高能医用电子直线加速器的机房屏蔽设计方案国内外比较

目的 分别根据中、外放射治疗机房辐射屏蔽标准,对低能医用电子直线加速器机房设计方案进行对比,为修订和完善现行国家标准提供参考。方法 按照美国国家辐射防护与测量委员会（NCRP）151号报告、英国电离辐射法规（IRR）17号和国家标准GBZ/T 201,对于一个每日平均治疗125例患者（90%为调强放疗技术）的6 MV X射线医用电子直线加速器机房,分别设计机房屏蔽方案,对比关注点（主束次屏蔽区A、B点、主束主屏蔽区C、D点、侧墙次屏蔽点E、室顶主屏蔽点F和室顶次屏蔽点G）所需的混凝土屏蔽厚度、治疗室内使用面积、室内层高和室顶承重。结果 按照NCRP 151号报告和IRR 17号法规,计算得到的A、B、C、D、E、F和G点所需的混凝土屏蔽厚度分别为79、105、136、166、104、137、76 cm和94、126、183、189、119、175、92 cm。而按照我国标准GBZ/T 201计算得到的相应关注点所需的混凝土屏蔽厚度是最厚的,特别是主束主屏蔽厚度的增加明显,分别为117、133、207、227、121、175、94 cm。与此同时,与NCRP 151号报告计算得到的屏蔽方案相比,治疗室内使用面积、室内层高显著降低,分别减小11.24%和7.13%,室顶承重增加更为明显（25.20%）。结论 与NCRP 151号报告和IRR 17号法规相比,按照我国现行屏蔽标准所推荐的计算方法和评价指标计算得到的屏蔽厚度是最大的,特别是现行国家标准中要求的瞬时剂量当量率评价指标会显著增加主屏蔽区所需的屏蔽厚度。     

螺旋断层加速器自屏蔽结构对机房屏蔽防护厚度的影响

目的 探讨新型放射治疗设备螺旋断层加速器机房的屏蔽计算方法以及该型加速器自屏蔽结构对机房屏蔽防护厚度的影响,为螺旋断层加速器机房的屏蔽防护设计提供依据.方法 根据国家相关标准要求,结合机房几何结构,分别计算无自屏蔽存在情况下屏蔽主射线、散射线和漏射线所需的屏蔽厚度;根据螺旋断层加速器自屏蔽特点以及其辐射场特性,计算自屏蔽存在情况下机房辐射防护屏蔽厚度.结果 有自屏蔽结构的螺旋断层加速器机房防护屏蔽体的厚度与没有自屏蔽结构相比,其计算结果差异有统计学意义(t=3.576,P＜0.05);主射束区包括南墙、北墙、顶棚和地板,自屏蔽结构可以分别减少约95.59%、63.63%、80.73%和51.30%的屏蔽厚度.结论 螺旋断层加速器自屏蔽结构可显著减少其机房主射束区所需的辐射防护屏蔽厚度.对有自屏蔽结构的加速器机房的屏蔽厚度,应该根据其辐射场数据进行计算,也可将无自屏蔽情况下主射束区的计算结果减去自屏蔽等效屏蔽材料厚度来估算.

Abstract：

Objective To study the calculation of the room shielding thickness of tomotherapy accelerator,a new type of radiotherapy facility,especially the impact of the beam block on the shielding design.Methods According to the relevant standards,combined with the room geometry,the shielding thickness was calculated without the presence of the beam block,considering the primary beam,the scattered beam and leakage.Meanwhile,the shielding thickness was also calculated as comparison with the presence of the beam block,based on the characteristics of tomotherapy facility and its radiation field.Results There was statistical difference between the shielding thicknesses calculated with the presence of the beam block and those without the beam block,to the primary beam direction including the south wall,north wall,the roof and the floor,the shielding thickness were decreased by 95.59%,63.63% ,80.73%and 51.30% ,respectively.Conclusions For the tomotherapy accelerator,the beam block could be of great help to minify the shielding thickness of the room.The radiation field of the tomotherapy facility could be used for the calculation to improve accuracy,and the shielding thickness can also be estimated by subtracting the initial shielding thickness without beam block of the beam block equivalent thickness in the primary beam direction alternatively.     

重混凝土屏蔽质子放疗机房的感生放射性估算

目的 估算肿瘤质子治疗时重混凝土屏蔽墙中铁元素因中子活化产生的感生放射性⁵⁶Mn及其水平。方法 采用Geant4程序构建某质子治疗机房的重混凝土屏蔽墙模型,模拟245 MeV的质子束照射水模体产生的次级中子,统计屏蔽墙内放射性核素⁵⁶Mn的分布。将屏蔽墙按每10 cm厚度分层,计算前3层屏蔽墙中放射性核素⁵⁶Mn产生的周围剂量当量率。结果 在最大的束流照射条件（1.872×10¹⁰个）下,前3层屏蔽墙内的放射性核素⁵⁶Mn个数分别为3.10×10⁸、1.60×10⁸和9.33×10⁸个;对治疗室内1 m远处产生的周围剂量当量率分别为2.13×10^-3、8.82×10^-4 和9.10×10^-4 μSv/h,总的周围剂量当量率为3.92×10^-3 μSv/h。结论 在质子治疗时,距离射束中心轴越近,屏蔽墙的感生放射性越强;屏蔽墙前端中子活化铁元素产生的感生放射性最强,感生放射性随着屏蔽墙厚度增大呈指数形式减小,应主要考虑质子治疗机房屏蔽墙前端产生的感生放射性。     

有用线束朝向迷路内墙的加速器机房辐射屏蔽计算

目的 探讨有用线束朝向迷路内墙的放射治疗机房的辐射屏蔽计算方法。方法 根据国家职业卫生标准GBZ/T 201.2对某改建机房进行屏蔽计算,并与实际检测结果进行比较。结果 迷路入口处瞬时剂量率的理论计算结果和实际检测结果,防护门内分别为89和86 μSv/h,防护门外分别为5.7和6.2 μSv/h,理论计算结果与实际检测结果具有较好的一致性。结论 通过理论计算结果与检测结果的比较,验证了理论计算方法的准确性。     

蒙特卡罗方法在质子重离子加速器治疗场所屏蔽计算中的应用

目的 利用蒙特卡罗方法建立质子重离子加速器治疗场所的屏蔽计算模型,为治疗场所的屏蔽设计提供可靠的计算方法。方法 采用基于蒙特卡罗方法的FLUKA程序建立质子重离子治疗场所的屏蔽计算模型,模拟质子重离子加速器治疗场所辐射场的分布,通过对质子重离子加速器治疗场所的检测,验证计算模型。结果 FLUKA程序模拟计算结果与现场检测结果具有较好的符合性。结论 FLUKA程序建立的质子重离子加速器治疗场所屏蔽计算模型能够模拟质子重离子产生的辐射场。基于FLUKA程序建立的屏蔽计算模型,质子重离子治疗场所屏蔽设计应根据加速器最高可达的束流强度及能量进行计算。在质子和重离子加速器运行时的治疗室辐射场中,中子对剂量当量的贡献是主要的,因此,屏蔽设计中应重点考虑中子的屏蔽。     

中外近距离治疗机房辐射屏蔽设计标准应用比对

目的 中外近距离治疗机房辐射屏蔽设计考虑因素不尽相同,本研究以常见的高剂量率¹⁹²Ir源为例,分别应用国内外标准进行后装机房的屏蔽核算,比较计算结果分析差异产生的原因,为修订和完善现行国家标准提供参考。方法 对于典型的后装机房进行工作量估算,放射源初始活度10 Ci （1 Ci=3.7×10¹⁰ Bq）,分别按照英国医学物理与工程研究所IPEM75号报告、美国辐射防护委员会NCRP151报告和GBZ/T 201.3-2014国家标准设计后装机房屏蔽方案,详细比较不同参考标准的屏蔽限值、居留因子及其他因子的差异。结果 典型后装机房的年照射时长约为330 h,按照NCRP151报告、IPEM法规和GBZ/T 201.3-2014国家标准计算得到的控制室、屏蔽墙外、候诊区、相邻控制室和无人居留室顶等关注点位所需的混凝土厚度分别为70、65、61、70、50 cm,41、43、30、40、39 cm和84、79、46、88、39 cm。按照GBZ/T 201.3-2014国家标准计算得到的相应关注点所需的混凝土屏蔽厚度普遍偏厚,与NCRP151报告结果差别较小,IPEM75号报告计算得到的屏蔽厚度最薄;三者计算出的防护门的等效铅屏蔽厚度分别为1.170、0.854和1.040 cm,厚度相近。结论 我国现行后装机房屏蔽标准所推荐的计算方法和评价指标计算得到的屏蔽厚度与NCRP151报告的相似但偏保守,特别是现行国家推荐标中要求的瞬时剂量当量率评价指标以及过于保守的居留因子取值会显著增加主屏蔽区所需的屏蔽厚度。     

射波刀机房屏蔽的特殊考虑

目的 验证某射波刀机房的迷路外墙屏蔽的辐射防护效果,发现特殊情况下的屏蔽防护设计缺陷并予以纠正。方法 按照生产厂家提供的某射波刀机房辐射防护屏蔽设计方案,主要考虑有用线束经过影像中心,不会直接照射迷路外墙。在对已经建成的机房实施放射防护验收检测时,发现存在有用线束不经过影像中心实施照射的情况并补建屏蔽防护设施,并加以验证。结果 经过现场验证检测,在有用线束经过影像中心的情况下,距迷路外墙30 cm相关关注点处的最高周围剂量当量率为0.31 μSv/h,低于参考控制水平10 μSv/h。当有用线束不经过影像中心的情况下,距迷路外墙30 cm相关关注点处的最高周围剂量当量率达到301.67 μSv/h,接近参考控制水平的30倍。对此部分迷路外墙增加厚度以后,距其30 cm处的最高周围剂量当量率为2.14 μSv/h。检测结果符合标准要求。结论 建议设计射波刀机房的迷路外墙屏蔽时,应当根据加速器的运动范围确定有用线束是否经过影像中心,是否存在直接照射的迷路外墙的特殊情况,并根据照射范围和辐射源点至关注点的距离,按照有用线束计算屏蔽厚度,以符合标准要求,同时避免在机房迷路外墙相关专注点位置居留的人员受到超剂量照射。     

质子治疗

随着质子治疗应用的增多，它在眼部黑色素瘤和斜坡脊索瘤治疗方面表现出独特的优势，本就其在临床方面的应用进行了报道。     

闪速放射治疗(FLASH)技术对机房屏蔽设计带来的挑战

与常规放疗技术相比, FLASH治疗技术在保护正常组织方面具有优势, 但剂量率提升100倍以上。如果按照现有标准对机房进行屏蔽设计, 将显著提升改造成本, 且仍有可能无法满足标准要求, 导致FLASH治疗技术无法开展。通过调研国内外标准及文献, 分析了FLASH治疗技术对机房屏蔽设计带来的挑战, 并着重对比了不同国家在放疗机房屏蔽设计时采用的剂量率控制标准。部分国家屏蔽设计时采用考虑实际治疗工况下的平均剂量率;我国主要采用考虑居留因子条件下的瞬时剂量率方法进行控制。如果在我国开展FLASH治疗技术, 瞬时剂量率的要求将很难满足。为了提高FLASH等高剂量率放射治疗技术, 在管理目标限值不变的前提下, 建议考虑对现有标准进行修订, 采用一定时间内的平均剂量率限值进行控制, 或增加FLASH治疗条件下的控制标准。     

质子治疗恶性肿瘤的进展

质子治疗作为一种较新的肿瘤放射治疗手段正在发展和完善。质子束具有较好的物理特性，生物效应基本与常规照射相近。目前质子治疗的分类主要有质子适形及调强放疗、质子立体放射治疗、质子扫描照射等。质子治疗的优势在于利用Bragg峰，提高肿瘤区域放射剂量，降低正常组织受量，其适应证较为广泛，治疗效果取得一定进展，但还有待于进一步完善。     

低能X射线术中放射治疗的辐射屏蔽

目的 依据国内外标准和指南评估低能X射线术中放射治疗室的屏蔽需求,测量屏蔽材料的透射系数、关注位置的周围剂量当量率水平以及防护装置的应用效果,为此类设备屏蔽方案的设计和防护装置的应用提供参考。方法 分别依据我国GBZ 121标准、英国医学物理与工程研究所（IPEM）75号报告和美国国家辐射防护与测量委员会（NCRP）151号报告计算INTRABEAM术中放射治疗室所需的屏蔽厚度。实际测量固体水板、屏蔽贴片和防辐射围裙对于此设备产生低能X射线的透射系数,对模拟治疗条件下关注位置处的周围剂量当量率进行测量并评估辐射防护屏的应用效果。结果 依据不同标准和指南计算得到治疗室全部关注点处所需铅屏蔽厚度均<0.6 mm,差异为亚毫米水平。此设备产生的低能X射线在屏蔽物质中衰减明显,0.05 mm铅当量屏蔽贴片和0.25 mm铅当量防辐射围裙的透射系数为0.068和0.0038。使用球形施用器在空气中进行照射时,距离射线源1和2 m处测得的周围剂量当量率为10.7和2.6 mSv/h。将施用器置于小水箱中后,相应的周围剂量当量率降为3.8和0.9 μSv/h,防护屏的使用可以使2 m处的周围剂量当量率降为本底水平。结论 低能X射线术中放射治疗设施的屏蔽需求较低,设备产生的射线有效能量低,但在邻近未屏蔽辐射源位置的剂量率较高,应优化设计治疗室屏蔽方案并合理使用防护装置。     

Spot-scanning beam proton therapy vs intensity-modulated radiation therapy for ipsilateral head and neck malignancies: A treatment planning comparison

Radiation therapy for head and neck malignancies can have side effects that impede quality of life. Theoretically, proton therapy can reduce treatment-related morbidity by minimizing the dose to critical normal tissues. We evaluated the feasibility of spot-scanning proton therapy for head and neck malignancies and compared dosimetry between those plans and intensity-modulated radiation therapy (IMRT) plans. Plans from 5 patients who had undergone IMRT for primary tumors of the head and neck were used for planning proton therapy. Both sets of plans were prepared using computed tomography (CT) scans with the goals of achieving 100% of the prescribed dose to the clinical target volume (CTV) and 95% to the planning TV (PTV) while maximizing conformity to the PTV. Dose-volume histograms were generated and compared, as were conformity indexes (CIs) to the PTVs and mean doses to the organs at risk (OARs). Both modalities in all cases achieved 100% of the dose to the CTV and 95% to the PTV. Mean PTV CIs were comparable (0.371 IMRT, 0.374 protons, p = 0.953). Mean doses were significantly lower in the proton plans to the contralateral submandibular (638.7 cGy IMRT, 4.3 cGy protons, p = 0.002) and parotid (533.3 cGy IMRT, 48.5 cGy protons, p = 0.003) glands; oral cavity (1760.4 cGy IMRT, 458.9 cGy protons, p = 0.003); spinal cord (2112.4 cGy IMRT, 249.2 cGy protons, p = 0.002); and brainstem (1553.52 cGy IMRT, 166.2 cGy protons, p = 0.005). Proton plans also produced lower maximum doses to the spinal cord (3692.1 cGy IMRT, 2014.8 cGy protons, p = 0.034) and brainstem (3412.1 cGy IMRT, 1387.6 cGy protons, p = 0.005). Normal tissue V₁₀, V₃₀, and V₅₀ values were also significantly lower in the proton plans. We conclude that spot-scanning proton therapy can significantly reduce the integral dose to head and neck critical structures. Prospective studies are underway to determine if this reduced dose translates to improved quality of life.     

新型自屏蔽放射治疗系统辐射屏蔽性能防护检测与评估

目的 通过对新型自屏蔽ZAP-X治疗系统辐射屏蔽性能的全面检测,依据我国相关标准对该设备的辐射屏蔽性能进行评估,探讨无屏蔽治疗室的放射治疗系统用于我国的可能性。方法 ZAP-X治疗系统辐射源为3 MV的直线加速器,在该设备周边、距设备边缘1.3、2.3和3.3 m处,共选择了33个检测点位,在5种固定方向的照射条件下,使用电离室巡检仪分别测量33个检测点位在每种照射条件下的最大周围剂量当量率。选用临床常用治疗计划模拟临床治疗过程,对于一次完整治疗过程,测定了上述33个点位的累积剂量。并选择适用的我国现行放 射治疗辐射防护标准,对该系统辐射屏蔽性能进行评估。结果 依据设备周边33个检测点位周围剂量当量率测量结果,在该自屏蔽放射治疗设备现有的1 m控制区外,提出了重新划定控制区的建议,使得新控制区外任意点的周围剂量当量率不大于10 μSv/h,满足我国标准GBZ 121-2020中的要求。结论 依据我国现有标准,该无屏蔽治疗室的自屏蔽放射治疗系统具有在我国开展临床应用的可能性,但针对该新型自屏蔽放射治疗系统,我国应制定出与之相应的性能检测与辐射防护新标准。     

质子碳离子治疗腺样囊性癌的近期疗效及不良反应

目的 观察束流调强粒子放射治疗头颈部腺样囊性癌的不良反应和近期疗效。方法 2015年5月至2016年3月,8例初治的病理证实的头颈部腺样囊性癌患者,5例患者为局部晚期（T_3-4期）,3例患者为R1切除,5例患者为活检术后或R2切除。7例患者采用束流调强质子放射治疗（IMPT）联合束流调强碳离子放射治疗（IMCT）,IMPT放射临床靶区体积（CTV）56 GyE/28次后,采用IMCT给予局部加量治疗15 GyE/5次。1例患者接受了单纯的IMPT治疗。结果 根据新版实体瘤疗效评价标准（RECIST）评估标准,本组5例具有明确肿瘤病灶的患者,在放疗结束时和结束后1个月,3例肿瘤部分缓解（PR）,2例疾病稳定（SD）;4例放疗结束后3个月随访时,有2例达到完全缓解（CR）,1例PR,1例SD。至2016年3月所有患者均无肿瘤进展和死亡。放疗期间,2例发生了3级口腔黏膜反应,随访3个月无重度皮肤反应发生。结论 束流调强粒子放射治疗头颈部腺样囊性癌安全、有效,但后期不良反应和远期疗效尚需更长时间的观察。     

Temporal lobe changes following radiation therapy: imaging and proton MR spectroscopic findings

Radiation therapy for nasopharyngeal carcinoma affects the temporal lobes. This paper characterizes proton MR spectroscopic findings of the temporal lobes and correlates them with imaging changes. Single-voxel proton MR spectroscopic examinations were acquired from 13 healthy adult volunteers (25 spectra) and 18 patients (28 spectra). All patients had biopsy-confirmed nasopharyngeal carcinoma and were previously treated with radiation therapy. Six patients (33 %) had a single treatment and12 (67 %) patients had two treatments. Point resolved spectroscopy (PRESS) method was used (TR = 3000 ms, TE = 135 ms) and data processed automatically using the LCModel software package for metabolite quantification. Voxel size and geometry were adapted to the lesion to reduce skull-base lipid contamination. The metabolites were quantitated relative to water signal. For each location, an additional non-water-suppressed reference scan in fully relaxed conditions was performed. The imaging findings were divided into four categories: I, normal; II, edema only; III, contrast-enhancing lesions; and IV, cystic encephalomalacia. The N-acetyl-aspartate levels were reduced in 27 (96 %) spectra. Choline was increased in 3 (11 %), normal in 4 (14 %), and reduced in 21 (75 %) spectra. The creatine level was normal in 8 (29 %) spectra and reduced in 20 (71 %) spectra. Imaging showed 4 (14 %) spectra with category-I imaging findings; 5 (18 %) spectra with category-II findings; 15 (54 %) spectra with category-III findings; and 4 (14 %) spectra with category-IV findings. Magnetic resonance spectroscopy showed reduced N-acetyl-aspartate in radiation-induced temporal lobe changes. Creatine levels were relatively more stable. Choline levels may be increased, normal, or reduced. Imaging findings ranged from normal to contrast-enhancing lesions and cystic encephalomalacia. Received: 1 October 1999/Revised: 25 February 2000/Accepted: 23 May 2000     

Study for reducing lung dose of upper thoracic esophageal cancer radiotherapy by auto-planning: volumetric-modulated arc therapy vs intensity-modulated radiation therapy

This study aimed to investigate the dosimetric differences and lung sparing between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) in the treatment of upper thoracic esophageal cancer with T3N0M0 for preoperative radiotherapy by auto-planning (AP). Sixteen patient cases diagnosed with upper thoracic esophageal cancer T3N0M0 for preoperative radiotherapy were retrospectively studied, and 3 plans were generated for each patient: full arc VMAT AP plan with double arcs, partial arc VMAT AP plan with 6 partial arcs, and conventional IMRT AP plan. A simultaneous integrated boost with 2 levels was planned in all patients. Target coverage, organ at risk sparing, treatment parameters including monitor units and treatment time (TT) were evaluated. Wilcoxon signed-rank test was used to check for significant differences (p?<?0.05) between datasets. VMAT plans (pVMAT and fVMAT) significantly reduced total lung volume treated above 20?Gy (V₂₀), 25?Gy (V₂₅), 30?Gy (V₃₀), 35?Gy (V₃₅), 40?Gy (V₄₀), and without increasing the value of V₁₀, V₁₃, and V₁₅. For V₅ of total lung value, pVMAT was similar to aIMRT, and it was better than fVMAT. Both pVMAT and fVMAT improved the target dose coverage and significantly decreased maximum dose for the spinal cord, monitor unit, and TT. No significant difference was observed with respect to V₁₀ and V₁₅ of body. VMAT AP plan was a good option for treating upper thoracic esophageal cancer with T3N0M0, especially partial arc VMAT AP plan. It had the potential to effectively reduce lung dose in a shorter TT and with superior target coverage and dose homogeneity.     

Multifield optimization intensity-modulated proton therapy (MFO-IMPT) for prostate cancer: Robustness analysis through simulation of rotational and translational alignment errors

To evaluate the dosimetric consequences of rotational and translational alignment errors in patients receiving intensity-modulated proton therapy with multifield optimization (MFO-IMPT) for prostate cancer. Ten control patients with localized prostate cancer underwent treatment planning for MFO-IMPT. Rotational and translation errors were simulated along each of 3 axes: anterior-posterior (A-P), superior-inferior (S-I), and left-right. Clinical target-volume (CTV) coverage remained high with all alignment errors simulated. Rotational errors did not result in significant rectum or bladder dose perturbations. Translational errors resulted in larger dose perturbations to the bladder and rectum. Perturbations in rectum and bladder doses were minimal for rotational errors and larger for translational errors. Rectum V45 and V70 increased most with A-P misalignment, whereas bladder V45 and V70 changed most with S-I misalignment. The bladder and rectum V45 and V70 remained acceptable even with extreme alignment errors. Even with S-I and A-P translational errors of up to 5 mm, the dosimetric profile of MFO-IMPT remained favorable. MFO-IMPT for localized prostate cancer results in robust coverage of the CTV without clinically meaningful dose perturbations to normal tissue despite extreme rotational and translational alignment errors.