调强放射治疗计划的剂量学验证

目的探讨调强放射治疗计划的剂量学验证方法。方法利用VarianClinacIX直线加速器6MVX线．对Eclipse治疗计划系统设计的调强治疗计划;采用PTW公司的30013型0．6cc电离室配合UNIDOSE型剂量仪及验证模体进行绝对点剂量的验证．采用PTW二维电离室矩阵进行平面剂量的验证。结果绝对点剂量验证结果显示,测量点的测量值与计划值偏差均〈3％。平面剂量验证采用Gamma分析（3mm／3％）,结果是计划的测量点通过率均〉90％。结论实践证明该剂量学验证方法切实有效,简单可行。     

利用电离室矩阵验证IMRT的绝对剂量和相对剂量

调强放疗计划的剂量验证要求验证绝对剂量和相对剂量,绝对剂量采用指形电离室测量,相对剂量采用平板电离室测量,导致IMRT验证必须频繁更换验证设备,繁琐并且容易出错,工作效率低并容易损坏仪器.利用用指形电离室校准平板电离室,电离室矩阵经指形室电离室校准后,可用其对直线加速器的输出量进行刻度,并验证调强放射治疗计划的绝对剂量和相对剂量.     

利用二维电离室矩阵进行调强放疗计划剂量验证的探讨

目的：探讨二维电离室矩阵在调强放疗（IMRT）计划剂量验证中的应用价值。方法选取于我院行IMRT的患者16例,先在治疗计划系统中进行计划设计,然后移植到固体水上,得到体模杂交计划;利用二维电离室矩阵对杂交计划的计算剂量进行验证;参照3%/3 mm标准对结果进行分析。结果所有治疗野的绝对剂量验证结果通过率为86.4%-100%;相对剂量验证结果通过率为88.5%-100%。结论二维电离室矩阵是一种快速的剂量测量系统,在IMRT计划剂量验证中有重要价值。     

静态调强放疗射野等中心选择对二维电离室矩阵验证通过率的影响

探讨静态调强放疗计划设计中射野等中心选择对二维电离室矩阵剂量验证通过率的影响.选10例患者资料,以相同目标约束条件分别设计以靶区中心(PO)、x/y方向各偏离靶中心8 cm(PX/PY)为射野等中心的3组计划,采用PTW729二维电离室矩阵行机架角归零式二维绝对剂量验证,以不同验证条件行计划整体和单野γ分析.发现PO通过率最高,整体高于单野,PY组随窄缝漏射量的增加而变差.表明射野等中心选择直接影响验证通过率,设计中应尽量靠近靶区中心.     

一种用于调强适形放疗剂量验证模型的研究

目的：为了提高调强适形放疗治疗效率,保证调强适形放疗治疗计划临床实施的正确性,建立并应用两参数指数模型,以验证调强适形放疗的剂量准确性。方法：利用德国西门子公司Primus直线加速器6 MV X线,测定百分深度剂量及射野相对输出因子;根据患者的CT图像资料,设计患者治疗计划,并移植到模体中,重新计算出体模中过等中心点横截面上的剂量分布;将模体移放到加速器治疗床上,调用模体调强适形放疗计划对模体进行照射;使用Capintec0.65 cc PR-06C Farmer型（AE帽）电离室测量出体模内等中心点的吸收剂量,然后与使用两参数指数模型预测的中心轴上的剂量值相比较。结果：空间绝对吸收剂量的测量值与模型预测值的偏差小于3%,符合ICRU第24号报告指出的原发灶根治剂量的精确性应好于5%的要求。结论：两参数指数模型用于验证调强适形放疗剂量是可行的。     

探讨MatriXX在验证调强放射治疗计划中的应用

目的:通过二维电离室矩阵MatriXX对调强放射治疗计划进行二维剂量分布验证,根据验证结果来探讨其在调强放射治疗计划剂量验证中的应用。方法:利用德国IBA公司的MatriXX二维电离室矩阵及SP34等效固体水模对加速器执行的128例患者的调强放射治疗计划实施测量,获取特定层面二维剂量分布。利用OmniPro I’mRT软件,把患者计划植入模体后计划系统计算的剂量与MatriXX实测得到输出剂量进行比对,然后进行Gamma分析。结果:实际测量的相对剂量分布与计划系统模体中计算的相对剂量分布采用Gamma法(3 mm/3%)和(4 mm/4%)进行分析,以γ值小于1的百分比>95%作为要求,所有计划γ<1的百分比>95%的通过率为100%。结论:MatriXX在验证调强放射治疗计划中具有省时省力、快速简便等优势,是目前剂量验证的较为准确的QA工具之一。     

通过剂量验证检测MLC运动的准确性

目的:通过剂量学验证检测加速器多叶准直器(multi-leaf collimator,MLG)运动的准确性.方法:使用MatriXX测量Open野与MLC动态射野的剂量分布,验证5例鼻咽癌动态调强放疗患者在MLC校准前后的剂量分布.结果:(1)Open野的中心点剂量与TPS一致,3％/3 mmγ通过率为98.91％; (2)MLC动态射野的中心点剂量测量值和TPS的差异校准前和校准后分别为3.23％和-0.36％,校准前和校准后3％/3 mmy通过率分别为95.89％和98.94％;(3)5例鼻咽癌患者计划校准前后3％/3 mm γ通过率分别为(90.234±5.485)％和(99.528±0.321)％.结论:动态调强放疗中MLC的运动精度直接影响靶区内的剂量准确性,通过剂量学验证可以检测MLC运动的准确性.     

用60Co射线校准CT电离室的研究

目的探讨CT电离室用60Co射线进行剂量长度乘积刻度的方法。方法 PTW TM30009 CT电离室放在T40017头部模体中心插孔中,用20 cm＆#215;20 cm 60Co射线照射60 s,用UNIDOS剂量仪测量电荷量。相同条件下TM300130.6 mL电离室测量吸收剂量。CT电离室的刻度因子用剂量长度乘积表示。同时测量CT电离室在MV级辐射场中的剂量线性和剂量响应均匀性。结果 CT电离室的剂量-长度刻度因子可以从测量数据计算得到。电离室的剂量线性和剂量响应的均匀性很好。结论用60Co射线进行吸收剂量刻度后,CT电离室可以用于MVCT设备的CT剂量指数测量。     

基于MatriXX调强放疗计划的剂量学验证

目的探讨利用二维空气电离室矩阵MatriXX验证调强放疗计划的可行性。方法选择一患者,在美国NOMOS公司CORVOS6.2计划系统设计调强放疗计划,然后将其移植到剂量模体上。将调强放疗计划的计算结果导入MatriXX系统;执行一次完整的调强放疗计划,利用MatriXX测量其输出剂量。通过MatriXX系统的支持软件对调强放疗计划的计算结果和MatriXX测量所得数据进行分析、比较。结果MatriXX系统的支持软件分析,在感兴趣平面高剂量、低梯度区选定某点比较后,得出两者的点剂量差异为0.51%。Gamma分析结果（按3mm和3%的误差标准）95.86%通过。二维等剂量曲线及离轴比具有较好的一致性。结论MatriXX系统验证调强放疗计划简便、可行。     

针尖电离室水中吸收剂量校准方法研究

目的 ⁶⁰Co γ射线下,建立针尖电离室水中吸收剂量校准方法。方法 参考剂量仪（DOSE 1静电计+FC65-G型电离室）经过中国计量科学研究院校准,得到水中吸收剂量校准因子。采用⁶⁰Co γ射线,IAEA TRS-398测量程序,用参考剂量仪测量水下10 cm吸收剂量。替代法,用针尖电离室剂量仪进行水吸收剂量测量并对其进行水吸收剂量因子校准。更换⁶⁰Co γ射线辐射场,用参考剂量仪、针尖电离室剂量仪进行剂量验证测量。结果 参考剂量仪在水下10 cm处,参考条件下测得水吸收剂量结果为0.249 9 Gy。两台针尖电离室剂量仪测量结果分别为0.248 0 Gy和0.250 0 Gy;两台针尖电离室剂量仪测量结果与参考剂量仪测量结果相对偏差均在±0.8%内,针尖电离室剂量仪测量水吸收剂量不确定度为2.8%（k=2）。结论 针尖电离室可用于小野水中吸收剂量的测量。     

Intensity modulated radiotherapy dosimetry with ion chambers, TLD, MOSFET and EDR2 film

Purpose of this study was to report in a together our experience of using ion chambers, TLD, MOSFET and EDR2 film for dosimetric verification of IMRT plans delivered with dynamic multileaf collimator (DMLC). Two ion chambers (0.6 and 0.13 CC) were used. All measurements were performed with a 6MV photon beam on a Varian Clinac 6EX LINAC equipped with a Millennium MLC. All measurements were additionally carried out with (LiF:Mg,TI) TLD chips. Five MOSFET detectors were also irradiated. EDR2 films were used to measure coronal planar dose for 10 patients. Measurements were carried out simultaneously for cumulative fields at central axis and at off-axis at isocenter plane (+/- 1, and +/- 2 cm). The mean percentage variation between measured cumulative central axis dose with 0.6 cc ion chamber and calculated dose with TPS was -1.4% (SD 3.2). The mean percentage variation between measured cumulative absolute central axis dose with 0.13 cc ion chamber and calculated dose with TPS was -0.6% (SD 1.9). The mean percentage variation between measured central axis dose with TLD and calculated dose with TPS was -1.8% (SD 2.9). A variation of less than 5% was found between measured off-axis doses with TLD and calculated dose with TPS. For all the cases, MOSFET agreed within +/- 5%. A good agreement was found between measured and calculated isodoses. Both ion chambers (0.6 CC and 0.13 CC) were found in good agreement with calculated dose with TPS.     

调强计划验证中MatriXX电离室的角度响应修正

目的 用MatriXX验证调强计划时其存在角度响应问题,本工作旨在对MatriXX电离室矩阵中的每个电离室分别进行角度响应修正。方法 在0°机架角且射野开野28 cm×28 cm条件下,用MatriXX测量平面剂量分布,并与计划系统的计算值对比,得到MatriXX中各单元电离室的剂量校准系数。在此基础上,测量不同机架角且开野条件时的平面剂量分布,通过相应计算值对各角度各电离室的测量值进行角度修正。用MatriXX测量实际调强计划中的剂量分布,比较角度响应修正后和未修正时的验证结论,评价该修正方法的作用。结果 0°机架角时,各电离室的剂量校准系数随X、Y坐标值增加略有增加,平均为1.00±0.01。各电离室的角度响应修正系数在机架角为60°~150°和210°~300°范围内时变化范围大且波动大,且分别在90°和270°附近达到最小。经过修正后的计划验证结论好于未修正的。结论 经角度响应修正后,MatriXX可以更好适用于多机架角IMRT计划的验证。     

Intensity modulated radiation therapy (IMRT) surface dose measurements using a PTW advanced Markus chamber

A new PTW advanced Markus ionization chamber has been implemented in IMRT fields, to measure surface dose at ICRU and ICRP reference depth of 0.07 mm [ICRU Report 39, Determination of dose equivalents resulting from external radiation sources, 1985; ICRP Publication 60, 1990 recommendations of the International Commission on Radiological Protection, 1991]. This chamber has a small radius with a revised guard ring design, therefore less prone to surface over-response effects. The over response correction for advanced Markus chamber is 3.3%, which is significantly smaller than 10.1% which was the original Markus chamber over response. After over response correction, the surface dose can be accurately measured by either data extrapolation or by adding one layer of plastic sheet protector to the top of Markus chamber. The surface dose measurements for small fields, e.g 3 × 3 cm, the polarity effect of advanced Markus chamber is 12%, which is significantly higher than the 5% polarity effect of the original Markus. For a 12 × 12 cm field size, surface dose (at 0.07 mm) measured by advanced Markus chamber is 19.8% for open field and 19.2% for an unmodulated step-and-shoot IMRT field. The variation in surface dose due to intensity modulated IMRT fields has also been investigated. For an intensity modulated, step-wedge IMRT field, surface dose varies from 15.7 ± 1% for the highest intensity segment to 26.9 ± 1% for the lowest intensity segment. The results of chamber measurements have been compared against EBT type GAFCHROMIC^® film results.     

Incorporation of gantry angle correction for 3D dose prediction in intensity-modulated radiation therapy

Pretreatment dose verification with beam-by-beam analysis for intensity-modulated radiation therapy (IMRT) is commonly performed with a gantry angle of 0° using a 2D diode detector array. Any changes in multileaf collimator (MLC) position between the actual treatment gantry angle and 0° may result in deviations from the planned dose. We evaluated the effects of MLC positioning errors between the actual treatment gantry angles and nominal gantry angles. A gantry angle correction (GAC) factor was generated by performing a non-gap test at various gantry angles using an electronic portal imaging device (EPID). To convert pixel intensity to dose at the MLC abutment positions, a non-gap test was performed using an EPID and a film at 0° gantry angle. We then assessed the correlations between pixel intensities and doses. Beam-by-beam analyses for 15 prostate IMRT cases as patient-specific quality assurance were performed with a 2D diode detector array at 0° gantry angle to determine the relative dose error for each beam. The resulting relative dose error with or without GAC was added back to the original dose grid for each beam. We compared the predicted dose distributions with or without GAC for film measurements to validate GAC effects. A gamma pass rate with a tolerance of 2%/2 mm was used to evaluate these dose distributions. The gamma pass rate with GAC was higher than that without GAC (P = 0.01). The predicted dose distribution improved with GAC, although the dosimetric effect to a patient was minimal.     

A study into the relationship between the measured penumbra and effective source size in the modeling of the Pinnacle RTPS

The effect of detector size in the broadening of the penumbra on the model in the Pinnacle RTPS is investigated. A second order polynomial was devised to correlate the source size parameter with the RTPS-calculated penumbra. The optimal source size parameter was calculated for penumbra measurements based on the diamond detector and a standard ionization chamber (IC). This work was done for Jaw fields, MLC fields with a leaf end radius of 8 cm, and MLC fields with a leaf end radius of 12 cm. The optimum source size of the 8 cm MLC fields matched the jaw fields, and an average (based on field sizes studied) of 1.1 mm for the diamond detector data and 2.4 mm for the ionization chamber was established. The effect of this overestimation of the source size parameter based on detector-induced penumbra broadening was considered for a clinical IMRT prostate plan by using two models (diamond and IC). There were differences in the DVH of the PTV and of OARs but these effects were of negligible clinical significance. Dose difference distributions showed dose difference areas to be in penumbra regions of the segments, with larger dose differences where penumbras intersected and/or there was a significant weighting on the segment. Gamma analysis was also performed between the two plans, and was found to increase the amount of fail rates significantly for both 2%/2 mm and 3%/3 mm criteria. This decreases the sensitivity of IMRT QA in the detection of systematic errors.     

Patient specific dosimetry for intensity-modulated radiotherapy delivered with first helical tomotherapy in India — our initial experience of 50 patients

Two-dimensional (2D) treatment verifications were performed for fifty patients planned and treated with helical tomotherapy (HT). The treatment verification consisted of an extended dose range (EDR2) film measurement as well as point dose measurements made with an A1SL ion chamber. The agreement between the calculated and the measured film dose distributions was evaluated with the gamma parameter calculated (3 mm and 3%). Good agreement was found between measured and calculated distributions with dose parameter registration using reference marks. The mean percent discrepancy for the point dose measurements was -0.4 (SD 1.4) for the high dose, low dose-gradient region. Thus the treatment verification results confirmed the safe delivery of the planned dose to the patient with helical tomotherapy.     

四川省医用辐射危害评价与控制技术的研究结果

目的通过对放射诊断患者剂量水平、放射治疗输出剂量和调强放射治疗(IMRT)小野输出因子等医用辐射危害关键因素进行研究,实现辐射危害的风险评估。方法在10个市30余家医院按设备类型、体位等因素抽样1510例放射诊断患者剂量调查,采用TLD粉末剂量计、指形电离室及测量支架对5条放射治疗光子线束进行剂量核查,并采用TW31014型0.015 cc针尖电离室测量7台医用电子加速器IMRT小野输出因子。结果X线诊断患者剂量调查结果为0.48~9.15 mGy,CT患者剂量调查结果剂量长度乘积(DLP)为252~676 mGy·cm;5条光子线束放射治疗输出剂量与TPS值的相对偏差为1.3%~6.3%,均在±7.0%以内,符合相关标准要求;IMRT小野输出因子TPS计算值与剂量仪测量值偏差为-1.6%~0.9%,符合标准要求。结论本研究总结了医用辐射危害评价与控制技术的关键问题,为制定医用辐射安全监测相关标准、及时发现放射诊疗过程中存在的安全问题并预警、避免发生过量照射和医用辐射事故、降低公众剂量负担、实现医用辐射危害的风险评估提供重要依据。     

调强适形放射治疗的质量保证及剂量验证

目的　介绍和探讨调强适形放射治疗的质量保证和质量控制方法。方法　 (1)通过体模移植的方法分别用电离室在水模体中测量 4 2例病人的IMRT治疗计划某点的绝对剂量 ,验证逆向计划系统剂量计算的准确性 ,进一步修正它的计算校正因子。 (2 )为验证MIMiC纵向的对称性、叶片横向的可靠性、稳定性 ,把剂量胶片放在两块有机玻璃板之间每周拍摄验证片。结果　 (1)测量所得的相对误差均在 3%以内 ,故逆向计划系统计算校正因子不需进行修正。 (2 )每周胶片验证的结果偏差均小于 1mm ,则无需对其进行机械调整。结论　近一年的IMRT工作实践证明所采用的质量保证和剂量验证措施是可行。