Introduction: Radioiodinated iodo deoxyuridine (IUdR) is a novel,cycle-specific agent that has potential for the treatment of residual malignant glioma after surgery. Because this thymidine analogue kills only roliferating cells. However, maligment cells which are not synthesizing DNA during exposure to the radio pharmaceutical will be spared. To determine whether tumour incroporation [125 I]IUdR could be enhanced by protracted administration we employed three different delivery methods such as single injection, polymer implant and using osmotic pump in an in vivo study in compare with an in vitro study using multicellular glioma spheroids of a range of sizes and incubation times. Methods and Materials: We used a C6 cell line, growing in the brains of Wistar rats, as a glioma model and compared biodistribution of radiopharmaceutical in glioma cells by using autoraiogarphy method. Autoradiogarphy technique also used to discribe means of [125 I]IUdR incorporation at different times and depths within UVW multicellular glioma spheroids of a range of sizes. Results: Twenty-four hours after administration of drug, autoradiography of brain section demonstrated nuclear uptake of the radiopharmaceutical in cells throughout tumour while normal brain cells remained free of radioactivity. The [125 I]IUdR labelling indices (%±s.e.m.) achieved were 6.2 (0.4) by single injection, 22.5 (4.1) using a sustained release polymer implant (poly lactide-co-glycolide) and 34.3 (2.0) mini-osmotic pump. The results of the spheroids study confirm that incorporation of [125 I]IUdR decreased markedly with increasing size of spheroid. The distribution of IUdR was uniform throught small spheroids (<200μm), while the concentration of IUdR occurred predominantly in the peripheral cells of larger spheroids. The IUdR uptake enhancement occurred by increasing the incubation time from 52 hours to 104 hours i.e. one or two multiples of the initial volume doubling time. Cunclusion: The results obtained from in vitro and in vivo studies emphasize the need for a sustained delivery system as a prerequisite for effective treatment. Thses findings are also encouraging for the development of a sustained release for radiolabelled IUdR for use in the treatment of intracranial tumours, particularly in the immediate postoperative setting.  

Radioactive stents loaded with I-125 seeds have been widely used for the treatment of advanced esophageal cancer. Understanding the dose distribution of such stents before the clinical use is essential. This study provides a dosimetric investigation of I-125 seed-loaded stents based on the seed’ s arrangement and activity. A cylindrical water equivalent phantom with an esophageal stent loaded with I-125 seeds, were employed. The seeds arrangements were determined based on the distance between the centers of two adjacent seeds (z) along the stent length. EBT3 fi lms as well as Geant4 Monte Carlo toolkit were used to obtain the dose distribution around the stent. By modeling the MIRD phantom, the dose delivered to the related organs at risk was calculated. The appropriate dose distribution is achieved for z = 15 mm, in which the absorbed dose at a depth of 5 mm reaches about 45% of the absorbed dose near the stent surface, thereby the therapeutic dose is delivered to the reference points. Both arrangements (z = 15 and 20 mm) seemed to be clinically eligible and their utilization depends on the patient and the hospital facilities. Using esophageal stents with z > 20 mm is not recommended due to the presence of cold spots in the dose distribution.

Low energy I-125- seeds are considered as a common source in different brachytherapy techniques for treatment of different cancers. In this study, at first, we simulated and validated I-125 (model 6711) seed according to the TG-43U1 recommendation, by GEANT4 Monte Carlo toolkit. Moreover, we simulated new seeds containing cylindrical Ag+Al2O3 markers with different ratio of Ag and Al2O3 in the final composition of the marker and compared the radial dose functions and anisotropy functions of the sources. For validation and evaluation purposes, the radial dose function and anisotropy function were calculated at various distances from the center of the different simulated sources. The source validation results show that GEANT4 Monte Carlo toolkit produces accurate results for dosimetric parameters of the I-125 seed by choosing the appropriate physics list. On the other hand, results show a similarity between calculated dosimetric parameters of the I-125 seed (6711) and other sources, with a percentage difference of about 5%.

Introduction: Treatment planning systems use TG-43 dose calculation protocol for brachytherapy sources. Dose calculations based on TG-43 formalism do not correct the perturbations due to the presence of tissue inhomogeneity, applicators, and inter-seed effects. Inter-seed attenuation has an important effect on dosimetry in permanent implant brachytherapy. The aim of this study is to evaluate the inter-seed attenuation effect for I-125 permanent implants. Then, software was developed to find the real dose distribution for different combinations of sources. Material and Methods: In the first step, a hypothetical generic source model was designed based on the configurations of different commercial source types. MCNP5 Monte Carlo code was utilized to simulate the single active generic source at the center of the phantom, and an inactive placed at various positions inside the phantom. An algorithm was introduced using artificial neural network models that can estimate the dose distribution in presence of inactive sources. Results: The Monte Carlo calculation results showed that the dose distribution is affected by the inter-seed attenuation effect. Comparison of the artificial neural network results with the Monte Carlo simulation results show that the artificial neural networks can predict the inter-seed attenuation with acceptable accuracy. Comparison of the MC calculations, and the ANN output does not show statistically significant differences between the results (P value>0. 95). Conclusion: Inter-seed effect is dependent on the distance between the seeds. Decreasing distances would cause more effect. According to the results, it seems that the artificial neural network can be used as a tool for correction of inter-seed attenuation effect in treatment planning systems.