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.     

伤速康涂膜剂的质量标准研究

目的建立伤速康涂膜剂的质量标准。方法采用TLC法对处方中大黄、栀子进行定性鉴别，并采用反相高效液相色谱法对涂膜剂中的大黄素、绿原酸进行含量测定。结果大黄素的平均回收率为101．8％，RSD为1．96％，绿原酸的平均回收率为102．1％，RSD为2．0％。结论该方法简便易行，重现性好，可作为本品的质量控制标准。     

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.     

升膜式蒸发器生产能力的提高

通过解决生产实际问题的例子。探讨在不增加设备投资前提下强化升膜式蒸发器生产能力的若干途径。确定采用增加蒸汽压力和提高真空度方法，可提高生产能力30％左右。     

RP-HPLC法测定止痒涂膜剂中地塞米松的含量

【目的】建立一种测定止痒涂膜剂中地塞米松含量的高效液相色谱法。【方法】采用反相高效液相色谱法,以Shim packvpODS柱(4.6mm×250mm,5μm作分析柱,以甲醇水(70∶30,v/v)为流动相,流速0.8ml/min。柱箱温度30℃,对羟基苯甲酸丁酯为内标,检测波长为245nm。【结果】本法的日内RSD小于0.5%,日间RSD小于1%,平均回收率为100.3%。标准曲线在5～20μg/ml浓度范围内,呈现良好的线性关系(r=0.9999)。【结论】该法用于涂膜剂的含量测定,快速、准确。     

传片故障原因的判断分析与快速排除方法

目的探讨胶片库技术装置传片故障的常见原因分析,从而准确判断故障所处的部位并得以快速排除。方法根据该装置的工作原理及使用说明,结合自我院使用的经验和维修记录,将传片故障的部位、现象、可能产生的原因与快速排除的方法进行分类,为操作人员在传片故障的排查时提供有价值的参考资料。结果操作者熟知并掌握该装置传片故障原因的判断分析与快速排除方法,不但强化了自身素质,而且可进一步了解该装置的性能及保养方法,正确使用该装置,将人为失误控制在最低限度是保证其高效运行的必要条件。结论数字化影像诊断设备胶片库技术以传片故障最为常见,多数情况下操作者利用简单的工具可以快速排除。若对常见的传片故障不能及时排除,停机等待专职维修人员或售方工程技术人员来维修,不但耽误了患者的诊治时机,同时也影响了医院的社会效益与经济效益。