容积旋转调强与固定野调强在宫颈癌术后放疗中的剂量学比较

目的：比较容积旋转调强（vMAT,美国瓦里安公司商品名为RapidArc）与9野固定野调强（IMRT）两种放射治疗技术在宫颈癌术后放疗中的剂量学差异。方法：采用两种治疗技术对10例宫颈癌术后患者设计计划,处方剂量设置为46ay／23次．危及器官限量参考临床常规要求,靶区接受标准为95％处方剂量要包绕97％以上靶区体积。比较两种技术的剂量体积直方图、治疗时间、机器跳数、靶区和危及器官剂量分布差异。结果：RapidArc技术靶区平均剂量略高于9IMRT技术．且具有统计学意义,靶区均匀性、适形度、危及器官受量相比9IMRT技术,虽然都没有统计学意义,但是RapidArc技术机器跳数较9IMRT减少63．6％,平均治疗时间节省70％。结论：RapidArc技术在剂量学分布上与9IMRT技术相当或略有优势,治疗时间及机器跳数大大减少。     

不同能量X线胸段食管癌调强放疗计划的剂量学研究

目的:研究不同能量X射线治疗胸段食管癌调强放疗(IMRT)计划的剂量学差异。方法:选择l2例胸段食管癌患者,在ADAC Pinnacle3三维治疗计划系统(TPS)中分别采用6 MV、10 MV和15 MV X线给每位患者设计三个调强放疗计划,在规定计划靶区(PTV)至少达到95%处方剂量的前提下,根据剂量体积直方图(DVH)比较三种计划的靶区剂量分布及脊髓、肺、心脏等正常组织受照射剂量的差异。结果:三种计划中靶区的最大剂量、最小剂量、平均剂量及靶区适形度指数、均匀性指数均无明显差异,但15 MV计划高剂量覆盖程度大于6 MV和10 MV计划,脊髓、双肺及心脏受照剂量都在可耐受的范围内,差异也无统计学意义(P>0.05)。结论:6 MV、10 MV、15 MV X射线都能满足胸段食管癌临床调强放疗需求。     

GATE based Monte Carlo simulation of planar scintigraphy to estimate the nodular dose in radioiodine therapy for autonomous thyroid adenoma

The recommended target dose in radioiodine therapy of solitary hyperfunctioning thyroid nodules is 300-400 Gy and therefore higher than in other radiotherapies. This is due to the fact that an unknown, yet significant portion of the activity is stored in extranodular areas but is neglected in the calculatory dosimetry. We investigate the feasibility of determining the ratio of nodular and extranodular activity concentrations (uptakes) from post-therapeutically acquired planar scintigrams with Monte Carlo simulations in GATE.The geometry of a gamma camera with a high energy collimator was emulated in GATE (Version 5). A geometrical thyroid-neck phantom (GP) and the ICRP reference voxel phantoms “Adult Female” (AF, 16 ml thyroid) and “Adult Male” (AM, 19 ml thyroid) were used as source regions.Nodules of 1 ml and 3 ml volume were placed in the phantoms. For each phantom and each nodule 200 scintigraphic acquisitions were simulated. Uptake ratios of nodule and rest of thyroid ranging from 1 to 20 could be created by summation. Quantitative image analysis was performed by investigating the number of simulated counts in regions of interest (ROIs). ROIs were created by perpendicular projection of the phantom onto the camera plane to avoid a user dependant bias.The ratio of count densities in ROIs over the nodule and over the contralateral lobe, which should be least affected by nodular activity, was taken to be the best available measure for the uptake ratios. However, the predefined uptake ratios are underestimated by these count density ratios: For an uptake ratio of 20 the count ratios range from 4.5 (AF, 1 ml nodule) to 15.3 (AM, 3 ml nodule).Furthermore, the contralateral ROI is more strongly affected by nodular activity than expected: For an uptake ratio of 20 between nodule and rest of thyroid up to 29% of total counts in the ROI over the contralateral lobe are caused by decays in the nodule (AF 3 ml). In the case of the 1 ml nodules this effect is smaller: 9-11% (AF) respectively 7-8% (AM).For each phantom, the dependency of count density ratios upon uptake ratios can be modeled well by both linear and quadratic regression (quadratic: r² > 0.99), yielding sets of parameters which in reverse allow the computation of uptake ratios (and thus dose) from count density ratios. A single regression model obtained by fitting the data of all simulations simultaneously did not provide satisfactory results except for GP, while underestimating the true uptake ratios in AF and overestimating them in AM.The scintigraphic count density ratios depend upon the uptake ratios between nodule and rest of thyroid, upon their volumes, and their respective position in a non-trivial way. Further investigations are required to derive a comprehensive rule to calculate the uptake or dose ratios based on post-therapeutic scintigraphy.     

Effective point of measurement for parallel plate and cylindrical ion chambers in megavoltage electron beams

The presence of an air filled ionization chamber in a surrounding medium introduces several fluence perturbations in high energy photon and electron beams which have to be accounted for. One of these perturbations, the displacement effect, may be corrected in two different ways: by a correction factor p_dis or by the application of the concept of the effective point of measurement (EPOM). The latter means, that the volume averaged ionization within the chamber is not reported to the chambers reference point but to a point within the air filled cavity. Within this study the EPOM was determined for four different parallel plate and two cylindrical chambers in megavoltage electron beams using Monte Carlo simulations. The positioning of the chambers with this EPOM at the depth of measurement results in a largely depth independent residual perturbation correction, which is determined within this study for the first time. For the parallel plate chambers the EPOM is independent of the energy of the primary electrons. Whereas for the Advanced Markus chamber the position of the EPOM coincides with the chambers reference point, it is shifted for the other parallel plate chambers several tenths of millimeters downstream the beam direction into the air filled cavity. For the cylindrical chambers there is an increasing shift of the EPOM with increasing electron energy. This shift is in upstream direction, i.e. away from the chambers reference point toward the focus. For the highest electron energy the position of the calculated EPOM is in fairly good agreement with the recommendation given in common dosimetry protocols, for the smallest energy, the calculated EPOM positions deviate about 30% from this recommendation.     

直线加速器低MU时的剂量学特性研究

目的 直线加速器剂量监测系统的准确性是放射治疗处方剂量准确的前提,本研究旨在研究放射治疗低MU设置时的剂量学特性.方法 对Siemens Mevatron MD7745直线加速器6MV-X线辐射源,10 cm × 10 cm射野,机器跳数设置1～100 MU,在最大剂量深度1.5 cm和5 cm深度处,测量相应MU数时的吸收剂量D<,MU>,并计算每MU对应的cGy;源皮距SSD 100 cm,预置1 MU、5 MU和100 MU条件下测量10 cm×10 cm射野百分深度剂量PDD和边长3～20 cm范围方野的总散射因子Scp,然后分析数据.结果 不同大小MU设置,MU与cGy的对应关系有很大的差别,误差最大达10.6%,MU设置的大小对百分深度刺量PDD和总散射因子Scp影响很小,小于1%.结论 为保证体模中剂量计算精度达到WHO规定的精度要求(好于3%),当MU设置小于10时,必须对MU与cGy的对应关系进行修正,而低MU设置对百分深度剂量PDD和总散射因子Scp的影响可忽略不计.     

物理楔形野两种处方剂量计算方法的对比实验研究

目的比较物理楔形野两种不同方法计算处方剂量与实测值的偏差,为物理楔形野处方剂量计算提供参考。方法在SIEMENS Primus-M型医用加速器产生的6MV X线和15MV X线条件下,用SCAN-DITRONIX RFA300三维水箱采集处方剂量计算所需的各种物理数据,2种方法分别计算处方剂量,与NEFarmer2670剂量仪实测值进行比较。结果传统方法计算值与实测值偏差较大,在6MV X线、45°楔形板、25cm×25cm射野、20cm深度条件下偏差达9.1%,而改进方法计算值与实测值偏差不超过1.2%。结论物理楔形野处方剂量计算的传统方法在某些条件下存有较大误差,建议完善物理楔形野处方剂量计算所需相关物理数据,采用改进方法进行计算。     

Radiation dose,chemotherapy and risk of lung cancer after breast cancer treatment

It is of particular concern to evaluate the risk of lung cancer occurrence after breast cancer treatment as women with breast cancer quite often undergo radiation therapy as part of their initial treatment and their life expectancy remains long. From a roster of 7711 women initially treated for breast cancer between 1954 and 1984, a cohort-study was performed among 4171 1-year survivors followed during the period 1975-1995. The relationship between the radiation dose received by the lung and the risk of lung cancer was then evaluated in a nested case-control study of 11 breast-cancer patients who developed lung cancer and 22 controls matched for age at diagnosis of breast cancer, period of initial treatment and length of follow-up. Among the 4171 women, six developed lung cancer during the entire follow-up as compared to 5.4 cases expected (SIR = 1.1, 95% CI: 0.4-2.3). When considering only the women initially treated by radiotherapy with or without adjunction of chemotherapy and excluding the 10 first years of follow-up, the SIR was significantly increased (SIR = 3.2, 95%CI: 1.0-7.4). In the case-control study, nine of the 11 lung cancers occurred in the ipsilateral lung and two in the trachea. The overall odds ratio (OR) of lung cancer associated with initial radiotherapy was 1.4 (95% CI: 0.2-11.1) and an excess in the OR of 7% (90% CI: ? to 41%, p = 0.10) per gray delivered to the site of lung cancer was evidenced. Our results agree with previous studies in favor of an increased risk of lung cancer after radiation therapy for breast cancer.     

Dose-image optimisation in digital radiology with a direct digital detector: an example applied to pelvic examinations

In diagnostic radiology increasing attention has been focused on dose reduction while maintaining a clinically good image quality. With the use of digital detectors balancing dose vs image quality is done differently than in film-screen radiography, since dose and image brightness are uncoupled in digital imaging. In this study a new direct digital detector (flat-panel detector) was used in a dose-image optimisation of a simulated pelvic examination. X-ray images were taken with a direct digital detector (DDD), of the pelvic of a phantom using varying tube current (varying stochastic noise). The entrance surface dose was measured for each image. These images were scored by two radiologists according to EU guidelines. A dose comparison was made with an older PCR system (storage phosphor plates). With decreasing tube current the noise in the images increased and the image with the lowest dose and still acceptable image quality was identified. The results showed that the entrance surface dose using the DDD decreased from 1.4 mGy (PCR value) to 0.48 mGy (DDD standard settings). Through the optimisation the dose could be further decreased to 0.24 mGy while still maintaining an acceptable image quality. A substantial dose reduction was obtained with this new direct digital detector. This simple but efficient optimisation approach is easily applicable to other examinations and both DDD and storage phosphor plate detectors.     

~(125)I粒子源治疗前列腺癌的剂量分布研究

目的研究放射性125I粒子源治疗前列腺癌的剂量分布。方法采用三维治疗计划系统(3-DTPS)进行实验模拟,前列腺癌用肿瘤模型代替,应用热释光剂量学方法,模拟测量前列腺癌中的剂量分布。结果实验表明,125I粒子源治疗前列腺癌是在不均匀剂量模式下受照,剂量直接与粒子源的数量和几何位置有关。结论125I粒子源表面剂量最高,随着距离增加而剂量迅速下降。粒子源的间距越小瘤内剂量越高。