Evaluation of a Proposed Biodegradable 188Re Source for Brachytherapy Application

This study aimed to evaluate dosimetric characteristics based on Monte Carlo (MC) simulations for a proposed beta emitter bioglass Re seed for internal radiotherapy applications. The bioactive glass seed has been developed using the sol-gel technique. The simulations were performed for the seed using MC radiation transport code to investigate the dosimetric factors recommended by the AAPM Task Group 60 (TG-60). Dose distributions due to the beta and photon radiation were predicted at different radial distances surrounding the source. The dose rate in water at the reference point was calculated to be 7.43 0.5 cGy/ h/mCi. The dosimetric factors consisting of the reference point dose rate, D(r0,u0), the radial dose function, g(r), the 2-dimensional anisotropy function, F(r,u), the 1-dimensional anisotropy function, fanðrÞ, and the R90 quantity were estimated and compared with several available betaemitting sources. The element Re incorporated in bioactive glasses produced by the sol-gel technique provides a suitable solution for producing new materials for seed implants applied to brachytherapy applications in prostate and liver cancers treatment. Dose distribution of Re seed was greater isotropic than other commercially attainable encapsulated seeds, since it has no end weld to attenuate radiation. The beta radiation-emitting Re source provides high doses of local radiation to the tumor tissue and the short range of the beta ejad, PhD, and S. Hamed Hosseini, PhD Abbreviations: HCC = hepatocellular carcinoma, MCNP = Monte Carlo N-Particle. INTRODUCTION O ver the last few decades, worldwide interest in the treatment of cancer has continually increased. Liver cancer is the sixth most common cancer worldwide. An estimated 30,640 new cases of liver cancer were expected to occur in the United States during 2013. More than 80% of these cases were rapid-growing hepatocellular carcinoma (HCC) tumors. The prognosis of HCC remains extremely poor, and a curative treatment (liver transplantation, surgical resection, and radiofrequency ablation) can only be carried out in approximately 25% to 30% of cases. Although surgery (hepatectomy or liver transplantation) is the main form of curative treatment, the majority of patients are not eligible for surgery due to extent of tumor and dysfunction of liver. Radiotherapy is a method of cancer treatment in which radiation is used to destroy a tumor, or, at least, to hinder its growth. The use of conventional external beam radiation therapy in HCC treatment has been limited by the low radiation tolerance of the cirrhotic liver that often resulted in radiation-induced liver disease (RILD). Internal radioisotope therapy is another technique that has been developed and used for the treatment of HCC. A variety of radioisotopes, such as Iodine-131, Yttrium-90, Rhenium-188, Holmium-166 etc, are applied for this purpose. Brachytherapy is a type of internal radiotherapy that places solid radioactive sources in or adjacent to target tissues. In this study, a beta-emitting Re biodegradable glass seed is proposed for the brachytherapy treatment of small hepatocellular carcinomas. Diverse photonor electron-emitting radioactive isotopes have been utilized or suggested for use over brachytherapy. Beta emitter radionuclides such as P, Re, and Sr/Y are the most commonly used sources in intravascular brachytherapy. The general properties of some beta emitter radionuclides with therapeutic potential are demonstrated in Table 1. Re (17 h half-life, 84% beta with 2.12 MeV maximum energy, and 16% gamma 155 keV) is of current interest for the variety of therapeutic applications. It has a gamma-line at 155 keV (16%) allowing imaging at the normal Tc-99m settings of a gamma-camera. The beta emissions of Re have a sufficient penetration over a maximum range of 10.8 mm for the tumor ablation, involving pericapsular lesions, while avoiding damage to adjacent nontumorous tissue. Due to its high energy and short physical half-life, Re offers the possibility of higher energy deposition in a shorter time period relative to radionuclides with longer half-lives. Re has been used with glass microspheres, human serum albumin microspheres, poly (L-lactide) micros embolic platforms. ctive and biocompatible materials and e been developed in medicine for more www.md-journal.com | 1 T A B L E 1 . S ev e ra lB et a E m it te r R ad io n u cl id e s W it h T h e ra p e u ti c P o te n ti al fo r B ra ch yt h e ra p y (L ef t) ;C o m p a ri so n o ft h e M o n te C a rl o C al cu la te d D o se R a te (c G y/ h /m C i) A m o u n ts o f th e 1 4 2 P r G la ss S o u rc e W it h th e P u b lis h e d D at a (M id d le ); C o m p ar is o n o ft h e M o n te C ar lo C al cu la te d R ad ia lD o se Fu n ct io n o ft h e 1 4 2 P r G la ss S o u rc e W it h th e P u b lis h e d D a ta (R ig h t)