External Auditing on Absorbed Dose Using a Solid Water Phantom for Domestic Radiotherapy Facilities / 대한방사선종양학회지

PURPOSE: We report the results of an external audit on the absorbed dose of radiotherapy beams independently performed by third parties. For this effort, we developed a method to measure the absorbed dose to water in an easy and convenient setup of solid water phantom. MATERIALS AND METHODS: In 2008, 12 radiotherapy centers voluntarily participated in the external auditing program and 47 beams of X-ray and electron were independently calibrated by the third party's American Association of Physicists in Medicine (AAPM) task group (TG)-51 protocol. Even though the AAPM TG-51 protocol recommended the use of water, water as a phantom has a few disadvantages, especially in a busy clinic. Instead, we used solid water phantom due to its reproducibility and convenience in terms of setup and transport. Dose conversion factors between solid water and water were determined for photon and electron beams of various energies by using a scaling method and experimental measurements. RESULTS: Most of the beams (74%) were within +/-2% of the deviation from the third party's protocol. However, two of 20 X-ray beams and three of 27 electron beams were out of the tolerance (+/-3%), including two beams with a >10% deviation. X-ray beams of higher than 6 MV had no conversion factors, while a 6 MV absorbed dose to a solid water phantom was 0.4% less than the dose to water. The electron dose conversion factors between the solid water phantom and water were determined: The higher the electron energy, the less is the conversion factor. The total uncertainty of the TG-51 protocol measurement using a solid water phantom was determined to be +/-1.5%. CONCLUSION: The developed method was successfully applied for the external auditing program, which could be evolved into a credential program of multi-institutional clinical trials. This dosimetry saved time for measuring doses as well as decreased the uncertainty of measurement possibly resulting from the reference setup in water.

A Comprehensive Computer Program for Monitor Unit Calculation and Beam Data Management: Independent Verification of Radiation Treatment Planning Systems / 의학물리

We developed a user-friendly program to independently verify monitor units (MUs) calculated by radiation treatment planning systems (RTPS), as well as to manage beam database in clinic. The off-axis factor, beam hardening effect, inhomogeneity correction, and the different depth correction were incorporated into the program algorithm to improve the accuracy in calculated MUs. A beam database in the program was supposed to use measured data from routine quality assurance (QA) processes for timely update. To enhance user's convenience, a graphic user interface (GUI) was developed by using Visual Basic for Application. In order to evaluate the accuracy of the program for various treatment conditions, the MU comparisons were made for 213 cases of phantom and for 108 cases of 17 patients treated by 3D conformal radiation therapy. The MUs calculated by the program and calculated by the RTPS showed a fair agreement within +/-3% for the phantom and +/-5% for the patient, except for the cases of extreme inhomogeneity. By using Visual Basic for Application and Microsoft Excel worksheet interface, the program can automatically generate beam data book for clinical reference and the comparison template for the beam data management. The program developed in this study can be used to verify the accuracy of RTPS for various treatment conditions and thus can be used as a tool of routine RTPS QA, as well as independent MU checks. In addition, its beam database management interface can update beam data periodically and thus can be used to monitor multiple beam databases efficiently.

Development of Immobilization Devices for Patients with Pelvic Malignancies and a Feasibility Evaluation during Radiotherapy / 대한방사선종양학회지

PURPOSE: Immobilization devices that improve the setup reproducibility of pelvic cancer patients and that provide comfort to patients during radiotherapy were designed and the feasibility of the devices was evaluated. MATERIALS AND METHODS: A customized device was designed to immobilize a knee, thigh, and foot of a patient. Sixty-one patients with prostate cancer were selected and were divided into two groups-with or without devices. The setup errors were measured with respect to bony landmarks. The difference between digitally reconstructed radiographs (DRR) and simulation films, and the differences between DRR and portal films were measured. RESULTS: The left-right (LR), anterior-posterior (AP) and craniocaudal (CC) errors between the DRR and simulation films were 1.5+/-0.9 mm, 3.0+/-3.6 mm, and 1.6+/-0.9 mm, respectively without devices. The errors were reduced to 1.3+/-1.9 mm, 1.8+/-1.5 mm and 1.1+/-1.1 mm, respectively with the devices. The errors between DRR and portal films were 1.6+/-1.2 mm, 4.0+/-4.1 mm, and 4.2+/-5.5 mm, respectively without the devices and were reduced to 1.0+/-1.8 mm, 1.2+/-0.9 mm, and 1.2+/-0.8 mm, respectively, with the devices. The standard deviations among the portal films were 1.1 mm, 2.1 mm, and 1.0 mm at each axis without the devices and 0.9 mm, 1.6 mm and 0.8 mm with the devices. The percentage of setup errors larger than 3 mm and 5 mm were significantly reduced by use of the immobilization devices. CONCLUSION: The designed devices improved the setup reproducibility for all three directions and significantly reduced critical setup errors.

Patient Setup Aid with Wireless CCTV System in Radiation Therapy / 대한방사선종양학회지

PURPOSE: To develop a wireless CCTV system in semi-beam's eye view (BEV) to monitor daily patient setup in radiation therapy. MATERIALS AND METHODS: In order to get patient images in semi-BEV, CCTV cameras are installed in a custom-made acrylic applicator below the treatment head of a linear accelerator. The images from the cameras are transmitted via radio frequency signal (~2.4 GHz and 10 mW RF output). An expected problem with this system is radio frequency interference, which is solved utilizing RF shielding with Cu foils and median filtering software. The images are analyzed by our custom-made software. In the software, three anatomical landmarks in the patient surface are indicated by a user, then automatically the 3 dimensional structures are obtained and registered by utilizing a localization procedure consisting mainly of stereo matching algorithm and Gauss-Newton optimization. This algorithm is applied to phantom images to investigate the setup accuracy. Respiratory gating system is also researched with real-time image processing. A line-laser marker projected on a patient's surface is extracted by binary image processing and the breath pattern is calculated and displayed in real-time. RESULTS: More than 80% of the camera noises from the linear accelerator are eliminated by wrapping the camera with copper foils. The accuracy of the localization procedure is found to be on the order of 1.5+/-0.7 mm with a point phantom and sub-millimeters and degrees with a custom-made head/neck phantom. With line-laser marker, real-time respiratory monitoring is possible in the delay time of ~0.17 sec. CONCLUSION: The wireless CCTV camera system is the novel tool which can monitor daily patient setups. The feasibility of respiratory gating system with the wireless CCTV is hopeful.

Development of Devices for Improving the Reducibility of Patient Positioning on a Breast Board / 대한방사선종양학회지

PURPOSE: We wanted to improve the setup reproducibility of breast cancer patients when utilizing a commercially available breast board for radiation therapy. The breast board was modified by using a new head rest and 2 types of board fixation devices. MATERIALS AND METHODS: A conventional head/neck rest was modified to be positioned in various slots of the breast board, and it was fabricated 1 cm thinner to provide more comfort to a patient when the patient's neck was rotated. This rest improves the uncertainty of the daily setup. Also, the sagging problems at the left and right sides became negligible with the two types of board fixation devices: (1) the stair type, and (2) the arm type. The first device consists of an upper/lower holder with 4 stair-types of grooves and 4 rectangular inserts. In order to cover the whole range of vertical setup of the breast board, 4 rectangular inserts were needed, and each covered 10 steps. The arm-type fixation device was also fabricated and attached to the breast board. It had two aluminum bars that were fixed by utilizing a lock-type of screw. These devises were evaluated with two volunteers in order to prove the effectiveness of the improved setup accuracy. RESULTS: The developed cranio-caudal fixation device demonstrated that it could reduce the cranio-caudal error by nearly 55% compared to the old device. As for left-and-right inclination, the stair-type and arm-type fixation devices can reduce the relative inclination by nearly 80% and 90%, respectively, compared to the breast board without the fixation device. CONCLUSION: It was verified that the developed devices were effective for positioning the patients and for avoiding inclination of the breast board.