws, and spatial variations. Cyclic voltammetry (CV) scans provided information about the electrochemical processes involved in the deposition process. Uniform distribution of radioactivity on surface of source was ascertained by autoradiography. Swipe tests of the encapsulated sources confirmed negligible removable surface contamination. The 54Mn sources containing up to 185KBq of 54Mn on stainless steel discs were prepared. These sources along with other longer lived sources were supplied to various users as a package of radiation sources for characterization of gamma counting systems over a wide energy range.

Fabrication of miniature 141Ce sources by chemical deposition towards possible use in the performance evaluation of gamma cameras - A feasibility study.

141Ce sources were fabricated for quality assurance of gamma cameras. The fabrication process consisted of electro-deposition of Ni on a Cu sphere in 0.01 N H2SO4 containing 30 mg/mL H3BO3 and 50 µg of NiSO4·7H2O at pH 2-3 followed by deposition of 141Ce on it. > 95% deposition of 141Ce on substrate could be achieved at pH 5. Source core was loaded in custom-made Al holder. Autoradiography confirmed uniform activity distribution. SEM and EDS analyses confirmed deposition of Cerium on substrate.

Utilization of Chemical Deposition Technique for Preparation of Miniature 170Tm Sources and Preliminary Quality Assessment for Potential Use in Brachytherapy.

OBJECTIVE: This article describes the preparation of a 170Tm source by chemical deposition technique, its encapsulation in a titanium holder, and preliminary quality evaluation for potential utility as a brachytherapy source. METHODS: The procedure consisted of electrodeposition of Ni on a Cu wire followed by chemical deposition of 170Tm on it. Influence of feed solution pH, carrier Tm concentration, and reaction time were studied for optimum deposition of 170Tm on substrate. After sealing the source core in a titanium capsule, quality control tests were performed. Distribution of 170Tm on substrate was evaluated by autoradiography. Inactive Tm source was characterized by scanning electron microscope (SEM) and energy-dispersive X-ray (EDS) analyses. RESULTS: Under optimized conditions (pH 5, 10 µg Tm carrier, 5 h), 170Tm source core could be prepared by deposition of >95% of 170Tm radioactivity on substrate. Swipe tests and immersion tests on encapsulated sources confirmed that removable radioactivity and radioactivity leakage levels were within stipulated limits. Autoradiography of 170Tm source confirmed uniformity of radioactivity distribution. While SEM analysis confirmed good adhesion of Tm on substrate, EDS analysis confirmed elemental constituents of the Tm-deposited substrate. CONCLUSION: The objective of preparing a 170Tm source by chemical deposition for potential brachytherapy applications could be successfully achieved.

Preparation of Radioactive Skin Patches Using Polyhydroxamic Acid-Grafted Cellulose Films Toward Applications in Treatment of Superficial Tumors.

The primary objective of this investigation is the development of a strategy for the synthesis of polyhydroxamic acid (PHA)-grafted cellulose film, its characterization, and evaluation of its usefulness for the preparation of 177Lu skin patches for superficial brachytherapy applications. PHA-grafted cellulose films were synthesized and characterized by Fourier transformed infrared spectrometer analysis and visual color test with Fe(III) solution. Uptake of 177Lu on the PHA-grafted cellulose was investigated by varying the experimental conditions such as the pH of feed solution, amount of nonradioactive Lu carrier, time, and temperature of the reaction. Under the optimized conditions, >95% loading of 177Lu on the PHA-cellulose film could be achieved. Autoradiography studies of 177Lu-PHA-cellulose film confirmed the uniform distribution of 177Lu on the surface. Energy dispersive X-ray analysis of nonradioactive Lu-PHA-cellulose film confirmed the loading of Lu on PHA-cellulose film. The utility of PHA-functionalized cellulose films for the fabrication of radioactive sources for superficial brachytherapy applications could be successfully demonstrated.

A Novel 141Ce-Based Flood Field Phantom: Assessment of Suitability for Daily Uniformity Testing in a Clinical Nuclear Medicine Department.

Daily quality control testing of a γ-camera is of the utmost importance in assessing whether the camera is suitable for clinical use. The aim of our study was to assess the suitability of a fillable 141Ce-based flood field phantom developed in-house for daily quality control testing of γ-cameras. Methods: Daily uniformity testing was performed for 113 d using the fillable 141Ce phantom and a commercially available sheet-type 57Co phantom, and the results were compared. Results: The average integral uniformity obtained by the 141Ce and 57Co phantoms was 3.24% and 2.72%, respectively, for detector 1 and 3.31% and 2.78%, respectively, for detector 2. Conclusion: The 141Ce phantom we developed is a suitable alternative to the commercially available 57Co phantom.

Development of a phantom and assessment of (141)Ce as a surrogate radionuclide for flood field uniformity testing of gamma cameras.

This paper describes an indigenous method for development and deployment of rechargeable liquid filled phantom with newly proposed radionuclide (141)Ce for determination of extrinsic uniformity of gamma cameras. Details about design of phantom, neutron irradiation of cerium targets, chemical processing of (141)Ce, charging of phantom with (141)Ce solution and their performance evaluation are presented. Suitability of (141)Ce in quality assurance of gamma cameras used in in-vivo diagnostic imaging procedures has been amply demonstrated.

Determination of surface dose rate of indigenous (32)P patch brachytherapy source by experimental and Monte Carlo methods.

Isotope production and Application Division of Bhabha Atomic Research Center developed (32)P patch sources for treatment of superficial tumors. Surface dose rate of a newly developed (32)P patch source of nominal diameter 25 mm was measured experimentally using standard extrapolation ionization chamber and Gafchromic EBT film. Monte Carlo model of the (32)P patch source along with the extrapolation chamber was also developed to estimate the surface dose rates from these sources. The surface dose rates to tissue (cGy/min) measured using extrapolation chamber and radiochromic films are 82.03±4.18 (k=2) and 79.13±2.53 (k=2) respectively. The two values of the surface dose rates measured using the two independent experimental methods are in good agreement to each other within a variation of 3.5%. The surface dose rate to tissue (cGy/min) estimated using the MCNP Monte Carlo code works out to be 77.78±1.16 (k=2). The maximum deviation between the surface dose rates to tissue obtained by Monte Carlo and the extrapolation chamber method is 5.2% whereas the difference between the surface dose rates obtained by radiochromic film measurement and the Monte Carlo simulation is 1.7%. The three values of the surface dose rates of the (32)P patch source obtained by three independent methods are in good agreement to one another within the uncertainties associated with their measurements and calculation. This work has demonstrated that MCNP based electron transport simulations are accurate enough for determining the dosimetry parameters of the indigenously developed (32)P patch sources for contact brachytherapy applications.

Studies on the development of ¹69Yb-brachytherapy seeds: New generation brachytherapy sources for the management of cancer.

This paper describes development of (169)Yb-seeds by encapsulating 0.6-0.65 mm (ϕ) sized (169)Yb2O3 microspheres in titanium capsules. Microspheres synthesized by a sol-gel route were characterized by XRD, SEM/EDS and ICP-AES. Optimization of neutron irradiation was accomplished and (169)Yb-seeds up to 74 MBq of (169)Yb could be produced from natural Yb2O3 microspheres, which have the potential for use in prostate brachytherapy. A protocol to prepare (169)Yb-brachytherapy sources (2.96-3.7 TBq of (169)Yb) with the use of enriched targets was also formulated.

On the application of Nafion membrane for the preparation of (90)Y skin patches, quality control, and biological evaluation for treatment of superficial tumors.

This article describes the preparation, quality control, and biological evaluation of (90)Y-skin patches based on Nafion(®) membrane as a viable treatment modality for superficial skin tumors such as melanoma. To arrive at the conditions for optimum uptake of (90)Y on the membrane, influence of various experimental parameters, such as pH of the feed solution, inactive yttrium carrier concentration, reaction volume, contact time, and temperature, was systematically investigated. Under the optimized conditions, >95% of the (90)Y activity (37-185 MBq) could be incorporated in the Nafion membranes to prepare (90)Y-skin patches. Quality control tests were carried out to ensure nonleachability, uniform distribution of activity, and stability of the (90)Y-patches. Mice bearing transplanted melanoma tumors that were treated with two doses of 74 MBq (90)Y-Nafion membrane sources showed complete tumor regression. Histopathological examination of the treated area showed absence of tumor. The results of the study indicate the potential of (90)Y-Nafion membrane sources for treatment of superficial skin tumors.

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.

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.

Nafion-zirconium phosphate composite membrane: a new approach to prepare (32)P patches for superficial brachytherapy applications.

This article describes a method for the preparation of (32)P patch for the treatment of skin cancer. It is based on the surface modification of a Nafion film by treatment with ZrOCl(2) solution, impregnation of a predicted quantity of (32)P into the film, and its subsequent immobilization into a nonleachable matrix by lamination. The effect of variations of critical parameters on the incorporation of (32)P into the membrane, such as solution pH, contact time, reaction volume, inactive carrier concentration of the feed, reaction temperature, and so on, was investigated to arrive at the conditions resulting in optimum retention of (32)P activity. The morphology of the membrane was evaluated by scanning electron microscope and energy dispersive spectral analyses. Quality control tests were carried out to ensure nonleachability, uniform distribution of activity, and stability of the patches.

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.

A facile, viable approach toward the preparation of 32p patches for the treatment of skin cancer.

A facile, viable, "green" two-step, inexpensive technique was developed for the preparation of (32)P patch for the treatment of skin cancer. This technique consists of impregnation of H(3)(32)PO(4) solution into an inert solid carrier followed by immobilization into a nonleachable matrix by lamination. The morphology of the impregnated paper was evaluated by scanning electron microscope and energy-dispersive spectral analyses. Radioactive patches containing up to ∼37 MBq/cm(2) of (32)P could be prepared. Distribution of (32)P on sources was uniform and release of (32)P from the sealed source in water and saline was found to be well within the permissible levels of 185 Bq. Custom-shaped (32)P-patches after quality assurance were supplied to AIIMS, New Delhi, for clinical evaluation. (32)P-impregnated paper protected by a laminated film holds promise for treatment of superficial cancers.

A novel approach to prepare (90)Y-EGMP patches for superficial brachytherapy.

A novel method to prepare (90)Y-EGMP patches has been developed for brachytherapy applications.EGMP films of 1cmx1cm size, incorporating approximately 185MBq of (90)Y were prepared and sealed between thin plastic sheets with uniform distribution of (90)Y. The leachability of (90)Y from radioactive patches was less than 0.01%. There was no leakage of radioactivity from radioactive patches, when tested in water or saline. The studies related to establish therapeutic efficacy of these patches are warranted.

Development of a new design (125)I-brachytherapy seed for its application in the treatment of eye and prostate cancer.

Palladium coated silver beads of 0.5mm (slashed circle) were used to adsorb (125)I and encapsulated inside a titanium capsule by Nd:YAG laser, for use as a brachytherapy source. Experimental conditions were optimized for maximum adsorption of (125)I and uniformity of radioactivity was ascertained. Leachability of (125)I was found to be<0.01%. The dose rate constant of the new source was estimated to be 1.045cGyh(-1)U(-1). This newly developed source could be an alternative to other (125)I 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.

Bioevaluation studies of 32P incorporated mould brachytherapy sources for potential application in treatment of superficial tumors.

AIM: To prepare 32P-based user-friendly mould brachytherpy sources for the treatment of superficial tumors. METHODS: 32P as orthophosphoric acid was adsorbed on 15-25 mm (diameter) circular sheets of cellulose-based adsorbent paper to prepare sources containing approximately 37-74 MBq of 32P per cm of strip. The sources were immobilized between plastic sheets of 40 microm thickness. Autoradiography studies were carried out to determine the uniformity of 32P deposition in the source. Dosimetric evaluation of the sources was also carried out. Bioevaluation studies were carried out in C57BL6 mice bearing melanoma using 37-74 MBq sources. RESULTS: Cellulose-based sources containing 37-74 MBq of 32P per cm2 could be prepared from which no radioactivity leakage could be detected in water or saline. Autoradiography studies revealed 32P to be uniformly distributed in these sources. Dosimetric evaluation showed that the contact dose imparted was 10 Gy/h, sufficient for treatment of superficial tumors. In mice bearing melanoma, complete tumor regression could be achieved with two applications of 37-74 MBq sources, at an interval of 3 days. Histopathological examination of the skin tissue from the treated area proved the absence of tumor as compared with the controls. CONCLUSION: Preparation of P sources of various shapes and sizes (based on the tumor size) having uniform 32P activity distribution could be achieved. Efficacy of these sources in treating melanoma tumors could be established in the animal model.