Whole-brain radiation therapy alone vs. combined therapy with stereotactic radiosurgery for the treatment of limited brain metastases: A systematic review

Objective The aim of the study was to compare the efficacy and safety of whole brain radiotherapy(WBRT) used alone and combined with stereotactic radiosurgery(SRS) in the treatment of limited(1–4)brain metastases. Methods We searched for randomized controlled and matched-pair analysis trials comparing WBRT plus SRS versus WBRT alone for brain metastases. The primary outcomes were the overall survival(OS), intracranial control(IC), and localcontrol(LC). The secondary outcome was radiation toxicity. The log hazard ratios(lnHRs) and their variances were extracted from published Kaplan-Meier curves and pooled using the generic inverse variance method in the RevMan 5.3 software. The non-pooled outcome measures were evaluated using descriptive analysis. Results Three randomized controlled trials and two matched-pair analysis studies were included. There was no difference in the OS for limited brain metastases between the two groups [lnHR 0.91(95% CI 0.76–1.09, P = 0.32) vs. 0.72(95% CI 0.44–1.19, P = 0.20)]. The LC and IC were significantly higher in the combined treatment group [lnHR 0.69(95% CI 0.55–0.86, P = 0.001) vs. 0.41(95% CI 0.29–0.58, P < 0.0001)]. For patients with a single lesion, one trial showed a higher survival in the combined treatment group(median OS: 6.5 months vs. 4.9 months, P = 0.04). The combined treatment was not associated with significantly higher incidence of radiation toxicity. Conclusion Combined treatment with WBRT plus SRS should be recommended for patients with limited brain metastases based on the better LC and IC without increased toxicity. It should also be considered a routine treatment option for patients with solitary brain metastases based on the prolonged OS.

Value of serial magnetic resonance imaging in the assessment of brain metastases volume control during stereotactic radiosurgery

AIM To evaluate brain metastases volume control capabilities of stereotactic radiosurgery(SRS) through serial magnetic resonance(MR) imaging follow-up. METHODS MR examinations of 54 brain metastases in 31 patients before and after SRS were reviewed. Patients were included in this study if they had a pre-treatment MR examination and serial follow-up MR examinations at 6 wk, 9 wk, 12 wk, and 12 mo after SRS. The metastasis volume change was categorized at each follow-up as increased(> 20% of the initial volume), stable(± 20% of the initial volume) or decreased(< 20% of the initial volume). RESULTS A local tumor control with a significant(P < 0.05) volume decrease was observed in 25 metastases at 6-wk follow-up. Not significant volume change was observed in 23 metastases and a significant volume increase was observed in 6 metastases. At 9-wk followup, 15 out of 25 metastases that decreased in size at 6 wk had a transient tumor volume increase, followed by tumor regression at 12 wk. At 12-wk follow-up there was a significant reduction in volume in 45 metastases, and a significant volume increase in 4 metastases. At 12-mo follow-up, 19 metastases increased significantly in size(up to 41% of the initial volume). Volume tumor reduction was correlated to histopathologic subtype.CONCLUSION SRS provided an effective local brain metastases volume control that was demonstrated at follow-up MR imaging.

Therapeutic usability of two different fiducial gold markers for robotic stereotactic radiosurgery of liver malignancies:A pilot study

AIM: To assess how the application of different types of markers affects the tracking accuracy of Cyber Knife's.METHODS: Fifteen patients were recruited and subjected to the ultrasound-guided placement of markers. Two different type of needles 25 gauge(G) and 17 G containing two different fiducial marker, gold notched flexible anchor wire 0.28 mm × 10 mm(25 G needle) and gold cylindrical grain 1 mm × 4 mm(17 G), were used. Seven days after the procedure, a Cyber Knife planning computed tomography(CT) for the simulation of radiation treatment was performed on all patients.A binary CT score was assigned to the fiducial markers visualization. Also, the CT number was calculated for each fiducial and the values compared with a specific threshold.RESULTS: For each patient from 1 to 5, intra-hepatic markers were placed(one in 2 patients, three in 8 patients, four in 3 patients, and five in 2 patients). A total of 48 needles were used(thirty-two 17 G and sixteen 25 G) and 48 gold markers were placed(32 Grain shaped markers and 16 Gold Anchor). The result showed that the CT visualization of the grain markers was better than the anchor markers(P = 5 × 10^(-9)). Furthermore, the grain markers were shown to present minor late complications(P = 3 × 10^(-6)), and the best CT threshold number(P = 0.0005). CONCLUSION: The study revealed that the Gold Anchor fiducial marker is correlated with a greater number of late minor complications and low visualization by the CT.

Dosimetric Advantages of Volumetric Modulated Arc Therapy Based Coronal Arc Delivery Technique in Brain Stereotactic Radiosurgery: A Feasibility Study

The feasibility of a volumetric modulated arc therapy (VMAT) based coronal arc (cARC) technique for treating a single brain metastasis or lesion proximal to the brainstem or optic chiasm was evaluated. Coplanar (CP) and non-coplanar (NCP) treatment plans to an anthropomorphic head/neck phantom scanned head-first supine were compared to a cARC plan with the phantom rotated vertically. A set of planning target volumes (PTVs) were contoured centrally between the brainstem and optic chiasm (“Ant PTVs”) and posterior to brainstem (“Post PTVs”). Dosimetric indices such as conformity index (C.I.), gradient measure (G.M.), and dose volume histograms (DVHs) were compared for CP, NCP and cARC techniques. The TG101 guidelines for organs-at-risk (OARs), and 95% of PTV receiving at least 100% of the prescription dose (D95 = 100%) were used as plan objectives. Reductions in D50 and D30 to the brainstem of 85.1% ± 3.9% and 87.6% ± 3.2%, respectively were seen for “Post PTVs”, and 51.1% ± 17.8% and 85.6% ± 6.0% respectively for “Ant PTVs” using cARC versus CP (p ≤ 0.01). For chiasm, reductions of D50 and D30 were 61.7% ± 3.2% and 44.2% ± 8.9% for “Ant PTVs”, by 69.3% ± 8.0% and 74.3% ± 8.2% for “Post PTVs” (p ≤ 0.01). Comparing cARC to NCP led to similar dosimetric improvements. The conformity index (C.I.) was measured to be 1.101 ± 0.038, 1.088 ± 0.054, and 1.060 ± 0.040 for cARC, CP and NCP respectively (p ≤ 0.01). The overall GM in cm was 0.581 ± 0.097, 0.708 ± 0.064, and 0.476 ± 0.050 for cARC, CP and NCP respectively (p ≤ 0.01). The mean distance gradient fall-off (in cm) was 0.249 ± 0.038 (cARC), 0.749 ± 0.107 (CP), and 0.621 ± 0.068 (NCP) at the center slice in anterior-posterior direction of the target volume (p ≤ 0.01). The objective of this study is to compare the dosimetric indices of cARC with CP and NCP techniques. In conclusion, cARC can provide improved dosimetry as compared to CP and NCP for lesion proximal to the brainstem or optic chiasm.

A Statistical Index for Evaluating the CTV Coverage Loss of Brain Stereotactic Radiosurgery When the PTV Margin Is Zero

Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by the prescription dose, for evaluating the coverage loss of brain (fractionated) stereotactic radiosurgery (SRS/fSRS) when the PTV (planning target volume) margin is zero. Methods: The random variable Q for CTV percent coverage was derived using a previously developed model for CTV random motion that follows a three-dimensional (3D) independent normal distribution with a zero mean and a standard deviation of 𝜎𝑆(for translation) or 𝜎𝛿(for rotation). Assuming both CTV and PTV are spherical with the same diameter dCTV, the cumulative distribution function of Q could be obtained analytically using the relation of sphere-sphere intersection. The %CCP was then derived as the reliability function of Q and was used to quantify the coverage loss for selected dCTV. Results: The 95%-95% clinical goal (95% of the times, at least 95% of the CTV is covered) is not achievable with dCTV mm. For common CTVs (dCTV mm) encountered in SRS/fSRS, only 60%-90% of the CTV could be reliably covered by the prescription dose 95% of the time. For 𝜎𝑆=0.5mm and 𝜎𝛿 =0.4˚, the 95% CCP was the highest when the distance between the CTV and the isocenter 𝑑𝐼⇔𝑇=0 and gradually decreased with the increasing 𝑑𝐼⇔𝑇. Conclusions: The %CCP was successfully derived for evaluating the CTV coverage loss for brain SRS/fSRS. When the PTV margin is zero, the 95%-95% clinical goal cannot be achieved for most targets (dCTV mm).

Use of stereotactic radiosurgery in the treatment of gynecologic malignancies:A review

Recent retrospective studies have reported the use ofstereotactic radiosurgery(SRS) in the treatment of gy-necologic cancers. SRS uses real-time imaging and highdose radiation beams attached to precise robotic armsto target malignant lesions while sparing normal tissue.The purpose of this review is to examine the indicationsfor SRS in gynecologic oncology, review the currentliterature regarding the use of SRS in gynecologic can-cers, and identify future directions for research in thisarea. Literature on stereotactic radiosurgery was re-viewed using the PubMed search engine. Articles writ-ten in English from 1993-2013 were reviewed, and 20 case series and clinical trials were included. The safetyand efficacy SRS has been demonstrated in all gyne-cologic disease sites including cervical, endometrial,vulvar, vaginal, and ovarian cancers. Indications for itsuse include non-central pelvic recurrences in previouslyirradiated patients, complex or non-resectable diseaserecurrence, and solitary brain metastases. Toxicitiesare usually mild, though grade 3-4 toxicities have been reported. SRS is a promising second line treatment modality for patients with primary or recurrent disease who cannot undergo standard surgical or radiation therapy. Further research is required to determine optimal dosing and fractionation schedules, delineate appropriate patient populations, and assess longterm morbidity and survival.

Stereotactic radiosurgery:a“targeted”therapy for cancer

The developments of medicine always follow innovations in science and technology.In the past decade,such innovations have made cancer-related targeted therapies possible.In general,the term "targeted therapy" has been used in reference to cellular and molecular level oriented therapies.However,improvements in the delivery and planning of traditional radiation therapy have also provided cancer patients more options for "targeted" treatment,notably stereotactic radiosurgery(SRS) and stereotactic body radiotherapy(SBRT).In this review,the progress and controversies of SRS and SBRT are discussed to show the role of stereotactic radiation therapy in the ever evolving multidisciplinary care of cancer patients.

Observation of Stereotactic Radiosurgery (Cyberknife) on Hepatocellular Carcinoma with Portal Vein Tumor Thrombosis

The purpose of the study was to analyze the clinical effect of stereotactic radiosurgery(SRS)(Cyberknife)on hepatocellular carcinoma with portal vein tumor thrombosis(HCC-PVTT).Data from 50 patients with HCC-PVTT who received Cyberknife from August 2013 to April 2016 was collected for efficacy analysis.Moreover,survival correlation was evaluated by Cox proportionalhazards model.The total effective rate in 1-3 months after treatment was 64.00%,including 7 cases in complete remission,12 cases in partial remission,13 cases in stable conditions,and 18 cases with enlargement;a 4-24-months follow-up(with an average of 11.58±2.58 months)showed that median survival,1-year cumulative survival rate,and 2-year cumulative survival rate were,respectively,11.86±1.79 months,48.00%,and 20.00%.Moreover,the Cox proportional-hazards model indicates that it was with no correlation between lesion diameter,classification of liver function,pre-operative alphafetoprotein,types of hepatitis,number of tumors,ascites,types of tumor emboli,total dose,and survival rate.SRS is effective for HCC-PVTT and serves as an ideal treatment clinically to help preserve patients’lives,which is worthy of clinical promotion and application.

Observations on the role of brain stereotactic radiosurgery

As a research paradigAs a research paradigm （1） evaluated measures of animal performance correlated with markers of microglia activation and inflammation as they sought to see the effects of more focused radiation in two-month-old male athymic nude rats.The authors used intensity modulated radiation therapy （IMRT） and volumetric modulated arc therapy （VMAT） to irradiate the hippocampus either unilaterally or bilaterally.Treatment plans delivered a total dose of 10 Gy to either one or both hemispheres of the rat brain.Their data suggests that specific behavioral tasks could be reduced by focused radiation delivered to the hippocampus,and in unilaterally treated animals,the contralateral brain seemed to up-regulate repair mechanisms.This report provides additional information relative to the mechanisms of radiobiological effect using targeted radiation.

SRS和SBRT的临床疗效:能用经典放射生物学来阐述吗?

立体定向放射外科（stereotactic radiosurgery,SRS）与体部立体定向放射治疗（stereotactic body radiotherapy,SBRT）又称立体定向消融放疗（stereotactic ablative radiotherapy,SABR）,是放疗界近年来的一项新技术,正逐渐成为某些肿瘤的常规治疗手段。SRS和SBRT一般采用一次或多次的高剂量照射（每次8-30 Gy）,与20世纪兴起的每周5次、

SRS MapCHECK与EDOSE在立体定向放疗计划剂量验证中的对比

目的:使用SRS MapCHECK和EDOSE对立体定向放疗(SRT)计划进行剂量验证,并比较它们的验证结果。方法:首先比较两种系统在不同方野(2 cm×2 cm、4 cm×4 cm、6 cm×6 cm、10 cm×10 cm)的γ通过率(3%/3 mm),然后选择29例SRT计划,分析两种系统在不同γ标准下的绝对剂量通过率,最后分析EDOSE建立的4种不同物理模型对SRT计划剂量验证的影响。结果:SRS MapCHECK在所有方野和29例SRT计划的绝对剂量γ通过率均高于EDOSE,两者的验证结果有统计学差异(P<0.05);SRS MapCHECK及EDOSE在29例SRT计划的γ通过率(2%/2 mm)分别是为98.60%±2.14%和96.53%±2.41%。基于EDOSE的不同物理模型验证结果有统计学差异,平均γ通过率(2%/2 mm)偏差为1.8%~5.1%。结论:SRS MapCHECK和EDOSE系统均满足SRT计划剂量验证的要求,且SRS MapCHECK的剂量验证通过率优于EDOSE;不同的EDOSE物理模型对SRT计划剂量验证有影响。

SRS、WBRT及WBRT+SRS治疗1～4个脑转移瘤的Meta分析

目的：探讨立体定向放射外科（SRS）、全脑放疗（WBRT）及全脑放疗联合立体定向治疗1~4个脑转移瘤,并为进一步研究提供循证医学依据。方法：根据设定的纳入、排除标准,在Pub Med、Springer-link、Cancer list数据库、中国生物医学文献数据库（CBM）、万方数据库、CNKI知识网络服务平台及其他期刊进行相关随机对照试验检索。单变量计数资料的效应量用优势比（OR）和95%可信区间（95%CI）表示,用Revman 5.2软件对数据进行异质性检验后采用固定效应模型或随机效应模型对数据进行分析。结果：共检索出1985-2014年间发表的126篇相关文献,最终得到8篇包含1 213例脑转移瘤患者的随机对照试验符合所纳入的标准。SRS与WBRT＋SRS比较：WBRT＋SRS虽能提高脑转移瘤1年局部控制率及远处肿瘤控制率（OR=0.43,95%CI：0.29~0.63,P〈0.000 1;OR=0.42,95%CI：0.30~0.57,P〈0.000 01）;但不能提高1年生存率且不良反应及神经认知异常发生率高（OR=1.27,95%CI：0.93~1.73,P=0.14;OR=0.50,95%CI：0.28~0.89,P=0.02;OR=0.41,95%CI：0.21~0.78,P=0.006）。SRS与WBRT比较：SRS治疗脑转移瘤可明显提高患者1年生存率及1年局部肿瘤控制率,但远处肿瘤控制率与WBRT相当（OR=2.78,95%CI：1.57~4.92,P=0.000 4;OR=4.8,95%CI：2.69~8.57,P〈0.000 01;OR=0.52,95%CI：0.15~1.83,P=0.31）。WBRT＋SRS与单独WRBT比较：1年局部肿瘤控制率及1年生存率无明显差别（OR=1.23,95%CI：0.81~1.86,P=0.32;OR=1.21,95%CI：0.76~1.93,P=0.42）。结论：1~4个脑转移瘤患者,单独SRS是理想治疗方法。

Initial experience with stereotactic body radiotherapy for intrahepatic hepatocellular carcinoma recurrence after liver transplantation

BACKGROUND Graft hepatocellular carcinoma(HCC)recurrence after liver transplant is more frequently encountered.Graft hepatectomy is technically challenging and is associated with high morbidity.Stereotactic body radiation therapy(SBRT)has been shown to be safe and effective for the treatment of primary HCC.However,its role in HCC recurrence in a liver graft remains unclear.AIM To evaluate the safety and efficacy of SBRT for the treatment of graft HCC recurrence after liver transplantation.METHODS A retrospective study was conducted.From 2012 to 2018,6 patients with intrahepatic HCC recurrence after liver transplant were treated with SBRT at Queen Mary Hospital,the University of Hong Kong.The primary outcome was time to overall disease progression and secondary outcomes were time to local progression and best local response,as assessed with the Modified response Evaluation Criteria for Solid Tumours criteria.Patients were monitored for treatment related toxicities and graft dysfunction.RESULTS A total of 9 treatment courses were given for 13 tumours.The median tumour size was 2.3 cm(range 0.7-3.6 cm).Two(22%)patients had inferior vena cava tumour thrombus.The best local treatment response was:5(55%)complete response,1(11%)partial response and 3(33%)stable disease.After a median follow up duration of 15.5 mo,no local progression or mortality was yet observed.The median time to overall disease progression was 6.5 mo.There were 6 regional progression in the liver graft(67%)and 2 distant progression in the lung(22%).There was no grade 3 or above toxicity and there was no graft dysfunction after SBRT.CONCLUSION SBRT appears to be safe in this context.Regional progression is the mode of failure.

Concise review of stereotactic irradiation for pediatric glial neoplasms:Current concepts and future directions

Brain tumors,which are among the most common solid tumors in childhood,remain a leading cause of cancer-related mortality in pediatric population.Gliomas,which may be broadly categorized as low grade glioma and high grade glioma,account for the majority of brain tumors in children.Expectant management,surgery,radiation therapy(RT),chemotherapy,targeted therapy or combinations of these modalities may be used for management of pediatric gliomas.Several patient,tumor and treatment-related characteristics including age,lesion size,grade,location,phenotypic and genotypic features,symptomatology,predicted outcomes and toxicity profile of available therapeutic options should be considered in decision making for optimal treatment.Management of pediatric gliomas poses a formidable challenge to the physicians due to concerns about treatment induced toxicity.Adverse effects of therapy may include neurological deficits,hemiparesis,dysphagia,ataxia,spasticity,endocrine sequelae,neurocognitive and communication impairment,deterioration in quality of life,adverse socioeconomic consequences,and secondary cancers.Nevertheless,improved understanding of molecular pathology and technological advancements may pave the way for progress in management of pediatric glial neoplasms.Multidisciplinary management with close collaboration of disciplines including pediatric oncology,surgery,and radiation oncology is warranted to achieve optimal therapeutic outcomes.In the context of RT,stereotactic irradiation is a viable treatment modality for several central nervous system disorders and brain tumors.Considering the importance of minimizing adverse effects of irradiation,radiosurgery has attracted great attention for clinical applications in both adults and children.Radiosurgical applications offer great potential for improving the toxicity profile of radiation delivery by focused and precise targeting of well-defined tumors under stereotactic immobilization and image guidance.Herein,we provide a concise review of stereotactic irradiation for pediatric glial neoplasms in light of the literature.

ExacTrac图像引导系统结合六维床在SRS治疗摆位中的可靠性研究

目的:研究ExacTrac图像引导系统结合六维床修正立体定向放射外科(SRS)摆位误差数据的可靠性。方法:选取医院收治的62例实施放射治疗患者,根据治疗方法的不同,将其分为观察组(32例)和对照组(30例)。观察组患者应用ExacTrac图像引导系统结合六维床摆位,并利用电子射野影像装置(EPID)拍摄0°和90°验证片后行SRS治疗;对照组患者直接应用EPID系统拍片验证后行常规调强放射治疗(IMRT)。分析比较两组患者的摆位误差在左右方向(x)、头脚方向(y)和腹背方向(z)3个方向的差异性。结果:观察组采用ExacTrac图像引导系统结合六维床修正摆位误差后得到的EPID系统摆位在x、y和z的3个方向上误差小于对照组直接获取的EPID系统摆位误差,其差异均具有统计学意义(Z=-3.696,Z=-3.810,Z=-3.436;P<0.05);观察组在x、y和z的3个方向的平移误差分别为(0.12±0.10)mm、(0.14±0.14)mm和(0.09±0.07)mm,旋转误差分别为(0.09±0.08)°、(0.10±0.08)°和(0.18±0.14)°。结论:ExacTrac图像引导系统结合六维床在SRS治疗时所获取的摆位误差数据可靠,且明显提高摆位精度。

SRS MapCHECK、ArcCHECK及Portal Dosimetry在立体定向治疗计划剂量验证对比

目的探究SRS MapCHECK(SRS)、ArcCHECK(Arc)及Portal Dosimetry(PD)3种剂量验证系统在立体定向治疗计划验证中的应用情况。方法随机选取在我院行立体定向放疗的肿瘤患者45例,依据治疗计划分别设计SRS、Arc及PD的验证计划,并在Varian VitalBeam直线加速器上执行。在10%剂量阈值下,记录3%/2 mm、3%/1 mm、2%/2 mm、2%/1 mm和1%/1 mm的γ评价标准下3种剂量验证系统治疗计划的通过率情况。结果3种剂量验证系统在不同的评价标准下得到的治疗计划的γ通过率存在差异,但在3%/2 mm和2%/2 mm评价标准下,SRS和PD验证得到的γ通过率无显著差异(P值均>0.05);在3%/1 mm、2%/1 mm和1%/1 mm评价标准下,Arc和PD验证得到的γ通过率无显著差异(P值均>0.05);在确定治疗计划是否可行上,SRS优于Arc和PD,PD略优于Arc。结论3种剂量验证系统都可用于立体定向治疗计划的剂量验证,其中SRS因具有较高的空间分辨率,在立体定向治疗计划验证上优势明显,临床应用时可优先考虑,此外,SRS剂量验证较严格的γ评价标准可采用2%/1 mm,Arc和PD剂量验证较严格的γ评价标准可采用2%/2 mm或3%/1 mm。

RapidArc与Novalis Knife在多发脑转移瘤SRS中的剂量学比较

目的:比较基于多叶准直器的RapidArc与基于圆形限光筒的Novalis Knife在多发脑转移瘤立体定向放射外科(SRS)中的剂量学差异。方法:选取10例已进行Novalis Knife治疗的多发脑转移瘤患者(转移瘤3~5个/人),共37个转移瘤。重新设计单中心、非共面4弧的RapidArc SRS计划,靶区处方剂量统一为16 Gy。比较Novalis Knife计划和RapidArc SRS计划中靶区的剂量适形度指数和均匀性指数、靶区周围剂量梯度指数、正常脑组织等剂量线体积(V16、V12、V9、V6、V3)以及治疗所需的机器跳数。结果:RapidArc SRS计划相较于Novalis Knife计划,适形度指数更接近于1(0.79±0.10 vs 0.50±0.22,P=0.000),均匀性指数更接近于0(0.07±0.01 vs 0.15±0.07,P=0.000),但靶区周围剂量梯度指数较大(15.92±12.43 vs 5.05±3.53,P=0.000)。对于正常脑组织等剂量线体积,RapidArc SRS计划中V16明显小于Novalis Knife计划(P=0.005);两计划的V12、V9无明显差异(P=0.445,0.059);而RapidArc SRS计划中V6、V3明显大于Novalis Knife计划(P=0.005,0.005)。RapidArc SRS计划的机器跳数明显少于Novalis Knife计划(P=0.005)。结论:RapidArc SRS计划通过设置单一治疗等中心可实现颅内多个转移瘤的同步放射外科治疗,具有更高的靶区剂量适形度及均匀性;但靶区周边剂量跌落陡度不及Novalis Knife计划,正常脑组织低剂量受照范围较大。治疗依从性较差的多发脑转移患者可考虑选择治疗效率更高的RapidArc技术,并根据临床实际情况调整剂量分割模式,以减少放射损伤风险。

SRS MapCHECK探测器阵列的剂量学特性及其在立体定向放疗计划剂量验证中的应用研究

目的:测量SRS MapCHECK探测器阵列的剂量学特性,并探讨其是否满足立体定向放疗计划剂量验证的要求。方法:采用Varian VitalBeam医用电子直线加速器测量6 MV X射线均整(flattening filter,FF)模式与非均整(flattening filter free,FFF)模式下SRS MapCHECK探测器阵列的重复性、剂量线性、剂量率线性及角度响应,记录多次测量的探测器中心点绝对剂量的平均值。使用SRS MapCHECK探测器阵列对在某院行立体定向放疗的56例放疗计划进行剂量验证,记录不同评价标准下的γ通过率。采用R语言进行统计学分析。结果:6 MV X射线FF模式与FFF模式下SRS MapCHECK探测器阵列的重复性测量值归一后的平均值分别为1.0000±0.0008、1.0000±0.0005,与各测量值归一值的偏差百分比不超过0.20%;2种模式下SRS MapCHECK探测器阵列的剂量线性分析的R^(2)值均大于0.99999;剂量率线性的变化及机架角度的变化对SRS MapCHECK探测器阵列的测量结果影响很小,其中6 MV X射线FF模式与FFF模式下各剂量率线性测量值的归一值与归一后的平均值的最大偏差百分比分别为0.89%、0.15%,各角度响应测量值的归一值与归一后的平均值的最大偏差百分比分别为1.30%、1.92%。在放疗计划剂量验证中,除1%/1 mm评价标准外,3%/2 mm、3%/1 mm和2%/1 mm评价标准下的γ通过率均>95%。结论:SRS MapCHECK探测器阵列具有良好的剂量学特性,可满足临床立体定向放疗计划剂量验证的要求。当采用γ分析进行剂量验证时,可采用更严格的2%/1 mm评价标准。

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Purpose: The purpose of this study is to provide technical information on commissioning the TrueBeam STx 6 MV flattening-filter free (FFF) beam in the RayStation treatment planning system (TPS) for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) treatments. Methods: For beam modeling, percent depth dose curves, profiles and output factors for jaw-collimated fields and stereotactic cones as well as X-jaws transmission were measured. For multi-leaf collimator (MLC) modeling, MLC model parameters such as offset, gain, curvature, leaf tip width, tongue and groove and transmission were determined and output factors for MLC-collimated fields were measured. Absolute dose calibration was also performed. For beam model and MLC model validation, the American Association of Physicists in Medicine Task Group-119 plans, clinical SRS and SBRT plans and end-to-end testing were performed. Results: Beam characteristics of the 6 MV FFF beam agreed well with those in the literature. Validation results showed that our beam model and MLC model were acceptable for SRS and SBRT treatments. Conclusions: The technical information and dosimetric data provided in this study will be a useful reference for other clinics/institutions which will commission the same machine energy in the RayStation TPS.

Treatment-Plan Comparison of Three Advanced Radiation Treatment Modalities for Fractionated Stereotactic Radiotherapy to the Head and Neck

Purpose: Fractionated stereotactic radiosurgery (FSRS) can be given with at least three modalities: Gamma Knife, with the noninvasive frameless extend system (GKE);linear accelerator-based volumetric modulated arc therapy (VMAT);and intensity-modulated proton therapy (IMPT). We extracted treatment plans for patients who had received FSRS with GKE for recurrent skull base or intracranial tumors, created corresponding plans for VMAT and IMPT, and compared the quality of the three sets of plans. Methods and materials: Plans were extracted for 9 patients with recurrent malignant skull-base tumors (n = 6) or large intracranial tumors (n = 3) who had received FSRS with GKE (median dose 24 Gy in 3 fractions) in 2013 through 2015. Plans for VMAT were generated with a TrueBeam STx LINAC machine using 6-MV photons, and plans for IMPT were generated with multi-field optimization. The optimized VMAT and IMPT plans were normalized to achieve the best possible target coverage while meeting the same dose-volume constraints on organs at risk (OARs) as the GKE plans. Plans were evaluated on the basis of target coverage, conformity index, homogeneity index, gradient index, and treatment efficiency. Results: The median target volume was 10.2 cm3 (range 1.9 - 33.8 cm3). The VMAT and IMPT plans met all OAR constraints, and target coverage and conformity were comparable among all plans. VMAT and IMPT plans showed significantly better target uniformity and treatment delivery efficiency (P P Conclusion: FSRS for skull base and large intracranial lesions delivered by VMAT and IMPT can achieve comparable target coverage, conformity, and sparing of critical structure as the GKE while providing superior target uniformity and treatment delivery efficiency. The GKE had superior high-dose gradients outside the target and thus better protected surrounding normal structures.