听神经瘤伽玛刀治疗

目的：研究γ－刀治疗脑听神经瘤的效果。方法;对６４例γ－刀术后听神经瘤患者随访２;５年,定期ＭＲ复查及神经系统检查,结果：肿瘤中央增强密度区消失占８２．８％（５３／６４）,肿瘤生长控制摔（９５．３％）,有用听力保留率５２．４（１３／２４）。结论：对于无手术适应症或拒绝手术的听神经瘤患者γ－刀治疗无疑是值得选择的治疗方法。     

肿瘤坏死因子-α联合干扰素-γ治疗肝癌的实验研究

目的：探讨干扰素-γ体内外增强TNF-α治疗原发性肝癌（HCC）的作用。 方法： 采用结晶紫染色法测定肿瘤坏死因子-α（TNF-α）、干扰素-γ（IFN-γ）和两者联合用药体外杀灭肝癌细胞的能力。以已建立的人肝癌裸小鼠肝内移植模型为对象，采用瘤体内注射的直接给药途径，观察TNF-α、IFN-γ和联合用药体内抗肝癌的效果。 结果： 细胞毒性试验：TNF-α对肝癌细胞有较强的细胞毒性作用，呈剂量依赖性。当浓度超过107 U/L时，有明显杀伤作用(P<0.05)；联合应用IFN-γ具有协同抗瘤效果，单独应用107 U/L TNF-α和106 U/L IFN-γ时，肝癌细胞杀伤率分别为27.1％和7.9%，两者联合用药可达83.7%。单独使用IFN-γ未见移植瘤生长受抑制及荷瘤鼠生存期延长(P＞0.05)，移植瘤仅见小灶性坏死；单独应用TNF-α，表现为抑制移植瘤生长(抑制率17.2％)，移植瘤呈不完全性小片状坏死，但不能延长荷瘤鼠的生存时间(P>0.05)。两者联合用药能明显抑制肿瘤生长(抑癌率35.9%)，移植瘤呈大片状坏死，荷瘤鼠生存期延长(P<0.05)，血甲胎蛋白（AFP）浓度降低。 结论： TNF-α联合IFN-γ直接瘤体内注射有可能成为临床治疗原发性肝癌一个新的有效方法。     

眶内肿瘤伽玛刀放射外科治疗

目的 总结伽玛(γ)刀放射外科治疗眶内肿瘤的适应症、疗效和并发症。方法 本组32例，其中20例首选γ刀治疗，12例为手术后残留或复发瘤的治疗；其中神经鞘瘤6例，脑膜瘤16例，视神经胶质瘤7例，视网膜母细胞瘤1例，静脉血管畸形1例，脉络膜黑色素瘤1例；肿瘤最大直径0．7～4．0cm，平均为2．08cm；采用Leksell立体定位系统、MRI或CT影像定位，Gamma Plan(3．01—5．20)设定治疗计划，用Leksell 23004B型γ刀治疗。结果 全部病例随访3～59个月，平均27．5个月，其中症状好转18例(56．25％)，无变化10例(31．25％)，恶化4例(12．50％)，总有效率87．50％；影像学显示，肿瘤消失2例(6．25％)，缩小17例(51．13％)，无变化9例(28．13％)，增大4例(12．50％)；治疗后不良反应多在3个月左右出现，主要表现为球结膜的充血水肿、眼睑水肿、眼部疼痛，可持续3～6个月，经对症治疗后缓解。结论 γ刀放射外科是一种无创性、安全有效治疗眼眶内肿瘤的方法，既可以作为眼眶内肿瘤的首选治疗，也可作为手术后残余或复发肿瘤的治疗，弥补手术不能完全切除的缺撼。     

关于体部X刀治疗的QA与QC

体部Ｘ刀适形放射治疗是传统放疗技术的革命性进展。在ＣＴ定位、治疗方案设计、模具制作以及治疗实施均应严格质量保证（ＱＡ）和质量控制（ＱＣ）体系。我们对前期应用体部Ｘ刀治疗５４例患者满一月后随访疗效分析，总有效率达９８．５％，未控率１．８５％，认为，体部Ｘ刀比常规放疗精度高，其ＱＡ与ＱＣ措施是有效保证该治疗方式高有效率的重要内容     

伽玛刀治疗后病员的出院指导

我院于1993年12月～1997年10月用γ刀治疗脑瘤、脑血管畸形等颅内疾病2000余例。对治疗后患者采取定期随访观察,积累了一定的经验。通过临床随访及影像学观察,我们认为,γ刀治疗后病灶组织的病理变化是一个逐渐演变的过程。多数病人3个月影像显示病灶大小无变化,中心呈盘状坏死,部分病灶周围有经,中度水肿:少数病人病灶无缩小甚至增大,并出现相应的高颅压症状,但随着治疗时间的推移,坏死组织逐渐吸收,病灶可缩小或消失。因此,对每位γ刀治疗后     

艾灸对胃荷瘤大鼠瘤体内Th1、Th2类细胞因子表达的影响

目的观察艾灸对胃荷瘤大鼠瘤体内Th1、Th2类细胞因子表达的影响。方法 40只体质量200～240 g SPF级SD大鼠适应性喂养1周后,采用手术胃部移植Walker-256瘤组织建立胃荷瘤模型。7 d后随机选取10只验证造模成功,剩余30只随机分入模型组、艾灸组及红外组,每组10只。自入组当日起,艾灸组第1日悬灸中脘、关元、双侧足三里,第2日悬灸双侧脾俞及胃俞;红外组第1日红外线照射胃脘部,第2日照射背部T12-T13棘突间区域;模型组第1日仰卧位固定,第2日俯卧位固定。各组每次干预20 min,每日1次,连续21 d。干预期间密切观察动物摄食量、体质量,对生存状态进行积分。干预结束后,处死动物,测量胃部瘤体体积,测算生长抑制率。利用细胞因子微阵列芯片对瘤体中Th1、Th2类细胞因子进行筛查,ELISA法测定其含量。结果干预结束后,与模型组比较,艾灸组动物生存状态改善,摄食量及体质量增加(均P0.01),胃部瘤体增长受限(P0.01),抑制率达41.89%,瘤体内Th1类细胞因子TNF-α、INF-γ含量增加(P0.01,P0.05),Th2类细胞因子IL-6、IL-22含量减少(P0.01,P0.05);与模型组比较,红外组动物生存状态、体质量稍改善(均P0.05),胃部瘤体增长稍受限,抑制率为28.09%,瘤体内TNF-α含量增加(P0.05),IL-6含量减少(P0.01);与红外组比较,艾灸组动物摄食量、生存状态积分改善更明显(P0.01,P0.05),胃部瘤体体积更小(P0.05),瘤体内INF-γ含量更高(P0.05)。结论艾灸及红外治疗能不同程度地改善荷瘤动物的生存状态,抑制瘤体生长,其作用可能与增加瘤体内Th1类细胞因子TNF-α、INF-γ,减少Th2类细胞因子IL-6、IL-22有关。     

CT引导下125I放射性粒子组织间植入对非小细胞肺癌患者血清肿瘤标志物及瘤体大小的影响

目的 研究CT引导下125I放射性粒子组织间植入对非小细胞肺癌(NSCLC)患者血清肿瘤标志物及瘤体大小的影响.方法 纳入68例需行姑息性治疗的晚期NSCLC患者,均行CT引导下125I放射性粒子组织间植入治疗,评估疗效.结果 术后2、3、6和12个月,患者治疗总有效率为70.59％、79.41％、67.65％和50.77％,术后12月显著低于其他月份(P＜0.05);患者术前、术后2、3、6和12个月瘤体大小为29.13±5.13cm2、22.53±4.09cm2、17.45±3.86cm2、14.56±3.46cm2和12.74±2.43cm2,不同时间点比较,差异均具有统计学意义(P＜0.05);术后血清CYFRA21-1、CEA、CA50和SCC-Ag呈先降低后上升(P＜0.05),术后3月达最低点(P＜0.05);患者无进展生存期18.2±3.1月,3年、5年生存率为41.18％和30.88％;治疗期间,患者出现气胸(19.12％)和痰中带血(5.88％)等症状,治疗后缓解.结论 CT引导下125I粒子植入治疗NSCLC,可明显降低患者瘤体大小和肿瘤标志物水平,近远期疗效确切,安全可靠,是NSCLC姑息性治疗的有效方案.     

RGZ对PPARgamma在裸小鼠移植瘤内表达的调控研究

目的探讨罗格列酮(RGZ)对裸小鼠移植瘤过氧化物酶体增殖物激素受体-γ(PPAR-γ)表达的影响。方法采用不同浓度和剂量的RGZ对荷瘤裸小鼠进行灌胃干预3周后,RT-PCR实时荧光定量检测PPAR-γ的△Ct值和表达拷贝数,测量各组瘤体体积(TV)和重量(TW),计算相对肿瘤体积(RTV)和相对肿瘤增值率(T/C%)。结果胆管癌移植瘤随RGZ剂量增高PPAR-γ的表达升高,而相对肿瘤增值率T/C%减少;高剂量组与对照组比较差异显著(P<0.001)。结论在裸小鼠移植瘤内RGZ能呈剂量依赖性地上调PPAR-γ表达。     

固相转染HPV16-siRNA对荷宫颈癌细胞SiHa小鼠瘤体体积及P53、P16表达的影响

目的: 观察靶向基因治疗后不同时点荷宫颈癌细胞小鼠HPV16-DNA、瘤体体积、P53及P16蛋白的变化,探讨在体固相转染HPV16-siRNA的有效性。方法: 采用 SiHa细胞皮下注射建立荷宫颈癌细胞SCID小鼠模型。制备HPV16靶向siRNA-Lipo2000-卡波姆凝胶。将40只荷宫颈癌细胞SCID小鼠随机分为对照组8只和研究组32只和研究组使用HPV16靶向siRNA-Lipo2000-卡波姆凝胶进行基因治疗,对照组仅使用Lipo2000-卡波姆凝胶处理;分别于治疗后4 d、8 d、12 d、16 d处死小鼠,每个时点研究组处死8只、对照组处死2只。PCR检测两组小鼠瘤体中HPV16-DNA滴度,测各时点的瘤体体积,常规病理切片检测肿瘤细胞形态,免疫组化检测P16及P53的表达。结果: (1)研究组治疗后8 d及12 d时点瘤体内HPV16-DNA明显降低,与对照组之间的差异显著(P<0.05),4 d及16 d 2个时点与对照组之间的差异不显著(P>0.05);(2)治疗后12 d瘤体平均体积明显缩小,与对照组之间的差异显著(P<0.05);(3)转染后12 d肿瘤细胞核异质性较对照组减轻,核浆比例减小;(4)P16的表达强度在各时点研究组与对照组之间的差异不显著(P>0.05);治疗后8 d及12 d研究组P53 的表达强度明显降低,与对照组之间的差异显著(P<0.05)。结论: SCID小鼠所荷宫颈癌细胞瘤体经靶向转染HPV16-siRNA后8 d及12 d时点瘤体内HPV16-DNA和P53均较对照组明显下降,12 d瘤体体积较对照组明显下降;在体固相转染siRNA可以在一定时段内有效抑制HPV-DNA的复制及肿瘤的生长速度。     

淋巴结切除在颈动脉体瘤手术治疗中的作用

目的 总结手术治疗良恶性颈动脉体瘤的经验,探讨颈动脉体瘤手术中瘤体周围淋巴结切除的临床价值。方法 回顾性分析中国医学科学院肿瘤医院1976年1月—2013年10月手术治疗的106例良、恶性颈动脉体瘤患者的临床资料。其中男37例,女69例;年龄7～67岁;肿瘤发生于左侧62例,右侧42例,双侧2例。术前诊断为颈动脉体瘤86例,另20例术前诊断为颈部肿物待查;无一例术前诊断为恶性颈动脉体瘤。根据术中是否行瘤体周围淋巴结切除活检分为淋巴结切除组(54例)和未切除组(52例),随访其术后生存及复发情况。采用Kaplan-Meier生存分析法计算并比较两组患者术后无复发生存率。结果 106例患者中,98例获随访,8例失访,其中淋巴结切除组失访5例,未切除组失访例3例。随访时间7个月~38年,中位随访时间8年。淋巴结切除组术后无复发生存率为97.0%,高于淋巴结未切除组的73.7%(χ²=9.938, P＜0.01);明确诊断良恶性者术后无复发生存率93.4%,高于未行淋巴结切除从而诊断恶性证据不足者的14.0%(χ²=45.054, P＜0.01)。淋巴结切除组神经损伤发生率为35.2%(19/54),低于淋巴结未切除组的55.8%(29/52),差异有统计学意义(χ²=4.530, P＜0.05)。结论 颈动脉体瘤手术中,瘤体周围淋巴结切除活检有助于明确诊断、指导治疗,从而提高颈动脉体瘤手术治疗后无复发生存率;同时,还有利于暴露术野,降低神经损伤发生率。     

Glass rod detectors for small field, stereotactic radiosurgery dosimetric audit

This paper demonstrates the feasibility of using glass rod detectors for quality assurance audit of radiosurgery units. Five radiosurgery units (3 Gamma Knife model C, 1 Gamma Knife model U and 1 Cyberknife) located in California participated in the study. At each center glass rod detectors were used to measure a number of dosimetric parameters including relative collimator output factor and absolute dose rate. The Gamma Knife data obtained is in excellent agreement with the commissioning data generated by the manufacturer for each unit and the Cyberknife data is in general agreement with the data published by other centers. In particular the output factor of the 4 mm Gamma Knife helmet factor, a subject of abundant debate, was measured in the range 0.863-0.872 with an accuracy of better than 1% across the four participating centers. It is hoped that this pilot study will facilitate a nationwide postal audit of stereotactic radiosurgery units.     

Monte Carlo calculated output factors of a Leksell Gamma Knife unit

The Leksell Gamma Knife is a standard radiosurgical tool for treating brain lesions by directing beams of gamma radiation to a specific region. The diameter of the gamma beams is confined by collimator systems and available collimator sizes are 4, 8, 14 and 18 mm. The reduction in dose rate for each collimator helmet is called the output factor (OPF). Experimental determination of OPFs is difficult due to the extremely narrow beams for which the dose is determined. In the present work, the PRESTA version of the EGS4 Monte Carlo code was used to obtain relative OPFs for the Leksell Gamma Knife for collimator sizes of 14, 8 and 4 mm (relative to that of the 18 mm collimator). A spherical probe with a radius of 1 mm was utilized in this computer experiment. Our Monte Carlo results gave OPFs of 0.974, 0.951 and 0.872 for the 14 mm, 8 mm and 4 mm collimators respectively, relative to the 18 mm collimator. Our calculated OPF for the 4 mm collimator helmet was more than 8% higher than the value currently used, but in good agreement with the average of experimental values obtained by various Gamma Knife centres throughout the world and with the value now recommended by the manufacturer, Elekta (Elekta Instrument AB, Skeppargatan 8, S-114 52 Stockholm, Sweden).     

Calibration of the Gamma Knife using a new phantom following the AAPM TG51 and TG21 protocols

PURPOSE: To compare calibration of the Leksell Gamma Knife according to the American Association of Physicists in Medicine Task Groups 21 and 51 protocols. A new phantom was fabricated for this purpose. Its design, physical properties, and composition are described. MATERIALS AND METHODS: The Gamma Knife TG-51 calibration phantom is designed to be filled with water and support an ionization chamber positioned at its center. The phantom is thimble-shaped, with a 2 mm plastic wall to contain water. The phantom and chamber assembly was mounted in a Leksell stereotactic frame. The location of the chamber's sensitive volume was determined using computed tomography. The chamber-phantom assembly was attached to the 18 mm helmet in the Gamma Knife by the stereotactic frame. The phantom's geometry allowed radiation beams from each of the 201 Gamma Knife cobalt-60 sources to converge after an 8 cm path to the ionization chamber's sensitive volume. This is similar to the arrangement by which one calibrates the Gamma Knife using the manufacturer-supplied polystyrene phantom. RESULTS: The phantom was attached to the Gamma Knife so that the ionization chamber was reproducibly positioned at the convergence of the radiation beams. Because of the phantom's design, the phantom could be affixed to either trunnions or the automatic patient positioning system, once mounted in the Leksell stereotectic frame. Comparisons using different phantoms and protocols resulted in the following calibration ratios for TG-21 in the polystyrene sphere phantom, TG-21 in the water phantom, and TG-51 in the water phantom, respectively: 1.000, 1.008, 0.986, when corrected for transmission through the plastic water reservoir wall and using the same ionization chamber. Transmission measurements using a 1 cm thickness of the same material in the Co-60 beam determined that the phantom's 2 mm plastic wall resulted in a reduction in the measured the output by 0.5%. CONCLUSIONS: Calibration of the Gamma Knife can be performed in liquid water using the AAPM TG-51 protocol and this new phantom, thereby eliminating uncertainties with respect to the composition of the manufacturer's phantom. Perturbation of calibration measurements by nonwater materials was characterized and could be corrected. Calibration values for the Gamma Knife that were obtained using the three methods for our phantoms agree to within 1.4%. TG21 and TG51 calibration of the Gamma Knife using the water phantom agreed to within 2.2%.     

Monte Carlo simulation of the Leksell Gamma Knife: I. Source modelling and calculations in homogeneous media

The Monte Carlo code PENELOPE has been used to simulate photon flux from the Leksell Gamma Knife, a precision method for treating intracranial lesions. Radiation from a single 6OCo assembly traversing the collimator system was simulated, and phase space distributions at the output surface of the helmet for photons and electrons were calculated. The characteristics describing the emitted final beam were used to build a two-stage Monte Carlo simulation of irradiation of a target. A dose field inside a standard spherical polystyrene phantom, usually used for Gamma Knife dosimetry, has been computed and compared with experimental results, with calculations performed by other authors with the use of the EGS4 Monte Carlo code, and data provided by the treatment planning system Gamma Plan. Good agreement was found between these data and results of simulations in homogeneous media. Owing to this established accuracy, PENELOPE is suitable for simulating problems relevant to stereotactic radiosurgery.     

Effects of bone- and air-tissue inhomogeneities on the dose distributions of the Leksell Gamma Knife calculated with PENELOPE

Monte Carlo simulation with PENELOPE (version 2003) is applied to calculate Leksell Gamma Knife dose distributions for heterogeneous phantoms. The usual spherical water phantom is modified with a spherical bone shell simulating the skull and an air-filled cube simulating the frontal or maxillary sinuses. Different simulations of the 201 source configuration of the Gamma Knife have been carried out with a simplified model of the geometry of the source channel of the Gamma Knife recently tested for both single source and multisource configurations. The dose distributions determined for heterogeneous phantoms including the bone- and/or air-tissue interfaces show non-negligible differences with respect to those calculated for a homogeneous one, mainly when the Gamma Knife isocentre approaches the separation surfaces. Our findings confirm an important underdosage (approximately 10%) nearby the air-tissue interface, in accordance with previous results obtained with the PENELOPE code with a procedure different from ours. On the other hand, the presence of the spherical shell simulating the skull produces a few per cent underdosage at the isocentre wherever it is situated.     

Comparative analyses of linac and Gamma Knife radiosurgery for trigeminal neuralgia treatments

Dedicated linac-based radiosurgery has been reported for trigeminal neuralgia treatments. In this study, we investigated the dose fall-off characteristics and setup error tolerance of linac-based radiosurgery as compared with standard Gamma Knife radiosurgery. In order to minimize the errors from different treatment planning calculations, consistent imaging registration, dose calculation and dose volume analysis methods were developed and implemented for both Gamma Knife and linac-based treatments. Intra-arc setup errors were incorporated into the treatment planning process of linac-based deliveries. The effects of intra-arc setup errors with increasing number of arcs were studied and benchmarked against Gamma Knife deliveries with and without plugging patterns. Our studies found equivalent dose fall-off properties between Gamma Knife and linac-based radiosurgery given a sufficient number of arcs (>7) and small intra-arc errors (<0.5 mm) were satisfied for linac-based deliveries. Increasing the number of arcs significantly decreased the variations in the dose fall-off curve at the low isodose region (e.g. from 40% to 10%) and also improved dose uniformity at the high isodose region (e.g. from 70% to 90%). As the number of arcs increased, the effects of intra-arc setup errors on the dose fall-off curves decreased. Increasing the number of arcs also reduced the integral dose to the distal normal brain tissues. In conclusion, linac-based radiosurgery produces equivalent dose fall-off characteristics to Gamma Knife radiosurgery with a high number of arcs. However, one must note the increased treatment time for a large number of arcs and isocentre accuracies.     

Study of scattered photons from the collimator system of Leksell Gamma Knife using the EGS4 Monte Carlo code

In the algorithm of Leksell GAMMAPLAN (the treatment planning software of Leksell Gamma Knife), scattered photons from the collimator system are presumed to have negligible effects on the Gamma Knife dosimetry. In this study, we used the EGS4 Monte Carlo (MC) technique to study the scattered photons coming out of the single beam channel of Leksell Gamma Knife. The PRESTA (Parameter Reduced Electron-Step Transport Algorithm) version of the EGS4 (Electron Gamma Shower version 4) MC computer code was employed. We simulated the single beam channel of Leksell Gamma Knife with the full geometry. Primary photons were sampled from within the 60Co source and radiated isotropically in a solid angle of 4pi. The percentages of scattered photons within all photons reaching the phantom space using different collimators were calculated with an average value of 15%. However, this significant amount of scattered photons contributes negligible effects to single beam dose profiles for different collimators. Output spectra were calculated for the four different collimators. To increase the efficiency of simulation by decreasing the semiaperture angle of the beam channel or the solid angle of the initial directions of primary photons will underestimate the scattered component of the photon fluence. The generated backscattered photons from within the 60Co source and the beam channel also contribute to the output spectra.     

Peripheral dose in ocular treatments with CyberKnife and Gamma Knife radiosurgery compared to proton radiotherapy

Peripheral radiation can have deleterious effects on normal tissues throughout the body, including secondary cancer induction and cataractogenesis. The aim of this study is to evaluate the peripheral dose received by various regions of the body after ocular treatment delivered with the Model C Gamma Knife, proton radiotherapy with a dedicated ocular beam employing no passive-scattering system, or a CyberKnife unit before and after supplemental shielding was introduced. TLDs were used for stray gamma and x-ray dosimetry, whereas CR-39 dosimeters were used to measure neutron contamination in the proton experiments. Doses to the contralateral eye, neck, thorax and abdomen were measured on our anthropomorphic phantom for a 56 Gy treatment to a 588 mm(3) posterior ocular lesion. Gamma Knife (without collimator blocking) delivered the highest dose in the contralateral eye, with 402-2380 mSv, as compared with 118-234 mSv for CyberKnife pre-shielding, 46-255 mSv for CyberKnife post-shielding and 9-12 mSv for proton radiotherapy. Gamma Knife and post-shielding CyberKnife delivered comparable doses proximal to the treatment site, with 190 versus 196 mSv at the thyroid, whereas protons doses at these locations were less than 10 mSv. Gamma Knife doses decreased dramatically with distance from the treatment site, delivering only 13 mSv at the lower pelvis, comparable to the proton result of 4 to 7 mSv in this region. In contrast, CyberKnife delivered between 117 and 132 mSv to the lower pelvis. In conclusion, for ocular melanoma treatments, a proton beam employing no double scattering system delivers the lowest peripheral doses proximally to the contralateral eye and thyroid when compared to radiosurgery with the Model C Gamma Knife or CyberKnife. At distal locations in the pelvis, peripheral doses delivered with proton and Gamma Knife are of an order of magnitude smaller than those delivered with CyberKnife.     

Concomitant GRID boost for Gamma Knife radiosurgery

We developed an integrated GRID boost technique for Gamma Knife radiosurgery. The technique generates an array of high dose spots within the target volume via a grid of 4-mm shots. These high dose areas were placed over a conventional Gamma Knife plan where a peripheral dose covers the full target volume. The beam weights of the 4-mm shots were optimized iteratively to maximize the integral dose inside the target volume. To investigate the target volume coverage and the dose to the adjacent normal brain tissue for the technique, we compared the GRID boosted treatment plans with conventional Gamma Knife treatment plans using physical and biological indices such as dose-volume histogram (DVH), DVH-derived indices, equivalent uniform dose (EUD), tumor control probabilities (TCP), and normal tissue complication probabilities (NTCP). We found significant increase in the target volume indices such as mean dose (5%-34%; average 14%), TCP (4%-45%; average 21%), and EUD (2%-22%; average 11%) for the GRID boost technique. No significant change in the peripheral dose coverage for the target volume was found per RTOG protocol. In addition, the EUD and the NTCP for the normal brain adjacent to the target (i.e., the near region) were decreased for the GRID boost technique. In conclusion, we demonstrated a new technique for Gamma Knife radiosurgery that can escalate the dose to the target while sparing the adjacent normal brain tissue.     

Selective source blocking for Gamma Knife radiosurgery of trigeminal neuralgia based on analytical dose modelling

We have developed an automatic critical region shielding (ACRS) algorithm for Gamma Knife radiosurgery of trigeminal neuralgia. The algorithm selectively blocks 201 Gamma Knife sources to minimize the dose to the brainstem while irradiating the root entry area of the trigeminal nerve with 70-90 Gy. An independent dose model was developed to implement the algorithm. The accuracy of the dose model was tested and validated via comparison with the Leksell GammaPlan (LGP) calculations. Agreements of 3% or 3 mm in isodose distributions were found for both single-shot and multiple-shot treatment plans. After the optimized blocking patterns are obtained via the independent dose model, they are imported into the LGP for final dose calculations and treatment planning analyses. We found that the use of a moderate number of source plugs (30-50 plugs) significantly lowered (approximately 40%) the dose to the brainstem for trigeminal neuralgia treatments. Considering the small effort involved in using these plugs, we recommend source blocking for all trigeminal neuralgia treatments with Gamma Knife radiosurgery.