血管内近距离放射治疗剂量影响因素的研究

目的　研究32 P球囊预防血管再狭窄的影响因素。方法　采用组织等效血管和热释光剂量学方法。结果　 2 5mm× 2 0mm空球囊内残留32 P对血管壁造成的剂量影响是 0 92Gy min。当球囊内导管偏离中心时 ,球囊外表面的吸收剂量将降低 2 0 %。气泡位置处的吸收剂量比球囊外表面平均吸收剂量低约 30 %。结论　32 P球囊表面轴向剂量分布较均匀 ,但径向吸收剂量随距离增加迅速减少。血管内近距离放射治疗有很好的临床应用前景。     

放射性液体球囊剂量分布的影响因素探讨

目的研究放射性液体球囊在血管组织内剂量分布的影响因素。方法用模拟实验和理论计算两种方法估算注射压力对球囊的扩张能力、球囊内气泡、导管内核素对血液的不必要照射等影响因素。结果不同注射压力下球囊对血管组织产生的剂量不同，在压力大于4个大气压后，达到最大平衡。球囊内的气泡体积随着压力的增加而减少，对血管剂量的影响也变小。导管内的液体对血液组织有一定剂量的照射。结论用放射性球囊治疗患者时，注射压力、球囊内气泡和导管内的液体对剂量分布有影响。     

32P液体球囊在血管内吸收剂量的研究

目的　研究32 P球囊在血管内的剂量分布。方法　用肌肉等效材料代替血管壁 ,采用热释光剂量学方法模拟测量靶血管轴向和径向吸收剂量率分布 ,并对相关影响因素 (球囊内压力 ,气泡 )进行了研究。结果　 3 0mm× 2 0mm 32 P球囊 ,活度为 92MBq时 ,血管表面平均吸收剂量率为0 48Gy min ,在径向 0 4mm处为 0 2 2Gy min。结论　血管壁表面剂量分布较均匀 ,径向剂量随距离迅速衰减 ,但存在诸多影响因素。     

32P液体球囊在血管组织中的剂量分布

目的　研究放射性液体球囊治疗冠状动脉再狭窄时在血管组织内的剂量分布。方法　用模拟实验和理论计算两种方法估算剂量分布。结果　模拟测量和理论计算的剂量平均值分别为 9 0 ,9 7mGy·min-1 ,两者差异为 7 8%。结论　3 2 P液体球囊的剂量分布在轴向上均匀 ,在径向上快速衰减     

037 源偏离中心和残余斑块对以导管为基础的血管内近距离β源的剂量测定影响

目的：以导管为基础的辐射传递系统使用β和γ放射源能抑制经皮冠状动脉介入术后的再狭窄。放射源在血管腔内偏离中心和残余斑块的存在会影响血管组织的剂量均匀性分布。因此，对临床使用的血管内近距离放射源３２P和９０Sr－９０Y在偏离中心时对血管壁的剂量分布影响进行了调查。方法：计算时假设放射源分别放在血管中心轴上、偏离中心０．５mm和１mm处，血管和周围的组织模拟成均匀分布的水介质，用羟基磷灰石材料，密度为１．４５、１．５５和３．１g／cm３三种模拟不同的斑块；用MCNP４B的蒙特卡罗模拟代码计算剂量，同时考虑残存斑…     

模拟测定103Pd放射性支架在血管中的剂量分布

目的 测定血管内^103Pd放射性支架的剂量分布。方法 采用肌肉组织等效材料代替血管壁，用热释光剂量计模拟测量血管内的剂量分布。结果 当支架活度为9．8MBq时，支架表面累积吸收剂量为9．8Gy(17d)。^103Pd支架表面的剂量分布随径向距离增加而迅速减少，在支架表面径向距离0．4mm处80％的剂量被血管壁吸收。结论 血管内^103Pd支架对血管周围的器官和组织无明显损害。     

β核素球囊预防血管再狭窄的临床剂量估算

目的 探讨核素球囊内照射血管内的吸收剂量分布规律。方法 ①依据吸收剂量点核函数模拟计算^90Y、^186Re、^32P灌注球囊时血管组织中的吸收剂量率分布；②用非线性最小二乘法对吸收剂量率随球囊外径及组织深度的变化进行曲线拟合，并由此导出便于临床使用的经验公式。结果 球囊中吸收剂量率峰值出现在血管腔内球囊中，血管表面位于吸收剂量率曲线的拐点处，血管壁及周围组织中的吸收剂量率以近双指数方式下降。吸收剂量、持续照射时间、初始放射性浓度、组织深度及球囊外半径间的关系可用一经验公式表达。结论 血管组织中的β核素吸收剂量分布呈快速下降。该经验公式具有实用价值。     

放射性充液球囊的剂量学研究

单纯经皮冠脉血管成形术 (ＰＴＣＡ)最大的缺陷是术后再狭窄 ,发生率高达 30 %～ 5 0 %。血管内放射治疗是近年发展起来的防治再狭窄的有效手段。目前其照射方法大致有以下几种 :放射性导丝、放射性液体充盈球囊和放射性支架。放射性液体充盈球囊是将放射性液体注入球囊 ,达到局部照射的目的。放射性液体球囊容易使用 ,并最适合导管室的操作步骤 ,它易进入弯曲血管的中远段 ,具有均匀精确的剂量分布 ,很少受血管大小和形态变异的影响。缺点是有可能发生放射性泄漏 ,但其迅速的代谢和排泄对病人和操作人员影响较小。一、材料和方法1 放射源剂…     

血管内β照射治疗后边缘现象及近期疗效的研究

目的：研究血管内β照射治疗冠状运用动脉支架内再狭窄后边缘现象的发生机制。方法：46例支架内再狭窄患者随机分为放射治疗组（26例，28个支架内再狭窄）和单纯球囊组（20例，20个支架内再狭窄）。放射治疗球囊导管长度为40mm，在普通球囊扩张满意后（残余狭窄＜20％）沿标准导引导丝送到病变远端。放射治疗组均未再植入新的支架。随访记录术后6个月内临床及冠状动脉造影结果。结果：两组患者均以前降支内的病变最多见，而右冠状动脉及左回旋支内的病变较少；放射治疗组弥漫性及局限性支架内再狭窄（分别为43％和35％）远远多于增生性狭窄（22％，P＜0．01），手术成功率为100％，术中及随访期内无死亡及急性心肌梗死发生，病变部位血运重建率为19．2％。其中2例患者接受外科冠状动脉搭桥手术，3例患者行再次单纯球囊扩张。6个月内冠状动脉造影随访率为89％。病变部位再狭窄发生率为13％，显著低于单纯球囊治疗组（60％）。延迟血栓栓塞见于2例患者。放射治疗血管段远端正向重构显著。放射治疗段边缘现象发生率为20％，结论：血管内放射治疗支架内再狭窄安全有效，正确定位导管及放射源是减少边缘现象发生的主要方法。     

冠状动脉腔内近距离放疗的剂量点核函数算法

近年的基础和临床研究表明,在冠状动脉血管成形术中和术后用15~30Gy剂量的腔内近距离照射能使再狭窄发生率降低。剂量点核函数的解析方法被用来计算冠状动脉及其周围组织的剂量分布。本文总结了近年来文献发表的主要剂量点核函数算法。     

Dosimetry of rhenium-188 diethylene triamine penta-acetic acid for endovascular intra-balloon brachytherapy after coronary angioplasty

To examine the possibility of using rhenium-188 diethylene triamine penta-acetic acid (DTPA) for endovascular intra-balloon brachytherapy after angioplasty, dose distribution around the balloon was calculated and validated by film dosimetry. Medical internal radiation dosimetry (MIRD) was calculated assuming that the balloon had ruptured and that the contents had been released into the systemic circulation. 188Re-perrhenate eluate from the 188W/188Re generator was concentrated using an ion column and used to label DTPA. The dose distribution around the angioplasty balloon (20 mm length, 3 mm diameter cylinder) was estimated by Monte Carlo simulation using the EGS4 code. The time required for 17.6 Gy to be absorbed at 1 mm from the balloon's surface following application of 3700 MBq/ml of 188Re was found to be 278 s. Fifty percent of the energy was deposited in the first millimetre of the vessel wall from the balloon's surface. The calculated radiation absorbed dose agreed with that measured by film dosimetry, which was performed using a water phantom, with errors ranging from 9.4% to 17%. Upon balloon rupture the total amount of 188Re-DTPA was presumed to enter the systemic circulation. The resulting radiation absorbed dose was calculated using the MIRDOSE3 program and residence times obtained from dogs and amounted to 0.0056 mGy/MBq to the whole body and 4.56 mGy/MBq to the urinary bladder. The absorbed dose of 188Re-DTPA to the whole body was one-tenth of that of 188Re-perrhenate. A window-based program was developed to calculate the exposure time and the radiation dose absorbed as a function of the 188Re concentration and the arbitrary distance from the balloon to the surrounding tissues. We conclude that 188Re-DTPA is easy to prepare, safe to use and suitable for intra-balloon brachytherapy after coronary angioplasty.     

Rectal wall sparing by dosimetric effect of rectal balloon used during intensity-modulated radiation therapy (IMRT) for prostate cancer.

The use of an air-filled rectal balloon has been shown to decrease prostate motion during prostate radiotherapy. However, the perturbation of radiation dose near the air-tissue interfaces has raised clinical concerns of underdosing the prostate gland. The aim of this study was to investigate the dosimetric effects of an air-filled rectal balloon on the rectal wall/mucosa and prostate gland. Clinical rectal toxicity and dose-volume histogram (DVH) were also assessed to evaluate for any correlation. A film phantom was constructed to simulate the 4-cm diameter air cavity created by a rectal balloon. Kodak XV2 films were utilized to measure and compare dose distribution with and without air cavity. To study the effect in a typical clinical situation, the phantom was computed tomography (CT) scanned on a Siemens DR CT scanner for intensity-modulated radiation therapy (IMRT) treatment planning. A target object was drawn on the phantom CT images to simulate the treatment of prostate cancer. Because patients were treated in prone position, the air cavity was situated superiorly to the target. The treatment used a serial tomotherapy technique with the Multivane Intensity Modulating Collimator (MIMiC) in arc treatment mode. Rectal toxicity was assessed in 116 patients treated with IMRT to a mean dose of 76 Gy over 35 fractions (2.17-Gy fraction size). They were treated in the prone position, immobilized using a Vac-Loktrade mark bag and carrier-box system. Rectal balloon inflated with 100 cc of air was used for prostate gland immobilization during daily treatment. Rectal toxicity was assessed using modifications of the Radiation Therapy Oncology Group (RTOG) and late effects Normal Tissue Task Force (LENT) scales systems. DVH of the rectum was also evaluated. From film dosimetry, there was a dose reduction at the distal air-tissue interface as much as 60% compared with the same geometry without the air cavity for 15-MV photon beam and 2x2-cm field size. The dose beyond the interface recovered quickly and the dose reductions due to air cavity were 50%, 28%, 11%, and 1% at 2, 5, 10, and 15 mm, respectively, from the distal air-tissue interface. Evaluating the dose profiles of the more clinically relevant situation revealed the dose at air-tissue interface was approximately 15% lower in comparison to that without an air cavity. The dose built up rapidly so that at 1 and 2 mm, there was only an 8% and 5% differential, respectively. The dosimetric coverage at the depth of the posterior prostate wall was essentially equal with or without the air cavity. The median follow-up was 31.3 months. Rectal toxicity profile was very favorable: 81% (94/116) patients had no rectal complaint while 10.3% (12/116), 6.9% (8/116), and 1.7% (2/116) had grade 1, 2, and 3 toxicity, respectively. There was no grade 4 rectal toxicity. DVH analysis revealed that none of the patients had more than 25% of the rectum receiving 70 Gy or greater. Rectal balloon has rendered anterior rectal wall sparing by its dosimetric effects. In addition, it has reduced rectal volume, especially posterior and lateral rectal wall receiving high-dose radiation by rectal wall distension. Both factors may have contributed to decreased rectal toxicity achieved by IMRT despite dose escalation and higher than conventional fraction size. The findings have clinical significance for future very high-dose escalation trials whereby radiation proctitis is a major limiting factor.     

Die bedeutung eines rektumballons als interne immobilisation bei der konformalen strahlentherapie des prostatakarzinoms

BACKGROUND: As known from the literature, prostate motion depends on different bladder and/or rectum fillings. The aim of this study was to analyze the influence of a rectum balloon catheter, used as an internal immobilization device, on prostate and rectum motion during the treatment course. Moreover we have analyzed if the balloon enables an increase of the distance between the prostate and the posterior rectum wall. PATIENTS AND METHODS: Ten patients with localized prostate cancer (T1 to T3) underwent computed tomographic examinations with and without rectal balloon (filled with 40 ml air) at 3 times during treatment course (at the start, middle and end of treatment). Edges of prostate, rectum and bladder were measured in relation to bony reference structures and compared for both examination series (with and without balloon). RESULTS: An increase of the distance between the prostate and the posterior rectal wall of 8 mm was observed at the base of the prostate when using the rectum balloon (Figures 1a,b and 2). Moreover prostate motion in the ventrodorsal direction > or = 4 mm (1 SD) was reduced from 6/10 patients (60%) to 1/10 patients (10%) using the rectal balloon (Table 3, Figure 3). In general, deviations in the latero-lateral and cranio-caudal directions were less (mean < or = 2 mm, 1 SD), no difference between both examination series (with and without balloon) was observed. CONCLUSION: Rectal balloon catheter offers a possibility to reduce prostate motion and rectum filling variations during treatment course. In addition it enables an increase in the distance between prostate and posterior rectal wall, which could enable an improved protection of the posterior rectal wall.     

CT analysis of mucosal surface dose in intraluminal irradiation for esophageal cancer

PURPOSE: Balloon applicators are generally used in intraluminal irradiation for esophageal cancer. CT exhibits a distortion of the applicator during treatment. Because little attention has been paid to dose non-uniformity in the esophageal mucosa, we analyzed mucosal surface dose using CT. MATERIALS AND METHODS: Eleven patients with esophageal cancer treated with a double-lumen balloon applicator (balloon length: 15 cm, diameter: 20 mm) were evaluated. Reference dose was prescribed at 5 mm under the mucosal surface. Mucosal surface points were determined from CT images, and relative surface dose to reference dose was calculated. Hot and cold spots were defined respectively, as dose points receiving at least 200% and less than 100% of the reference dose. RESULTS: The mean mucosal dose ranged from 138% to 174%. Mucosal dose was distributed widely from 100% to 199% in 94% of all patients. Hot and cold spots accounted for 5.3% and 0.7% of mucosal dose points, respectively. CONCLUSION: 1) CT analysis exhibited the inhomogeneity of esophageal mucosal dose in intraluminal irradiation. 2) At present, it is acceptable to prescribe the reference dose at 5 mm under the esophageal surface. 3) Balloon applicators should be improved to achieve dose uniformity in the esophageal mucosa.     

Post-stenting intravascular brachytherapy trials on hypercholesterolemic rabbits using 32P liquid sources: implications for prevention of in-stent restenosis

PURPOSE: Liquid sources of radiation delivered in angioplasty balloons may be a convenient self-centering device used for prevention of in-stent restenosis. To test the effectiveness of this method an intravascular brachytherapy study was performed using 32P liquid sources in an animal model. METHODS: The radial dose distribution around angioplasty balloons filled with solutions of Na 2H 32PO 4 was calibrated by thermoluminescence dosimetry. The animal experiments were performed in rabbits with induced hypercholesterolemia. The balloons containing 32P were introduced into iliac arteries immediately after stent implantation. Estimated 7-49 Gy doses required 30-100 min irradiations. Radiation effects were evaluated by comparing the thickness of various components of the artery wall. RESULTS: Doses of 7, 12, 16 or 49 Gy on the internal artery surface required 30-100 min of irradiation. The dose of 49 Gy at "zero" distance corresponding to 16 Gy at 1.0 mm from the balloon surface reduced hypertrophy in every layer of the arterial wall: in the intima the cross-sectional areas were 0.13 versus 0.91 mm 2, in the media were 0.5 versus 0.46 mm 2 and in the adventitia were 0.04 versus 0.3 mm 2 (p <0.05). A dose of 7 Gy at the balloon surface produced adverse irradiation effects: the intimal area of the artery was 2.087 versus 0.857 mm 2, the medial area was 0.59 versus 0.282 mm 2 and the adventitial area was 0.033 versus 0.209 mm 2 in treated and control arteries, respectively. CONCLUSION: Application of a 49 Gy irradiation dose to the internal arterial surface effectively prevented in-stent restenosis.     

Dosimetry of rhenium-188 diethylene triamine penta-acetic acid for endovascular intra-balloon brachytherapy after coronary angioplasty

To examine the possibility of using rhenium-188 diethylene triamine penta-acetic acid (DTPA) for endovascular intra-balloon brachytherapy after angioplasty, dose distribution around the balloon was calculated and validated by film dosimetry. Medical internal radiation dosimetry (MIRD) was calculated assuming that the balloon had ruptured and that the contents had been released into the systemic circulation. ¹⁸⁸Re-perrhenate eluate from the ¹⁸⁸W/¹⁸⁸Re generator was concentrated using an ion column and used to label DTPA. The dose distibution around the angioplasty balloon (20 mm length, 3 mm diameter cylinder) was estimated by Monte Carlo simulation using the EGS4 code. The time required for 17.6 Gy to be absorbed at 1 mm from the balloon’s surface following application of 3700 MBq/ml of ¹⁸⁸Re was found to be 278 s. Fifty percent of the energy was deposited in the first millimetre of the vessel wall from the balloon’s surface. The calculated radiation absorbed dose agreed with that measured by film dosimetry, which was performed using a water phantom, with errors ranging from 9.4% to 17%. Upon balloon rupture the total amount of ¹⁸⁸Re-DTPA was presumed to enter the systemic circulation. The resulting radiation absorbed dose was calculated using the MIRDOSE3 program and residence times obtained from dogs and amounted to 0.0056 mGy/MBq to the whole body and 4.56 mGy/MBq to the urinary bladder. The absorbed dose of ¹⁸⁸Re-DTPA to the whole body was one-tenth of that of ¹⁸⁸Re-perrhenate. A window-based program was developed to calculate the exposure time and the radiation dose absorbed as a function of the ¹⁸⁸Re concentration and the arbitrary distance from the balloon to the surrounding tissues. We conclude that ¹⁸⁸Re-DTPA is easy to prepare, safe to use and suitable for intra-balloon brachytherapy after coronary angioplasty. Received 27 May and in revised form 7 September 1999     

Monte Carlo dose simulation for intracoronary radiation therapy with a rhenium 188 solution-filled balloon with contrast medium

BACKGROUND: The therapeutic efficacy of percutaneous transluminal coronary angioplasty is limited by the incidence of restenosis. Intracoronary irradiation has shown to be effective in restenosis control by inhibiting the neointimal proliferation. METHODS AND RESULTS: Monte Carlo simulation has been performed to calculate the dose to the vessel wall for intracoronary irradiation with a rhenium 188 solution-filled balloon for restenosis inhibition. With a 3-mm-diameter and 30-mm-long balloon, the radiation dose at 1 mm from the balloon surface was 5.3% lower when the balloon structure was included in geometric modeling of the angioplasty catheter, as compared with that obtained by ignoring the structure. The additional dose reduction due to Hexabrix 320 contrast medium added in 30% of volume ratio was 4.7%. With regard to axial dose distribution, the dose was uniform over the balloon length except near the balloon end, at which the dose was reduced by 35% at a 1-mm-deep layer in the vessel wall. With the Re-188 solution mixed with 30% of Hexabrix 320 in volume ratio, the Re-188 activity to be injected for delivery of 15 Gy to the 1-mm-deep layer by 1-minute irradiation was 27.3 GBq/mL. CONCLUSIONS: Dose estimates produced in this study should be helpful in determining the Re-188 activity to be injected or the irradiation time for a varying situation in terms of length and diameter of the irradiated arterial segment and depth of the target layer.     

Radiation field feature of 188Re esophageal stent

OBJECTIVE: To evaluate the radiation field feature of Re esophageal stent and provide scientific basis for clinical application. METHODS: We measure the beta-ray, gamma-ray and bremssfrahlung dose of every selected point on the bionics esophageal stent and then draw out computer software by mathematical formula. RESULTS: The radiation field of Re esophageal stent has its own feature: the max range of beta-ray is 11 mm, 90% dose construction field is within 1.5 mm, 95% dose range is within 2.5 mm, and only 4.21% of total energy of gamma-ray and bremssfrahlung is out of 6.5 mm range. The absorption dose of every direction in same point of the esophageal model was similar (P>0.05). CONCLUSION: Beta ray is the major radiation of Re esophageal stent while gamma-ray and bremssfrahlung are 4.21% among the radiation field. The max dose construction field is within 0.5-1.5 mm, just short at the depth of esophagus mucosa within 0.5-1.5 mm range. So Re stent is a good choice of palliative intracavitary radiotherapy of esophageal carcinoma.