A procedure to determine the radiation isocenter size in a linear accelerator

Measurement of radiation isocenter is a fundamental part of commissioning and quality assurance (QA) for a linear accelerator (linac). In this work we present an automated procedure for the analysis of the stars-shots employed in the radiation isocenter determination. Once the star-shot film has been developed and digitized, the resulting image is analyzed by scanning concentric circles centered around the intersection of the lasers that had been previously marked on the film. The center and the radius of the minimum circle intersecting the central rays are determined with an accuracy and precision better than 1% of the pixel size. The procedure is applied to the position and size determination of the radiation isocenter by means of the analysis of star-shots, placed in different planes with respect to the gantry, couch and collimator rotation axes.     

A simple isocenter checking procedure for radiotherapy treatment machines using the optical pointer

Techniques are described for simple and convenient checks on the position and size of the isocenter of radiotherapy treatment machines by measuring the displacement of the optical pointer on a flat scale on the surface of the treatment couch.     

An independent dose calculation algorithm for MLC-based radiotherapy including the spatial dependence of MLC transmission

An analytical dose calculation algorithm was developed and commissioned to calculate dose delivered with both static and dynamic multileaf collimator (MLC) in a homogenous phantom. The algorithm is general; however, it was designed specifically to accurately model dose for large and complex IMRT fields. For such fields the delivered dose may have a considerable contribution from MLC transmission, which is dependent upon spatial considerations. Specifically, the algorithm models different MLC effects, such as interleaf transmission, the tongue-and-groove effect, rounded leaf ends, MLC scatter, beam hardening and divergence of the beam, which results in a gradual MLC transmission fall-off with increasing off-axis distance. The calculated dose distributions were compared to measured dose using different methods (film, ionization chamber array, single ionization chamber), and the differences among the treatment planning system, the measurements and the developed algorithm were analysed for static MLC and dynamic IMRT fields. It was found that the calculated dose from the developed algorithm agrees very well with the measurements (mostly within 1.5%) and that a constant value for MLC transmission is insufficient to accurately predict dose for large targets and complex IMRT plans with many monitor units.     

Use of EPID for leaf position accuracy QA of dynamic multi-leaf collimator (DMLC) treatment

We describe in this paper an alternative method for routine dynamic multi-leaf collimator (DMLC) quality assurance (QA) using an electronic portal imaging device (EPID). Currently, this QA is done at our institution by filming an intensity-modulated radiotherapy (IMRT) test field producing a pattern of five 1-mm bands 2 cm apart and performing a visual spot-check for leaf alignment, motion lags, sticking and any other mechanical problems. In this study, we used an amorphous silicon aS500 EPID and films contemporaneously for the DMLC QA to test the practicality and efficacy of EPID vis-à-vis film. The EPID image was transformed to an integrated dose map by first converting the reading to dose using a calibration curve, and then multiplying by the number of averaged frames. The EPID dose map was then back-projected to the central axis plane and was compared to the film measurements which were scanned and converted to dose using a film dosimetry system. We determined the full-width half-maximum (FWHM) of each band for both images, and evaluated the dose to the valley between two peaks. We also simulated mechanical problems by increasing the band gap to 1.5 mm for some leaf pairs. Our results show that EPID is as good as the film in resolving the band pattern of the IMRT test field. Although the resolution of the EPID is lower than that of the film (0.78 mm/pixel vs 0.36 mm/pixel for the film), it is high enough to faithfully reproduce the band pattern without significant distortion. The FWHM of the EPID is 2.84 mm, slightly higher than the 2.01 mm for the film. The lowest dose to the valley is significantly lower for the EPID (15.5% of the peak value) than for the film (28.6%), indicating that EPID is less energy independent. The simulated leaf problem can be spotted by visual inspection of both images; however, it is more difficult for the film without being scanned and contrast-enhanced. EPID images have the advantage of being already digital and their analysis can easily be automated to flag leaf pairs outside tolerance limits of set parameters such as FWHM, peak dose values, peak location, and distance between peaks. This automation is a new feature that will help preempt MLC motion interlocks and decrease machine downtime during actual IMRT treatment. We conclude that since EPID images can be acquired, analyzed and stored much more conveniently than film, EPID is a good alternative to film for routine DMLC QA.     

等中心扫描降低多层螺旋CT冠状动脉血管成像辐射剂量的随机对照研究

目的 探讨等中心扫描对降低冠状动脉多层螺旋CT血管成像(MSCTA)辐射剂量的价值。方法 采用前瞻性随机对照研究方法。纳入广东省中医院珠海医院2016年11月—2018年4月144例行冠状动脉MSCTA检查患者,将患者按随机区组法分为A、B、C、D 4组,每组36例。A组采用常规扫描定位,电流为智能毫安;B、C、D组采用等中心位置扫描,电流分别为智能毫安、智能毫安的90%、智能毫安的80%。4组扫描管电压均为120 kV。比较4组患者冠状动脉MSCTA图像的客观图像质量噪声、信噪比(SNR),主观质量评分比及辐射剂量(ED),对直径＞1.5 mm的血管节段采用冠状动脉15分段法评分,用以评价主观图像质量。客观噪声方面,4组重建图像中的主支气管选择,感兴趣区(面积约15.0 mm²),测量其标准差值作为噪声值,SNR为其CT值/标准差。结果 MSCTA图像分析显示,以D、A、C、B组为序,噪声依次降低(分别为15.09±2.97、2.68±2.47、2.57±2.29和2.45±4.36),SNR依次升高(分别为63.74±19.78、78.64±14.66、78.66±14.84和79.66±22.90);D组与A、B、C组两两比较,噪声高而SNR低,差异均有统计学意义(P值均＜0.05);A、B、C组间噪声及SNR两两比较,差异均无统计学意义(P值均＞0.05)。4组冠状动脉图像质量主观评分优良率98.9%(1 939/1 960),4组间比较差异均无统计学意义(P值均＞0.05);A、B、C、D辐射剂量依次降低,分别为(3.39±1.39)mSv、(2.89±1.21)mSv、(2.56±1.05)mSv,(2.14±0.87)mSv,其中A组明显高于C、D组,B组高于D组,差异均有统计学意义(P值均＜0.05)。结论 在不降低冠状动脉成像质量的情况下,等中心扫描能降低冠状动脉MSCTA的辐射剂量。     

An ELISA procedure for the diagnosis of dengue infections

Although the hemagglutination-inhibition (HI) test has been the standard test used by the World Health Organization (WHO) for the classification of serologic response in dengue infections, it is slow, requiring paired specimens. Furthermore, not all investigators have accepted the classification. Thus, there is an urgent need to develop a rapid test which employs a single specimen. We developed an enzyme-linked immunosorbent assay (ELISA) for rapid classification of serologic responses in dengue infections based on the ratio of IgM and IgG in a single specimen. Using the criteria established by the WHO (1986) for comparison, concordant results were obtained in 81% and 95% of primary and secondary infections, respectively, when serum specimens were tested as pairs. When tested as single specimens, the diagnoses by ELISA and HI agreed in 41% and 52% of acute specimens of primary and secondary infections, respectively. The lower rate of concordance in acute-phase samples was due to the absence of detectable IgM in acute specimens collected at outpatient clinics. On the other hand, diagnoses by ELISA and HI agreed in 79% and 95% of primary and secondary infections when single convalescent specimens were used. Analysis of the discordant results between the two tests revealed that the interpretation by the IgM-IgG ratio agreed better with HI classifications practised by some investigators than it did with the WHO.     

An approach to the surveying of radiation environments for radiation protection purposes.

Many of the inadequacies of the system presently used for surveying environments containing penetrating radiation stem from the impossibility of defining a radiation parameter which is additive, measurable and closely related to peak dose equivalent in the body. Many of the present conceptual difficulties would be eliminated if surveys were made in terms of a quantity 'dose equivalent ceiling' defined as the sum of the peak dose equivalents generated by all the components of the field if each were incident normally to the front face of an anthropomorphic phantom. 'Dose equivalent ceiling' is close to the quantity measured by existing instruments, is both additive and measurable, and can be rigorously related to primary radiation field quantities. It is always greater than peak dose equivalent in the body, and would be used to define an exposure period during which a given dose equivalent could not be exceeded. The dose to specific parts of the person's body would then be estimated by personal dosimetry. Fields of low penetrating radiation could continue to be surveyed in terms of dose to specific superficial organs. Dose equivalent ceiling, which corresponds to the instrumental measurement, exceeds dose equivalent index, an indication of peak dose equivalent in the body, by a factor which can be as large as six.     

The direct measurement using an imaging plate for coincidence of radiation centre and laser position in external radiation therapy

A new method of quality assurance has been studied to measure coincidence of the radiation centre and a patient-setup laser position on a transverse plane to the beam at the isocentre. This measurement is achieved by using an imaging plate (IP). When radiation is applied to an IP, the energy is stored as trapped electrons. The number of electrons is decreased by local laser exposure. As a result, the radiation field produced by external beam irradiation is recorded as 'positive' information and the position of the patient-setup laser is recorded as 'negative' on an IP. The advantages of this method are the direct measurement, short time and high resolution. These are required for daily and monthly quality checks. We confirmed the advantage of this method by an experiment using a proton beam.     

用Catphan体模进行CT机的QA检测方法研究

本文目的是研究ＣＴ机的质量保证检测方法,用美国体模公司生产的Ｃａｔｐｈａｎ４１２体模和美国Ｒａｄｃａｌ公司生产的多用剂量仪检测１４３台ＣＴ机的定位光精度,诊视床运动精度,层厚,ＣＴ值线性,场均匀性,噪声,高对比高分辨力,低地比度分辨力和剂量指数（ＣＴＤＩ）,结论：Ｃａｔｐｈａｎ４１２体模可以检测除了水的ＣＴ值以外国家对ＣＴ机应用质量检测所要求的所有性能参数,检测项目多,使用方便使它成为ＣＴ机质量保     

An improved procedure for the rapid one-step-cloning of full-length viroid cDNA

Summary The efficiency of viroid cloning can be increased by three to four orders of magnitude when the synthesis of viroid cDNA is primed in such a way that it carries identical sticky ends on both termini and when the multiion transformation is applied.     

An improved immunoblotting procedure for the detection of antibodies against HIV

Immunoblotting ('Western blotting') is routinely used for detection of antibodies against HIV in the diagnosis of HIV infection. We describe an improved procedure, which does not require virus purification and is easy to control for 'false-positive' results. The technique also does not produce erroneous results due to reactivity of the developing system with residual cellular proteins or viral antigens and does not give high nonspecific background staining. The technique can be applied to the detection of antibodies to HIV in serum, plasma, and blood products.     

Half-value layer and intensity variations as a function of position in the radiation field for film-screen mammography

Differences in half-value layer (HVL) and radiation intensity are investigated as a function of position in the mammographic radiation field. Sources of systematic variation include the heel effect, the inverse square law, and differential photon path lengths through thicknesses of inherent and added filtration. The combination of these effects can increase the HVL by as much as 9% and reduce intensity by as much as 40% along the cathode-anode axis. To the left and right of the x-ray field central axis, reductions in radiation intensity of up to 9% and minor increases in HVL are noted as well. Optical density variations as a function of position in the field correlate well with the measured radiation intensity changes.     

An alternative procedure for the preparation of immunogenic liposomal model membranes

This investigation describes a new procedure for the preparation of immunogenic liposomes which circumvents the need to synthesize the N-(hapten)-substituted derivatives of phosphatidylethanolamine that were previously employed for this purpose. The method is based on the generation of liposomes containing the N-hydroxysuccinimide (NHS) esters of either palmitic acid, cholesteryl-hemisuccinate, or N-succinyl-phosphatidylethanolamine. Reaction of these preformed liposomes with a hapten that possesses a substitutable amino group (e.g., DNP-lysine) results in covalent attachment of the hapten to the lipid bilayers. As a consequence of this binding, the liposomes can elicit formation of hapten-specific plaque-forming cells in mice. The reliability of this procedure is indicated by the fact that these liposomes share the essential immunological properties of liposomes sensitized by incorporation of N-substituted phosphatidylethanolamine derivatives (e.g., DNP-Cap-PE). Thus, the magnitude of the response was found to be dependent on: (a) the presence of lipid A in the liposomes; (b) the phospholipid composition of the liposomes; (c) the distance separating the DNP determinant from the liposomal surface. Additional applications of liposomes, which contain the NHS esters, are indicated.     

An improved procedure for the ''dot immunobinding'' analysis of hybridoma supernatants

A computer-assisted method for the positive/negative discrimination of ELISA data is described. This method was applied to a rapid ELISA procedure for IgG class antibodies to Aspergillus fumigatus in which the performance time of the test was reduced to 1 h. The method gives results which compare well with those by agar gel double diffusion (AGDD). The computer-assisted reading, calculation and tabulation of ELISA results from one microtitre plate is performed in less than 2 min and permits analysis of large numbers of specimens.