[Utility of Point Dose Verification Using Measured Ionization Amount Ratio of Reference Irradiation to Volumetric Modulated Arc Therapy].

In the point dose verification of intensity-modulated radiation therapy (IMRT), we compared the commonly used method of measuring absolute dose (absolute method) with the measurement method by the American Association of Physicists in Medicine Task Group 119, which describes the point dose verification for IMRT using the ratio of reference irradiation and measured ionization. The target was 66 plans for head and neck cancer, 46 plans for lung cancer with 6 MV X-ray, and 31 plans for prostate cancer with 10 MV X-ray. They were treated with volumetric-modulated arc therapy (VMAT). Each plan was evaluated by the absolute method and the TG119 method using 3D-array. The average and 2SD of the verification results for head and neck cancer, lung cancer, and prostate cancer were 0.129±2.185%, 0.963±2.125%, and 0.259±2.019% by the absolute method, and 0.952±2.039%, 1.704±2.080%, and 0.524±1.274% by the TG119 method. The ratio between the average of the TG119 method and the absolute method corresponded to the error of reference irradiation dose. Considering that the measurement method is simple, the TG119 method enables more stable point dose verification of VMAT.

Impact of different Ir-192 source models on dose calculations in high-dose-rate brachytherapy.

In high-dose-rate brachytherapy, the geometry of the radioactive source is sometimes updated. Some institutions use a different source model for the dose calculation in treatment planning and treatment. The effects of this discrepancy were examined for four types of treatment plans, and ten patients were selected for each treatment plan. The impact of different source models depended on the types of treatment plan, patients, and dose index. To reduce the uncertainty and improve the reliability of the data, it would be better to use more robust metrics (D90 and D2cc) for treatment planning evaluation in facilities with this problem.

[Bedside chest radiography and optimization of radiographic conditions in the NICU with the Fuji Computed Radiography System].

We devised an application that uses the "Maximum value reading method (AutoIV)" for bedside chest radiography in a neonatal intensive care unit (NICU) that used the Fuji Computed Radiography (FCR) System. The application, named AutoIV-N, uses the relationship for density correction between radiographic conditions (mAs) and the Display Parameter (GS). GS=f (mAs) can be considered the relationship that connects FCR and the X-ray generator. When AutoIV-N is used, radiographic image contrast does not change. Further, radiographic image density fluctuation can be eliminated by random elements such as X-ray output fluctuation of the X-ray generator and the decline of photo-stimulated luminescence caused by fading of the imaging plate. Accordingly, image recording that is suitable for follow-up chest radiography is made possible. We choose nine patients and performed a comparison of radiographic density fluctuation in AutoIV-N and Fix. AutoIV-N was found to be more stable than Fix. It is possible to use the radiographic imaging condition that is optimized for all patients in the NICU by AutoIV-N. This facilitates radiation exposure optimization in medicine. (Article in Japanese).

[Availability and improvement of a vacuum-type immobilization device in pediatric CT].

The essential factors for an immobilization device in pediatric CT are 1) absence of artifacts, 2) safety, 3) no disturbance of the patient's sedation, and 4) ease of handling. We evaluated the suitability of a commercially available vacuum-type immobilization device designed for radiation therapy (Vac-Lok) that meets these requisites. There were no artifacts in scans of the water phantom. The device easily immobilized the patient, was quick to release, and was superior to previous immobilization systems, according to replies to a questionnaire administered to physicians, technologists, and nurses. Schedule delays were reduced by using this device to examine sedated patients (up to 1 year of age). Despite these advantages, the device was too small to immobilize both extremities together when examining older patients. In order to overcome this problem, we invented a special immobilization device for pediatric CT. The new device could be applied to taller patients, up to 85 cm in height(the average height of 2-year-old infants), and was able to contribute to efficient utilization of the examination room.