The structural principles and technical performances of different ionization chamber dosimeters used in radiotherapy have been briefly introduced in this paper. In the mean time, a comparison of technical performances of four different kinds of ionization chamber dosimeter used in hospitals in China has also been made. The data show their quality meet the required specification specified by IEC731 and JJG912-96, so they can be used as field survey dosimeters in hospitals. Some precautions in using these dosimeters are given here too.
Equipment Design ; Radiometry ; classification ; instrumentation ; methods ; Radiotherapy ; instrumentation ; Radiotherapy Dosage

An intensity modulated method by scanning for the focusing therapy machine is introduced in this paper. At first, the 3-D model of the focus is delaminated through the treatment planning system, and the dose distributing of each lay is calculated by an inverse design method. Then, the exposure time of the focus at each position is determined and converted to a scanning parameter, such as position, speed and so on. Afterward, the focus continuously scans the tumor at different speeds along the planned track under the control of the computer. Consequently the point-by- point intensity modulation is achieved through the diversification of the scanning speed of the focus.
Humans ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted ; instrumentation ; methods ; Radiotherapy, Conformal ; instrumentation ; methods

The security system plays an important role to protect the safety of patients and equipment in radiotherapy. The principle and structure of three kinds of security system of the Siemens digital linear accelerator were analyzed with some examples.
Equipment Safety ; Particle Accelerators ; instrumentation ; Radiotherapy Planning, Computer-Assisted ; instrumentation

This text probes into the usage of PLC controller which controls the X-ray generator's basic parameters.
Equipment Design ; Radiography ; instrumentation ; Radiotherapy ; instrumentation ; X-Rays

Existence of rays with different decay rate between radiotherapy CT bed and radiotherapy bed, this paper discusses the rate induced and identified two kinds of simple solution.
Equipment Failure ; Radiotherapy ; instrumentation ; Tomography, X-Ray Computed ; instrumentation

OBJECTIVETo evaluate the image quality of megavoltage computed Tomography imaging.

METHODSThe HU uniformity and linearity, image noise, spatial resolution, low contrast resolution and spatial linearity in MVCT mode were evaluated with Catphan 600 phantom, and the factor of pitch was also evaluated. Influencing factors of image quality were also discussed.

RESULTSThe MVCT values depended linearly on the physical density of the sample. The MVCT values uniformity was good. The spatial resolution was 4 lp/cm. The use of an MV Beam for imaging results in the loss of low contrast resolution, but it is sufficient for pretreatment image guidance. The geometric accuracy was good.

CONCLUSIONSThe image quality of MVCT is less than that of KVCT, but is good enough for IGRT.

To synchronize the radiation of microSelectron-HDR (Nucletron afterloading machine) and measurement of MOSFET dose system, a trigger system based on interface circuit was designed and corresponding monitor and trigger program were developed on Qt platform. This interface and control system was tested and showed stable operate and reliable work. This adopted serial port detect technique may expand to trigger application of other medical devices.
Equipment Design ; Radiotherapy Dosage ; Radiotherapy, Computer-Assisted ; instrumentation ; methods

To investigate the dose effect of isocenter difference during IMRT dose verification with the 2D chamber array. The samples collected from 10 patients were respectively designed for IMRT plans, the isocenter of which was independently defined as P(o), P(x) and P(y). P(o) was fixed on the target center and the other points shifted 8cm from the target center in the orientation of x/y. The PTW729 was used for 2D dose verification in the 3 groups which beams of plans were set to 0 degrees. The γ-analysis passing rates for the whole plan and each beam were gotten using the different standards in the 3 groups, The results showed the mean passing rate of γ-analysis was highest in the P(o) group, and the mean passing rate of the whole plan was better than that of each beam. In addition, it became worse with the increase of dose leakage between the leaves in P(y) group. Therefore, the determination of isocenter has a visible effect for IMRT dose verification of the 2D chamber array, The isocenter of the planning design should be close to the geometric center of target.
Gamma Rays ; Humans ; Radiotherapy Dosage ; Radiotherapy, Intensity-Modulated ; instrumentation ; methods

UNLABELLEDThe aim of this study is to investigate the characteristics of Elekta delivery system for volumetric modulated arc therapy (VMAT). Five VMAT plans were delivered in service mode and dose rates, and speed of gantry and MLC leaves were analyzed by log files. Results showed that dose rates varied between 6 dose rates. Gantry and MLC leaf speed dynamically varied during delivery.

CONCLUSIONThe technique of VMAT requires linac to dynamically control more parameters, and these key dynamic variables during VMAT delivery can be checked by log files. Quality assurance procedure should be carried out for VMAT related parameter.

This article presents and discusses some special problems about the dose calibration of high-energy elections for Linear Accelerator according to the practice of the authors. Thus the paper explain the issues of this work, and clarify the wrong understanding of real work for the aim of attaining the rules of quality assurance in radiotherapy by WHO.
Calibration ; Particle Accelerators ; Radiotherapy Dosage ; Radiotherapy, High-Energy ; instrumentation ; methods