Intensity modulated radiation therapy (IMRT) is a treatment that irradiates high dose to target volume while providing minimum dose to surrounding tissue by making optimal dose distribution with non-uniform fluence compared with 3-dimentional conformal radiation therapy (3D CRT).¹⁾ The introduction of such highly advanced treatment techniques has made the examination of the dose measurement also very important, not only increased the necessity of dose-based validation but also the importance of the dose distribution and the dose transfer characteristic unique to the inverse planning technique. Accurate dose delivery in radiation therapy is highly dependent on the accuracy of the measured beam data during acceptance test procedures (ATP) and commissioning. Especially, the beam commissioning in the treatment planning system is very essential for clinical applications of IMRT. Most of the acquired beam data is input to the treatment planning system to determine or model the characteristics of the treatment device and is treated as standard data for clinical use. These standard data not only affect the treatment plan of all patients, but also serve as a basis for the quality assurance of the treatment device. Therefore, the linear accelerator ATP and commissioning phases are very important steps because they are the first step in the risk management system of the corresponding treatment equipment. When installation of linear accelerator, the clinically qualified medical physicist (CQMP) must take all the steps from the detailed construction plan to the treatment room design, installation supervision, ATP and beam data measurement to ensure the safety and accuracy of radiation therapy.²⁾ Furthermore, it is very important to maintain and guarantee the quality control standard value of radiotherapy equipment. The American Association of Physicists in Medicine (AAPM), European Society for Radiotherapy & Oncology (ESTRO), and International Atomic Energy Agency (IAEA) have published reports on dose quality control protocols^3,4) and mechanical quality control protocols.^5,6) Reports on beam commissioning related to accelerator beam data measurement or dose verification of advanced treatment techniques have also been published, ^7–10) but there are no official reports for ATP items, yet. Despite the fact that new high precision radiotherapy devices are constantly being introduced in many hospitals in Korea, there are no guidelines for ATP or commissioning stages that are appropriate for domestic situations.

Thus, we propose risk management items for the dosimetry system itself, ATP and commissioning, and propose risk management guidelines for them.

ATP of high precision external radiation therapy equipment is part of an agreement to accept the acquisition, which means that the manufacturer verifies that the performance and operation of the device meet the specifications with the user. Step items and tolerances of ATP were derived based on the acceptance procedure of Varian (Varian Medical Systems, Inc. 3100 Hansen Way Palo Alto, CA, USA) and Elekta (Elekta Instrument AB Kungstensgatan 18, Stockholm, Sweden) linear accelerators. The extracted ATP items were confirmed by comparing the AAPM report items as the quality assurance items of medical accelerators and the IMRT recommendation criteria. Commissioning is classified based on the following: (1) acquisition of beam data for treatment planning and dose calculation, (2) modeling of beam data and various parameters entered into the treatment planning system, and classification and approval according to the calculation algorithm, and (3) the dose verification process, which compares the calculated dose with actual measurement results to verify that it is within the tolerance. The step-by-step procedures and risk management items for commissioning and dosimetry system preparation were derived based on reports from overseas associations such as the AAPM TG-106 report,⁷⁾ the TG-120 report,¹⁰⁾ the AAPM TG-142 report,⁶⁾ the AAPM TG-119⁸⁾ and ESTRO booklet no. 9 report.⁹⁾ The modeling and dose verification process were previously reported for the commissioning of the radiation treatment plan (RTP) system.¹¹⁾ In this paper, we derive procedures focusing on the acquisition of beam data in high precision external radiation therapy equipment.

Dosimetry systems used in the ATP and commissioning phases include ionization chambers, electrometers for one-dimensional dose measurement, radiochromic films, and two-dimensional array detectors for two-dimensional dose distribution measurements. In this paper, it derived risk management items based on the procedures of using ionization chambers and electrometers, which are most widely used for profile and point dose measurement during beam commissioning. The ATP of high-precision radiotherapy devices were divided into three sub-steps: 1) mechanical and dose aspects, 2) multi-leaf collimator (MLC), and 3) imaging system. The risk management items for each procedure in the commissioning stage are subdivided into a measurement preparation step and an acquiring beam data.

1. Dosimetry system

2. ATP of high-precision radiotherapy equipment

The manufacturer must demonstrate that the radiotherapy unit is operating in accordance with the specifications required by the consignor. Then CQMP shall establish the therapeutic beam characteristics required for clinical use during ATP and commissioning, shall establish a reference value, and verify that it is operating within the specified tolerances. CQMP play a key role in the team conducting shielding, design of the radiotherapy room, and ATP of radiotherapy machine. Furthermore, CQMP should establish and conduct ATPs based on procedures (ATP or customer acceptance procedure, CAP documents) provided by the manufacturer. The CQMP will consult with the manufacturer engineers to coordinate the installation and maintenance programs of the equipment, ensure the safe and optimized performance of the equipment. In addition, CQMP performs installation, quality control to determine clinical use after each maintenance procedure, supervises calibration and measurement.

We have derived the ATP step-by-step check items and tolerances for high-precision radiotherapy devices with reference to the linear accelerator acquisition procedure recommended by Varian and Elekta. The step-by-step checklist of ATP was divided into three divisions: “Dosimetry and mechanical check” (34 items), “multi-leaf collimator” (22 items), and “imaging system” (36 items). A total of 34 items were deduced from dosimetry and mechanical checklists as shown in Fig. 3. For The MLC was subdivided into 22 items by mechanical inspection, static MLC, radiological examination and dynamic MLC as shown in Fig. 4. The imaging system derives the risk management items as ATP based on the Varian linear accelerator’s on-board imager (OBI) and electronic portal imaging device (EPID). Risk management items for ATP of imaging system were classified into 21 items for OBIs and 15 items for EPIDs (Fig. 5).

The risk management items in the derived ATP procedure were compared with the items listed in the AMPM TG-142 report as quality control inspection items and the IMRT recommendation criteria, and the linkages were evaluated as shown in Table 1. This is a step to confirm whether the equipment performance is in accordance with the manufacturer’s recommendation specifications from the mechanical point of view when the ATP is introduced for the first time, and it will be linked with the quality control inspection item based on the reference value obtained from ATP and commissioning.

3. Commissioning of high-precision radiotherapy equipment

The risk management items in the commissioning phase were derived in detail to the performance evaluation and the clinical application evaluation of the high precision radiotherapy equipment, classified with preparation of beam measurement setup and beam measurement. Fig. 6 shows that the beam measurement preparation stage was 28 items, which were scanning system check, scanning system measurement preparation, and data acquisition preparation. In the beam measurement, the steps are divided into X-ray scan data, X-ray point dose data, MLC data, electron scan data, electron point dose data, data file acquisition and save, and data processing. In the beam measurement stage, step-by-step procedures and risk management items of 32 were derived based on reports from overseas associations such as the AAPM TG-106 report,⁷⁾ the TG-120 report, ¹⁰⁾ the AAPM TG-142 report,⁶⁾ the AAPM TG-119⁸⁾ and ESTRO booklet no. 9 report,⁹⁾ etc., as shown in Fig. 7.

The reference data for comparing measured beam data can be used as the golden data provided by the manufacturer when conducting the beam data measurement. However, it is not recommended to replace or combine it with the commissioning data. After measured beam data, it is recommended that measurement results and technical reports be recorded and prepared for clarity of accountability. When creating a report, clearly describe and summarize the measurement range, target, method, the device used for measurement, and the results. It is recommended that CQMP check the collected data and reports and perform independent audits. The items to be measured and the reports include X-ray open field/wedge field percent depth dose (PDD) and tissue maximum ratio (TMR) table, phantom-scatter factor (S_p), total scatter factor (S_cp), inair scatter ratio (S_c), wedge factor and soft wedge factor for various depths and field sizes, the transmission factor, open field off-axis ratio at selected depths of large field, the electron cone factor, the effective source-to-surface distance, and the electron PDD table. It is recommended to keep the iso-dose curve and scan data measured in the reference field of X-ray and electron, and record the data comparison to similar model of the institution (or other institution) or the golden data provided by the manufacturer. It is recommended that you also back up the analyzed data, spreadsheets, electronic data, etc., and include a detailed description of the beam data collection method and conditions.

Commissioning data may vary depending on the requirements and the measurement conditions, such as the requirements of the RTP and the clinical needs of the user. Under these conditions, the time required for commissioning can be expected to vary. According to the AAPM TG-106 report, the time allocated for beam data measurement during commissioning procedures is generally 1.5 weeks for photon beam scanning, 1 to 2 weeks for point dose data measurement, 1 to 2 weeks for verification and 1 to 2 weeks for verification. It was suggested that about 4 to 6 weeks were needed for whole commissioning.⁷⁾ For example, in two photon energies, the time required to scan single PDD and five depths profile for fifteen field sizes was estimated to be about 30 hours,⁷⁾ and the time required for the electron should also be considered. In addition, it has been suggested that there is a need to estimate additional time for non-scan data measurement and integration, quality assurance baseline reading, and treatment planning system data validation. The time required for commissioning is determined by the amount of measurement data to be acquired and the work efficiency of the medical physicist participating in the measurement and should be estimated before the acceptance of the radiation therapy device. The data measured at the commissioning stage is the source for beam modeling. Therefore, It is recommended that at least two CQMPs from the measurement preparation phase apply the so-called “2 person rule”,^2,13) which is carried out while performing a double verification. In the case of that facility has only single CQMP then we recommend that you perform a double verification through collaboration a CQMP from another facility.

In this study, risk management items at each stage were derived based on the ATP documents of linear accelerators that are most representative of high precision external radiation therapy and reports from overseas associations. The literature related to the high precision external radiation therapy equipment’s ATP does not exist, the ATP documents presented by manufacturers have been limited to ensure that they meet a certain range of criteria, both mechanically and dosimetry. This guideline provides step-by-step suggestions on the items of ATP, along with risk management items that may occur during each step. In addition, it could check that each step of the ATP is linked to the quality assurance items presented in AAPM TG-142 report.

Commissioning was presented step-by-step with possible risk management items in the process of measuring beam data and various parameters needed for beam modeling. The guidelines established each step based on the AAPM TG-106 report and ESTRO booklet no.9 report that describe what should be measured generally for beam data measurements and what criteria are acceptable. Possible risk management items for each step were presented on the basis of recommendations given in AAPM TG-120 report about dosimetry tool of IMRT, the AAPM TG-142 and TG-119 report as described for external radiation therapy equipment quality assurance and IMRT dose verification. Therefore, this guideline presented both step-by-step risk management items necessary for preparation of measuring beam data and risk management items that may occur when measuring beam data. Therefore, it will also be of interest to medical physicists who are introducing new radiation therapy equipment for safety and accuracy of measurement. It recommends that each item presented in the guideline apply the clinical situation of the user and, in necessary, can be modified and used it. While measuring beam data and the dose verification process must be carried out with a “2 person rule”.

In this study, the introduction and installation process of high precision radiotherapy equipment is presented through a process map. And the guidelines for carrying out the ATP and commissioning steps of high-precision radiotherapy devices are presented. When using the guideline given in this study, it is recommended that the manufacturer, characteristics, institutional procedures by the relevant agency be duly reflected. The result of this study is expected to be able to prevent radiation accidents in stages by introducing a risk management system from introduction of radiotherapy and system installation process beyond machine-centered quality control. Furthermore, it is anticipated that risk management based technologies for radiation therapy will be developed and applied to the development of risk management guideline in the field of nuclear medicine and radiology in the future.

This work was supported by the General Researcher Program (2018R1D1A1B07050217), and the Nuclear Safety Research Program (Grant No. 1603016) through the Korea Foundation of Nuclear Safety (KOFONS), using the financial resource granted by the Nuclear Safety and Security Commission (NSSC), Republic of Korea.