Can intermediate-energy sources lead to elevated bone doses for prostate and head & neck high-dose-rate brachytherapy?

PurposeSeveral radionuclides with high (⁶⁰Co, ⁷⁵Se) and intermediate (¹⁶⁹Yb, ¹⁵³Gd) energies have been investigated as alternatives to ¹⁹²Ir for high-dose-rate brachytherapy. The purpose of this study was to evaluate the impact of tissue heterogeneities for these five high- to intermediate-energy sources in prostate and head & neck brachytherapy.Methods and MaterialsTreatment plans were generated for a cohort of prostate (n = 10) and oral tongue (n = 10) patients. Dose calculations were performed using RapidBrachyMCTPS, an in-house Geant4-based Monte Carlo treatment planning system. Treatment plans were simulated using ⁶⁰Co, ¹⁹²Ir, ⁷⁵Se, ¹⁶⁹Yb, and ¹⁵³Gd as the active core of the microSelectron v2 source. Two dose calculation scenarios were presented: (1) dose to water in water (D_w,w), and (2) dose to medium in medium (D_m,m).ResultsD_w,w overestimates planning target volume coverage compared with D_m,m, regardless of photon energy. The average planning target volume D₉₀ reduction was ∼1% for high-energy sources, whereas larger differences were observed for intermediate-energy sources (1%–2% for prostate and 4%–7% for oral tongue). Dose differences were not clinically relevant (<5%) for soft tissues in general. Going from D_w,w to D_m,m, bone doses were increased two- to three-fold for ¹⁶⁹Yb and four- to five-fold for ¹⁵³Gd, whereas the ratio was close to ∼1 for high-energy sources.ConclusionsD_w,w underestimates the dose to bones and, to a lesser extent, overestimates the dose to soft tissues for radionuclides with average energies lower than ¹⁹²Ir. Further studies regarding bone toxicities are needed before intermediate-energy sources can be adopted in cases where bones are in close vicinity to the tumor.     

瓦里安高剂量率铱源剂量学参数的蒙特卡罗模拟研究

目的 采用美国医学物理师学会（AAPM）和欧洲放射治疗和肿瘤学会（ESTRO）推荐的蒙特卡罗方法对瓦里安GammaMed Plus HDR ¹⁹²Ir源的剂量学参数进行模拟研究。方法 基于EGSnrc蒙特卡罗软件,建立该型号¹⁹²Ir源精确的计算模型。采用公式推导、双线性插值及单位转换等方法,分别得到了单位活度空气比释动能强度、剂量率常数、径向剂量函数以及各向异性函数,并将结果与文献报道数据进行分析比较。结果 研究得到的单位活度空气比释动能强度为9.781×10^-8 U/Bq,剂量率参数为1.113 cGy·h^-1·U^-1,与文献报道的相差在0.4%以内。本研究的径向剂量函数、各向异性函数与文献数据能较好吻合。结论 基于EGSnrc蒙特卡罗软件能对¹⁹²Ir源剂量学特性进行定量研究,这将为进一步研究后装剂量分布,精确评价临床放疗剂量提供理论依据。     

Evaluation of Scatter Contribution and Distance Error by Iterative Methods for Strength Determination of HDR 192Ir Brachytherapy Source

High-dose rate (HDR) ¹⁹²Ir brachytherapy sources are commonly used for management of malignancies by brachytherapy applications. Measurement of source strength at the hospital is an important dosimetry requirement. The use of 0.6-cm³ cylindrical ionization chamber is one of the methods of measuring the source strength at the hospitals because this chamber is readily available for beam calibration and dosimetry. While using the cylindrical chamber for this purpose, it is also required to determine the positioning error of the ionization chamber, with respect to the source, commonly called a distance error (c). The contribution of scatter radiation (M_s) from floor, walls, ceiling, and other materials available in the treatment room also need to be determined accurately so that appropriate correction can be applied while calculating the source strength from the meter reading. Iterative methods of Newton-Raphson and least-squares were used in this work to determine scatter contribution in the experimentally observed meter reading (pC/s) of a cylindrical ionization chamber. Monte Carlo simulation was also used to cross verify the results of the least-squares method. The experimentally observed, least-squares calculated and Monte Carlo estimated values of meter readings from HDR ¹⁹²Ir brachytherapy source were in good agreement. Considering procedural simplicity, the method of least-squares is recommended for use at the hospitals to estimate values of f (constant of proportionality), c, and M_s required to determine the strength of HDR ¹⁹²Ir brachytherapy sources.     

High dose rate brachytherapy using molds after chemoradiotherapy for oral cavity cancer

Purpose  

The aim of this study was to investigate the role of the combined use of customized molds and a high dose rate (HDR) remote afterloading brachytherapy apparatus with a ¹⁹²Ir microsource in the treatment of superficial oral carcinomas after chemoradiotherapy.     

Calibration coefficient of reference brachytherapy ionization chamber using analytical and Monte Carlo methods

A cylindrical graphite ionization chamber of sensitive volume 1002.4 cm³ was designed and fabricated at Bhabha Atomic Research Centre (BARC) for use as a reference dosimeter to measure the strength of high dose rate (HDR) ¹⁹²Ir brachytherapy sources. The air kerma calibration coefficient (N_K) of this ionization chamber was estimated analytically using Burlin general cavity theory and by the Monte Carlo method. In the analytical method, calibration coefficients were calculated for each spectral line of an HDR ¹⁹²Ir source and the weighted mean was taken as N_K. In the Monte Carlo method, the geometry of the measurement setup and physics related input data of the HDR ¹⁹²Ir source and the surrounding material were simulated using the Monte Carlo N-particle code. The total photon energy fluence was used to arrive at the reference air kerma rate (RAKR) using mass energy absorption coefficients. The energy deposition rates were used to simulate the value of charge rate in the ionization chamber and N_K was determined. The Monte Carlo calculated N_K agreed within 1.77 % of that obtained using the analytical method. The experimentally determined RAKR of HDR ¹⁹²Ir sources, using this reference ionization chamber by applying the analytically estimated N_K, was found to be in agreement with the vendor quoted RAKR within 1.43%.     

Biological effective dose evaluation in gynaecological brachytherapy: LDR and HDR treatments, dependence on radiobiological parameters, and treatment optimisation

Purpose

This study was undertaken to compare the biological efficacy of different high-dose-rate (HDR) and low-dose-rate (LDR) treatments of gynaecological lesions, to identify the causes of possible nonuniformity and to optimise treatment through customised calculation.

Materials and methods

The study considered 110 patients treated between 2001 and 2006 with external beam radiation therapy and/or brachytherapy with either LDR (afterloader Selectron, ¹³⁷Cs) or HDR (afterloader microSelectron Classic, ¹⁹²Ir). The treatments were compared in terms of biologically effective dose (BED) to the tumour and to the rectum (linear-quadratic model) by using statistical tests for comparisons between independent samples.

Results

The difference between the two treatments was statistically significant in one case only. However, within each technique, we identified considerable nonuniformity in therapeutic efficacy due to differences in fractionation schemes and overall treatment time. To solve this problem, we created a Microsoft Excel spreadsheet allowing calculation of the optimal treatment for each patient: best efficacy (BED_tumour) without exceeding toxicity threshold (BED_rectum).

Conclusions

The efficacy of a treatment may vary as a result of several factors. Customised radiobiological evaluation is a useful adjunct to clinical evaluation in planning equivalent treatments that satisfy all dosimetric constraints.     

American Brachytherapy Society–Groupe Européen de Curiethérapie–European Society of Therapeutic Radiation Oncology (ABS-GEC-ESTRO) consensus statement for penile brachytherapy

PurposeTo develop a consensus statement between the American Brachytherapy Society (ABS) and Groupe Européen de Curiethérapie/European Society for Therapeutic Radiation and Oncology (GEC-ESTRO) for the use of brachytherapy in the primary management of carcinoma of the penis.Methods and MaterialsThe American Brachytherapy Society and Groupe Européen de Curiethérapie/European Society for Therapeutic Radiation and Oncology convened a group of expert practitioners and physicists to develop a statement for the use of ¹⁹²Ir in low-dose-rate (LDR), pulse-dose-rate, and high-dose-rate (HDR) brachytherapy for penile cancer.ResultsDecades of brachytherapy experience with LDR ¹⁹²Ir wire and pulse-dose-rate ¹⁹²Ir sources for this rare malignancy indicate a penile preservation rate of 70% at 10 years postimplant. Chief morbidities remain stenosis of the urethral meatus and soft tissue ulceration at the primary site. Nonhealing ulceration can be successfully managed with various measures including hyperbaric oxygen treatment. HDR brachytherapy implant procedures are technically similar to LDR. The optimal HDR dose and fractionation schemes are being developed.ConclusionsThe good tumor control rates, acceptable morbidity, and functional organ preservation warrant recommendation of brachytherapy as the initial treatment for invasive T1, T2, and selected T3 penile cancers.     

Comparison of high-dose-rate 192Ir source strength measurements using equipment with traceability to different standards

PurposeAccording to the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism used for dose calculation in brachytherapy treatment planning systems, the absolute level of absorbed dose is determined through coupling with the measurable quantity air-kerma strength or the numerically equal reference air-kerma rate (RAKR). Traceability to established standards is important for accurate dosimetry in laying the ground for reliable comparisons of results and safety in adoption of new treatment protocols. The purpose of this work was to compare the source strength for a high-dose rate (HDR) ¹⁹²Ir source as measured using equipment traceable to different standard laboratories in Europe and the United States.Methods and MaterialsSource strength was determined for one HDR ¹⁹²Ir source using four independent systems, all with traceability to different primary or interim standards in the United States and Europe.ResultsThe measured HDR ¹⁹²Ir source strengths varied by 0.8% and differed on average from the vendor value by 0.3%. Measurements with the well chambers were 0.5% ± 0.1% higher than the vendor-provided source strength. Measurements with the Farmer chamber were 0.7% lower than the average well chamber results and 0.2% lower than the vendor-provided source strength. All of these results were less than the reported source calibration uncertainties (k = 2) of each measurement system.ConclusionsIn view of the uncertainties in ion chamber calibration factors, the maximum difference in source strength found in this study is small and confirms the consistency between calibration standards in use for HDR ¹⁹²Ir brachytherapy.     

Comparison of 3D dose distributions for HDR 192Ir brachytherapy sources with normoxic polymer gel dosimetry and treatment planning system

Radiation fluence changes caused by the dosimeter itself and poor spatial resolution may lead to lack of 3-dimensional (3D) information depending on the features of the dosimeter and quality assurance of dose distributions for high–dose rate (HDR) iridium-192 (¹⁹²Ir) brachytherapy sources is challenging and experimental dosimetry methods used for brachytherapy sources are limited. In this study, we investigated 3D dose distributions of ¹⁹²Ir brachytherapy sources for irradiation with single and multiple dwell positions using a normoxic gel dosimeter and compared them with treatment planning system (TPS) calculations. For dose calibration purposes, 100-mL gel-containing vials were irradiated at predefined doses and then scanned in an magnetic resonance (MR) imaging unit. Gel phantoms prepared in 2 spherical glasses were irradiated with ¹⁹²Ir for the calculated dwell positions, and MR scans of the phantoms were obtained. The images were analyzed with MATLAB software. Dose distributions and profiles derived with 1-mm resolution were compared with TPS calculations. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. The x-, y-, and z-axes were defined as the sagittal, coronal, and axial planes, respectively, the sagittal and axial planes were defined parallel to the long axis of the source while the coronal plane was defined horizontally to the long axis of the source. The differences between measured and calculated profile widths of 3-cm source length and point source for 70%, 50%, and 30% isodose lines were evaluated at 3 dose levels using 18 profiles of comparison. The calculations for 3-cm source length revealed a difference of > 3 mm in 1 coordinate at 50% profile width on the sagittal plane and 3 coordinates at 70% profile width and 2 coordinates at 50% and 30% profile widths on the axial plane. Calculations on the coronal plane for 3-cm source length showed > 3-mm difference in 1 coordinate at 50% and 70% and 2 coordinates at 30% profile widths. The point source measurements and calculations for 50% profile widths revealed a difference > 3 mm in 1 coordinate on the sagittal plane and 2 coordinates on the axial plane. The doses of 3 coordinates on the sagittal plane and 4 coordinates on the axial plane could not be evaluated in 30% profile width because of low doses. There was good agreement between the gel dosimetry and TPS results. Gel dosimetry provides dose distributions in all 3 planes at the same time, which enables us to define the dose distributions in any plane with high resolution. It can be used to obtain 3D dose distributions for HDR ¹⁹²Ir brachytherapy sources and 3D dose verification of TPS.     

Dosimetry errors in endovascular high-dose-rate brachytherapy

Monte Carlo data were used to demonstrate the dosimetry of the microSelectron high-dose-rate (HDR) iridium 192 (¹⁹²Ir) stepping source. These data were used to assess the accuracy of the Nucletron brachytherapy planning system (BPS version 13) for peripheral vessel endovascular brachytherapy. Dose rates from the high-dose-rate (HDR) source are calculated using the Monte Carlo code MCNP4A. Calculations are made at 0.25-cm intervals in the longitudinal direction on sleeves of radii of 1 and 0.25 cm. The Monte Carlo data are summed and weighted to simulate the longitudinal dose distribution at a distance of 1 and 0.25 cm from an ¹⁹²Ir source stepping through a straight pathway. A comparison is made between the simulated Monte Carlo dosimetry and the Nucletron brachytherapy planning system’s dosimetry. This study illustrates and quantifies the dosimetric errors at small distances associated with a point source dose calculation algorithm. The effects of step size, dwell time optimization, and active length on the accuracy of BPS v.13 for HDR endovascular brachytherapy are demonstrated.     

Dosimetric characterization of a newly designed encapsulated interstitial brachytherapy source of iodine-125—model LS-1 BrachyseedTM

A newly designed encapsulated ¹²⁵I source has been introduced (Model LS-1 BrachySeed^TM manufactured by DRAXIMAGE Inc.) for interstitial brachytherapy . In this source ¹²⁵I radionuclide is contained in two ceramic beads positioned at each end of a titanium capsule. The source contains a rod of Pt–Ir, which serves as a radiographic marker for source localization in the patient. Principle photon emissions are 27.4 and 31.0 keV X-rays and a 35.5 keV gamma-ray. The 22.2 and 25.5 keV silver X-rays produced by fluorescence of the silver dopant in the ceramic bead radioisotope carriers, are also emitted. In this work, the dosimetric characteristics of the ¹²⁵I source were measured with micro LiF TLD chips and dosimetry parameters were characterized based upon the American Association of Physicists in Medicine, Task Group, No. 43 formalism. The corrected 1999 National Institute of Standards and Technology standard for low energy interstitial brachytherapy sources was used to specify the air kerma strength of the sources used in this study. The dose rate constant of the sources was determined to be 1.02±0.07 cGyh⁻¹ U⁻¹. The radial dose function was measured and was found to be similar to that of the silver-based model 6711 ¹²⁵I source. However, the anisotropy function of the Model LS-1 BrachySeed^TM source is considerably better than that of model 6711 ¹²⁵I source, especially on the points along and close to the longitudinal axis of the source. The BrachySeed^TM model LS-1 provides more isotropic angular dose distribution in tissue than model 6711 ¹²⁵I source. The anisotropy constant for the model LS-1 source was determined to be 1.006, which is considerably better than the value of 0.93 for the model 6711 source.     

Comparative study of dosimetry between high-dose-rate and permanent prostate implant brachytherapies in patients with prostate adenocarcinoma

PURPOSE: To compare the dose coverage, conformity, and homogeneity between high-dose-rate (HDR) brachytherapy and permanent prostate implant (PPI) in the treatment of prostate adenocarcinoma. METHODS AND MATERIALS: From January 2003 to August 2004, 54 patients (108 implants) underwent HDR brachytherapy of prostate cancer with iridium-192 stepping source. Of patients who underwent PPI brachytherapy with iodine-125, 72 patients were randomly selected for the purpose of dosimetric comparison. PPI preplan was done based on transrectal ultrasound study, and postplan was done using CT 1 month after implant. Dosimetric parameters of HDR were compared to that of PPI preplan and postplan. RESULTS: HDR brachytherapy had lower D90 (111.5% vs. 120.2%), lower V100 (97.2% vs. 99.6%), lower natural dose ratio (1.03 vs. 1.13), higher conformal index (0.69 vs. 0.62), and higher homogeneity index (0.63 vs. 0.52) than PPI preplan (all p < 0.0001). All the dosimetric parameters of PPI postplan including D90 (86.7%), V100 (82.0%), natural dose ratio (0.92), conformal index (0.53), and homogeneity index (0.42) were inferior to HDR brachytherapy (all p < 0.0001). CONCLUSIONS: HDR brachytherapy of the prostate can provide better dose coverage, conformity, and homogeneity compared to PPI.     

Single dose irradiation response of pig skin: a comparison of brachytherapy using a single, high dose rate iridium-192 stepping source with 200 kV X-rays

An experimental brachytherapy model has been developed to study acute and late normal tissue reactions as a tool to examine the effects of clinically relevant multifractionation schedules. Pig skin was used as a model since its morphology, structure, cell kinetics and radiation-induced responses are similar to human skin. Brachytherapy was performed using a microSelectron high dose rate (HDR) afterloading machine with a single stepping source and a custom-made template. In this study the acute epidermal reactions of erythema and moist desquamation and the late dermal reactions of dusky mauve erythema and necrosis were evaluated after single doses of irradiation over a follow-up period of 16 weeks. The major aims of this work were: (a) to compare the effects of iridium-192 (192Ir) irradiation with effects after X-irradiation; (b) to compare the skin reactions in Yorkshire and Large White pigs; and (c) to standardize the methodology. For 192Ir irradiation with 100% isodose at the skin surface, the 95% isodose was estimated at the basal membrane, while the 80% isodose covered the dermal fat layers. After HDR 192Ir irradiation of Yorkshire pig skin the ED50 values (95% isodose) for moderate/severe erythema and moist desquamation were 24.8 Gy and 31.9 Gy, respectively. The associated mean latent period (+/- SD) was 39 +/- 7 days for both skin reactions. Late skin responses of dusky mauve erythema and dermal necrosis were characterized by ED50 values (80% isodose) of 16.3 Gy and 19.5 Gy, with latent periods of 58 +/- 7 days and 76 +/- 12 days, respectively. After X-irradiation, the incidence of the various skin reactions and their latent periods were similar. Acute and late reactions were well separated in time. The occurrence of skin reactions and the incidence of effects were comparable in Yorkshire and Large White pigs for both X-irradiation and HDR 192Ir brachytherapy. This pig skin model is feasible for future studies on clinically relevant multifractionation schedules in a brachytherapy setting.     

后装治疗源192 Ir空气比释动能强度检测 与评价

目的 研究用井型电离室测量后装192Ir源空气比释动能强度的方法.方法 用CDX-2000A静电计和HDR 1000井型电离室,现场检测30台后装192Ir源空气比释动能强度,根据源外观活度与空气比释动能强度转换系数,计算源外观活度.用实测源活度与厂家给出的初始源活度比较,相对偏差应在±5%内符合要求.结果 对所有检测的30台后装192Ir源活度与厂家初始源活度比较,相对偏差在-0.1%～4.4%范围内.结论 井型电离室测量法简便,准确度高,在医院可用于质量控制检测.

Abstract：

Objective To study the method of measuring air kerma strength of afterloading units with 192Ir source by using well type ionization chamber.MethodsThe air kerma strength of 30 afterloading units with 192Ir source was measured using 2000A electrometer and 1000 plus well type ionization chamber,and apparent activity of the source was calculated with the air kerma strength and apparent activity conversion factor.The measured activity of the source was compared with the original value of the source provided by the manufacturer,and the relevant deviation should be within ± 5%.Results Theair kerma strength of afterloding units with 192Ir sources was tested.The relevant deviation of the measured activity and the original value was within -0.1%-4.4%.Conclusions The measurement method with a well type ionization chamber is convenient and highly accurate which can be used for the test of quality control in hospitals.     

免冲洗胶片法测量后装机192Ir放射源到位精度及步进距离精度

目的 研究使用免冲洗胶片测量后装机¹⁹²Ir放射源到位精度及步进距离精度的方法。方法 使用GAFCHROMIC^® EBT³型免冲洗胶片对1台国产后装机¹⁹²Ir放射源到位精度及步进距离精度进行测量。曝光后的胶片使用EPSON PREFACTION V700 PHOTO胶片扫描仪扫描成胶片分析软件要求的图像格式,然后用SNC Patient 5.2软件中的胶片分析软件对图像进行分析。 结果 以源活性中心为基准点,该后装机使用胶片法测量的¹⁹²Ir放射源到位精度为-0.75 mm。免冲洗胶片分析方法能够分辨2个驻留点间5 mm的步进距离精度,不能够分辨2个驻留点间2.5 mm的步进距离精度;2.5 mm步进距离精度可通过测量3个连续驻留点第1点和第3点间距离是否为5 mm的方法进行间接判断。该后装机使用胶片法测量的连续9个驻留点间的5 mm步进距离无偏差;2.5 mm步进距离精度间接判断结果无偏差。使用胶片法测量的后装机¹⁹²Ir放射源到位精度符合国家标准要求。结论 免冲洗胶片方法可以用于后装机¹⁹²Ir放射源到位精度及步进距离精度的测量。     

192Ir高剂量率近距离放疗在结直肠癌术后复发肺内寡转移治疗的初步应用

目的 初步探讨运用近距离放射治疗结直肠癌术后复发肺内寡转移患者的临床疗效,评估其可行性。方法 回顾性收集河北省沧州中西医结合医院自2013年5月至2017年10月入院的结直肠癌术后肺内寡转移患者的病例,10例患者共15个病灶,采用CT引导下¹⁹²Ir高剂量率近距离放射治疗肺部转移病灶。应用定位CT扫描图像,将插植针置入肿瘤,在CT引导下调整插植针至合适位置,将插植完成后图像传至计划系统,勾画靶区和危及器官,进行三维重建,制定放疗计划,计划通过后实施治疗,采用单次放疗,剂量20 Gy。结果 10例患者均顺利完成治疗,1级不良事件发生率30%,其中1例为轻度咳嗽,2例为痰中带血,无严重不良事件发生。治疗后1年肿瘤局部控制率（LC）为93.3%,其中1例患者治疗6个月后局部进展,再次实施近距离放射治疗,中位无进展生存期（PFS）为8.5个月,中位总生存（OS）为14.7个月。结论 对于无法手术的结直肠癌术后复发肺内寡转移患者来说,近距离放射治疗是一种可选择的安全可行的治疗方式,短期内可重复治疗,不良反应小,肿瘤局部控制率佳。     

Radiation recall reaction with docetaxel administration after accelerated partial breast irradiation with electronic brachytherapy

PurposeAccelerated partial breast irradiation (APBI) offers several advantages over whole breast irradiation. Electronic brachytherapy may further reduce barriers to breast conserving therapy by making APBI more available. However, its toxicity profile is not well characterized.Methods and MaterialsA 60-year-old woman was treated with APBI using Axxent (Xoft, Sunnyvale, CA) electronic brachytherapy. One month after APBI, a cycle of docetaxel and cyclophosphamide was given. Within 3 weeks, the patient developed an ulcerative radiation recall reaction in the skin overlying the lumpectomy cavity. To investigate this toxicity, the skin dose from electronic brachytherapy was compared with the dose that would have been delivered by an iridium-192 (¹⁹²Ir) source. Additionally, a dose equivalent was estimated by adjusting for the increased relative biologic effectiveness (RBE) of low energy photons generated by the electronic source.ResultsUsing electronic brachytherapy, the skin dose was 537 cGy per fraction compared with 470 cGy for an ¹⁹²Ir source. Given an RBE for a 40 kV source of 1.28 compared with ¹⁹²Ir, the equivalent dose at the skin for an electronic source was 687 cGy-equivalents, a 46% increase.ConclusionsWe present a case of an ulcerative radiation recall reaction in a patient receiving APBI with electronic brachytherapy followed by chemotherapy. Our analysis shows that the use of electronic brachytherapy resulted in the deposition of significantly higher equivalent dose at the skin compared with ¹⁹²Ir. These findings suggest that standard guidelines (e.g., surface-to-skin distance) that apply to ¹⁹²Ir-based balloon brachytherapy may not be applicable to electronic brachytherapy.