Dosimetric investigation of 103Pd permanent breast seed implant brachytherapy based on Monte Carlo calculations

PurposePermanent breast seed implant using ¹⁰³Pd is emerging as an effective adjuvant radiation technique for early stage breast cancer. However, clinical dose evaluations follow the water-based TG-43 approach with its considerable approximations. Toward clinical adoption of advanced TG-186 model-based dose evaluations, this study presents a comprehensive investigation for permanent breast seed implant considering both target and normal tissue doses.Methods and MaterialsDose calculations are performed with the free open-source Monte Carlo (MC) code, egs_brachy, using two types of virtual patient models: TG43sim (simulated TG-43 conditions) and MCref (heterogeneous tissue modeling from patient CT, seeds at implant angle) for 35 patients. The sensitivity of dose metrics to seed orientation and tissue segmentation are assessed.ResultsIn the target volume, D₉₀ is 14.1 ± 5.8% lower with MCref than with TG43sim, on average. Conversely, normal tissue doses are generally higher with MCref than with TG43sim, for example, by 22 ± 13% for skin D_1cm2, 82 ± 7% for ribs D_max, and 71 ± 23% for heart D_1cm3. Discrepancies between MCref and TG43sim doses vary over the patient cohort, as well as with the tissue and metric considered. Skin doses are particularly sensitive to seed orientation, with average difference of 4% (maximum 28%) in D_1cm2 for seeds modeled vertically (egs_brachy default) compared with those aligned with implant angle.ConclusionsTG-43 dose evaluations generally underestimate doses to critical normal organs/tissues while overestimating target doses. There is considerable variation in MCref and TG43sim on a patient-by-patient basis, motivating clinical adoption of patient-specific MC dose calculations. The MCref framework presented herein provides a consistent modeling approach for clinical implementation of advanced TG-186 dose calculations.     

Preparation of 103Pd seed-molecular plating of 103Pd onto silver rod.

A method for 103Pd "molecular plating" onto the surface of a silver rod is reported. The optimal composition of the plating bath is as follows: palladium chloride 0.1 mol/l, formaldehyde 2 mol/l, nitric acid 1 mol/l, and formic acid 0.4 mol/l. The 103Pd molecular plating procedure will last 25 min at 30 degrees C. This article provides a valuable experience for the preparation of 103Pd brachytherapy seed.     

103Pd种子源植入治疗肿瘤近期疗效观察

目的评估^103Pd种子源植入治疗恶性肿瘤的近期疗效。方法2l例确诊的恶性肿瘤患者，由治疗计划系统(TPS)通过不同术式植入^103Pd种子源(196．1—2127．5MBq)，其中15例采用均-布源，6例前列腺癌采用中心消融，外周布源。观察肿瘤大小、局部复发和远处转移情况；并按肿瘤放射协作组，欧洲肿瘤研究及治疗(RTOG／EORTC)急性或后期放疗副作用评分标准进行评分。结果随访期内2l例患者均未见局部复发和远处转移，RTOG／EORTC评分为0分19例，占90．5％，1分2例。占9．5％。结论^103Pd种子源植入治疗肿瘤近期效果安全可行。     

103Pd loaded cartridge air kerma strength verification.

Using radioactive 125I or 103Pd seeds in large number to treat prostate cancer has become popular. This procedure's popularity translates to increased physicist and dosimetrist workloads with regard to performing source strength assays. In addition, radiation exposure to the physicists' and dosimetrists' hands as a result of source handling has increased significantly. As a result of these increases, a method of source calibration using applicator cartridges was developed to allow safe handling of sources and expedited source assays. The method uses a holder which allows a cartridge loaded with five to fifteen seeds to be placed in a standard well ionization chamber. Ionization readings are converted to air kerma source strengths which are compared with the manufacturer's stated activity. Excellent agreement between individual seed air kerma strength as well as comparison with the vendor's air kerma strength statement proves the validity of this assay technique. Absorption/geometry correction factors were experimentally derived during the development of this method. These factors allow accurate determination of air kerma source strength from a shipment of Iodine or Palladium seeds.     

A possible in vivo generator (103)Pd/(103m)Rh-Recoil considerations.

The use of Auger emitters as potential radiopharmaceuticals is increasingly investigated. One such radionuclide of interest is (103m)Rh. This can be produced from (103)Ru or from (103)Pd in an in vivo generator. A potential problem with this concept is the recoil of the (103m)Rh out of the carrier molecule and even out of the target cell. In order to determine whether this would happen in the (103)Pd/(103m)Rh case calculations were done to prove that this does not happen. From theoretical considerations it seems that the (103)Pd/(103m)Rh in vivo generator system would be possible.     

Measurements of the dosimetric constants for a new 103Pd brachytherapy source

PURPOSE: This report provides dosimetry information for a new brachytherapy 103Pd source (Model 2335) manufactured by Best Medical International and, through comparisons with data from another published report for the same source, presents a suggested hybrid dataset for clinical applications. METHODS AND MATERIALS: Dose measurements were made using thermoluminescent dosimeters (TLD), with the 103Pd source in the center of a Virtual Water phantom on a rotating insert, allowing for a number of different possible angles, and 12 TLD cubes (1.0 x 1.0 x 1.0 mm) and 16 TLD rods (1.0 x 1.0 x 3.0 mm) arranged in an outward spiral pattern at distances ranging from 0.5 to 5.0 cm. All measurements are based on the 2000 correction of the National Institute of Standards and Technology 1999 standard. RESULTS: From these measurements, tables are presented for the radial dose function and the anisotropy function. The dose rate constant=0.71 +/- 0.07 cGy h(-1) U(-1) and the anisotropy constant=0.96 +/- 0.03. CONCLUSIONS: The dose rate constant for the hybrid=0.70 and the anisotropy constant for the hybrid=0.92, Hybrid tables are presented.     

Measurement of a 103Pd solution using the TDCR method by LSC.

Palladium 103 is a radionuclide used in brachytherapy sources for the treatment of prostate cancers and also for other medical applications. It decays through electron capture to excited levels of 103Rh. This paper describes the calculation method used to compute the detection efficiency in the framework of the triple to double coincidence ratio model. The calculation of the energy transferred to the scintillator is made by considering the various atomic events following the electron capture and the electron conversion. The energy deposited in the scintillator after the absorption of X-rays is calculated using the PENELOPE stochastic calculation code. The main contributors to the final uncertainty and their covariance matrix are discussed. As the calculation method cannot be reduced to an explicit function, this paper describes the Monte Carlo method used for the evaluation of uncertainties.     

103Pd支架预防胆道再狭窄的实验研究

目的　探讨用1 0 3Pd支架预防胆道再狭窄的可行性。方法　实验犬 12只 (15～ 2 0kg) ,随机分为普通支架组和1 0 3Pd支架组各 6只。术后 30d分别行病理形态学和细胞凋亡定量检测 ,用免疫组织化学方法测定增殖细胞核抗原 (PCNA) ,原位杂交方法测p5 3基因表达 ,并测定外周血和支架周围放射性。结果　术后 30d ,与普通支架组比较 ,1 0 3Pd支架组胆管最大内膜厚度显著减少 (P <0 0 1) ,2组胆管狭窄面积百分比分别为 (5 4 73± 2 1 6 4 ) %和 (17 6 1± 14 5 2 ) % ,差异有显著性 (P <0 0 1) ,1 0 3Pd支架组胆管腔周长及胆管腔面积均较普通支架组明显增加 (P <0 0 1)。1 0 3Pd支架组胆管组织p5 3基因表达增高 ,而普通支架组p5 3基因表达降低 ;前者胆管平滑肌PCNA表达较弱 ,后者平滑肌PCNA表达增高。结论　1 0 3Pd支架照射可抑制平滑肌细胞增殖 ,预防胆管再狭窄。     

A computer program for I-125 seed implant

A computer program, written in FORTRAN, for I-125 permanent interstitial implants has been developed. After implantation, isocentric radiographs are taken using radiotherapy simulator (Siemens) in order to obtain two X-ray images of seeds on the same film. Honeywell DPS8 computer and Hewlett-Packard 7221A plotter are used for the dose calculation. The program calculates the dose distribution at the plane desired using 100 X 100 matrix.     

Treatment planning considerations for permanent breast seed implant

PurposeTo determine an optimal planning strategy for permanent breast seed implant that minimizes dose heterogeneity without degrading coverage and conformity.Methods and MaterialsA simple model was developed to investigate planning strategies incorporating a range of ¹⁰³Pd seed activities, needle and seed spacings, and implants in which seed positions are either restricted to or permitted outside of spherical planning target volumes (PTVs). To address more realistic target geometries, model parameters were used to retrospectively replan a 10-patient cohort in MIM Symphony.ResultsWe confirm that the current clinical modified uniform implantation pattern provides the most favorable dose distributions, given the resolution of the template grid and spacer length. We show that needle and seed counts for replans with seed placement permitted 0.3 cm outside of the PTV are most comparable to clinical preplans, but offer a 13 ± 11% average reduction in the V_PTV150%. Replans produced with seed placement 0.5 cm outside of the PTV provide the largest improvement in dose homogeneity, at the cost of a slight increase in irradiated volume and an increase in the number of needles and seeds.ConclusionsImplanting seeds beyond the PTV within a 0.3–0.5 cm margin, and optimizing seed activity on a per patient basis, allows for improvement in dose homogeneity. However, these plans require higher needle and seed counts and result in a small increase in irradiated volume. Before planning recommendations can be made, the implications of these changes must be investigated in the context of clinical outcome for permanent breast seed implant.     

103Pd支架预防血管成形术后再狭窄量效关系研究

目的　探讨1 0 3Pd支架对血管成形术后再狭窄预防作用的量效关系及是否导致边缘再狭窄。方法　 5 0只雄性新西兰兔随机分为普通支架组和核素支架各剂量组 (8只 组 )。支架植入术后 8周行腹主动脉血管内超声和造影检查。结果　核素支架组随剂量增加 ,支架段血管最小内径和支架段血管管腔切面积均增大 ,狭窄程度减小 ;核素支架 2 5及 35Gy组支架边缘段血管管腔内增生内膜切面积及外弹力板切面积变化 (缩小值 )均小于普通支架组 (P <0 .0 5 )。结论　1 0 3Pd支架可抑制支架内内膜增生 ,减轻支架内狭窄程度 ,且不引起边缘再狭窄。     

Monte Carlo study of the relationship between skin dose and optically stimulated luminescence dosimeter dose in Pd-103 permanent breast seed implant brachytherapy

PurposeTo establish a method for estimating skin dose for patients with permanent breast seed implant based on in vivo optically stimulated luminescence dosimeters (OSLDs) measurements.Methods and MaterialsMonte Carlo simulations were performed in a simple breast phantom using the EGSnrc user code egs_brachy. Realistic models of the IsoAid Advantage Pd-103 brachytherapy source and Landauer nanoDot OSLD were created to model in vivo skin dose measurements where an OSLD would be placed on the skin of a patient with permanent breast seed implant following implantation. Doses to a 0.2 cm³ volume of skin beneath the OSLD and to the sensitive volume within the OSLD were calculated, and the ratio of these values was found for various seed positions inside the breast phantom. The maximum value of this ratio may be used as a conversion factor that would allow skin dose to be estimated from in vivo OSLD measurements.ResultsConversion factors of 0.5 and 1.44 are recommended for OSLDs calibrated to dose to Al₂O₃ and water, respectively, at the point of measurement in the OSLD. These factors were not significantly affected by the addition of extra seeds in the dose calculations.ConclusionsA method for estimating skin dose from OSLD measurements was proposed. Individual institutions should calibrate OSLDs to Pd-103 seeds to apply the results of this work clinically.