Nowadays intensity-modulated radiation therapy became the dominant method for delivering radiation therapy to patients and the safety of radiation therapy became essential. Therefore the importance of the record related to the radiation therapy to patients and the quality assurance (QA) are emphasized.^1,2) In addition, the importance of calibration and record of radiation measurement instrument is also issued. The ionization chamber and the electrometers are the representative instrument requiring the calibration. And also the thermometers and the barometers, are needed to be calibrated. Many reports recommend that the QA and the calibration of the instruments are to be performed periodically.^3-5) Especially, the annual QA must be checked by using the calibrated instrument. The department of radiation oncology generally has many instruments of radiation measurement. However, to calibrate every instruments are difficult due to economic and calibration period reasons in most of clinics. Therefore, the protocols such as TRS-398 recommend using cross-calibrated instrument about reference calibrated by secondary standard dosimetry laboratory.³⁾ Cross-calibrated instruments also have the advantage of replacing the reference measurement instrument during calibration period. These instruments are important to consider traceability and easy management for efficient use. Each institution maintains its instrument through a separate form. Therefore, if the management system for radiation measurement instrument is easy to use and can be used integrally, it will not only be possible to cross-check the instrument by each institution, but also it will be easy to maintain.

Therefore, we developed web-based programs to simplify complex cross-calibration and to maintain radiation measurement instrument.

1. Development environment and configuration

The program was built with Java Server Pages (JSP) language based on web service considering compatibility and accessibility. Developed program were composed of the session related to recording of measurement instrument and a cross-calibration shown as Fig. 1.

2. The session of the measuring equipment

In the measuring equipment session, every instrument listed its period of calibration, recording and management. Each instrument can be configured to be able to record certification, calibration reports and necessary information for each instrument.

3. The session of the cross-calibration

The central axis transfer method proposed by Serré⁶⁾ was applied for the cross-calibration. The ionization chamber for field to be crossly used in clinical was calibrated by the ionization chamber for reference which was calibrated by accredited institution. We supposed the measurement environment as source-to-surface of 100 cm and field size of 10×10 cm². The reference and field ionization chambers were respectively inserted along the beam central axis at two different depths in the Solid Water™ (PTW, Freiburg, Germany) phantom. Radiation doses of same monitor unit were irradiated twice and the measured values of each chamber were read and averaged. And then, the depth of both ionization chambers was switched and the process of previous irradiation and reading was repeated as shown Fig. 2. According to the theory of the central axis transfer, the absorbed dose to water calibration factor for the field ionization chamber is given by the following relationship:

Where, (Mc_)ref and (Mc_)field are the mean of the values at the top and bottom position of the phantom for field and reference ionization chambers, respectively. (ND,W60Co)field and (ND,W60Co)ref are the absorbed-dose-to-water calibration factor for the field and reference chambers. (kQ)ref and (kQ)field are quality factors.

In this study, the cross-calibration factor was defined by the ratio between (Mc_)ref and (Mc_)field.

The web-based program was developed to facilitate the maintenance by simplifying the complex cross-calibration by constructing the data of the measurement instrument in the clinical site. The program was designed to access the program through subscription so that the list of instrument can be managed by each user or organization. After creating account, user can easily access with his/her ID and PW on the main screen as shown Fig. 3a. Through the whole view, it was made easy to figure out the status of the measurement instrument possessed by each institution and to maintain the records in Fig. 3b.

Fig. 4 shows the session for registering calibration and recording instrument in the program. Registered instruments were classified as ionization chamber and detector, survey meter, thermometer, barometer, electrometer, phantom, and other instrument according to their use and management characteristics. The registration session of ionization chamber includes the basic information with the management number and serial number. And also, information of ionization chamber includes the diameter and operating voltage that should be considered when measuring doses to enhance program usability. In the lower section, a calibration report issued by an accredited calibration laboratory or user institution can be attached as a PDF file. There are other additional functions to browse the list and to add pictures of the instrument for easy management. In Fig. 5, Table 1, and Table 2 show the detail information of each instrument.

Fig. 6 shows the cross-calibration session. In the first step of cross-calibration, the date and instrument for cross-calibration are selectable though the management number. In the second step, the temperature and pressure at the time of measurement and the reading values of each ion chamber at two depths are recorded. In the file data session, the calibration procedure and the final results for the certification are recorded.

The department of radiation oncology has a lot of information of radiotherapy machines, and various radiation measurement instruments. Recording and management of them are also closely related to efficient and accurate radiation therapy. Although automated recording and management of patient information such as electronic medical records system has been used in most hospitals, databases and management systems for radiation measurement instrument are not use by every institutions.^7-9)

The web-based program for the recording of the radiation measurement instrument developed in this study is advantages in that the user can easily input information and trace it according to the instrument. The program can be also accessed anywhere because it is based on the web. In addition, it is advantageous that the ion chamber can be more easily managed for the cross-calibration.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2015R1D1A1A01060463 and No. 2013R1A1A2012013) and the Radiation Safety Research Programs (1305033) through the Nuclear Safety and Security Commission.

The authors have nothing to disclose.

All relevant data are within the paper and its Supporting Information files.