125I Sources Research Articles

Evolution of dose distribution for a 125I eye plaque using MCNPX and Plaque Simulator software

AbstractObjectiveEye plaque radiation therapy is the treatment of choice for small‐ and medium‐sized choroidal melanomas. This study investigated the dose distribution around eye plaques containing 125I seeds to treat ocular melanoma using Monte Carlo N‐Particle eXtended (MCNPX) and Plaque Simulator (PS) software.MethodsDosimetry evaluation and comparison of the resulting isodose curves for 125I COMS plaques were performed using the MCNPX code. The isodose curves and dose distributions were calculated using PS treatment planning for a 125I COMS plaque.ResultsIn the validation, the maximum relative difference between the results of this study and those reported in other literature was approximately 9%–10% for the COMS plaques. The dose distributions of MCNPX were lower than those of PS with a relative difference of approximately 27.7%–35.4%. The dose distribution may differ depending on the 125I source spectra and seed design used in the two methods. In addition, the dose algorithm used in PS made a major contribution to the relative differences between the results.ConclusionThe PS did not provide accurate details of dose distribution near the surface of the plaque insert. The source parameters used in each program should be studied more carefully to determine the source of the differences in the estimated dose values.

Experimental Study on The Gamma Ray Absorption Properties of Lanthanum and Cerium Borides

The objective of this study is to investigate the mass attenuation coefficients (μm) of lanthanumhexaborides and ceriumhexaborides over a wide photon energy range emitted from the main radioactive sources used in medicine and industry. 125I, 99mTc, 131I, 137Cs, 60Co and 152Eu gamma ray sources were used in the experiments. The materials synthesized in powder form were first pelletized and then irradiated by photon beams. At the end, it was seen that there is successful consistency between the obtained experimental data and the previous theoretical results. It was also observed that the investigated samples are comparable enough to the known standard gamma shielding materials, especially to lead which is one of the most common one. In conclusion, it is understood that the presently investigated samples have a promising aspect in terms of developing new shielding materials against gamma rays.

DICOM CT-based Monte Carlo dose calculations for prostate permanent implant using 125I seed sources

Dose distributions are calculated for a clinical prostate implant consisting of multiple 125I sources using Monte Carlo-based egs_brachy code. A voxelised heterogeneous CT phantom, generated from DICOM CT images is used. Dose distributions vary significantly with scoring and transport media. About 3% interseed attenuation and 12% dose differences between prostate tissue and water are observed at D90. Monte Carlo-calculated dose values are smaller as compared to the TG-43 formalism-based TPS-generated dose values at a given location. Hence, patient-specific model-based dose calculation algorithm is preferred over TG-43 formalism-based TPS.

Validation of the TOPAS Monte Carlo toolkit for LDR brachytherapy simulations

Purpose:This work has the purpose of validating the Monte Carlo toolkit TOol for PArticle Simulation (TOPAS) for low-dose-rate (LDR) brachytherapy uses. Methods and Materials:Simulations of 12 LDR sources and 2 COMS eye plaques (10 mm and 20 mm in diameter) and comparisons with published reference data from the Carleton Laboratory for Radiotherapy Physics (CLRP), the TG-43 consensus data and the TG-129 consensus data were performed. Sources from the IROC Houston Source Registry were modeled. The OncoSeed 6711 and the SelectSeed 130.002 were also modeled for historical reasons. For each source, the dose rate constant, the radial dose function and the anisotropy functions at 0.5, 1 and 5 cm were extracted. For the eye plaques (loaded with 125I sources), dose distribution maps, dose profiles along the central axis and transverse axis were calculated. Results:Dose rate constants for 11 of the 12 sources are within 4% of the consensus data and within 2% of the CLRP data. The radial dose functions and anisotropy functions are mostly within 2% of the CLRP data. In average, 92% of all voxels are within 1% of the CLRP data for the eye plaques dose distributions. The dose profiles are within 0.5% (central axis) and 1% (transverse axis) of the reference data. Conclusion:The TOPAS MC toolkit was validated for LDR brachytherapy applications. Single-seed and multi-seed results agree with the published reference data. TOPAS has several benefits such as a simplified approach to MC simulations and an accessible brachytherapy package including comprehensive learning resources.

A Comprehensive Analysis of Radiosensitization Properties of Metallic Nanoparticles in Brachytherapy of Gastric Adenocarcinoma by I-125 Seed: A Simulation Study by MCNPX and MCNP6 Codes

Purpose: In the current study, we aimed to look into the macroscopic and microscopic dose enhancement effect of metallic nanoparticles in interstitial brachytherapy of gastric adenocarcinoma by Iodine-125 source using a nano-lattice model in MCNPX (2.7) and MCNP6.1 codes. Materials and methods: Based on a nano-lattice simulation model containing a radiation source and a tumor tissue with cellular compartments loaded with 7 mg/g spherical nanoparticles, the microscopic and macroscopic levels of energy deposition by the secondary electrons was estimated. Results: The results show that the values of macroscopic DEF are higher than microscopic DEF values and the macroscopic DEF values decrease by increasing the distance from the surface of brachytherapy source. Accordingly, it could be noted that gold nanoparticles have the highest radiosensitization effect among the other nanoparticles and the related DEF value is close to the resultant DEF values for bismuth nanoparticles. Moreover, the results revealed a remarkable discrepancy between the DEF and secondary electron spectra calculated by MCNPX (2.7) and MCNP6.1 codes, which could be justified by the difference in energy cut-off and electron transport algorithms of two codes. Conclusions: According to the both MCNPX (2.7) and MCNP6.1 outputs, it could be concluded that the presence of metallic nanoparticles in the tumor tissue of gastric adenocarcinoma increases the physical effectiveness of brachytherapy by I-125 source. This study aims to provide recommendations for future preclinical studies. Actually, the results presented herein give a physical view of radiosensitization potential of different metallic nanoparticles and could be considered in design of analytical and experimental radiosensitization studies in tumor regions using various radiotherapy modalities in the presence of heavy nanomaterials.

Investigation the effect of a magnetic field on the dose distribution of I-125, Ir-192, Yb-169, and Co-60 brachytherapy sources by Monte Carlo simulation

Magnetic resonance imaging (MRI) during brachytherapy may alter the dose distribution of radioactive sources implanted in the tumor. This study investigates the impact of a magnetic field of 1.5 T, 3 T, and 7 T strengths on the dose distribution of high dose rate Co-60, Ir-192, and Yb-169, and low dose rate I-125 sources, using Geant4 Monte Carlo toolkit. After validating the simulation results by calculating the AAPM-TG43 dosimetric parameters, seven sources of each radioisotope were simulated in a water phantom, and their dose distributions were compared under the influence of a magnetic field. The simulation results indicate that using Co-60 brachytherapy under the MRI guidance is not recommended. Furthermore, the impact of a magnetic field of up to 7 T strength on the dose distribution of Ir-192, Yb-169, and I-125 sources is negligible, provided that there is no air pocket near brachytherapy sources.

How to explain the sensitivity of DNA double-strand breaks yield to 125I position?

Purpose Auger emitters exhibit interesting features due to their emission of a cascade of short-range Auger electrons. Maximum DNA breakage efficacy is achieved when decays occur near DNA. Studies of double-strand breaks (DSBs) yields in plasmids revealed cutoff distances from DNA axis of 10.5 Å–12 Å, beyond which the mechanism of DSBs moves from direct to indirect effects, and the yield decreases rapidly. Some authors suggested that the average energy deposited in a DNA cylinder could explain such cutoffs. We aimed to study this hypothesis in further detail. Materials and methods Using the Monte Carlo code CELLDOSE, we investigated the influence of the 125I atom position on energy deposits and absorbed doses per decay not only in a DNA cylinder, but also in individual strands, each modeled as 10 spheres encompassing the fragility sites for phosphodiester bond cleavage. Results The dose per decay decreased much more rapidly for a sphere in the proximal strand than for the DNA cylinder. For example, when moving the 125I source from 10.5 Å to 11.5 Å, the average dose to the sphere dropped by 43%, compared to only 13% in the case of the cylinder. Conclusions Explaining variations in DSBs yields with 125I position should consider the probability of inducing damage in the proximal strand (nearest to the 125I atom). The energy received by fragility sites in this strand is highly influenced by the isotropic (4π) emission of 125I low-energy Auger electrons. The positioning of Auger emitters for targeted radionuclide therapy can be envisioned accordingly.

Low and high-dose-rate brachytherapy in combination with external beam radiotherapy for high risk prostate cancer

Background. Prostate cancer (PCa) in the Russian Federation takes the leading place in the prevalence of cancer among the male population.Objective: to investigate the effect of increasing a single focal dose in high-dose-rate brachytherapy (HDR-BT) in combination with external beam radiotherapy on biochemical failure-free survival and local control in patients with high-risk PCa. Materials and methods. The study included 350 men with PCa in the group of high and extremely high risk of progression. All patients included in the study were divided into 4 groups. Groups 1, 2 and 3 included 276 patients who received HDR-BT with a 192Ir source with a single dose per fraction: 10 Gy (n = 83), 12 Gy (n = 46) and 15 Gy (n = 147). Group 4 included 74 patients who received low-dose-rate brachytherapy with 125I sources up to a total focal dose of 110 Gy. At the 2 stage, external beam radiotherapy was a conventional fractionation (single dose of 2 Gy, total - 44-46 Gy).Results. Of 350 patients over a 5-year follow-up period, PCa recurrence was noted in 65 (18.6 %). The 3- and 5-year biochemical failure-free survival rates in the general cohort of patients were 87.4 and 81.4 %. 5-year biochemical failure-free survival was significantly higher in group 3 relative to group 4 and amounted to 89.8 and 74.2 % (p = 0.03). Increasing the dose for HDR-BT from 10 to 12 Gy per fraction significantly reduced the frequency of local relapses from 15.7 % (in group 1) to 2.2 % (in group 2) (p = 0.0001) while maintaining the level of genitourinary and gastrointestinal toxicity. Conclusion. The use of a combination of brachytherapy and external beam radiotherapy in patients with high risk PCa is highly effective in achieving local control of the tumor. The optimal fractionation regime for HDR-BT remains a matter of debate. The use of 15 Gy per fraction for HDR-BT in combination with external beam radiotherapy is the most optimal fractionation regimen in patients with high-risk PCa.

Comparative analysis of long-term results of external beam and combined radiotherapy in high-risk prostate cancer patients

Prostate cancer (PCa) of high risk is one of the crucial problems in urological oncology. Radiation therapy (RT), along with radical prostatectomy, is an important component of the complex treatment of patients with high‑risk PCa. To improve the long‑term oncological results of RT dose escalation is advocated. Currently, dose escalation can be reached via external beam irradiation and interstitial RT techniques. The study included 109 patients with high‑risk PCa who underwent either external beam RT up to 76 Gy, or combined RT (external beam + interstitial RT) using 125I sources with long‑term androgen deprivation therapy. Comparative analysis of long‑term results of patients with high‑risk PCa treatment showed an improvement in 5‑year disease‑free survival rates after combined RT compared with external beam RT. Acute rectal toxicity was decreased in combined RT group compared to patients after external beam RT: 13.2 % and 46.4 %, respectively (p < 0.01).

Hydrogel spacer shrinkage during external-beam radiation therapy following low-dose-rate brachytherapy for high-risk prostate cancer: a case series\xa0

BackgroundFew studies have assessed hydrogel spacer shrinkage during external-beam radiation therapy following brachytherapy for localized high-risk prostate cancer. This case presentation evaluated the changes in hydrogel spacer appearance by magnetic resonance imaging during external-beam radiation therapy after brachytherapy for prostate cancer and analyzed the effect of this shrinkage on the dose distribution in four cases.Case presentationIn all cases, we implanted 125I sources using a modified peripheral loading pattern for seed placement. The prescribed dose for each implant was 110 Gy. After delivering the sources, a hydrogel spacer was injected. All cases underwent external-beam radiation therapy approximately 1–2 months after brachytherapy. The prescribed dose of external-beam radiation therapy was 45 Gy in 1.8-Gy fractions. Magnetic resonance imaging was performed for evaluation on the day following seed implantation (baseline), at external-beam radiation therapy planning, and during external-beam radiation therapy. The median hydrogel spacer volume was 16.2 (range 10.9–17.7) cc at baseline, 14.4 (range, 9.4–16.1) cc at external-beam radiation therapy planning, and 7.1 (range, 2.0–11.4) cc during external-beam radiation therapy. The hydrogel spacer volume during external-beam radiation therapy was significantly lower than that at external-beam radiation therapy planning. The rectum V60–80 (rectal volume receiving at least 60–80% of the prescribed dose of external-beam radiation therapy) during external-beam radiation therapy was significantly higher than that at external-beam radiation therapy planning.ConclusionsThe potential reduction in hydrogel spacer size during external-beam radiation therapy following brachytherapy can lead to unexpected irradiation to the rectum. This case presentation would be helpful for similar cases.

Corrections for photons attenuation and scattering for the extrapolation chamber for measurement of air-kerma strength of 125I brachytherapy source

A type of extrapolation chamber was designed in China Institute of Atomic Energy, CIAE. The chamber was used for the measurement of the air-kerma strength of the medical radiation 125I source on primary standard level. In order to obtain the air-krema strength with a low uncertainty, some correction factors such as photon attenuation and scattering are needed to calculate. Correction factors for different types of 125I seeds were estimated with increasing chamber depth. Based on the relation between ionization current and average photon fluence, attenuation correction factors were calculated with the analytical solution. Additionally, the scattering correction factors were estimated by a suitable method of Monte Carlo simulation. Photon attenuation includes four components. katt-volume, katt-foil, katt-sf, and katt-Al. The differences of correction factors are concerned, mainly due to the variation of chamer depths and 125I seed types. katt-volume increases from 1.001 to 1.005. katt-foil varies between 1.0012 and 1.0014. katt-sf changes from 1.015 to 1.018. katt-Al varies between 1.038 and 1.048, which largely depend on the photon spectrum from the source. Meanwhile, the geometric dimension of the ionization chamber has a great influence on the scattering correction factors. The ksca values vary from 0.9960 to 0.9964 with different chamber depths, which only has 0.04% fluctuation.

Quantitative comparison between initial DNA-damage RBE of I-125 and Pd-103 brachytherapy sources through a hybrid simulation approach

Iodine-125 and palladium-103 are radioactive sources that are frequently used for interstitial brachytherapy purposes. The current study aims to quantitatively compare the initial DNA-damage relative biologic effectiveness (RBE) of these two brachytherapy sources through a hybrid Monte Carlo (MC) simulation approach. Two commercially available brachytherapy sources of SL-125/SH-125 and MED3633 were considered as 125I and 103Pd sources, respectively. At first, geometry of two selected brachytherapy sources was accurately simulated by MCNPX MC code. Then, energy spectrum of released secondary electrons at different distances of 0.5, 1, 3, and 5 cm was scored, and obtained spectra were imported to MCDS MC code. Finally, the RBE values, with respect to Co-60 reference source, were estimated through calculation of induced DNA damages, including single- and double-strand breaks (SSBs and DSBs), by MCDS code for both studied brachytherapy sources at different distances. No significant differences were observed between the calculated RBE values of both considered brachytherapy sources. Based on our findings, the RBE (DSB) for iodine-125 and palladium-103 is, respectively, equal to 1.14 and 1.15, while the RBE (SSB) is the same for both brachytherapy seeds and equal to 0.97.

Simulation-based correction of dose enhancement factor values in photon brachytherapy with metal nanoparticle targeting

The purpose of this study is to investigate and quantify the influence of nanoparticle composition, size, and concentration on the difference between dose enhancement values derived from Monte Carlo simulations with homogeneous and structured geometrical representations of the target region in metal nanoparticle-enhanced photon brachytherapy. Values of the dose enhancement factor (DEF) were calculated for Pd-103, I-125, and Cs-131 brachytherapy sources with gold, silver, or platinum nanoparticles acting as targeting agents. Simulations were performed using the Geant4 toolkit with condensed history models of electron transport. Stringent limits were imposed on adjustable parameters that define secondary electron histories, so that simulations came closest to true event-by-event electron tracking, thereby allowing part of the nanoparticle-laden volume used for calculating the dose to be represented as a structured region with uniformly distributed discrete nanoparticles. Fine-tuned physical models of secondary radiation emission and propagation, along with the discrete geometrical representation of nanoparticles, result in a more realistic assessment of dose enhancement. The DEF correction coefficient is introduced as a metric that quantifies the absorption of secondary radiation inside the nanoparticles themselves, a phenomenon disregarded when the target region is treated as a homogeneous metal–tissue mixture, but accounted for by discrete nanoparticle representation. The approach applied to correcting DEF values both draws from and expands upon several related investigations published previously. Comparison of the obtained results to those found in relevant references shows both agreement and deviation, depending on nanoparticle properties and photon energy.

Dosimetric Predictors of Ophthalmologic Toxicities in Choroidal Melanoma Treated with Modern Episcleral Brachytherapy

While episcleral plaque brachytherapy provides excellent control for small- to intermediate-size choroidal melanomas, radiation-related complications have historically been high. Here, we examine the effect of modern ultrasound-guided conformal plaque brachytherapy on ophthalmologic outcomes in patients with choroidal melanoma. We retrospectively reviewed the plans and clinical charts of patients consecutively treated with I-125 episcleral plaque brachytherapy at our institution between 2017 and 2019. Ophthalmologic and dosimetric data from patients with at least 6 months of clinical follow-up were recorded and analyzed using standard statistical methods. Plaques were placed under ultrasound-guidance and the activity of I-125 sources modulated to obtain conformal plans. 90 patients were included in the analysis. All had eye physics (EP) plaque plans that conferred 100% PTV coverage by the prescription isodose line of 85Gy, which was referentially set at approximately 5mm from the inner sclera. The vast majority of patients had COMS medium lesions (90%) and 1/3 of tumors were located in the macula or near the optic disc. Visual decline was observed in 58% of patients and radiation retinopathy in 18% of cases. Changes in visual acuity were not associated with doses to individual optic structures (disc, fovea, lens) or size and location of tumor targets (p>0.05). Plans with higher Dmax (p = 0.04) and higher V85 (p = 0.01) correlated with decremental visual acuity. Patients who developed radiation retinopathy tended to have higher optic disc doses (p = 0.05). Intensity modulated plaque brachytherapy was not associated with improved visual outcomes (p = 0.6) despite predicting for more conformal plans (p = 0.03). Complication rates and visual decline remain a challenge even with image-guidance and use of conformal brachytherapy techniques. Future studies are needed to reduce dose-dependent toxicities while maintaining acceptable tumor control.

Super-selective intra-arterial platinum-based chemotherapy concurrent with low-dose-rate plaque brachytherapy in the treatment of retinoblastoma: A simulation study.

Retinoblastoma is the most common cancer among children under 5 years of age. The common conventional methods for the treatment of retinoblastoma include chemotherapy and brachytherapy (BT). This study investigated the concurrent use of BT with 125I and 103Pd sources and chemotherapy with platinum-based chemotherapy drugs for retinoblastoma. The absorbed doses in different parts of the eye were measured with and without platinum. Platinum concentrations of 5, 7.5, 10, and 15 mg/g were evaluated, and the dose enhancement factors (DEFs) were calculated for different cases. For the 125I source, the DEFs at the tumor apex were 1.49, 1.67, 1.81, and 1.97 at concentrations of 5, 7.5, 10, and 15 mg/g, respectively. The DEF decreased dramatically beyond the apex at 0.85 cm from tumor base and was 0.87, 0.82, 0.76, and 0.63 for the abovementioned concentrations, respectively. For the 103Pd source, the DEFs were 1.15, 1.24, 1.21, and 1.07, respectively, at the apex and 0.76, 0.65, 0.56, and 0.39, respectively, beyond the apex. Our results showed that the concurrent use of low-dose-rate plaque BT and platinum-based chemotherapy significantly increased the tumor-absorbed dose and decreased the absorbed dose in areas outside the tumor and the treatment time.

APPLICABILITY OF PURE PROPANE GAS FOR MICRODOSIMETRY AT BRACHYTHERAPY ENERGIES: A FLUKA STUDY.

Applicability of pure propane gas for microdosimetric measurements at photon energies relevant in brachytherapy is studied using the Monte Carlo-based FLUKA code. Monoenergetic photons in the energy range of 20-1250 keV and brachytherapy sources such as 103Pd, 125I, 169Yb, 192Ir, 137Cs and 60Co are considered in the study. Using the calculated values of energy deposited in the sensitive region of LET-1/2 tissue-equivalent proportional counter filled with pure propane gas and tissue-equivalent propane gas, values of density scaling factor for the site sizes of 1 and 8 μm are obtained. The study shows that density of propane gas should be lowered by a factor of about 0.93 for 169Yb, 192Ir, 137Cs and 60Co sources for the site sizes of 1-8 μm. For 125I source, the density of propane gas requires a scaling of 0.93 for 1 μm site size, whereas for site sizes 2-8 μm, density need not be altered. 103Pd source does not require density scaling for site sizes 1-8 μm.

Remote afterloading patient-specific brachytherapy with liquid radioisotope for irradiation of extensive scalp lesions: A Monte Carlo study.

The aim of this study is to propose a remote afterloading patient-specific brachytherapy technique for total scalp irradiation by utilizing liquid radioisotope as well as a three-dimensional (3D) printer and to find an optimal radioisotope for the suggested technique. We designed a brachytherapy device composed of liquid radioisotope tank, tube, patient-specific applicator, and a thin flexible pouch. The liquid radioisotope tank, tube, and the flexible pouch are interconnected one another to constitute a closed loop system. The pouch is located inside the solid patient-specific applicator; therefore, when the liquid radioisotope is injected into the pouch, the pouch is inflated and fills the space inside the applicator. The 3D-printed patient-specific applicator keeps the uniform thickness of the liquid radioisotope conforming patient's contour. To investigate an optimum condition for the suggested system, we performed Monte Carlo simulation with the GEANT4 simulation toolkit. To find the optimal radioisotope, percent depth doses (PDDs) of P-32, Sr-89, Y-90, and I-125 solutions were acquired in a rectangular parallelepiped phantom. For the selected radiation source, PDDs as well as dose rates in spherical phantoms with radii of 7.7cm (infant head size) and 9.1cm (adult head size) were acquired. To deliver prescription doses at 4-mm depth regions (scalp region), 1-mm-thick Y-90 and 5-mm-thick I-125 in liquid form were found to be feasible for the suggested technique. For both spherical phantoms with radii of 7.7 and 9.1cm, when delivering 2Gy at the 4-mm depth region with the 1-mm-thick Y-90 and 5-mm-thick I-125 sources, 53.3 and 3.8Gy were delivered at the surface regions, respectively (delivery time=111.1 and 3.5min with 1GBq/ml solutions). The PDDs of Y-90 and I-125 became less than 1% at depths greater than 8 and 50mm, respectively. The remote afterloading patient-patient specific brachytherapy with I-125 or Y-90 in liquid form seems feasible for total scalp irradiation.

Proposed use of in vivo x-ray fluorescence to investigate health impact of Gd in MRI contrast agents and Sr in diet

Introduction: In vivo x-ray fluorescence (XRF), along with in vivo neutron activation can be used to measure elemental content in living human subjects. Two examples of current interest will be presented. Gadolinium based contrast agents (GBCA) are widely used, because they greatly facilitate magnetic resonance imaging studies. Initially considered completely benign, it was found that these GBCAs could be damaging to people with compromised kidney function. More recently concern has been raised about possible impact on people with normal kidney function. We have been developing an xrf method to measure Gd in bone. Strontium is harmful to bone in excess. However, Sr supplement administered to people diagnosed with osteoporosis reduced fracture risk. Because there were cardiovascular side effects, this treatment has been withdrawn. Risk of hip fracture varies from country to country. It is highest in North America and two times lower in East Asian countries. We developed an xrf method to measure Sr in bone. In an early study of a convenience sample of Canadian residents, we found that people of East Asian origin had three times the level of Sr in bone as people of Caucasian origin. This gives rise to an hypothesis that modest levels of Sr, perhaps acquired through lifelong diet, could reduce the risk of osteoporosis. Materials and methods: Xrf requires a source of x-rays or (-rays, which can then excite x-rays that are characteristic of a particular element in a sample. A detector is placed to collect the scattered x-rays and (-rays from the sample. For Gd measurement, we use 88keV (-rays from a 109Cd source and an array of four hyperpure germanium detectors. For Sr we use x-rays and (-rays from a 125I source, with energies between 22 and 35keV. We use a Si(Li) detector. The effective radiation dose in each of these measurements is less than 1:Sv. This compares, for example to annual background radiation dose of ∼1600:Sv in Lisbon. Results: We measured Gd in tibia of 11 people who had previously received GBCA and 11 control subjects [1]. As a group, the exposed subjects had significantly higher bone Gd than the controls, although the difference was small. We made repeated measurements of bone Sr in ten female volunteers who had chosen to take Sr supplements [2]. Over periods of up to four years, their bone Sr increased dramatically. The increase varied from a factor of ten to a factor of one hundred between subjects. Discussion and conclusions: We should like to improve the precision of the bone Gd measurement. However, the present system is sufficient to begin to investigate retention and storage of Gd for different GBCAs and in different types of subjects. The dramatic increase in bone Sr following supplementation raises the possibility that providing Sr to people already suffering from osteoporosis is too much, too quickly, too late and that a lifelong dietary adjustment might be a healthier option.

Improvement of dose distribution in ocular brachytherapy with 125I seeds 20-mm COMS plaque followed to loading of choroidal tumor by gold nanoparticles.

Brachytherapy using removable ophthalmic plaques loaded with suitable small sealed radioactive seeds adjacent to the ocular's tumor has been widely used as an effective treatment. The aim of this study was to investigate the dose distribution in a modeled eyeball followed to loading of an ocular melanoma tumor with different concentrations of gold nanoparticles (GNPs) as dose enhancement agent by Monte Carlo (MC) calculations. The MC code of MCNPX 2.6.0 was used to modeling of COMS standard eye plaque loaded with 24 125I sources (6711 model) located on the sclera of modeled eyeball with detailed structures and materials. A choroidal melanoma tumor was simulated and loaded with different concentrations of spherical gold GNPs (50 nm in diameter). Dose enhancement factors (DEFs) of ocular components were calculated. The dosimetric properties of 125I source (6711 model) and dose distribution of COMS standard eye plaque were calculated successfully as recommended by TG-43U1; AAPM. Loading of tumor with GNPs increased dose to the tumor and decreased dose to the normal tissues; the DEF was increased up to 2.280 and 2.030 for tumor apex, while it was decreased to 0.760 and 0.892 for macula and for gold-tumor mixture and nanolattice distributions, respectively. Loading the choroidal tumor volume with GNPs improves the dose distribution by increasing dose to the tumor and decreasing dose to the health components in ocular brachytherapy with 125I seeds 20-mm COMS plaque.

Dosimetric Parameters Estimation of I-125 Brachytherapy Source in fat phantom using GATE8.0 code

Introduction: Brachytherapy is one type of internal radiation therapy where radiation sources, which are usually encapsulated, are placed as close as possible to the tumor site or inside the patient's body. In this technique, it is important to determine dose distribution around the brachytherapy capsule to create optimal treatment plant. In this way, dosimetric parameters are estimated according to TG-43U1 protocol in the water phantom as reference medium while the attenuation coefficient of the sources in the water phantom is different from that of different tissues. The purpose of this study is to investigate the effects of the fat phantom materials on the TG-43U1 dosimetery parameters of the I-125 brachytherapy source using GATE 8.0 Monte Carlo code. Materials and Methods: In this work, we used GATE_v8.0 (Geant4 Application for Emission Tomography) to calculate of dosimetric parameters of the I-125 brachytherapy source model 2301. At first, validation of the GATE platform was performed by some criteria such as dose rate constant, radial dose function, 2D anisotropy function inside liquid water according to the AAPM TG-43. Then, the Monte Carlo simulated dosimetric parameters of the 2301 I-125 were calculated in fat phantom. The TG-43 dosimetry parameters of the brachytherapy source were compared with those of the fat phantom. Results: Dosimetric parameters of simulated I-125 brachytherapy capsule show good consistency compared with the other study of the Monte Carlo simulation of I-125 source. The maximum deviation was about 9%. The maximum relative deviation of radial dose function of the fat tissue compared with water medium were about 13% at distances below 1cm. These differences increased, when the distance from the source increased. At the distance of 5cm from the source, it approximately reached to 55.67%. The maximum relative deviation of the anisotropy parameter of the fat phantom was observed about 6.7% compared with the water phantom. Conclusion: There was a good agreement between the results of this work and other study in calculation of dosimetric parameters of brachytherapy I-125 (model 2301) brachytherapy base on the recommendations of TG-43U1 protocole, using GATE Monte Carlo simulation method. Acquired results show that the obtained data can be used to develop GATE code for treatment plan of brachytherapy I- 125 brachytherapy source. Furthermore, In the clinical application of the I-125 brachytherapy source, which is contracted in the treatment of the adjacent tumors to the fat tissues, the correction factors of the fat tissues must be applied after dosimetric parameters calculation in water phantoms in the treatment planning to estimate accurate results for brachytherapy treatment planning.