基于直线加速器虚拟源模型的蒙特卡洛剂量计算及在IMRT独立验算中的初步应用

目的：研究临床放疗蒙特卡洛剂量计算方法中虚拟源模型的可行性。方法通过蒙特卡洛方法模拟得到记录医用直线加速器机头出射粒子物理特性的相空间文件,分析提取相空间文件中粒子的种类、能谱及位置分布,建立半经验虚拟双光子源抽样模型。结合并行剂量计算引擎GMC,得到3 cm×3 cm、5 cm×5 cm、10 cm×10 cm、20 cm×20 cm和30 cm×30 cm射野及2例临床调强计划的三维水模剂量分布的蒙特卡洛模拟结果,将其与水箱测量结果或医科达Monaco计划系统结果比较,以验证基于虚拟源的蒙特卡洛剂量计算的准确性。结果对5个射野下的水箱中心轴的百分深度剂量曲线以及不同深度的离轴剂量曲线,蒙特卡洛模拟结果与测量结果相差在1％以内。对2例临床调强计划, Monaco计算结果与蒙特卡洛模拟结果的三维通过率分别为98．9％和99．4％（3％／3 mm）,95．1％和95．4％（2％／2 mm）。结论基于虚拟源模型的蒙特卡洛模拟能得到准确的放疗剂量计算结果。     

基于蒙特卡罗模拟散射效应和异质性对高剂量率192Ir近距离治疗剂量分布的影响

目的:探究散射效应和异质性对高剂量率¹⁹²Ir近距离治疗剂量分布的影响。方法:用MCNP5蒙特卡罗方法模拟Flexisource HDR ¹⁹²Ir放射源的TG-43剂量学参数：剂量率常数Λ、径向剂量函数g(r)、各向异性函数F(r,θ)。基于临床分别构建身体围度差异、偏心、浅表三种非完全散射和组织成分差异、肺插植、腔道插植三种异质性的简化模型,分别计算放射源的径向剂量分布,并通过比较各简化模型和标准模型的同点径向剂量的偏差来评价散射效应和异质性对剂量分布的影响。结果:Λ、g(r)和F(r,θ)模拟值和TPS数据的偏差均小于1%;非完全散射：TPS高估2 cm、5 cm、10 cm处的真实剂量可达约4%、14.8%、16.4%;皮质骨：TPS高估2 cm、5cm、10 cm处的真实剂量约0.7%、1.14%、10%;肿瘤介质：TPS高估真实剂量平均约1.1%;肺介质：TPS高估0.5 cm～6 cm内的真实剂量平均约1.80%,低估6 cm～15 cm内的真实剂量平均约7.77%;肺插植：半径1 cm肿瘤,TPS高估0.5 cm～8 cm内的...     

宫颈癌三维适形调强放疗剂量分布特性研究

目的研究宫颈癌调强放疗(IMRT)和三维适形放疗(3D-CRT)时靶区及其周围正常组织受照剂量的差异。方法用WiMRT三维适形调强放疗计划系统分别进行6~9个照射角度的3D-CRT和IMRT计划设计,肿瘤量45Gy,计算出正常组织和靶区的剂量-体积直方图以及所需照射的总跳数,并根据10cm×10cm射野外漏射线和散射线剂量率的测量值,估算3D-CRT和IMRT放疗时射野外正常组织所受漏射线和散射线剂量。结果照射野数和照射角度一致,IMRT时膀胱、直肠、阴道所受平均剂量分别只有3D-CRT时的19.5%(29.3/150.3)、64.5%(538.0/833.0)和61.0%(1553.6/2546.3),靶区平均受照剂量略高于3D-CRT。IMRT病人射野外正常组织所受散射线和漏射线剂量约为3D-CRT病人的1.5倍。结论宫颈癌IMRT时射野外正常组织受漏射线和散射线照射剂量较高,但射野内靶区和邻近器官剂量分布优于3D-CRT。     

金属植入物对放射治疗剂量影响的研究

目的：测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据。方法：按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传人放射治疗计划系统（treatment planning system,TPS）中进行模拟计算。按照相同条件,分别用6MV和15MVX线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较。结果：实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3．9％（6MV）和6．6％（15MV）,支架后表面的误差最大为2．8％（6MV）和6．3％（15MV）,距表面距离越远,误差越小。结论：镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤。TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正。     

体外照射加192Ir腔内后装治疗子宫颈癌198例临床结果分析

目的研究192Ir高剂量率腔内后装配合体外放射治疗中晚期宫颈癌的疗效和放射反应.方法198例宫颈癌患者采用192Ir高剂量率腔内后装配合体外放射治疗,体外全盆腔常规分割照射36Gy～40Gy后中间挡铅,前后野照射,宫旁剂量20Gy～24Gy.自第二周行腔内后装治疗,1次/周,"A"点6 Gy/次,剂量24Gy～30 Gy/4次～5次.结果全组3年生存率为77.5%,其中Ⅱa期83.3%,Ⅱb期80.6%,Ⅲa期73.6%,Ⅲb期62%.结果显示影响预后生存率的因素是FIGO分期(P=0.000)、总剂量(P=0.027)、有无化疗(P=0.002).早期尿道刺激症发生率11.3%、放射性膀胱炎反应发生率10.2%,放射性直肠炎反应发生率22.4%.结论192Ir高剂量率腔内后装配合体外放射治疗中晚期宫颈癌疗效肯定,副作用少.     

金属植入物对放射治疗剂量影响的研究

目的:测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据。方法:按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传入放射治疗计划系统(treatment planning system,TPS)中进行模拟计算。按照相同条件,分别用6MV和15 MVX线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较。结果:实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3.9%(6MV)和6.6%(15MV),支架后表面的误差最大为2.8%(6MV)和6.3%(15MV),距表面距离越远,误差越小。结论:镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤。TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正。     

Hi-ART螺旋断层治疗机剂量学参数的测量

目的 探讨Hi-ART螺旋断层治疗机照射野剂量学参数测量的内容和方法.方法 用断层治疗机专门配置的微型扫描水箱在治疗条件下测量了6 MV X线的百分深度剂量和射野离轴比,并与常规Primus加速器6 MV X线进行比较.根据AAPM TG51号报告用Tomotrometer剂量仪和A1SL电离室在源皮距85 cm、照射野40 cm×5 cm、1.5 cm深度条件下对断层治疗机进行输出剂量刻度,并对剂量线性和重复性进行测量分析.输出剂量率随机架角的变化分别用0.6 cm3电离室和Unidos剂量仪在直径为3 cm有机玻璃体模中测量和用治疗机自身的MVCT探测器测量.设置不同的照射范围,在固体水组织等效材料中对多叶准直器照射野输出因子进行测量.结果 Hi-ART断层治疗机6 MV X线百分深度剂量的最大剂量点在1.0 cm左右.Hi-ART断层治疗机和Primus 6 MV X线在源皮距85 cm、深度10 cm处的百分深度剂量分别为59.6%和64.7%.单个照射野内剂量分布是不均匀的,在人体左右方向剂量分布呈锥形,在人体头脚方向剂量分布和照射野的宽度有关,40 cm×5 cm照射野的输出剂量率为848.38 cGy/min.剂量仪的读数R和照射时间t的关系为R=-0.017+0.256t,线性相关系数为0.999.重复测量的输出剂量率的最大偏差为1.6%,标准偏差＜0.5%;输出剂量率随机架角度变化的最大偏差为1.1%,标准偏差＜0.5%.多叶准直器相邻叶片对单个叶片照射野的剂量贡献比较大,继续增加叶片数目输出因子基本保持不变.结论 Hi-ART断层治疗机的输出剂量率高,照射野剂量分布不均匀.独特的设计和剂量学特性使其剂量计算模型和调强实现方式更加简单、高效.     

基于蒙特卡罗实现容积调强弧形治疗计划独立剂量验证的应用研究

目的 开发基于蒙特卡罗(MC)的验证平台实现容积调强弧形治疗(VMAT)计划的独立剂量验证。方法 利用EGSnrc/BEAMnrc构建Varian TrueBeam医用直线加速器的机头和准直器模型,并基于机头模型和自编程序搭建患者VMAT计划的独立剂量验证平台,通过平台模拟不同射野大小百分深度剂量(PDD)曲线和离轴比、两个不规则野以及头颈部、胸部和盆腔各1例患者剂量分布。比较不同射野大小PDD曲线和离轴比与蓝水箱测量结果差异,不规则射野与ArcCHECK实测的差异,再通过γ分析法、剂量体积直方图对比分析患者MC模拟剂量、计划系统计算剂量、ArcCHECK实测剂量之间差异,验证平台是否可用于独立剂量验证。结果 对4cm×4cm~40cm×40cm的PDD曲线和离轴比,MC模拟结果和测量结果一致性较好。不规则射野MC模拟结果与ArcCHECK实测相比,在3%/2mm、3%/3mm下γ通过率都在98.1%、99.1%以上;3例不同部位VMAT患者MC模拟剂量和ArcCheck实测剂量在3%/2mm、3%/3mm下γ通过率均好于93.8%、95.9%。通过三维γ分析计划系统计算剂量和MC模拟剂量在3%/3mm下鼻咽癌、肺癌、直肠癌的γ通过率分别为95.2%、98.6%、98.9%;在3%/2mm下依次为90.3%、95.1%、96.7%。结论 基于MC开发的验证平台模拟结果与实际测量结果一致性较好,其模拟结果更接近于患者体内真实剂量分布,初步结果显示可用于VMAT计划的精准独立剂量验证。     

腔内高剂量与低剂量近距离放射治疗中晚期肺痛疗效比较

目的探讨高剂量率后装腔内放疗结合体外放疗治疗中晚期肺癌合适剂量分割与临床疗效.方法61例中晚期肺癌随机分为A组和B组.A组腔内放疗施源器中轴外5～10mm处参考剂量10Gy/次/周×2～3次/2～3周;B组腔内放疗施源器中轴外5～10mm处参考剂量5Gy次/周×4～6次/4～6周.体外放疗两组相同.结果A组1、3、5年局控率分别为74.2%、26.7%和16.7%.B组1、3、5年生存率分别为64.5%、45.2%和20.9%.两组比较,统计学无显著意义(P＞0.05).A组1、3、5年局控率分别为60.0%、33.3%和20.0%.B组1、3、5年局控率分别为74.2%、61.3%和41.9%,两组3、5年局控率有显著意义(P＜0.05).并发症:大咯血、放射性食管炎、气管-支气管炎、肺炎、气管及肺纤维化等A组明显高于B组(P＜0.01).结论192铱高剂量率后装腔内放疗低剂量放疗优于高剂量放疗,疗效高,并发症少.结合体外放射腔内放疗合适剂量应以5Gy/次周,总剂量20～30Gy为宜.     

静态调强放疗中剂量率和叶片位置容差对点吸收剂量的影响

目的 研究调强放疗中剂量率和多叶光栅的叶片位置容差对点吸收剂量(绝对剂量)的影响.方法 选取2例前列腺癌患者的调强治疗计划.将该计划移到封闭小水箱(水模)上,在剂量率分别为100、200、300、400、500 MU/min情况下,利用电离室测量点吸收剂量.调整水箱位置使电离室位于剂量梯度比较小区域,以使剂量梯度对测量结果的影响降到最低.在测量多叶光栅叶片位置容差对点吸收剂量影响时,剂量率不变,叶片位置容差分别为1、2、3、4 mm,调用该治疗计划进行实际测量.治疗计划系统为瓦里安Eclipse,实际测量用瓦里安加速器23EX.结果 随剂量率增大,点吸收剂量测量偏差也增大,最大值和最小值相差1.2%.在叶片控制系统正常工作情况下,叶片位置容差对点吸收剂量影响很小,测量结果相近.结论 因实际治疗时点吸收剂量(绝对剂量)偏差会随剂量率增大而增大,为提高治疗速度并考虑到剂量率对生物效应的影响,在提高剂量率同时也应尽量避免高剂量率所带来的误差,选择合适的剂量率进行治疗.叶片位置容差对点吸收剂量影响不大,但该数值不应设置太大,是为保证实际叶片位置尽可能接近于MLC文件中给出的数值,使实际剂量分布无论在剂量梯度大或剂量梯度小的区域都能与计划所给出的分布尽可能相近,如果叶片控制系统出现故障也可能尽早发现.     

Characterization of a soft X-ray source for intravascular radiation therapy

PURPOSE: A soft X-ray device for intravascular radiation therapy of restenosis is characterized in terms of dose delivery for several artery configurations, including arteries with implanted stents, calcified plaque, and noncentered sources. METHODS AND MATERIALS: The Monte Carlo code MCNP4B was used to determine the X-ray fluence and energy spectra for 15, 20, and 30-kV X-ray source generating voltages. Dose as a function of distance was calculated under a variety of artery conditions. RESULTS: Calculated depth-dose profiles for the X-ray sources are within presumed artery dose tolerance limits for the range of generating voltages considered. Treatment times to deliver 8 Gy to the adventitia range from 2.7 minutes to 6.7 minutes for the 20-kV generating voltage and a 3-cm-long lesion, depending on the diameter of the artery. The does perturbation due to stent wires or calcified plaque is found to be more severe for the X-ray sources than for the radioactive sources. The effects of noncentering are found to be similar for radioactive sources and X-ray sources with generating voltages of 20 kV or higher. CONCLUSION: The results of this study indicate that soft X-ray sources are suitable candidates for intravascular radiation therapy over a wide range of artery sizes, tissue compositions, and stent configurations.     

Some treatment planning considerations for 103Pd and 125I permanent interstitial implants.

Sealed sources of palladium-103 (103Pd), which decay with a half life of 17 days and emit on average 21 keV photons, are now in clinical use for permanent implants. For seed implantation of prostatic cancer, 103Pd implants are usually planned to deliver 115 Gy to full decay at an initial dose rate of 19.7 cGy/hr whereas 125I implants are usually planned to deliver 160 Gy at an initial dose rate of 7.72 cGy/hr. Because of the lower energy of photons emitted by 103Pd compared to the 125I sources (27 keV average energy), the tissue attenuation is more severe for 103Pd sources. The radial dose function drops more steeply with distance from the 103Pd sources compared to the 125I sources, raising a concern about the possibility of cold spots in the tumors implanted with 103Pd sources. To investigate this issue, a detailed analysis of the dependence of dose uniformity as a function of seed spacing for 125I and 103Pd sources in various cubic and spherical configurations was carried out. Using the measured single source dosimetry data as input, dose distributions for a variety of cubic and spherical implants were generated on a computerized treatment planning system. This study indicates that relative dose distributions for 125I and 103Pd implants with the same geometric configuration and number of seeds are very similar inside the implanted volume for implants. Dose uniformity within a target volume implanted with 103Pd seeds is also very similar to that for 125I. To expedite clinical implementation of 103Pd, an atlas of dose distributions for 103Pd implants has been produced for various seed configurations, seed spacings, and target volumes. Using 125I implants as a guideline, clinical procedures for planning of 103Pd implants have been developed. It was found that the total source strength implanted divided by the dimension of the implant can be expressed as an exponential function of implant size, resulting in a simple method for estimating the strength of seeds necessary in an implant. Also, the air kerma strength of 103Pd seeds is about 3.3 times that of 125I sources in an implant with the same geometric configuration and number of seeds, provided treatment doses of 115 Gy and 160 Gy are chosen for 103Pd and 125I implants, respectively.     

Three-dimensional lookup tables for Henschke applicator cervix treatment by HDR 192Ir remote afterloading

Purpose: We have generated three-dimensional (3D) lookup tables for dosimetric analysis and optimization of high-dose rate (HDR) gynecological treatments using the Henschke applicator. The new dosimetry data have been compared with two-dimensional (2D) data currently in use. The 3D dosimetry tables have been implemented in an existing cervix treatment-planning system and have been evaluated through analysis of clinical cases.Methods and Materials: A general Monte Carlo N-Particles (MCNP) transport code was used to compute absorbed dose distributions around the intrauterine tandem and tungsten-shielded ovoid separately. The dosimetry data are represented in the x–y coordinate system for the intrauterine tandem table. The 3D table for the ovoid contains a radial dose function and an anisotropy function, as formulated in the spherical coordinate system. Absorbed dose at a spatial point is calculated by applying bilinear interpolation for the anisotropy function and linear interpolation for the radial dose function. The geometry factor for a finite line source is used. 3D dose calculations and optimization were performed for 20 treatments of 10 patients. The absorbed dose to critical structures, bladder and rectum, was compared by applying both the 2D table currently in use and the new tables.Results: The new 2D table for the intrauterine tandem yields doses different by less than 10% from those with the current table. The 3D table for the shielded ovoids shows as large as a factor of 4 reduction of dose behind the shield compared with the present 2D table. This shielding effect leads to 21.6 ± 9.3% and 20.0 ± 6.6% dose reduction at rectum and bladder, respectively, for actual treatments.Conclusion: Our analysis indicates a need for patient-specific 3D dosimetry to permit more accurate dosimetric evaluation of HDR cervix treatments using shielded applicators. We have also shown that a Monte Carlo simulation code enabled us to derive the lookup tables necessary for 3D planning.     

Effect of Pd radioactive stent on caspase-9, cholangiocarcinoma cell growth and its radiosensitivity

Background

To investigate the effect of ¹⁰³Pd radioactive stent on Caspase-9, cholangiocarcinoma cell growth and its radiosensitivity.

Methods

Cholangiocarcinoma was treated with ¹⁰³Pd radioactive stent at different period. Radiosensitivity of the cells was detected by methyl thiazolyl tetrazolium (MTT) method. Apoptosis of cholangiocarcinoma cells was detected by immunohistochemistry and electron microscope. The activity of Caspase-9 was detected by non-radioimmunoprecipitation, while its protein expression was detected by Western blot.

Results

¹⁰³Pd radioactive stent had significant inhibitive effect on cholangiocarcinoma cells and it could induce apoptosis. After treatment by ¹⁰³Pd radioactive stent for 10 days, the activity of Caspase-9 was gradually enhanced, which was markedly decreased in common stent group. Cholangiocarcinoma cells had relatively high sensitivity to ¹⁰³Pd radiation.

Conclusion

¹⁰³Pd radioactive stent can activate caspase-9 gene to induce apoptosis of cholangiocarcinoma cell, inhibit its growth and enhance its radiosensitivity.     

Radiotherapy dose perturbation of metallic esophageal stents

PURPOSE: Metallic esophageal stents frequently present during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy. The dosimetric effects due to these metallic stents have not been reported. This work investigates these dose effects for various stent models presented during a radiotherapy procedure. METHODS AND MATERIALS: Two types of representative stent models, shell and ring stents, with various designs (e.g., composition and shell thickness or ring spacing), were studied. Three Monte Carlo code systems (EGS4/BEAM, EGSnrc/DOSRZnrc, and MCNP) were used to calculate the dose distributions for 6- and 15-MV external photon beams and for a (192)Ir brachytherapy source with and without a metallic esophageal stent in place. RESULTS: For a single external beam, a dose enhancement is generally observed in front of the stent (upstream) in the region within 4-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 20%. The dose behind the stent (downstream) is generally reduced. For a parallel-opposed pair (POP), a dose enhancement is always observed in the region within 3-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 10% for the 15-MV POP and 8% for the 6-MV POP. The dose effects depend on stent design (e.g., composition, thickness of shell stent, or ring spacing in ring stents). This dependence is reduced for a POP. In the case of the (192)Ir brachytherapy source, a dose enhancement is observed in the region within 1-mm distance from the stent surface. The dose enhancement is approximately 5% at 0.5-mm distance from the stent surface. CONCLUSION: The dose perturbations due to the presence of a metallic esophageal stent during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy should be recognized. These perturbations result in an overdose in esophageal mucosa. The overdose is within 5%-10% at a depth of 0.5 mm in the esophageal wall.     

A comparison of radial dose functions for 103Pd, 125I, 145Sm, 241Am, 169Yb, 192Ir, and 137Cs brachytherapy sources.

Recently, encapsulated sources of 103Pd (21 keV average), 145Sm (41 keV average), 241Am (60 keV), and 169Yb (93 keV average) have been introduced as alternatives to conventional brachytherapy sources of 125I Model 6711 (27 keV average), 125I Model 6702 (28 keV average), 192Ir (369 keV average), and 137Cs (662 keV). To illustrate the dependence of the penetrating ability of photons from brachytherapy sources as a function of photon energy, a comparison of their radial dose functions is presented. Using the ITS Monte Carlo simulation code for photon-electron transport, the radial dose functions were calculated for monoenergetic photon sources with energies in the range of 30 keV to 1 MeV. Also, similar calculations were performed using the photon spectra emitted by the encapsulated brachytherapy sources. To verify the accuracy of Monte Carlo calculations, comparisons are made with our new measured data for 241Am and existing experimental and theoretical data from other investigators. A comparison of radial dose functions indicates that for 241Am, 169Yb, 192Ir and 137Cs sources radial dose functions are close to unity for distances up to 10 cm, for 145Sm the radial dose function drops to about 0.4 at 10 cm, and for 125I and 103Pd it drops precipitously to less than 0.20 at 7 cm. At 5 cm, the measured radial dose functions for 103Pd, 125I Model 6711, 125I Model 6702, 145Sm, 241Am, and 192Ir have values of 0.09, 0.34, 0.38, 0.86, 1.12, and 0.97, respectively. While all of these radioisotopes provide adequate penetrating power for interstitial brachytherapy, only the radioisotopes emitting photons with energies greater than about 40 keV can provide adequate depth dose (that is, small or no tissue attenuation) for intracavitary irradiation. Our criterion for choice of minimum photon energy suitable for intracavitary irradiation is that the radial dose function at 5 cm should not be less than 0.90. Also, note that photons with energies around 80 keV exhibit maximum penetrating ability in solid water for distances up to 5 cm.     

Three-dimensional lookup tables for Henschke applicator cervix treatment by HDR Ir remote afterloading

Purpose: We have generated three-dimensional (3D) lookup tables for dosimetric analysis and optimization of high-dose rate (HDR) gynecological treatments using the Henschke applicator. The new dosimetry data have been compared with two-dimensional (2D) data currently in use. The 3D dosimetry tables have been implemented in an existing cervix treatment-planning system and have been evaluated through analysis of clinical cases.

Methods and Materials: A general Monte Carlo N-Particles (MCNP) transport code was used to compute absorbed dose distributions around the intrauterine tandem and tungsten-shielded ovoid separately. The dosimetry data are represented in the x–y coordinate system for the intrauterine tandem table. The 3D table for the ovoid contains a radial dose function and an anisotropy function, as formulated in the spherical coordinate system. Absorbed dose at a spatial point is calculated by applying bilinear interpolation for the anisotropy function and linear interpolation for the radial dose function. The geometry factor for a finite line source is used. 3D dose calculations and optimization were performed for 20 treatments of 10 patients. The absorbed dose to critical structures, bladder and rectum, was compared by applying both the 2D table currently in use and the new tables.

Results: The new 2D table for the intrauterine tandem yields doses different by less than 10% from those with the current table. The 3D table for the shielded ovoids shows as large as a factor of 4 reduction of dose behind the shield compared with the present 2D table. This shielding effect leads to 21.6 ± 9.3% and 20.0 ± 6.6% dose reduction at rectum and bladder, respectively, for actual treatments.

Conclusion: Our analysis indicates a need for patient-specific 3D dosimetry to permit more accurate dosimetric evaluation of HDR cervix treatments using shielded applicators. We have also shown that a Monte Carlo simulation code enabled us to derive the lookup tables necessary for 3D planning.     

Basic treatment planning parameters for a 90Sr / 90Y source train used in endovascular brachytherapy

Working groups of the AAPM, DGMP, and ESTRO have published recommendations for endovascular brachytherapy, introducing concepts of relevant parameters for dose specification and treatment planning. However, the procedures for this treatment remain often mainly based on trial protocols and manufacturer instructions. Treatment planning requires the essential knowledge of the radial and longitudinal dose distribution, as well as information about geometrical uncertainties. The present study includes a whole data set for daily clinical practice using a commercially available device for endovascular brachytherapy (Novoste Betacath). The dose distribution around the 90Sr seed train was calculated with Monte-Carlo algorithms and verified by film dosimetry. The radial dose profile was determined starting from the surface of the delivery catheter Calculated dose profiles were in good agreement to measured values. The geometrical uncertainties were estimated with a retrospective analysis of 51 patient treatments. This shows the importance of using a safety margin of at least 10 mm between Intervention Length and Reference Isodose Length. Based on the longitudinal dose profile and the necessary safety margins, the maximum treatable intervention length is 25 mm and 45 mm for a 40 mm and 60 mm source train, respectively.