Commissioning of TrueBeamTM Medical Linear Accelerator: Quantitative and Qualitative Dosimetric Analysis and Comparison of Flattening Filter (FF) and Flattening Filter Free (FFF) Beam

Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeamTM Medical Linear Accelerator. Critique of beam characterization and evolution of dosimetric properties for 6 MV, 10 MV, 15 MV FF beam and 6 MVFFF, 10 MVFFF FFF beam has been carried out. We performed the comparison of photon beam data for two standard FF photon energy 6 MV, 10 MV verses 6 MVFFF, and 10 MVFFF FFF beam. Determination and comparison of parameter involved PDD (Percentage depth dose), Depth dose profile, Symmetry, Flatness, Quality index, Relative output factor, Penumbra, Transmission factor, DLG (Dosimetric leaf gap), in addition to degree of Un-flatness and off-axis ratio of FFF beam. Outcomes of presenting study had shown that change of various parameters such as Percentage depth dose curves, Shape of the depth dose profile, Transmission, Value of quality index and significant rise in surface dose for FFF in comparison with FF beam. Differences in the output factor at lower and higher field sizes for FFF beam compared to that of FF beam were found. The maximum output factor deviation between 6 MV and 6 MVFFF was found to be 4.55%, whereas in 10 MV and 10 MVFFF was 5.71%. Beam quality TPR20/10 for FFF beam was found to be lesser in magnitude, 5.42% for 6 MVFFF whereas 4.50% for 10 MVFFF compared to 6 MV and 10 MV FF beam respectively. Jaw transmission and interleaf leakage for FFF beam were found to be lesser than FF beam. Also DLG for FFF beam was found to be lesser in magnitude comparable to that of flattened beam. This study is mainly inclined towards evaluation and comparison of the FF and FFF beam. It has been observed that, the outcome of a commissioning beam data generation fully complies with vendor specification and published literature.

Assessment of Monitor Units and Gamma Pass Rate for 6 MV and Flattening Filter Free (FFF) Beams in Volumetric Modulated Arc Therapy (VMAT)

Background: In linear accelerators, the treatment field’s uniform intensity is achieved by including a flattening filter in the beam. However, to produce more conformal dose distributions, contemporary radiotherapy practice now frequently uses fluence and aperture modifying techniques, such as volumetric modulated arc therapy. In these circumstances, the flattening filter in the beam manufacturing process is no longer required. It is therefore necessary to compare the monitor units of 6 MV and flattening filter free plans and how it influences the gamma pass rates to determine which is best for treating cervical cancer with pelvic lymph node metastasis. Methods: VMAT plans for fifteen patients with cervical cancer with pathological pelvic lymph node metastasis were included in this study. Each patient had two VMAT plans using conventional 6 MV beam with flattening filter and one with flattening filter free beam (FFF). The VMAT plans were made using two arcs, and then recalculated to give the planned dose distribution to the detectors in a Delta4 phantom. The VMAT plans were irradiated on the Delta4 phantom using an Elekta linear accelerator (6 MV). Results: The mean monitor unit for the 6 MV plans was 506.3 MU and a standard deviation of 48.6 while that of the FFF plans had a mean MU of 701.5 with a standard deviation of 87.6. The total monitor units (MUs) for the FFF plans were significantly greater than the 6 MV plans (p = 6.1 × 10-5). Conclusion: Flattening filter free (FFF) plans require more numbers of monitor units in comparison to conventional 6 MV filtered beams for external radiation of cervical cancer with pelvic lymph nodes involvement.

Case Report: Anaplastic Astrocytoma Treated with Postoperative Radiotherapy Using Flattening Filter-Free Volumetric Arc Therapy (FFF-VMAT) during Pregnancy—Acceptable Fetal Dosimetry

Background: Postoperative irradiation for brain tumor in pregnant women is a matter of concern. Aim: We aimed to assess the safety of radiotherapy for brain tumors in pregnancy. We here report a successful treatment for anaplastic astrocytoma during pregnancy: surgery + postoperative irradiation. We wish to emphasize how we devised irradiation procedure to achieve both therapeutic effectiveness and safety to the fetus/infant. Case Presentation: A 34-year-old pregnant woman suffered with brain anaplastic astrocytoma. Tumor resection under craniotomy was performed with success. We decided to conduct postoperative radiotherapy at 25 weeks of gestation to reduce the risk of recurrence. We used a flattening filter-free volumetric arc therapy (FFF-VMAT) technique, which can achieve lower out-of-field dose than VMAT with a flattening filter or helical tomotherapy. We prescribed 60 Gy over 30 fractions. During actual beam delivery, surface and rectal dose to the patient (mother) were measured. The total fetal dose was estimated at 0.006 - 0.018 Gy, which is under the threshold set by the ICRP. A male healthy infant was born vaginally at the 37th week of pregnancy. The patient (mother) and the infant are healthy at the time of writing. Conclusion: FFF-VMAT is a good choice for brain tumors during pregnancy.

基于Flatten-Filter Free模式治疗原发性肝癌的剂量学研究

目的:比较原发性肝癌的Flatten-Filter Free(FFF)模式和Flatten Filter(FF)模式的单弧、双弧以及七野固定野治疗的剂量学差异。方法:选取13例原发性肝癌患者,在增强CT图像上勾画靶区及危及器官和正常组织,并在同一套CT图片上设计单个全弧、双全弧和七野固定野的FFF模式和FF模式的调强计划,病人总的治疗剂量200 c Gy×30次。通过剂量体积直方图统计PTV相关的剂量学参数、适形度指数(CI)、均匀性指数(HI),肝脏的剂量体积学参数、机器跳数、治疗时间和计划时间等利用SPSS20.0进行配对非参数Wilcoxson符号秩检验的统计学处理。结果:3种放疗计划FF和FFF模式靶区的HI和CI均没有统计学差异(P>0.05),靶区的V95%、最大剂量、最小剂量和平均剂量有统计学差异(P<0.05),在单弧、双弧和七野固定野调强计划的FF和FFF模式中,靶区的V95%FFF比FF分别低34.3%、13%、1.2%,靶区最大剂量FFF模式比FF分别低1.54%、1.39%、2.2%,靶区的最小剂量分别降低17.9%、6.6%、9.23%,平均剂量分别降低9.23%、2.0%、2.3%。结论:FFF模式可以有效降低正常肝脏组织受量,减少病人治疗时间,可以在图像引导基础上进一步提高放疗的安全性。

Volumetric modulation arc radiotherapy with flattening filter-free beams compared with conventional beams for nasopharyngeal carcinoma:a feasibility study

There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams for nasopharyngeal carcinoma(NPC).Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams(RA-FFF) or conventional beams(RA-C).The doses to the planning target volumes(PTVs),organs at risk(OARs),and normal tissues were compared.The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams.Both techniques delivered adequate doses to PTVs.For PTVs,RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF.Both techniques provided similar maximum doses to the optic nerves and lenses.For the brain stem,spinal cord,larynx,parotid glands,oral cavity,and skin,RA-FFF showed significant dose increases compared to RA-C.The dose to normal tissue was lower in RA-FFF.The monitor units(MUs) were(536 ± 46) MU for RA-FFF and(501± 25) MU for RA-C.The treatment duration did not significantly differbetween plans.Although both treatment plans could meet clinical needs,RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.

A comparative study between flattening filter-free beams and flattening filter beams in radiotherapy treatment

Flattening filter-free(FFF) beams generated by medical linear particle accelerators(linacs) have recently been used in radiotherapy clinical practice.FFF beams have fundamental physical parameter differences with respect to standard flattening filter(FF) beams,such that the generally used dosimetric parameters and definitions are not always viable.This study investigates dosimetric parameters for use in the quality assurance of FFF beams generated by medical linacs in radiotherapy.The main characteristics of the photon beams are analyzed using specific data generated by a Varian True Beam linac having both FFF and FF beams of 6 and 10 MV(megavolt) energy,respectively.Definitions for dose profile parameters are suggested,starting from the renormalization of the FFF with respect to the corresponding FF beam.From this point,the flatness concept is translated into one of "un-flatness",and other definitions are proposed,maintaining a strict parallelism between FFF and FF parameter concepts.The quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given,maintaining similarity to those used for standard FF beams,and recommendations for the introduction of FFF beams into clinical radiotherapy application for breast cancer patients are provided as an example for comparison between FFF and FF for dose distribution and coverage for a target volume.Although there are many advantages of using a FFF beam,especially for advanced radiotherapy techniques,there are a few limitations(e.g.,using a relatively higher energy photon beam for stereotactic radiotherapy(SRT),limited speed of current multileaf collimators(MLCs),and off-axis distance-dependent modulation in intensitymodulated radiation therapy(IMRT)) as well as challenges(e.g.,criteria for beam quality evaluation and penumbra,establishment of dosimetry methods,and consequences of photon target burn-up) that need to be addressed for establishing the FFF beam as a viable alternative to the FF beam.

使用硅半导体探测器采集FFF小野光子束基础数据的扫描参数优选研究

目的探讨使用硅半导体探测器采集非均整模式小尺寸辐射野兆伏级光子束的百分深度剂量(Percentile Depth Dose,PDD)、射野离轴比(Field Off Axis Ratio,OAR)等基础数据的扫描参数优选问题。方法以蒙卡仿真结果为参考,使用PTW60016硅半导体探测器,采用均值±标准差、Gamma1D分析等方法,定量评价不同采样时间与采样步长对小野射线质及半影区宽度测量偏差的影响。结果不同测量参数组合条件下,四个典型小野(1cm×1cm^4cm×4cm)射线质的标准差均在0.005以内;采样时间的增加对PDD和OAR测量精度影响较小,采样步长的减小有利于提高OAR半影区和PDD建成区测量精度,对大深度处PDD测量精度的提高无意义;采样时间对半影区宽度影响较小(标准差均小于0.05mm),采样步长的增大导致半影区展宽。结论射线质对采样时间和步长不敏感;PDD测量精度对采样时间不敏感,4~50mm区域与采样步长成负相关,51~300mm深度不敏感;OAR半影区宽度对采样时间不敏感,与采样步长正相关;综合测量精度和效率,本研究推荐PDD数据采用0.5s、0.5mm(50mm以内)和1mm(51~300mm),OAR数据0.5s、0.5mm作为PTW60016的小野基础数据扫描参数。

基于IAEA 277和398报告在直线加速器FFF模式下绝对剂量校准结果对比

目的:基于IAEA 277和398号报告,分析对比直线加速器FFF模式下绝对剂量的校准结果。方法:利用上海交通大学医学院附属瑞金医院新安装的Varian Edge加速器,根据IAEA 398号报告,测量FFF模式下6X和10X光子线的射线质和百分深度剂量,计算电离室校准因子kQ、极化效应修正因子kpol、复合效应修正因子ks,并对比国内现阶段采用的IAEA 277号报告的校准值。结果:6X-FFF和10X-FFF下,射线质分别为0.629和0.708;校准深度均为10 cm,对应的kQ分别是0.997和0.988,kpol分别是1.0009和1.0012,ks分别是1.0050和1.0069。FFF模式下复合效应相比较FF模式略高,分别偏高0.36%和0.32%。IAEA 398号报告的校准结果与IAEA 277号报告相比,绝对剂量标准差异分别为-1.0%和-0.7%。结论:在FFF模式下,IAEA 398号报告的绝对剂量校准与现阶段国内采用的IAEA 277号报告相比,结果差异小于2%,且在临床实践中更便捷。

局限性前列腺癌SABR-VMAT的FF和FFF模式治疗的剂量学比较

目的比较Varian Clinac ix带均整过滤器(flattening filter,FF)和不带均整过滤器(flattening filter free,FFF)治疗模式对容积立体定向消融放射治疗(SABR-VMAT)局限性前列腺癌剂量学的影响。方法对9例局限性前列腺癌患者的治疗计划回顾分析。分别给予35 Gy处方剂量,总分次为5次。采用6MV-FF和6MV-FFF模式为该9例患者设计SABR-VMAT计划,分析2种治疗模式对肿瘤剂量CI,HI及危及器官(OARs)的影响;通过模拟实施治疗的方式比较2种治疗模式对治疗时间的影响。结果 FFF和FF治疗计划都有很好的CI,HI和CN,OARs的剂量也能满足预先设置的剂量限值。在2种治疗模式下,靶区及OARs的剂量没有显著的差异,靶区外2 cm处的近似最大剂量FFF略微优于FF,分别为17.4 Gy和17.8 Gy,但没有统计学意义。FFF的治疗时间(2.5 min)明显的低于FF(3.6 min)。结论SABR-VMAT FFF模式治疗局限性前列腺癌在不影响肿瘤及危及器官剂量分布的情况下减少治疗时间,有一定的临床实用价值。

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.

均整器对海马规避全脑非均分调强放射治疗的剂量学影响

目的:研究非均分9野调强放疗均整过滤器(9F-IMRT-FF)和9野调强放疗非均整过滤器(9F-IMRT-FFF)两种模式下海马规避全脑放疗的剂量学差异。方法:选取2023年1-12月在承德市中心医院已完成全脑放疗的20例颅内转移患者的模拟定位CT图像,在计划系统中重新设计全新9F-IMRT-FF和9F-IMRT-FFF两种模式放疗计划。在两种模式优化参数保持一致的条件下进行放疗计划优化。比较两种模式计划的剂量学参数差异,以及加速器照射效率差异。结果:9F-IMRTFFF模式计划靶体积(PTV)的2%靶区体积的受照剂量(D_(2%))为(33.36±0.79)Gy,低于9F-IMRT-FF的(36.44±0.36)Gy,差异有统计学意义(t=-2.496,P<0.05)。9F-IMRT-FFF模式计划左侧海马的100%靶区体积的受照剂量(D_(100%))、最大剂量(D_(max))和平均剂量(D_(mean))均低于9F-IMRT-FF模式计划,差异有统计学意义(Z=-3.179、-3.018、-2.145,P<0.05)。9F-IMRT-FFF模式计划右侧海马D_(100%)、D_(max)低于9F-IMRT-FF模式计划,差异有统计学意义(Z=-3.099、-3.260,P<0.05)。9F-IMRT-FFF模式计划机器总跳数(MU)比9F-IMRT-FF模式计划增加25%,而治疗时间比9F-IMRT-FF模式缩短38%,差异有统计学意义(t=-9.664、-13.312,P<0.05)。结论:9F-IMRT-FF和9F-IMRT-FFF两种模式均能满足临床要求。9F-IMRT-FFF模式具备更佳的束流调制能力,对于降低海马放疗剂量、减少治疗时间和提高治疗效率更具有优势。

基于国际原子能机构277和381报告对直线加速器双模式光子线和电子线输出量校准研究

目的:基于国际原子能机构(IAEA)TRS 277和TRS 381《高能电子束和光子束中使用平行电离室的国际剂量测定操作规范》报告,校准加速器配置的不同档能量射线水中的吸收剂量,确保临床放疗中直线加速器输出剂量的精确性。方法:采用Elekta Infinity直线加速器,光子线能量6 MV分别为均整(FF)模式和非均整(FFF)模式;电子线能量分别为4、6、8、10、12和15 MeV。根据IAEATRS277和TRS381报告,使用PTW剂量仪、PTW30013指型电离室和PTW34001平行板电离室分别进行光子线和电子线水中输出剂量的校准,对各步骤的误差进行分析,对比采用不同标准对直线加速器的输出量水中校准的准确性。结果:6 MV的FF模式和FFF模式光子线在水中最大剂量点处的输出量分别为1.003和1.008 cGy/MU;4、6、8、10、12和15 MeV的电子线每档能量在水中最大剂量点处的输出量分别为1.003、1.002、0.998、0.999、1.000和1.003 cGy/MU。每档能量的射线在水中最大剂量点处的输出量校准为1 MU对应1 cCy,误差<1%。结论:根据IAEA TRS277号和TRS381号报告对直线加速器的输出剂量在水中进行校准,可以保证直线加速器的输出剂量的准确性。

非均整模式与均整模式下儿童肾母细胞瘤容积调强放疗的剂量学研究

目的:对比在均整(flattening filter,FF)模式与非均整(flattening filter free,FFF)模式下儿童肾母细胞瘤容积调强放疗(volumetric modulated arc therapy,VMAT)的剂量学差异。方法:回顾性选取2022年8月至2023年10月于某院接受放疗的10例肾母细胞瘤患儿,均设计FF模式和FFF模式下的VMAT计划,比较2种计划的计划靶区(planning target volume,PTV)剂量学参数、危及器官(organ at risk,OAR)受照剂量、机器跳数、γ通过率及治疗时间。结果:FFF计划的D_(2)、D_(98)及均匀性指数均优于FF计划,差异有统计学意义(P<0.05);而2种计划的D50和适形性指数比较,差异无统计学意义(P>0.05)。FFF计划在对侧肾脏D_(mean)、V_(5)、V_(10),肝脏D_(mean)、V_(5)、V_(10)以及脊髓D_(max)方面均优于FF计划,差异有统计学意义(P<0.05)。FF计划在γ通过率、机器跳数方面均优于FFF计划,而FFF计划的治疗时间明显短于FF计划,差异有统计学意义(P<0.05)。2种计划的γ通过率均>95%。结论:FF模式和FFF模式下的VMAT计划均能满足临床治疗要求,FFF模式较FF模式在PTV剂量分布、OAR受照剂量和治疗时间方面更有优势,对提升患儿治疗效果和配合度有积极影响。

具有非均整模式的医用直线加速器 机房放射防护设计与效果分析

目的:分析研究具有非均整(FFF)模式的医用直线加速器机房放射防护设计与屏蔽效果,为医用直线加速器FFF模式的放射防护设计提供技术参考。方法:在Versa HD型医用直线加速器X射线能量10 MV、照射野40 cm×40 cm条件下,分别使用均整模式最大输出剂量率600 MU/min和FFF模式最大输出剂量率2200 MU/min照射,按照国家职业卫生标准(GBZ126-2011)规定的方法,对加速器机房外表面30 cm处剂量水平进行检测,对检测结果中的超标位点计算改造方案的屏蔽厚度,并在改造完成后重新进行检测。结果:按照均整模式设计的原屏蔽方案在10 MV的FFF模式下,机房外表面部分检测点辐射剂量率>2.5μSv/h,超出国家职业卫生标准(GBZ126-2011)限值(≤2.5μSv/h)要求;防护门外中子辐射剂量当量率最大为1.0μSv/h,明显高于预期值。根据检测结果计算需要增加的屏蔽厚度,改造完成后原超标位点辐射剂量率均<2.5μSv/h,满足标准限值要求。结论:在FFF模式下机房外表面辐射剂量率较均整模式明显增加,具备10 MV的FFF模式的医用直线加速器机房设计需要考虑中子防护,在不改变周围剂量当量率参考控制水平的情况下,需要增加屏蔽厚度才能达到国家标准要求。

医用直线加速器中心轴绝对剂量输出长期稳定性对比分析

目的：分析对比医用直线加速器中心轴光子绝对剂量输出的长期稳定性特点。方法：选取3 台Varian 加速器，以最新IAEA TRS-398 报告中推荐的水中直接剂量法监测15 个月内的剂量输出，用SPSS 和SigmaPlot 软件进行统计分析。结果：在390 条数据中，超过±2%允差有7 次（1.79%）。偏差主要分布在-0.2%~1.2%，最大＋2.55%。同一加速器均整模式下不同能量输出稳定性差异显著（P〈0.05），但无临床意义（〈1 cGy 量级）。不同加速器的均整模式输出稳定性显著依赖于机龄（P〈0.05），与机型无关，而非均整模式（FFF）间差异不显著。结论：包括较新的TrueBeam FFF 模式在内的 Varian 加速器中心轴绝对剂量输出的长期稳定性良好，错误率为1%~2%。放疗中心可以晨检仪和标准水箱测量相结合的方法，监测并及时纠正该偏差。

直线加速器均整和非均整模式下射线质和射野输出因子的蒙特卡罗模拟与实测值比较

目的:利用蒙特卡罗方法分别模拟True Beam直线加速器6 MV均整和非均整(Flattening Filter-Free,FFF)模式,计算其射线质和射野输出因子,并比较上述参数与实际测量结果的差异。方法:利用Beamnrc和Dosxyznrc程序建立加速器机头模型并计算两档能量在参考条件下不同射野的剂量学数据。输出上述数据,计算各个射野射线质与实际测量值的相对偏差,对其绝对值做统计分析;利用各个射野中心轴上水下10 cm处的剂量值获取射野输出因子,并计算与测量值的相对偏差,绝对化后做统计分析。结果:6 MV和6FFF两档能量射线质相对偏差绝对值分别为(0.459±0.462)%和(0.486±0.300)%,射野输出因子相对偏差绝对值分别为(1.315±1.868)%和(0.904±1.214)%。结论:该模型的射线质和输出因子与测量结果相对偏差较小,基本可用于临床剂量学研究。

非均整器模式下早期非小细胞肺癌3种放疗技术剂量学研究

目的从剂量学角度比较非均整器(FFF)模式下早期非小细胞肺癌(NSCLC)立体定向放射治疗的不同放疗技术。方法选取15例NSCLC作为研究对象,分别设计FFF模式下适形拉弧(CAT)、三维适形技术(3D-CRT)及容积弧形动态旋转调强(VMAT)计划。比较3种计划95%、105%的处方剂量覆盖靶区体积百分数(V95%、V105%)、靶区均匀度(HI)、适形度(CI)、最大剂量(Dmax)和平均剂量(Dmean)、危及器官(OAR)剂量、机器跳数(MU)及治疗时间(TT)。结果 CAT和3D-CRT计划中的计划靶区(PTV)V95%、CI低于VMAT计划(P<0.05),而V105%、HI、Dmax、Dmean高于VMAT计划(P<0.05);在患侧肺V5、V20、V30、V40、Dmean方面,CAT和3D-CRT计划高于VMAT计划(P<0.05);在患侧肺V20、V30方面,3D-CRT计划高于CAT计划(P<0.05);在脊髓Dmax,3D-CRT计划低于CAT与VMAT计划(P<0.05);CAT、3D-CRT计划的MU低于VMAT计划(P<0.05)。在治疗时间上CAT低于3D-CRT,且两者均少于VMAT(P<0.05)。结论 FFF模式下3种计划均能满足临床要求,靶区CI、HI及患侧肺保护的VMAT计划优于CAT和3D-CRT计划,但在执行效率,CAT和3D-CRT更具有优势。

射线能量和均整特性对直肠癌容积旋转调强计划质量的影响

目的探讨光子射线能量和均整特性对直肠癌VMAT计划质量的影响。方法回顾性选取30例直肠癌术前辅助放疗患者,每例患者使用4种能量模式(6 MV、10 MV、非均整射线6 FFF和10 FFF),用同样的处方和优化函数分别设计VMAT计划。通过剂量体积直方图计算靶区剂量、适形指数(CI)、均匀性指数(HI);统计膀胱、小肠、股骨头和正常组织的剂量;记录每个计划的机器跳数(MU)和计划执行时间,比较4种能量模式下VMAT计划的质量差异。结果 4种计划的靶区的剂量参数D_(98%)、D_(50%)、D_(2%)、CI、HI均值无显著差异;6 FFF、10 FFF能量模式下小肠的最高剂量D_(2%)比6 MV计划的结果小0.7%和1.5%(P<0.05),其余OAR的DVH结果无显著差异。正常组织NT的低剂量区域V_(5Gy)、V_(10Gy)和V_(20Gy)、6 FFF、10 FFF计划比6 MV计划的结果分别减少了0.9%、1.4%、1.1%、1.4%和1.2%、2.4%(P<0.05)。与6 MV能量计划相比,6 FFF、10MV和10 FFF VMAT计划的MU变化了24%、-3%、29%(P<0.05)。结论光子射线能量的变化对直肠癌VMAT计划质量的影响微小,非均整射线可以稍微降低VMAT计划的低剂量照射区体积。

非均整模式光子线在乳腺癌调强放疗的剂量学评估

目的:评估6 MV光子线高剂量率非均整模式(FFF)在右侧乳腺癌保乳术后大分割同步推量调强放疗(SIBIMRT)的可行性。方法:随机选取10例右侧乳腺癌保乳术后患者临床资料,分别给予瘤床靶区(PTV1)和全乳靶区(PTV2)处方剂量48 Gy和40 Gy,分15次照射。对每例患者分别制作FFF和均整模式(FF)两组SIB-IMRT计划,比较两组计划的靶区覆盖率、适形指数(CI)和均匀指数(HI)以及危及器官受量和计划执行效率。结果:两种计划靶区的覆盖率、HI和CI的差异幅度小于1%。FFF计划PTV1的D98%高于FF计划(t=-2.297,P<0.05);PTV2的D90%低于FF计划(t=2.479,P=0.019);PTV2的CI稍劣于FF计划(t=5.343,P<0.001)。FFF计划患侧肺的V_(4Gy)和V_(16Gy),健侧乳腺的D_(mean)和D_(5%),以及正常组织的D_(mean)、V_(5Gy)、V_(10Gy)和V_(20Gy)均低于FF计划(t=2.318~11.535,P<0.05);正常组织的V_(40Gy)(t=-2.967,P=0.016)和皮肤Dmean(t=-6.102,P<0.001)高于FF计划。FFF计划的MU值(1 417±230)高于FF计划MU值(1 106±208)(t=-8.220,P<0.001);照射时间比FF计划减少33%(t=11.788,P<0.001)。结论:两种模式均能满足临床要求,FFF模式高剂量率光子线更有利于保护危及器官,显著缩短照射时间,执行效率较高。

鼻咽癌容积调强放射治疗剂量验证比较研究

目的比较6 MV-X射线均整模式(6X)和非均整模式(6FFF)容积旋转调强治疗(volumetric modulated arc therapy,VMAT)技术在鼻咽癌放射治疗中的剂量验证结果,验证6FFF容积调强计划的临床可行性。方法用PTW公司二维电离室矩阵Array729和OCTAVIUS Octagonal模体对15例患者的6X和6FFF VMAT计划进行剂量验证。结果采用gamma 2D进行分析(按3 mm和3%的误差标准),6X 1ocal dose方法通过率为(95±3)%,max dose方法通过率为(96±3)%,6FFF local dose方法通过率为(94±3)%,max dose方法通过率为(95±3)%。结论 PTW Array729可用于6X和6FFF VMAT计划的临床验证,6FFF计划的通过率略低于6X,local dose方式二者之间差异无统计学意义(P>0.05),max dose方式二者之间差异具有显著的统计学意义(P<0.01)。同一计划的验证结果采用local dose评判方法通过率低于max dose,具有显著的统计学意义(P<0.001)。