Dosimetric characteristics of the Pharma Seed model BT-125-I source

Transcatheter Arterial Infusion Combined With Radioactive Particles in the Treatment of Advanced Body/Tail Pancreatic Cancer: A Retrospective Cohort Study

OBJECTIVES

This retrospective cohort study investigated the efficacy of routine intravenous chemotherapy (the control group), transcatheter arterial infusion (TAI) chemotherapy, and TAI combined with radioactive particles as therapeutic methods for advanced body/tail pancreatic cancer by assessing the short-term and overall survival rates.

METHODS

We screened our prospective database for patients with advanced body/tail pancreatic cancer, which tumor deemed unresectable, and no other confirmed malignant tumors, patients were assigned into 3 groups according to their treatment: routine intravenous chemotherapy, TAI, and TAI combined with radioactive particles.

RESULTS

The median survival time was 6 months in the control group, 10 months in the TAI group, and 13 months in the TAI combined group. The Kaplan-Meier estimates of the overall survival among the 3 groups, indicating that there is significant difference among 3 groups (P < 0.000). The clinical remission rates were 17.5% in the control group, 41.5% in the TAI group, and 48.0% in the TAI combined group. Covariates analyzed showed that different treatment methods and times affected the results significantly (P < 0.002).

CONCLUSIONS

In the treatment of advanced body/tail pancreatic cancer, TAI and TAI combined with radioactive particles significantly improved the clinical outcomes in patients compared with routine intravenous chemotherapy.

Inflammation-based prognostic scores in patients with extrahepatic bile duct lesions treated by percutaneous transhepatic biliary stenting combined with 125I seeds intracavitary irradiation

PURPOSE

This study aimed at investigating the efficacy of percutaneous transhepatic biliary stenting (PTBS) combined with ¹²⁵I seeds intracavitary irradiation in the treatment of extrahepatic cholangiocarcinoma (EHC) and to preliminarily explore the prognostic values of inflammation-based scores in these patients.

METHODS

A total of 113 clinically/pathologically diagnosed cases of EHC who received PTBS combined with ¹²⁵I seeds implantation were retrospectively analyzed. The postoperative changes of clinical symptoms and serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total serum bilirubin (TBIL), direct bilirubin (DBIL), and albumin (ALB) were observed. Preoperative clinical data were extracted to calculate inflammation-based scores, including systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), and platelets-to-lymphocyte ratio (PLR). Kaplan-Meier survival curves and Cox regression analyses were used to evaluate the prognostic significance of inflammation-based scores.

RESULTS

After operation, clinical symptoms such as jaundice and fever significantly improved in all patients. At 1 month and 3 months postoperatively, serum levels of ALT, AST, ALP, TBIL, and DBIL significantly reduced, and ALB significantly increased, compared with preoperative values. The median survival time of the patients was 12 months and the 1-year survival rate was 56.8%. Univariate analysis revealed that factors related to overall survival were CA19-9, TBIL, ALB, SII, and NLR. Multivariate analysis further identified SII and NLR as independent prognostic models.

CONCLUSION

The combination of PTBS and ¹²⁵I seeds intracavitary irradiation is an effective palliative treatment for advanced EHC. Elevated SII and NLR can be used to predict poor survival.

Dosimetric characterization of GMS BT-125-1 125 I radioactive seed with Monte Carlo simulations and experimental measurement

Purpose

To investigate the dosimetric characteristics of the new GMS BT‐125‐1 ¹²⁵I radioactive seed, including dose rate constant, radial dose functions, and anisotropy functions.

Methods

Dosimetric parameters of GMS BT‐125‐1 ¹²⁵I seed including dose rate constant, radial dose functions, and anisotropy functions were calculated using the Monte Carlo code of MCNP5, and measured with thermoluminescent dosimeters (TLDs). The results were compared with those of PharmaSeed BT‐125‐1, PharmaSeed BT‐125‐2 ¹²⁵I, and model 6711 ¹²⁵I seeds.

Results

The dose rate constant of GMS BT‐125‐1 ¹²⁵I seed was 0.959 cGy·h−1·U−1, with the difference of 0.94%, 0.83%, and 0.73% compared with the PharmaSeed BT‐125‐1 ¹²⁵I seed, PharmaSeed BT‐125‐2 ¹²⁵I seed, and Model 6711 ¹²⁵I seed, respectively. For radial dose function, the differences between the Monte Carlo and the experimental g(r) results were mostly within 10%. Monte Carlo results of g(r) for GMS BT‐125‐1 ¹²⁵I seed were found in agreement (within 3.3%) with corresponding results for the PharmaSeed BT‐125‐2 ¹²⁵I seed. The largest differences were 8.1% and 6.2% compared with PharmaSeed BT‐125‐1 ¹²⁵I seed and model 6711 ¹²⁵I seed, respectively. For anisotropy function, the difference between GMS BT‐125‐1 ¹²⁵I seed and PharmaSeed BT‐125‐2 ¹²⁵I seed was typically <10%.

Conclusions

The measured dose rate constant, radial dose functions, and two‐dimensional anisotropy functions for the GMS BT‐125‐1 ¹²⁵I seed showed good agreement with the Monte Carlo results. The dose rate constant of the GMS BT‐125‐1 ¹²⁵I seed is similar to that of the PharmaSeed BT‐125‐1 ¹²⁵I seed, the PharmaSeed BT‐125‐2 ¹²⁵I seed, and the model 6711 ¹²⁵I seed. For radial dose functions and two‐dimensional anisotropy functions, the GMS BT‐125‐1 ¹²⁵I seed is similar to the PharmaSeed BT‐125‐2 ¹²⁵I seed but different from the PharmaSeed BT‐125‐1 ¹²⁵I seed and the model 6711 ¹²⁵I seed.

Monte Carlo calculations and experimental measurements of the TG-43U1-recommended dosimetric parameters of 125I (Model IR-Seed2) brachytherapy source

A new design of I125 (Model IR‐Seed2) brachytherapy source has been manufactured recently at the Applied Radiation Research School, Nuclear Science and Technology Research Institute in Iran. The source consists of six resin beads (0.5 mm diameter) that are sealed in a cylindrical titanium capsule of 0.7 mm internal and 0.8 mm external diameters. This work aims to evaluate the dosimetric parameters of the newly designed I125 source using experimental measurements and Monte Carlo (MC) simulations. Dosimetric characteristics (dose rate constant, radial dose function, and 2D and 1D anisotropy functions) of the IR‐Seed2 were determined using experimental measurements and MC simulations following the recommendations by the Task Group 43 (TG‐43U1) report of the American Association of Physicists in Medicine (AAPM). MC simulations were performed using the MCNP5 code in water and Plexiglas, and experimental measurements were carried out using thermoluminescent dosimeters (TLD‐GR207A) in Plexiglas phantoms. The measured dose to water in Plexiglas data were used for verification of the accuracy of the source and phantom geometry in the Monte Carlo simulations. The final MC simulated data to water in water were recommended for clinical applications. The MC calculated dose rate constant (Λ) of the IR‐Seed2 I125 seed in water was found to be 0.992±0.025 cGy h−1U−1. Additionally, its radial dose function by line and point source approximations, gL(r) and gp(r), calculated for distances from 0.1 cm to 7 cm. The values of gL(r) at radial distances from 0.5 cm to 5 cm were measured in a Plexiglas phantom to be between 1.212 and 0.413. The calculated and measured of values for 2D anisotropy function, F(r,θ), were obtained for the radial distances ranging from 1.5 cm to 5 cm and angular range of 0°‐90° in a Plexiglas phantom. Also, the 2D anisotropy function was calculated in water for the clinical application. The results of these investigations show that the uncertainty of the experimental data is within ±7% between the measured and simulated data in Plexiglas. Based on these results, the MC‐simulated dosimetric parameters of the new I125 source model in water are presented for its clinical applications in brachytherapy treatments.

PACS number(s): 87.56.bg

Effect of improved TLD dosimetry on the determination of dose rate constants for (125)I and (103)Pd brachytherapy seeds

PURPOSE

To more accurately account for the relative intrinsic energy dependence and relative absorbed-dose energy dependence of TLDs when used to measure dose rate constants (DRCs) for (125)I and (103)Pd brachytherapy seeds, to thereby establish revised "measured values" for all seeds and compare the revised values with Monte Carlo and consensus values.

METHODS

The relative absorbed-dose energy dependence, f(rel), for TLDs and the phantom correction, Pphant, are calculated for (125)I and (103)Pd seeds using the EGSnrc BrachyDose and DOSXYZnrc codes. The original energy dependence and phantom corrections applied to DRC measurements are replaced by calculated (f(rel))(-1) and Pphant values for 24 different seed models. By comparing the modified measured DRCs to the MC values, an appropriate relative intrinsic energy dependence, kbq (rel), is determined. The new Pphant values and relative absorbed-dose sensitivities, SAD (rel), calculated as the product of (f(rel))(-1) and (kbq (rel))(-1), are used to individually revise the measured DRCs for comparison with Monte Carlo calculated values and TG-43U1 or TG-43U1S1 consensus values.

RESULTS

In general, f(rel) is sensitive to the energy spectra and models of the brachytherapy seeds. Values may vary up to 8.4% among (125)I and (103)Pd seed models and common TLD shapes. Pphant values depend primarily on the isotope used. Deduced (kbq (rel))(-1) values are 1.074 ± 0.015 and 1.084 ± 0.026 for (125)I and (103)Pd seeds, respectively. For (1 mm)(3) chips, this implies an overall absorbed-dose sensitivity relative to (60)Co or 6 MV calibrations of 1.51 ± 1% and 1.47 ± 2% for (125)I and (103)Pd seeds, respectively, as opposed to the widely used value of 1.41. Values of Pphant calculated here have much lower statistical uncertainties than literature values, but systematic uncertainties from density and composition uncertainties are significant. Using these revised values with the literature's DRC measurements, the average discrepancies between revised measured values and Monte Carlo values are 1.2% and 0.2% for (125)I and (103)Pd seeds, respectively, compared to average discrepancies for the original measured values of 4.8%. On average, the revised measured values are 4.3% and 5.9% lower than the original measured values for (103)Pd and (125)I seeds, respectively. The average of revised DRCs and Monte Carlo values is 3.8% and 2.8% lower for (125)I and (103)Pd seeds, respectively, than the consensus values in TG-43U1 or TG-43U1S1.

CONCLUSIONS

This work shows that f(rel) is TLD shape and seed model dependent suggesting a need to update the generalized energy response dependence, i.e., relative absorbed-dose sensitivity, measured 25 years ago and applied often to DRC measurements of (125)I and (103)Pd brachytherapy seeds. The intrinsic energy dependence for LiF TLDs deduced here is consistent with previous dosimetry studies and emphasizes the need to revise the DRC consensus values reported by TG-43U1 or TG-43U1S1.

(125)I particle implantation combined with chemoradiotherapy to treat advanced pancreatic cancer

OBJECTIVE

To evaluate the therapy effects of (125)I implantation combined with chemoradiotherapy on pancreatic cancer patients.

METHODS

30 patients with Stage III or IV pancreatic cancer were equally divided into two groups (control and treatment group). The patients in the treatment group (nine males, six females) received chemotherapy in the first week and (125)I implantation in the third week, followed by combined chemoradiotherapy in the fifth week. The patients in the control group (10 males, 5 females) received the same treatment except (125)I implantation. The therapy in the control group and treatment group was repeated every 4 weeks.

RESULTS

The median conformal radiotherapy dose in the treatment group (30.62 Gy) was significantly lower than that in the control group (47.86 Gy). The total radiation dose was 88.71 ± 27.39 Gy, and the surface activity was 0.6 mCi in the treatment group. After treatment, the average tumour size decreased both in the treatment group [9.17 cm(2), 95% confidence interval (CI): 5.60-12.74, p < 0.001] and in the control group (4.54 cm(2), 95% CI: 2.74-6.35, p < 0.001). The median survival time in the treatment group was 14 months (95% CI: 12.215-14.785) and in the control group was 12 months (95% CI: 10.884-13.116). There was no statistical significance in survival rates between the two groups (χ(2) = 0.908, p = 0.341).

CONCLUSION

(125)I implanted into tumour combined with chemoradiotherapy has higher local control rate of advanced pancreatic cancer than chemoradiotherapy.

ADVANCES IN KNOWLEDGE

We combined chemoradiotherapy with (125)I implantation to treat advanced pancreatic cancer and obtained a higher local control rate and better quality of life than when using chemoradiatherapy alone.

Dosimetric characteristics of three new design 125I brachytherapy sources

For roughly 25 years, 125I sources have been used in the treatment of various malignant diseases such as prostate cancer. Three new brachytherapy sources, IR01-125I, IR02-125I and IR03-125I, have been developed and are designed for permanent implant application. The Monte Carlo radiation transport code version MCNP 5 was used to calculate the dosimetry parameters around the sources in accordance with the updated report of the American Association of Physicists in Medicine (AAPM), Task Group No. 43. For each source, the dose rate constant Λ, the radial dose function gL(r), and the anisotropy function F(r, θ), were obtained. The results indicated a dose rate constant of 0.932 ± 0.01, 0.934 ± 0.01 and 0.939 ± 0.01 Gy h−1 U−1 for the IR01-125I, IR02-125I and IR03-125I sources respectively. With the goal of determining an optimal design for a 125I source, each seed's parameters were compared with other seeds. In this study, the optimal source IR03-125I provides the most isotropic dose distribution in water. Finally, the results for optimal source were compared with published results for those of other commercial sources.

Monte Carlo calculation of dosimetry parameters for the IR08-103Pd brachytherapy source

PURPOSE

For the treatment of some cancerous tumors using brachytherapy methods and low-energy photon sources, such as 125I and 103Pd, the American Association of Physicists in Medicine Task Group No. 43U1 report recommends that the dosimetric parameters of a new brachytherapy source must be determined in two experimental and Monte Carlo theoretical methods before using each new source clinically. This study presents the results of Monte Carlo calculations of the dosimetric parameters for IR08-103Pd brachytherapy source design. IR08-103Pd seed has been manufactured at the Agricultural, Medical and Industrial Research School.

METHODS

Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate the dosimetry parameters around the source. Three geometric models of the seed, based on different locations of beads inside the titanium capsule, were simulated. The seed contains five resin beads of 0.6 mm diameter having 103Pd uniformly absorbed in the bead volume, which were contained within a cylindrical titanium capsule having 0.8 mm outside diameter and 4.8 mm length.

RESULTS

The Monte Carlo calculated dose rate constant of the IR08-103Pd seed was found to be 0.695 +/- 0.021 cGyU(-1) h(-1). Also in this study, the geometry function G(r, theta), line and point-source radial dose functions gL(r) and gP(r), and the anisotropy function F(r, theta), have been calculated at distances from 0.25 to 7 cm. The results of these calculations have been compared with measured values for an actual IR08-103Pd seed.

CONCLUSIONS

There are no statistical significant dosimetric differences among the three seed orientations in this study (i.e., ideal, vertical, and diagonal). However, the observed differences between the calculated and measured values could be explained by the measurement uncertainty and the configuration of the resin beads within the capsule and capsule orientation.

Dosimetric comparison of four new design 103Pd brachytherapy sources: optimal design using silver and copper rod cores

Four new brachytherapy sources, IRA1-103Pd, IRA2-103Pd, IRA3-103Pd, and IRA4-103Pd, have been developed at Agricultural, Medical, and Industrial Research School and are designed for permanent implant application. With the goal of determining an optimal design for a 103Pd source, this article compares the dosimetric properties of these sources with reference to the authors' earlier IRA-103Pd source. The four new sources differ in end cap configuration and thickness and in the core material, silver or copper, that carries the adsorbed 103Pd. Dosimetric data derived from the authors' Monte Carlo simulation results are reported in accordance with the updated AAPM Task Group No. 43 report (TG-43U1). For each source, the authors obtained detailed results for the dose rate constant lambda, the radial dose function g(r), the anisotropy function F(r, theta), and the anisotropy factor phi(an)(r). In this study, the optimal source IRA3-103Pd provides the most isotropic dose distribution in water with the dose rate constant of 0.678(+/-0.1%) cGy h(-1) U(-1). The IRA3-103Pd design has a silver rod core combined with thin-wall, concave end caps. Finally, the authors compared the results for their optimal source with published results for those of other source manufacturers.

Dosimetry parameters of BARC OcuProsta I-125 seed source

A new model of 125I seed source, named OcuProsta seed, was designed and fabricated by Radiopharmaceuticals Division of Bhabha Atomic Research Centre for ophthalmic and interstitial applications. AAPM TG 43 recommended dosimetry parameters for this seed source were determined experimentally using TLD as well as by Monte Carlo (MC) simulation. Measured and MC calculated values of the dose rate constant (DRC) are 0.95 +/- 0.065 cGyh(-1)U(-1) and 0.972 +/- 0.005 cGyh(-1)U(-1), respectively. The mean of measured and calculated DRC (lambda = 0.96 cGyh(-1)U(-1)) was recommended for the clinical dosimetry of OcuProsta seed. Measured and MC calculated radial dose function, g(r), anisotropy function, F(r,theta), anisotropy factor and anisotropy constants are also found to be in good agreement to each other. Dosimetry parameters of OcuProsta seed were compared with the published values of similar in-design 125I seed sources. The DRC of BARC OcuProsta seed is very close to Amersham 6711 seed and is also comparable to the DRC of Best model 2301, Syncor PharmaSeed and Isotron selectSeed within the uncertainty of measurement/calculation. The g(r) of OcuProsta seed shows a difference of up to 10% in comparison to the g(r) values of the similar in-design seed sources. The values of anisotropy function of OcuProsta are 7-13% different from the anisotropy function of Amersham 6711 and Syncor PharmaSeed. The anisotropy constant of OcuProsta is close to Amersham 6711 seed while it is about 9% smaller than the anisotropy constant of Best model 2301 and Synchor PharmaSeed.

Evaluation of the new cesium-131 seed for use in low-energy x-ray brachytherapy

Characterization measurements and calculations were performed on a new medical seed developed by IsoRay Inc. in Richland, Washington, that utilizes the short-lived isotope 131Cs. This model has recently received FDA 510(k) clearance. The objective of this work was to characterize the dosimetric properties of the new seed according to the AAPM Task Group 43 recommendations. Cesium-131 is a low-energy x-ray emitter, with the most prominent peaks in the 29 keV to 34 keV region. The intended application is brachytherapy for treating cancers in prostate, breast, head and neck, lung, and pancreas. The evaluations performed included air-kerma strength, radial dose function, anisotropy in phantom, half-life, energy spectra, and internal activity. The results indicate the CS-1 seeds have a dose-rate constant of 0.915 cGy hr(-1) U(-1) in water, dose penetration characteristics similar to 125I and 103Pd, anisotropy function values on the order of 0.71 at short distances and small angles, and an average anisotropy factor of 0.964. The overall dosimetric characteristics are similar to 125I and 103Pd seeds with the exception of half-life, which is 9.7 days, as compared to 17 days for 103Pd and 60 days for 125I. The shorter half-life may offer significant advantages in biological effectiveness.

Polymer gel water equivalence and relative energy response with emphasis on low photon energy dosimetry in brachytherapy

The water equivalence and stable relative energy response of polymer gel dosimeters are usually taken for granted in the relatively high x-ray energy range of external beam radiotherapy based on qualitative indices such as mass and electron density and effective atomic number. However, these favourable dosimetric characteristics are questionable in the energy range of interest to brachytherapy especially in the case of lower energy photon sources such as 103Pd and 125I that are currently utilized. In this work, six representative polymer gel formulations as well as the most commonly used experimental set-up of a LiF TLD detector-solid water phantom are discussed on the basis of mass attenuation and energy absorption coefficients calculated in the energy range of 10 keV-10 MeV with regard to their water equivalence as a phantom and detector material. The discussion is also supported by Monte Carlo simulation results. It is found that water equivalence of polymer gel dosimeters is sustained for photon energies down to about 60 keV and no corrections are needed for polymer gel dosimetry of 169Yb or 192Ir sources. For 125I and 103Pd sources, however, a correction that is source-distance dependent is required. Appropriate Monte Carlo results show that at the dosimetric reference distance of 1 cm from a source, these corrections are of the order of 3% for 125I and 2% for 103Pd. These have to be compared with corresponding corrections of up to 35% for 125I and 103Pd and up to 15% even for the 169Yb energies for the experimental set-up of the LiF TLD detector-solid water phantom.

On the development of consensus values of reference dosimetry parameters for interstitial brachytherapy sources

The American Association of Physicists in Medicine recommends that the reference dose-rate distribution, used for treatment planning for low-energy photon brachytherapy sources in routine clinical use, must be based on at least two independent determinations: one using experimentally measured dose rates and one using Monte Carlo simulation dosimetry techniques. In this work, we present an approach for developing consensus dosimetry parameters from various independent reference dosimetry studies for interstitial brachytherapy sources. This approach is applied to four recently published papers on the dosimetric properties of the BrachySeed Model LS-1 125I seed. Consensus values for the dose-rate constant, radial dose function, and anisotropy parameters are presented for the LS-1 Model 125I seed.

A semi-analytic approach to determine dose rate constant of brachytherapy sources in compliance with AAPM TG 60 formalism

Values of dose rate constant (DRC) in compliance with AAPM TG 60 formalism recommended for intravascular brachytherapy (IVBT) were calculated for different point isotropic mono-energetic photon sources in the energy range E = 20-1000 keV using a semi-analytic model. Based on these DRC values, DRC of some existing models of 192Ir and 125I brachytherapy sources were then calculated using (1) bare energy spectra and (2) a single energy parameter which represents mean energy (photon number weighted or air-kerma weighted) for bare and actual sources or the most probable energy of the spectra (energy line with the highest probability of emission) of the investigated sources (192Ir and 125I). Applicability of the semi-analytic approach was examined by also computing the values of DRC of the investigated sources using MCNP Monte Carlo simulation code (Version 3.1) that involved modeling of the sources accurately. A comparison of values of DRC resulting from MCNP calculations with those resulting from the semi-analytic approach showed that for 192Ir sources the agreement was within 0.40% and for 125I sources it was within 2.3%.

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.

A seed specific dose kernel method for low-energy brachytherapy dosimetry

We describe a method for independently verifying the dose distributions from pre- and post-implant brachytherapy source distributions. Monte Carlo calculations have been performed to characterize the three-dimensional dose distribution in water phantom from a low-energy brachytherapy source. The calculations are performed in a voxelized, Cartesian coordinate geometry and normalized based upon a separate Monte Carlo calculation for the seed specific air-kerma strength to produce an absolute dose grid with units of cGy hr(-1) x U(-1). The seed-specific, three-dimensional dose grid is stored as a text file for processing using a separate visual basic program. This program requires the coordinate positions of each seed in the pre- or post-plan and sums the kernel file for a three-dimensional composite dose distribution. A kernel matrix size of 81x81x81 with a voxel size of 1.0x1.0x1.0 mm3 was chosen as a compromise between calculation time, kernel size, and truncation of the stored dose distribution as a function of radial distance from the midpoint of the seed. Good agreement is achieved for a representative pre- and post-plan comparison versus a commercial implementation of the TG-43 brachytherapy dosimetry protocol.

A Monte Carlo evaluation of the dosimetric characteristics of the Best Model 2301 125I brachytherapy source

Recently a new design of a 125I brachytherapy source was introduced for interstitial seed implants, particularly for prostate seed implants. This new source is the Best Model 2301 brachytherapy source. Due to the differences in source design and manufacturing process from one new source to the next, their dosimetric parameters should be determined according to the AAPM TG-43 guidelines. As per AAPM recommendation (Med. Phys. 25 (12) (1998) 2269), it is required to perform the seed dosimetry using at least one experimental study and one Monte Carlo simulation, preferably done by two separate investigators. Other investigators have experimentally determined the dosimetric parameters of this new source. In this project, the Monte Carlo simulated dosimetric parameters of the Best Model 2301 125I source have been provided. The results of this evaluation indicate the value of dose rate constant of 1.01 +/- 3% cGyh-1U-1 in liquid water, which is in good agreement with 1.02 +/- 8% cGyh-1U-1 reported by Nath and Yue, 2002. The anisotropy constant was found to be 0.98 in liquid water.

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

The adsorption of iodine-125 on silver wire bits coated with palladium to be sealed in titanium capsules as brachytherapy sources was studied. A method was optimized to obtain quantitative adsorption of 125I on the palladium treated silver wires. A comparative evaluation of palladium coated and uncoated (bare) silver wires on the adsorption of 125I was made. While, the adsorption of bare silver wires showed low, inconsistent uptake (approximately 60%) of 125I with high leachability (approximately 4%), the Pd coated silver wires showed quantitative and consistent uptake of 125I (approximately 90%) and exhibited low leachability (0.01%). 125I adsorbed on Pd coated silver wires could be used as a matrix for the preparation of interstitial sources in eye and prostate cancer therapy.

Monte carlo investigation of the dosimetric properties of the new 103Pd BrachySeedPd-103 Model Pd-1 source

Recently, 103Pd brachytherapy sources have been increasingly used for interstitial implants as an alternative to 125I sources. The BrachySeedPd-103 Model Pd-1 seed is one of the latest in a series of new brachytherapy sources that have become available commercially. The dosimetric properties of the seed were investigated by Monte Carlo simulation, which was performed using the Integrated Tiger Series CYLTRAN code. Following the AAPM Task Group 43 formalism, the dose rate constant, radial dose function, and anisotropy parameters were determined. The dose rate constant, A, was calculated to be 0.613 +/- 3% cGy h(-1) U(-1). This air kerma strength was derived from Monte Carlo simulation using the point extrapolation method. The radial dose function, g(r), was computed at distances from 0.15 to 10 cm. The anisotropy function, F(r,theta), and anisotropy factor, phi(an)(r), were calculated at distances from 0.5 to 7 cm. The anisotropy constant, phi(an), was determined to be 0.978, which is closer to unity than most other 103Pd seeds, indicating a high degree of uniformity in dose distribution. The dose rate constant and the radial dose function were also investigated by analytical modeling, which served as an independent evaluation of the Monte Carlo data, and found to be in good agreement with the Monte Carlo results.

Monte Carlo calculations of dosimetry parameters of the urocor prostaseed 125I source

This report presents the results of Monte Carlo calculations of the dosimetric parameters of the Urocor ProstaSeed 1251 seed source. This source contains five spherical silver markers, of 0.5 mm diameter, with 1251 deposited on the spheres through ion exchange. The silver spheres are then encapsulated within a 0.8 mm in diameter and 4.5 mm long cylindrical shell of titanium, as is common to this type of sources. Physical dimensions of the source are confirmed by measurement. Four (4) geometric models of the source, based on different assumptions on the locations of the silver spheres within the seed, were used in dose rate calculations. Monte Carlo photon transport simulation was used to calculate the dosimetric parameters of dose rate constant, radial dose function, and anisotropy function using these geometric models of the source. The Monte Carlo calculated dose rate constant of the ProstaSeed source was found equal to 0.925 cGy/Uh with approximate uncertainties of 5%. Radial dose function values and anisotropy function values were derived from the relative dose distribution around the source calculated by the Monte Carlo code. The calculated values of these dosimetric parameters agree with previously published thermoluminescence-dosimeter-measured values for this source after consideration of measurement and calculation uncertainties.

Thermoluminescent dosimetry of the selectseed 125I interstitial brachytherapy seed

This work presents experimental dosimetry results for the new selectSeed 125I prostate seed design for use with the seedSelectron afterloading device, in accordance with the AAPM advisory that all new low energy interstitial brachytherapy seeds should undergo one Monte Carlo (MC) and at least one experimental dosimetry characterization. TLD dosimetry was performed using 120 cylindrical LiF TLD type-100 rods calibrated using a 6 MV photon beam. They were irradiated in solid water phantoms for the experimental determination of the seed dose rate constant, radial dose functions and anisotropy functions. MC simulations were performed for the determination of the TLDs relative energy response that was found position independent and equal to 1.40+/-0.03, and for the calculation of the ratio of dose in liquid water to dose in solid water that was found to be well described by Dliquidwater/Dsolidwater= 1.013*r+0.030 presenting only a minor dependence on polar angle. The selectSeed dose rate constant in liquid water was found equal to 0.938+/-0.065 cGy h(-1) U(-1), which agrees within experimental uncertainties with corresponding MC results of lambdaselect Seed=0.954+/-0.005 cGy h(-1) U(-1). The experimental radial dose and anisotropy function results were also found in good agreement with corresponding MC calculations.

Dosimetric parameters for three low-energy brachytherapy sources using the Monte Carlo N-particle code

Monte Carlo calculations have been performed for the purpose of characterizing the dosimetric properties of three brachytherapy sources. The three sources are manufactured by Syncor Pharmaceuticals Inc. and consist of two 125I seeds (BT-125-1 and BT-125-2) and one 103Pd seed (BT-103-3). The BT-125-1 and BT-125-2 seed consists of a solid palladium and silver core, respectively. A thin layer (0.5 microm) of 125I is adsorbed onto the solid core for each seed and encased within a titanium housing. The BT-103-3 seed consists of a central gold marker and four resin balls encased within a titanium housing. A thin layer of 103Pd is bonded onto each resin ball. The dosimetric properties, including the dose rate constant, radial dose function, and anisotropy were calculated in water according to the TG-43 protocol using the Monte Carlo N-Particle code. The dose rate constant was calculated to be 0.955+/-0.005 and 0.967+/-0.005 cGyh(-1) U(-1) for the BT-125-1 and BT- 125-2 seeds, respectively. A dose rate constant of 0.659+/-0.005 cGy h(-1) U(-1) was calculated for the BT-103-3 seed. Radial dose function, g(r), calculated to a distance of 10 cm, and an isotropy function, F(r, theta), calculated for radii from 0.5 to 7.0 cm, were found to be in close agreement with previously published data.

Dosimetric properties of the new 125I BrachySeed model LS-1 source

The BrachySeed model LS-1 is one of the latest in a series of new brachytherapy 125I seeds that have recently become available commercially for interstitial implants. The dosimetric properties of the seed were investigated analytically, experimentally, and by Monte Carlo simulation. Following the AAPM Task Group 43 formalism, the radial dose function, dose rate constant, and anisotropy parameters were determined. Experimental measurements were made in solid water-equivalent phantoms using GafChromic MD-55-2 films, with correction for the low energy film response. Analyses were carried out from absolute measurements, as well as relative measurements against the Nycomed Amersham OncoSeed Model 6711, which also served to validate our experimental methodology. A small, but systematic difference in the absolute measurements was observed depending on the duration of the irradiation. Monte Carlo simulation was performed using the Integrated Tiger Series CYLTRAN code. We benchmarked the code by comparing the dose parameters of Model 6702 with published values. The radial dose function, g(r), of the Model LS-1 seed was computed at distances from 0.25 to 10 cm by analytical and Monte Carlo calculations with reasonably good agreement. The suggested dose rate constant, A, based on the Monte Carlo simulation is 0.90+/-0.03 cGy h(-1) U(-1). This value is smaller than, but overlaps the experimental determination of 0.98+/-0.06 cGy h(-1) U(-1). The anisotropy function, F(r, theta), and anisotropy factor, phi(an)(r), compared favorably with those of the Model 6711.

Dosimetric parameters of three new solid core I-125 brachytherapy sources

Monte Carlo calculations and TLD measurements have been performed for the purpose of characterizing dosimetric properties of new commercially available brachytherapy sources. All sources tested consisted of a solid core, upon which a thin layer of 125I has been adsorbed, encased within a titanium housing. The PharmaSeed BT-125 source manufactured by Syncor is available in silver or palladium core configurations while the ADVANTAGE source from IsoAid has silver only. Dosimetric properties, including the dose rate constant, radial dose function, and anisotropy characteristics were determined according to the TG-43 protocol. Additionally, the geometry function was calculated exactly using Monte Carlo and compared with both the point and line source approximations. The 1999 NIST standard was followed in determining air kerma strength. Dose rate constants were calculated to be 0.955+/-0.005, 0.967+/-0.005, and 0.962+/-0.005 cGy h(-1) x U(-1) for the PharmaSeed BT-125-1, BT-125-2, and ADVANTAGE sources, respectively. TLD measurements were in excellent agreement with Monte Carlo calculations. Radial dose function, g(r), calculated to a distance of 10 cm, and anisotropy function, F(r,theta), calculated for radii from 0.5 to 7.0 cm, were similar among all source configurations. Anisotropy constants, phi(an), were calculated to be 0.941, 0.944, and 0.960 for the three sources, respectively. All dosimetric parameters were found to be in close agreement with previously published data for similar source configurations. The MCNP Monte Carlo code appears to be ideally suited to low energy dosimetry applications.

A Monte Carlo evaluation of the dosimetric characteristics of the EchoSeed™ Model 6733 125I brachytherapy source

PURPOSE

Recently a new design of a (125)I brachytherapy source was introduced for interstitial seed implants, particularly for prostate seed implants. This new source is the EchoSeed Model 6733 (125)I brachytherapy source. Due to the differences in source design and manufacturing process from one new source to the next, their dosimetric parameters should be determined according to the American Association of Physicists in Medicine (AAPM) TG-43 guidelines.

METHODS AND MATERIALS

As per AAPM recommendation, it is required to perform at least one experimental study and one Monte Carlo simulation, preferably done by two independent investigators. Other investigators have experimentally determined the dosimetric parameters of this new source. In this project, the Monte Carlo simulated dosimetric parameters of the EchoSeed Model 6733 source have been provided.

RESULTS

The results of this evaluation indicate the value of the dose rate constant of 0.97 +/- 3% cGyh(-1)U(-1) in liquid water, which is in good agreement with the measured value of 0.99 +/- 8% cGyh(-1)U(-1) reported by Meigooni et al. The anisotropy constant of the EchoSeed (125)I brachytherapy source was found to be 0.960 in liquid water.

CONCLUSIONS

The Monte Carlo Simulated TG-43 dosimetric parameters of the EchoSeed were determined and the results were compared with the published measured data.

Prostate brachytherapy: comparison of dose distribution with different 125I source designs

PURPOSE

To evaluate the interchangeability of various commercially available iodine 125 ((125)I) sources and to assess the dosimetric effect of a change in source.

MATERIALS AND METHODS

A modified peripherally loading prostate brachytherapy plan to deliver 145 Gy was devised by using a model (125)I source, which until recently was the only available (125)I source. A dose-volume histogram was generated. By using the available radial dose functions and anisotropy distributions for eight other currently commercially available sources, the same implant placement was planned and dose-volume histogram distributions tabulated. This exercise was performed for 15-, 45-, and 60-cm(3) glands. No implants were placed, and no physical radiation measurements were made. Dose calculations were theoretic: They were generated by using a widely available treatment planning system.

RESULTS

There was little difference in dose distribution to the volume receiving 100% of the prescribed dose (<6%); only one source showed a difference greater than 2%. Large differences, up to -40% to +60%, were seen in the volume of tissue encompassed within internal high-dose regions receiving 150% or 200% of the prescribed dose. These findings held true, irrespective of gland size, within a clinically relevant range (15-60 cm(3)) and for a uniformly loaded radionuclide distribution.

CONCLUSION

Reviewing only peripheral dose at or near the prescription dose of 145 Gy revealed little difference in doses for various source designs. Marked differences in high-dose regions were seen and may affect the dose received by internal sites. Effects of these changes on cure and/or complications remain speculative.

Comparison of I-125 sources used for permanent interstitial implants

The increase in the number of manufacturers of 125I sources used in prostate brachytherapy has generated many questions in the radiation oncology community. In this investigation, the physical and dosimetric characteristics were evaluated for the following sources listed by marketing company and source model: Nycomed-Amersham 6711 (OncoSeed), Nycomed-Amersham 6702, Mentor IoGold, UroMed Symmetra, Imagyn IsoSTAR, UroCor, (PSA, Mallincrkrodt) ProstaSeed, Syncor PharmaSeed, SourceTech Medical, (BARD) 125Implant (BrachySource), Med-Tec I-Plant, Best Medical Model 2301, DraxImage BrachySeed, and International Brachytherapy, Inc. (IBT) InterSource125. The investigation examined the differences in design, construction, and the dosimetric characteristics created from each source. The dosimetric characteristics of the new sources were compared to that of the Amersham 6711 source. Parameter studies have led to the development of a simple equation that can be used to clinically convert the standard 6711 source strength to an equivalent strength of a new source.