SIEMENS 6MV X刀剂量测量

用Ｐ型半导体探测器测量Ｘ刀φ４ｍｍ～４１．２ｍｍ射野的输出因子Ｓｃｐ，体模散射因子Ｓｐ，百分深度剂量ＰＤＤ和离轴比曲线ＯＡＲ；用０．１ｃｃ电离室测量射野的输出因子，体模散射因子和组织最大剂量比（ＴＭＲ）。通过两者的比较及与发表文献比较，对结果给予评价，结果显示：用小型半导体探测器测量Ｘ刀，可获得准确的结果，测量百分深度剂量获得ＴＭＲ比用电离室直接测量ＴＭＲ更快捷更简便，０．１ｃｃ电离室测量射野输出     

60Co机准直器散射因子(Sc)的性质

目的测量６０Ｃｏ机准直器散射因子（Ｓｃ）的性质，为临床使用提供依据。材料与方法在两种类型６０Ｃｏ机上，用指形电离室测量Ｓｃ随各种因素的变化规律。测量时，电离室的轴线与照射野的射线束轴重合。结果获得了Ｓｃ与源皮距的关系数据。分析了不同矩形野Ｓｃ的变化，挡块对Ｓｃ影响等。结论在一般照射野大小，Ｓｃ与源皮距无关，并可用二次函数来拟合Ｓｃ随照射野大小的变化。挡块及有机玻璃托盘对Ｓｃ影响可忽略。但在大野时Ｓｃ略有不同。根据测量的数据提出了矩形照射野的Ｓｃ等效方野的计算公式     

SIEMENS 6MV X刀剂量测量

用P型半导体探测器测量X刀4mm~41．2mm射野的输出因子Scp、体模散射因子Sp、百分深度剂量PDD和离轴比曲线OAR；用0．1cc电离室测量射野的输出因子、体模散射因子和组织最大剂量比（TMR）。通过两者的比较及与已发表文献比较，对结果给予评价。结果显示：用小型半导体探测器测量X刀，可获得准确的结果；测量百分深度剂量获得TMR比用电离室直接测量TMR更快捷更简便；0．1cc电离室测量射野输出因子，电离室直径要小于射野直径的一半，否则将引起较大误差。     

直线加速器上、下铅门对准直器散射因子的影响

直线加速器上、下铅门对准直器散射因子的影响韩树奎，路长春准直器对束流的散射主要是准直器铅门侧面和深层的向前散射和折射及由准直器反散射到束流监测电离室（１）定义散射因子表示准直器的设置对散射的影响：ＳＦｃ（Ｄ＝Ｕ）＝Ｄａ（Ｄ×Ｕ）／Ｄａ（１０ｘ１０）（...     

外挂式多叶准直器对准直器散射因子的影响

目的　用电离室测量外挂式多叶准直器 (MLC)对准直器散射因子 (Sc)的影响 ,并用双源模型对结果进行分析。方法　测量MLC形成的 2个不规则射野序列 ,并与等效方野的测量值进行了比较 ,应用双源模型得出MLC对Sc产生影响时叶片所处的位置公式。结果　当MLC叶片位置离中心足够近时 ,叶片将对准直器散射因子产生影响 ;产生影响时叶片位置计算值与测量结果相符。结论　基于双源模型的MLC位置公式较好地描述了当外挂式准直器 (MLC或铅块 )形成的射野小于公式给出值时 ,准直器散射因子将受其影响。     

新型双能医用直线加速器非均整剂量学特性研究

目的 利用新型双能医用直线加速器(医科达,Versa HDTM),研究6、10 MV能量的FFF和FF光子束剂量学特点,期望找到FFF射束的剂量学特点及优势,为临床应用提供依据。方法比较FFF、FF射束的深度剂量分布,离轴比剂量分布,辐射野大小、半影宽度与野外剂量,准直器散射因子和总散射因子。结果 (1)束流能量匹配后的FFF射束与常规均整射束能量一致,各射野百分深度剂量在10 cm深度区域的匹配误差<1%。(2) FFF射束离轴比剂量分布随深度的变化较小。(3) FFF射束的射野大小、半影宽度均比FF射束的变化小,且FFF射束的射野大小、半影宽度,分别随射野和深度的增加逐渐增大;FFF射束各射野的野外剂量比均整射束更低。(4) FFF射束各射野的准直器散射因子和总散射因子,随射野、深度的变化趋势均比FF射束小。结论 去除均整器后可明显提高剂量率、减少放疗时间、降低机头的漏射和散射,故FFF除均整性外的剂量学优势,可用于临床SRT。     

HERMES系统的定标

瑞典Ｔｈｅｒｏｄｏｓ公司出品的ＨＥＲＭＥＳ射线分析仪系统由两部分组成,体模部分是一块25ｃｍ×25ｃｍ×6ｃｍ的聚苯乙烯块,在其表面下0.5ｃｍ处按图示方式排布着10个Ｐ型半导体探头,其中Ｃ用于测量剂量率或剂量/机器量比;4个Ｈ探头用于比较射野均匀性和对称性;4个Ｅ探头用于校验灯光野和照射野的重合性;在ＤＤ探头上按能量的不同迭加不同厚度的尼龙或铁质小圆片可监测能量的变化。体模中探头Ｃ旁还有个Ｆａｒｍｅｒ2571型电离室插孔,系统的另一部分为读数单元,(如附图)。该系统的设计旨在“通过一次测量获得所有照射野性能数据”。附图…     

不同探测器测量射波刀输出因子比较分析

目的 比较分析5种不同探测器测量射波刀输出因子,以选择适合的探测器。方法分别使用电离室探测器PTW30013、PTW31010,半导体探测器PTW 60017、60018,宝石探测器PTW60019及EBT3胶片测量射波刀12个孔径准直器的输出因子。比较分析不同探测器及探测器放置方向测量的输出因子。结果 准直器孔径>30 mm时5种探测器测量的输出因子差异<1%,准直器孔径<30 mm时不同探测器测量结果差异较大,准直器孔径越小差异越大。与胶片测量结果比较,PTW60019与胶片的一致性最好,偏差<2%。半导体探测器测量结果稍高,电离室探测器测量结果过小。探测器放置方向不同,输出因子测量结果不同。PTW60019探测器平行射野中心轴放置时,测量的输出因子比垂直射野中心轴放置的结果偏低,PTW31010探测器测量结果相反。结论 准直器孔径>30 mm时PTW31010、PTW60017、60018及PTW60019可直接用于射波刀输出因子测量,准直器孔径<30 mm时需要对上述探测器的测量结果进行修正。PTW30013不适合小野输出因子测量。     

基于双源光子模型的准直器散射因子新算法

目的　建立一种简单准确适合于临床应用的准直器散射因子(Sc)的计算模型。方法　建立双源光子束模型,将到达计算点的射线分成原射线和机头散射线两部分,原射线由位于靶点的点源产生,散射线由位于焦点外具有轴对称性的面源产生。并用一个反向散射修正因子对次级准直器的反向散射进行修正。结果　(1) 对于4 cm ×4cm ～40cm ×40 cm 的方野、长短轴比最大为10 的矩形野以及挡铅形成的不规则野,Sc 的计算结果与测量结果的最大偏差<0 .6 % 。(2) 等中心处射野设为10cm ×10cm ,源—电离室距(SCD)从75.5cm 到140 .0cm 变化时,Sc 的计算结果与测量结果的最大偏差< 0.4 % 。结论　该算法可用于准确计算不同SCD处的方野、对称和不对称矩形野、挡铅或多叶光栏(MLC) 形成的不规则野的Sc,是一种适合于临床应用的简单准确的计算Sc 方法     

治疗计划系统外照射光子束算法验证

目的系统验证三维治疗计划系统外照射光子束算法以确定其剂量计算是否符合误差限值要求。材料与方法采用ＡＡＰＭ５５号报告提供的基本剂量学数据做系统配置，计算报告中测试例的剂量分布，统计列表点误差分布情况，并重点分析４种典型测试条件的剂量分布特点。结果对４ＭＶＸ线，有２，８，１２个测试例的全部列表点剂量误差分别＜１％，２％和３％，唯有射野中心挡铅测试例只有８７．５％的列表点误差＜４％。对１８ＭＶＸ线，有３，５，９，１２个测试例的全部列表点剂量误差分别＜１％，２％，３％和４％，射野中心挡铅和不规则野测试例各有９３．８％的列表点误差＜４％。１０ｃｍ×１０ｃｍ平野、９ｃｍ×９ｃｍ楔形野和肺不均匀性测试例ＰＤＤ曲线计算值和测量值符合（误差＜２％），而野中心挡铅测试例计算值和测量值在挡块下体模浅部不符合，其它所有区域符合。４种典型测试条件ＯＡＲ曲线计算值与测量值符合，射野半宽度误差＜２ｍｍ。结论验证结果总体满意，所有测试例（不包括挡块）剂量计算误差在限值范围内（４％）；挡块测试例剂量误差在挡块下体模浅部超出限值要求，提示挡块处理算法尚需改进。ＡＡＰＭ５５号报告是验证治疗计划系统的有力工具     

直线加速器小照野物理数据的测量和比较

背景与目的：对于精确的肿瘤放射治疗特别是立体定向和调强放射治疗,为了建立可靠的治疗计划系统剂量计算模型,提供准确的小照射物理数据尤其重要。本研究通过测量不同能量下小照野的物理数据,分析和比较不同方法和不同电离室之间相应的测量误差。方法：在直线加速器4、6、8MV光子线下,采用0．65、0．13、0．01cm^3的三种指形电离室,在30cm×30cm×30cm的固体水体模中测量了1cm×1cm～10cm×10cm照射野的总散射因子（total scatter factor,Scp）、准直器散射因子（collimator scatter factor,Sc）和组织最大剂量比（tissue-maximum ratio,TMR）等物理数据。对相应的测量结果进行了分析和比较。结果：照射野〉3cm×3cm时,不同电离室的Scp和Sc测量结果偏差在0．8％以内：3cm×3cm以下的照射野的测量结果差别较大（最大64％）;在4、6、8MV光子线1cm×1cm和2cm×2cm照射野的Sc测量中。0．13cm^3电离室拉长源皮距（〉150cm）比标准源皮距处（100cm）的测量结果分别大25．4％、6．9％、24．6％和1．4％、1．4％、2．2％;两种电离室0．01cm^3和0．13cm^3拉长距离测量的Sc对≥2cm×2cm照射野没有明显的偏差．对1cm×1cm照射野0．13cm^3比0．01cm^3测量值小0．2％、8．5％、3．4％。在1cm×1cm照射野的TMR测量中,0．01cm,和0．13cm^3电离室在15cm以下区域的测量偏差较大,约为4％左右。对于2cm×2cm及以上照射野TMR的测量结果偏差较小（〈1％）。〉3cm×3cm的照射野中,TMR测量的结果与百分深度剂量（percentage depth dose,PDD）转换得到的TMR数据在深度15cm之前一致性较好。15cm深度之后有明显的偏差（〉2％）。结论：测量小照射野物理数据时。由于侧向电子散射不够,需要谨慎选择测量探头。不同的测量探头对小照野物理数据的准确性可能存在较大的影响。当侧向电子平衡不能建立时,测量?     

医用直线加速器矩形野散射因子的简便计算方法

 目的　建立一种适合于临床应用的加速器散射因子 Sc.p的简便计算方法。方法　 ( 1 )通过测量方野的散射因子 ,建立方野散射因子与射野边长的拟合公式 ;( 2 )利用 Kim的经验公式 ,计算矩形野的等效方边长 ;( 3)应用已拟合的方野散射因子公式计算矩形野的散射因子 ,并与矩形野的测量结果进行比较。结果　采用该方法计算医用加速器散射因子的最大误差在 0 .5%以下 ,而采用面积 -周长比原理确定的等效方边长 ,最大误差达到 3%左右。结论　该方法可用于简便快速地确定方野和矩形野的散射因子 ,精确度高 ,完全可应用于临床.     

Whole-body dose from tomotherapy delivery

Purpose: To measure whole-body dose in tomotherapy of the head and neck region resulting from internal patient scatter and linear accelerator leakage.Methods and Materials: Treatments are performed using a commercial computer-controlled intensity modulated radiation therapy planning and delivery system (Peacock, NOMOS Corp.) and a 6-MV linear accelerator (Clinac 6/100, Varian Corp.). The patient dose outside the treatment field is measured in a water-equivalent phantom using thermoluminescent dosimetry. The whole-body dose components from internal scatter and leakage are separately determined. The use of fixed-portal leakage and scattered radiation measurements to estimate the whole-body dose from tomotherapy is evaluated.Results: The internally scattered dose is significant near the target, but becomes negligible relative to the leakage dose beyond 15 cm from the target. Dose at 10 cm from the target volume, due to internal scatter and leakage, is approximately 2.5% of the total target dose, reducing to 0.5% at 30 cm. The measured dose is relatively uniform throughout the phantom.Conclusion: The whole-body dose equivalent from a tomotherapy treatment is greater than that from conventional radiation therapy. Further studies are required to assess the trade-off between improved dose distribution conformality and a possible slight increase in radiation-induced fatal malignancies. The accuracy of using fixed-portal leakage and scattered dose measurements to estimate the whole-body dose from tomotherapy treatments is adequate, if the appropriate fixed-portal field size equivalent is used.     

经IAEA-483报告修正前后高能光子束小野输出因子与蒙特卡罗模拟对比分析研究

目的 根据IAEA-483号报告对临床使用的各类半导体或电离室探头进行高能光子束小野输出因子(Scp)测量并修正,探讨其修正数据在小野Scp测量的准确性。方法 使用EGSnrc蒙特卡罗(MC)模拟软件模拟Varian Novalis Tx直线加速器参考测量剂量曲线(Profile)和百分深度剂量曲线,调整模拟参数。使用电离室A16、A14sL、CC01、CC13和半导体探头PFD、EFD、Razor在不同射野下(0.5~10.0cm方野)的剂量曲线测量值、半峰全宽等效方野Scp测量值分别与MC模拟结果对比分析。使用IAEA-483报告修正因子对测量Scp修正,比对和分析修正前后测量数据和MC模拟数据。结果 MC模拟对比PFD测量曲线偏差<2.0%。在<3.0cm方野时MC模拟Profile曲线与半导体探头测量吻合。野外低剂量区Razor相对于MC和PFD偏高(2.3%),随射野增加而增加,10.0cm方野达3.0%。CC13在10.0cm方野Profile曲线的20.0%~80.0%半影宽度最大偏差3.0 mm。随射野减小,7种探头修正前Scp测量均值相对MC模拟偏差增大,标准差在接近1.0cm方野时迅速变大,由5.0~1.5cm方野的0.009~0.014变化到1.0~0.5cm方野的0.030~0.089,修正前全体均值0.030。修正后的6种探头测量的Scp标准差均值0.008,0.8cm方野为0.013,0.6cm方野为0.021。等效方野≥1.0cm时修正后Scp与MC模拟偏差-3.6%~-0.5%,<1.0cm偏差-6.9%~-1.3%。结论 经IAEA-483报告修正后各探头测量Scp标准差较小,与MC模拟结果吻合较好,可用于高能光子束小野的临床剂量学研究。     

Investigations of peripheral dose for helical tomotherapy

PurposeWhenever treating a patient with percutaneous radiotherapy, a certain amount of dose is inevitably delivered to healthy tissue. This is mainly due to beam's entry and exit in the region of the target volume. In regions distant from the target volume, dose is delivered by leakage from the MLC and head scatter from the accelerator head and phantom scatter from the target volume (peripheral dose). Helical tomotherapy is a form of radiation therapy with a uniquely designed machine and delivery pattern which influence the peripheral dose. The goal of this work was to investigate peripheral dose in helical tomotherapy. The experiments were used to establish a complex characterization of the peripheral dose.Materials and methodsA 30*30*60cm³ slab phantom and TLD-100 (Lithium fluoride) were used for the experiments. Treatment procedures were generated with the tomotherapy planning system (TPS). Additionally, procedures were created on the Operator Station of the tomotherapy system without a calculation of the dose distribution. The peripheral dose which was produced by a typical tomotherapy treatment plan was measured. Furthermore, these procedures were used to differentiate the parts of the peripheral dose in phantom scatter dose and head scatter and leakage dose. Additionally, the relation between peripheral dose and treatment time and between peripheral dose and delivered dose was investigated. Additionally, the peripheral dose was measured in an Alderson phantom.ResultsDistances of 30cm or more resulted in a decrease of the peripheral dose to less than 0.1% of the target dose. The measured doses have an offset of approximately 1cGy in comparison to the calculated doses from the TPS. The separated head scatter and leakage dose was measured in the range of 1cGy for typical treatments. Furthermore, the investigations show a linear correlation between head scatter leakage dose and treatment time and between scatter dose parts and delivered dose. A peripheral dose of 0.28% of the target dose was measured in the Alderson phantom at a distance of 17.5cm from the edge of the target volume.ConclusionsThe peripheral dose delivered by a tomotherapy treatment is clinically unobjectionable. The measurements confirmed a linear correlation between head scatter and leakage and treatment time and between scatter dose and delivered dose.     

Thyroid dose in children undergoing prophylactic cranial irradiation

Purpose: To determine the radiation dose received by the thyroid gland as a result of prophylactic cranial irradiation (PCI) in childhood leukemia and the factors influencing that dose.Methods and Materials: The dose to the thyroid resulting from simulated cranial irradiation with parallel opposed lateral fields of an adult anthropomorphic (ART) phantom with both 6 MV X-rays and Cobalt-60 γ-rays was measured using thermoluminescent dosimeters (TLDs). The dependence of thyroid dose on the distance of the field from the thyroid and the proportions of thyroid dose from stray radiation (leakage, scatter from jaws, etc.) and tissue scattered radiation were measured. The effects of a shadow tray and shielding blocks were also determined. Calculation of thyroid dose using the Clarkson scatter integration method was performed for 6 MV X-rays to compare with the measured doses. In vivo thyroid dose estimates were made using TLD measurements for three children receiving PCI with 6 MV X-rays.Results: Using open, unshielded fields, the thyroid region of the phantom received 1.2–1.4% of the prescribed cranial dose for 6 MV X-rays and 1.5–1.7% for Cobalt-60. For both treatment units, stray radiation accounted for approximately two thirds of the thyroid dose and tissue scatter accounted for the remaining one third. The thyroid dose increased as the field moved closer to the thyroid, with an increasing proportion of the dose due to tissue scatter. Placement of a thyroid shielding block on a shadow tray reduced the thyroid dose by only 20% compared with the open, unshielded setup. Thyroid dose from 6 MV using open fields was affected by the orientation of the collimator. When the inferior field edge was defined by the lower jaw, the dose was reduced by 27% compared with the upper jaw. Good correlation of dose to the thyroid region was obtained between phantom measured doses, in vivo measured doses and calculation of dose using the Clarkson method.Conclusion: For PCI doses of 1800 or 2400 cGy in the adult phantom, the dose to the thyroid was 20–40 cGy (1–2%). For small children this could rise to approximately 5% of the prescribed dose, of which half was due to stray radiation. As the thyroid in children is very sensitive to radiation and the dose-response curve for thyroid tumor induction is linear, attempts to shield the thyroid during cranial irradiation are mandatory. Cobalt-60 units should not be used, as the thyroid dose was higher than using 6 MV X-rays. Collimator orientation and the use of shadow trays and shielding were important factors in determining thyroid dose.     

Effect of tertiary multileaf collimator (MLC) on foetal dose during three-dimensional conformal radiation therapy (3DCRT) of a brain tumour during pregnancy.

BACKGROUND AND PURPOSE: The aim of this work was to measure the dose to foetus both in vivo and in vitro during three-dimensional conformal radiation therapy (3DCRT) in a pregnant patient with a pituitary adenoma. The study was then extended to assess the components contributing to the foetal dose such as collimator scatter, internal scatter, head leakage, wedge scatter and multileaf collimator (MLC) effect. PATIENTS AND METHODS: A 30-year-old pregnant woman with a non-functioning pituitary macroadenoma was planned for 3DCRT with 6MV X-ray using four equally weighted MLC-shaped non-coplanar wedged portals. In vivo dosimetry was carried out using thermoluminescent (TL) phosphor powder, which was placed at different positions on the patient, corresponding to different locations in the uterus and also at external os. In vitro measurements were also performed on a simulated phantom using the same set-up parameters and beam arrangement to verify the in vivo measured dose. Experiments were carried out to measure the respective contributions of different components towards peripheral dose. RESULTS: In vitro measured dose to foetus was found to be slightly more than that of in vivo measurement with a maximum of 0.044% of the prescribed dose of 45Gy, which corresponded to 0.0199+/-0.0008Gy. Thermoluminescence dosimeter (TLD) kept at the external os of the patient showed a dose of 0.031% of the prescribed dose. Among the various components of the peripheral dose (foetal dose) measured, head leakage was found to be the leading cause contributing 52%, followed by wedge scatter (31%), collimator scatter (14%) and internal scatter (13%). The use of MLC reduced not only the volume of normal brain irradiation as compared to open fields but also the peripheral dose by 10%. CONCLUSION: Radiotherapy of brain tumours during pregnancy poses a unique clinical situation and decisions to deliver radiotherapy should be taken after detailed in vitro and in vivo dosimetric measurements. Our findings suggest that the beam arrangement using 3-4-fields generally used for 3DCRT of brain tumour with MLC for optimal coverage can be employed for pregnant patients even in early trimester. A possible increase in foetal dose from wedges to a large extent can be compensated with the use of MLC.     

The "Ring" method: a semi-empirical method to calculate dose distributions of irregularly shaped photon beams

The "Ring" method provides a fast dose calculation and isodose presentation for photon beams with blocks. The method takes into account the change in scatter due to the blocks at each calculation point. Firstly, the dose in a point is calculated assuming that no blocks are present. Secondly, the scatter reduction caused by the blocks is calculated and subtracted. To determine the scatter reduction the irradiated surface is divided in concentric rings around a point at the surface at the intersection with a ray line between focus and calculation point. The scatter reduction caused by blocks for each ring is calculated. The effect of scatter for rings with an outer radius greater than 15 cm where the scatter contribution is less than 1.0% is neglected. Results of the method for 4 MV photons using eight rings are presented. Comparison of dose measurements with calculations in an arrow-shaped photon field showed maximum deviations of 4.0%, using the IRREG program of Cunningham, 6.5% using the BLKINP program of Schlegel, which is based on Clarkson's method, 5.0% using the method of Wrede and 2.2% using the "Ring" method. Contrary to the first two calculation programs, the programs using the last two calculation methods provide isodose lines dose values at points.