Experimental research of shielding the patients during electron beam radiotherapy / 中华放射医学与防护杂志

Objective To explore the shielding effects of 1-4 layers of lead aprons (LPs) and body shielding devices (BSDs) against stray radiation (SR) outside the electron beam field of 6-15 MeV.Methods JR-115B LiF TLDs were used to measure the stray radiation doses (SRDs) to the patient undergoing treatment,before and after being shielding,for different distances,different energies,different applicators,variable layers of LPs,and different thickness of body shielding devices (BSDs),respectively,along long calculating and comparing the shielding ratios of LPs and BSDs against SR.Results When the applicator (10 cm × 10 cm) is unchanged,the shielding ratio increased with the increased distance from measuring point (r =0.717,P ＜ 0.05) and decreased with the increased electron energy (r =-0.678,P ＜ 0.05);when the energy was constant,there was no correlation between the shielding ratio and the size of applicator (P ＞ 0.05);For lower energy electron beam of 6 and 9 MeV,the shielding ratio for 1 mm Pb-BSD was slightly higher than that for 2 layers of LA (t =2.519,2 662,P ＜ 0.05),ranging from 81.5％ to 95.3％ and 55.4％ to 84.6％,respectively.For 12 and 15 MeV higher energy electron beam,the shielding ratio for 2 mm Pb-BSD was slightly higher than that for 4 layers of LA (t=3.768,7.934,P＜0.05),ranging from 64.6％ to 93.4％ and 51.1％ to 92.4％,respectively.Conclusions LAs or BSDs are availavle for effectively reducing the doses from stray radiation,and may help reduce the secondary risks from stray radiation.BSDs have more obvious advantages than LPs with regard to shielding effect.

Progress of magnetic resonance imaging in radiotherapy for cancer / 中华放射医学与防护杂志

In recent years,there has been a considerable research effort concerning the application of magnetic resonance imaging (MRI) for the external radiotherapy.This paper reviewed the progress of MRI in radiotherapy for cancer,such as magnetic resonance simulator,target volumes,dose calculation and efficacy evaluation.Furthermore,the potential applications of 4D-MRI and MRI guided radiotherapy are summarized.

Verification of the accuracy of Monte Carlo-based dose calculation algorithm, DPM, in homogeneous and inhomogeneous tissues / 生物医学工程学杂志

The present paper is to verify the accuracy of DPM, a Monte Carlo-based dose calculation algorithm, in homogeneous and inhomogeneous tissues. DPM was applied to calculate (1) depth dose curves and off-axis ratios at a depth of 10 cm in water using a 6 MeV photon beam with a 3 cm x 3 cm field and phase space file simulated Varian 60 degrees C medical linear accelerator with a 10 cm x 10 cm field at SSD = 100 (cm); (2) depth dose curves using 6 MeV photon beam in inhomogeneous tissues, such as water (6 cm)/lung (6 cm)/water (8 cm) with a 3 cm x 3 cm field and water (6 cm)/ bone (2 cm)/water (12 cm) with a 10 cm x 10 cm field; (3) depth dose curves using 6 MeV photon beam based on the CT data of a patient's head and abdomen. The doses based on DPM are compared to the doses calculated by DOSXYZnrc under the same condition. The error was within 3% in water phantom while the error was within 3% in inhomogeneous tissues, except a few points. It has been concluded that the DPM can accurately predict the dose to homogeneous and inhomogeneous tissues.

Vague expression and its translation in medical English / 中华医学教育探索杂志

In real life,vague expression is ubiquitous in any nation and any language.Medical English,as a branch of English for Science and Technology ( EST ),is typical in accuracy of word use.However,like other kind of language,it adopts vague expression,too.Vague expression plays an important role in medical practice.In communication of medical practitioners and patients,appropriate vague expression will improve language expression and communication efficiency.In medical English,the vague words that express approximate,presuming,or uncertain meaning are usually used to replace the exact meaning words.The correspondent translation methods such as literal translation,meaning translation,specialization etc can be used according to the different context.

Monte Carlo simulation of 6 MV medical electron linear accelerator / 中华放射医学与防护杂志

Objective To analyze the influence of the mean energy and the full-width of half msximum(FWHM)of incident electron beam intensity distilbution(assumed Gaussian distribution)on depth dose curves and off-axis ratios and to derive a most optimal combination of mean energy and FWHM of incident electron beam intensity distribution.Methods The study simulated 6 MV photon beam produced by Varian 600C medical linear accelerator with OMEGA/EGSnrc by matching the relative error of calculated and measured depth dose curves past depth of maximum dose and off-axis ratios at a depth of 10.0 cm in water within 2%.Results The depth dose curves were relatively insensitive to the mean energy past depth of maximum dose and the FWHM of the incident electron beam intensity distribution.Dose profiles were sensitive tO the mean energy and FWHM.The dose profiles horns decreased as the mean energy and tlle FWHM of the ineident electron beam intensity distilbution increased.The calculated value of the depth dose curves matched well with the measured value.The calculated value of the off-axis ratio was consistent with the measured value within the radiation field.However, the maximum errors of individual measurement points in the penumbra region and OUt of the field reached 18.5%.Conclusions In the field.the most optimal combination of mean energy and FWHM of incident electron beam intensitv distribution Can be derived, however,can not be derived out of the field and in the penumbra region.

MatriXX system in the study of the influence of respiratory motion on target dose distribution / 中华放射肿瘤学杂志

Objective To investigate the influence of respiratory motion on target dose distribution in three-dimensional conformal radiation therapy(3DCRT) and intensity modulated radiation therapy(IM-RT). Methods A 2D air vented ionization chamber array MatriXX system,a platform which can mimic the clip motion of lung tumor, and a home-made solid water(RW3) phantom were used to measure the 2D dose distribution of static and moving targets irradiated by 3DCRT and IMRT beams using multiple gantry an-gles. The period of the moving platform was set to 3.5 s and the amplitude was ± 1 cm. Then the differences of dose distribution between the static phantom and moving phantom were compared and analyzed with the MatriXX system software. Results Compared with the static phantom in 3DCRT, the penumbra of dose distribution of the periodic moving phantom along the moving directions was increased by 6-9 mm, the high dose area was shrinked by about 5 ram,and the low dose area was extended by 5 mm,but the area of 50% i-sodose and the dose center area changed very little. When a single segment beam of IMRT was delivered and measured and the maximum dose of measuring plane was normalized to 100% ,the average difference of dose distribution between the static and dynamic phantoms was ±27% (from -56.4% to 56.1%) ;When all of the segment beams of IMRT were dehvered and the integrated dose distribution was measured ,the dose differ-ences were less than ±3% ,and the maximum difference of dose distribution was about ±15% which mainly appeared at the field margin and were similar to 3DCRT. Conclusions The dose distribution of most cen-ter areas of the periodic moving target using multi-fraction 3DCRT/IMRT beams is similar to that of the static target, while the high dose area of the former is shrinked and the low dose area is extended.

Research on the application of 2-D air vented ionization chamber array MatriXX system / 中华放射医学与防护杂志

Objective To investigate the features of 2-D air vented ionization chamber array MatriXX system to use the QA procedures of radiotherapy. Methods Some important QA procedure of clinical radiotherapy practice were investigated by using a MatriXX system and a phantom made in house, mainly including the calibration of MatriXX, the off-axis rate (OAR) of virtual wedge fields, the connection between two half-fields or two asymmetry-fields, the skillful adjustment of the clinac flat filter, the 2-D dose distribution verification of radiotherapy planning, the influence of scatter screen to a large area electron beam field, the effect and best thickness and shielding position of block for a large area electron beam fields with scatter screen. Results The OAR of any virtual wedge field can be measured by a MatriXX system in a single irradiation. The conjunction accuracy of two half-fields or two asymmetry-fields may be less than 1 ram. The difference between the calculated and measured dose of any point or any isodose or any OAR of a field can be determined by using a MatriXX system. After the adjustment of the elinae flat filter with the help of MatriXX system, the flatness and symmetry of the field are 1. 85 % and 0.98 %, respectively. The dose characteristic of a large area electron beam field may be distinctively influenced by a scatter screen, and under this condition, the block faraway from the shielded target can hardly protect the organ at risk, and directe block which is put on or near the organ at risk is perfect. Conclusion Compared with conventional ionization chamber (Farmer type) or film dose measuring, the MatriXX combined with the OmniPre I'mRT software is much more convenient and effective in QA practice of clinical radiotherapy, and it's a perfect tool for the QA procedure of radiation therapy.

Study on dose calibration of thermoluminescent used in individual dosimetry / 医疗卫生装备

The TLD(thermoluminescent dosimetry)must be calibrated before used in individual dosimetry.In this paper,some related issues that affect the accuracy of calibration,including principle and performance of the instruments,conditions of annealing and measuring,method of curve fitting are discussed and an appropriate calibration method is proposed.The results show that the method we proposed is valid and efficient,which ensures the accuracy of individual dosimetry.

Training students for translation skills of medical English / 中华医学教育探索杂志

Medical translation is not onlya kind of transmission of medical information but also mutual communication in culture. It is absolutely necessary to train medical students for the translation skills of medical English. This paper has exemplified training on how to deal with medical terms,phrases,texts as well as culture when translating,which is of some importance for the education of medical students.

Motion Artifacts in Three-dimensional CT Images / 实用放射学杂志

Objective To investigate the influence of physiological motions on three-dimensional (3D) CT images and the rules of motion artifacts.Methods A mathematical model of motion artifact was set up based on the principle of spiral scanning, hereby the geometrical distortion of 3D image was analyzed.Experiments were carried out with home-made phantoms on a CT scanner.Results The details of 3D images with trivial distortion were legible under static condition.On the contrary, distinct distortion occured under moving condition, and its degree increased with the pitch and motion period. The 3D images were varied with difference of the motion initial phases.Conclusion The distortion of 3D-CT image depends on the motion characters of scanned objects and scanning parameters such as pitch and slice thickness.