Depth dose characteristics of photon beams released from a scanning-type racetrack microtron

The MM50 is a racetrack microtron that can emit photon beams or electron beams up to 50 MeV. The MM22 using the scanning beam method and the MM22 using a flattening filter method both to flatten the emission field and a water phantom with particular function measurable of PDD etc. in an accelerator using the scanning beam method to make up the PDD curve of photon beams from the linear accelerator. The Clinac21EX was thus employed. The maximum depth of beam flux was shallow, the gradient of the flux decrement large, the surface dose large, and the estimated nominal energy low to the same nominal energy. From these findings, it can be said that thorough comprehension of the characteristics of beam flux properties for these units is necessary when photon beams are to be used.     

Determination of virtual SSDs for electron beams from a dual energy linear accelerator.

Electron beams from an accelerator appear to originate from a point away from the vacuum window designated as virtual source. Virtual source to isocenter distances are determined experimentally by measurements in a polystyrene phantom with inverse square law method. Corrections required for percentage depth dose are also determined. Results of our study are compared with that of other investigators.     

Experimental evaluations of head scatter factor calculation by use of a Gaussian function

In external beam radiation therapy, it is important to calculate the output of the linear accelerator. The head scatter factor, S _h, is one of the important factors for calculation of Monitor Unit, which changes with the size of the irradiation field. In irregular fields shaped by multileaf collimators (MLCs), it is difficult to calculate S _h precisely. S _h comprises backscatter from the upper and lower secondary collimators and scatter from the flattening filter. We measured the effect of backscatter on a monitor chamber (S _b), and we modeled the scatter from a flattening filter using a Gaussian distribution. The modeled parameters used in this method are derived from measurements of square field sizes on the central axis. Furthermore, we divided an MLC irregular field in the shape of fans and integrated the scatter from a flattening filter by a method similar to Clarkson’s sector integration. We were able to calculate S _h with <1 % error in comparison with measurements, even with a field setting with an error of >3 % by the conventional method. This method requires no special measuring tools or software.     

Determination of beam output factors for the CGR Saturne 2+ linear accelerator beams

The demands of a busy clinic require that basic machine calculations be performed as accurately, rapidly and simply as possible. Simple method of predicting X-ray and electron beam output factors for rectangular field sizes on machines that have collimation similar to the CGR Saturne 2+ have been described. The calculated field output factors for rectangular and square field sizes were in agreement with measured data to within +/- 1% for all energies.     

A preliminary study identifying risk factors in drop-out from a prison therapeutic community

Three different groups of therapy leavers and current residents (total n = 80) from Dovegate Prison's Therapeutic Community (TC) were compared on various demographic, criminogenic and psychometric attributes. Statistically significant findings distinguished the leaver groups from current residents and differentiated between type of leavers. Those leavers judged as unsuitable for therapy were characterised by high scores of Psychopathy, Neuroticism, Criminality, Addiction, Venturesomeness, and Avoidant and Schizoid Personality Disorders. Those leavers who had elected to leave the TC were more likely to have a sexual index offence, significant scores on the Multiphasic Sex Inventory, and Paranoid and Depressive Personality Disorders. Logistic Regression analysis confirmed that particular personality disorders were predictive of therapy leaver group membership. Paranoid Personality Disorder was identified as a predictor of all types of drop-out. These findings provide a psychological profile of the different types of residents who have left a prison therapeutic community and can be used to support and inform selection and assessment practices.     

The contribution of the internal scatter to radiation dose during CT scan of the head

Summary An acrylic head phantom was irradiated during a computed tomographic scan with four commercial scanners. Measurements of the spatial distribution of the radiation dose on the surface and internal to the phantom were performed for the scan plane and the scattered beam at various distances from the scan plane. The surface scatter dose was found to be considerably smaller than that for internal scatter. A significant increase in radiation exposure within the head phantom due to internal radiation seatter, and an asymmetrical primary beam profile for dual slice scanners were also noted.     

Determination of absorbed dose for photon and electron beams from a linear accelerator by comparing various protocols on different phantoms.

Protocols developed for high-energy dosimetry IAEA (Technical Reports Series No. 277, 1997), AAPM (Med. Phys. 10 (1983) 741: Med. Phys. 18 (1991) 73: Med. Phys. 21 (1994) 1251), IPEMB (Phys. Med. Biol. 41 (1996) 2557), and HPA (Phys. Med. Biol. 28 (1983) 1097) have continued to enhance precision in dose measurements and the optimization of radiotherapy procedures. While recent dosimetry protocols, including those due to the IAEA and IPEMB, have made a number of improvements compared with previous protocols, it is further desirable to develop absolute dosimetry methods of dose measurements. Measurements based on careful implementation of procedures contained within the various protocols have been carried out in an effort to determine the extent to which discrepancies exist among the protocols. Dose in water at dmax was measured using cylindrical and parallel-plate ionization chambers for 6 MV photon beams and 5 and 12 MeV electron beams. Results obtained from the use of the AAPM and HPA protocols for 6 MV photon beams were found to be 0.9% larger and 0.1% smaller, respectively, than those measured following the IAEA protocol. Calibration dose measurements for 5 and 12 MeV electron beams in water phantoms were found to agree to within 1%, this being well within recommendations from the ICRU and other sources regarding the accuracy of dose delivery.     

Examination of phantom scatter factors in irregular fields with enhanced dynamic wedge

Use of an enhanced dynamic wedge (EDW) changes the size of the irradiation field in real time because of the shift of the flexible aperture during irradiation. Therefore, when EDW is used, it is speculated that the scatter factors proposed by Khan et al. may differ from that obtained in an open irradiation field. The aim of the present study was to investigate whether the total scatter factors (S(cp)) can also be separated into the collimator scatter factors (S(c)) and phantom scatter factors (S(p)) when using EDW, and whether S(p) in an irregular irradiation field using EDW and one without the use of EDW can likewise be handled. Results indicated that the values of S(cp) and S(c) in a square or rectangular irradiation field using EDW tended to differ from those in an open irradiation field, whereas S(p) was almost the same, with a slight variation of about 0.5%, indicating that S(cp) could be separated into S(c) and S(p). However, for an irregular irradiation field, the variations in S(p) exceeded 1% in some cases irrespective of the use or non-use of EDW. Depending on the size and geometry of the irradiation field, it was within the range of the degree of uncertainty of 2.5% in the evaluation of output radiation dosage, which was described in AAPM Report 13. Therefore, the theory proposed by Khan et al. was found to be valid also for an irregular irradiation field using EDW, which could be handled in the same manner as in the irregular irradiation field without using EDW.     

Determination of 129I in atmospheric samples by accelerator mass spectrometry.

A method for the radiochemical extraction of 129I from atmospheric charcoal filters and its measurement by accelerator mass spectrometry is presented. Either the 129I concentration or the 129I/127I atom ratio can be determined in the sample. With this method, air filters from Seville, in the Southwest of Spain (37.4 degrees N, 6 degrees W) have been analyzed. Sensitivities in the order of 10(4) atoms/m3 for 129I concentrations and 10(-10) for 129I/127I atom ratios are obtained. AMS measurements are performed with the 6 MV tandem accelerator at the ETH-H?nggerberg in Zurich.     

Initial evaluation of a Gaussian scatter correction technique

We have performed an initial evaluation of a new scatter correction algorithm, Gaussian Subtraction technique, for correction of SPECT images. This technique was evaluated by Monte Carlo simulations.The Gaussian Subtraction technique uses a non-scatter (standard 20% energy window) and high energy windows. The window on the high energy side of the non-scattered peak is used to fit a Gaussian to the spectral peak. This technique directly determines the number of unscattered photon events detected by a gamma camera.We find that this scatter correction technique can correct reasonably well (to within 10–15%) for scatter, for the simple phantom cases used here, using scatter windows < ∼ 20 keV wide, for ^99mTc. The Gaussian scatter technique does not require a priori knowledge of source distributions. Implementation of scatter correction would improve image contrast and quantitation in SPECT studies.     

136例H1、H2级胃癌肝转移患者的预后影响因素分析

目的 探讨不同治疗方法及临床病理因素对胃癌肝转移患者预后的影响.方法 纳入2003年1月-2013年1月北京大学第一医院普外科诊治的胃癌肝转移(H1、H2)患者136例,其中接受化疗48例、介入治疗45例、手术联合化疗43例.对相关临床病理因素进行单因素及多因素Cox回归分析及相关生存曲线研究.结果 化疗组、介入治疗组、手术联合化疗组中位生存期分别为8.7、10.1、13.3个月.单因素回归分析显示,治疗方式(P=0.002)、肝转移同时/异时性(P=0.009)、肝转移分级(P=0.001)、肝转移瘤最大直径(P=0.001)、原发肿瘤浸润深度(P=0.020)及淋巴结转移(P=0.006)与预后相关.多因素回归分析显示,治疗方式(P=0.041)、肝转移分级(e=0.018)、肝转移瘤最大直径(P=0.001)、淋巴结转移(P=0.008)为影响预后的独立预测因素.结论 对于符合手术适应证的胃癌肝转移患者应积极选择手术治疗联合化疗或介入治疗的综合治疗.肝转移分级高、转移瘤直径大于5cm以及淋巴结转移程度高提示预后不良.