Recently, new ortho screenfilm systems (Konica EX system, Fuji AD system and Kodak IEF system) are being developed. The granualities of these systems have been greatly improved and gross fogs are lower than those of traditional ortho screen-film systems.
Even if radiographs with the new ortho screen-film systems a re processed at higher temperature than with the old ortho systems, deterioration in the image quality is negligible.
Futhermore, the speed of the screen-film systems increases as the developing temperature rises. Therefore, there may be the potential to reduce patients's radiation exposure dose without greatly decreasing the image quality.
In this report, vol u nteers' clinical chest radiographs were processed at various developing temperatures and the comments about the higher limit of developing temperature were solicited from medical doctors who evaluated them.
Consequently, it has been confirmed that image quality is sufficient in the radiogrphs which processed at the significant higher developing temperature than at the temperature used in many facilities now.
Therefo re, it has been confirmed that there is the possible reduction of patients's radiation exposure dose by increasing developing temperature.

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The method and accuracy of absorbed dose determination have been investigated at 34 hospitals in Tokyo and its neighboring area. The measurement was made for a field of 10 × 10cm^-2 at the calibration point of X-rays (10,6 or 4MV) from a linear accelerator, using the reference dosemeter of each hospital, and the RAMTEC 1000 dosemeter and a water phantom, which were prepared for use in the present investigation. The obtained data were converted to the reference point absorbed dose per dose monitor unit for intercomparison.
The results are given in te r ms of the percentage deviation of absorbed dose determined according to the procedure of each hospital from that obtained with the RAMTEC 1000 dosemeter.
(1) The deviation without the corrections was within ± 1% for 17 hospitals (50%) a nd within ±2% for 30 hospitals (88%).
(2) With the corre ctions for ion recombination and absorbed dose conversion factor according to the JARP protocal,18 hospitals (53%) resulted in a deviation of ± 1% or less and 32 (94%) in ±2%or less.

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Quality assurance (QA) system has been established in radiation medicine in every advanced nations and in some of Asian nations. In the U. S., the research on QA program started in the 1980s, while Japan began similar research in the 1990s. The delay of QA establishment in Japan is mainly due to the lack of authorization for the medical physicist which has been a leading figure in the QA circles of radiation medicine in the U. S. and European nations. However, from the present status of hospital and medical treatment, “Not ready” is not allowed in the establishment of QA in Japan and all the medical physicists are requested to take up a positive attitude as much as they can.
QA system in radiation medicine are prepared each for diagnosis, therapy and nuclear medicine. Each system is composed of technical, physical and clinical QA protocols, while these protocols are interactive each other.

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In 1971, eleven regional centers (at the present time, the number of the center is expanded to fourteen) were established by the Japan Radiologcal Society upon the suggestion on the Japanese Association of Radiological Physicists to review the dosimetry of radiation therapy. A field insrument from a hospital can be calibrated at the nearest center and the then used at the hospital for the routine calibration of therapy equipment. There has been a great improvement in dosimetry over the two decades that the regional calibration centers have been calibrating dosimeters.

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Quality assurance (QA) in radiation therapy includes those procedures that ensure a consistent and safe fulfillment of the dose prescription to target volume, with minimal dose to normal tissues and minimal exposure to personnel. A comprehensive QA program is necessary because of the importance of accuracy in dose delivery in radiation therapy.
QA protocol for radiotherapy equipment of J ASTRO is compared with that of AAPM. Tolerance values related with isocenter of AAPM is hard than that of JASTRO
It is advisable to do several tests daily, including the accuracy o f the optical distance indicator, alignment of sidelight and check of 10 × 10cm. Pencil marks on the wall and floor can be used to check light alignment. Film is useful for testing the flatness/symmetry, and congruence of radiation and light field. Mechanical aligment is fundamentally important for performance of teletherapy unit. As a constancy check of the overall system, the split -field test is recommended due to its rapid and simple execution.

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Medical electron accelerator has developed for practical use since the early 1960s. Today, medical electron accelerator is invaluable to radiation therapy. To ensure safety of medical electron accelerator, JIS Z 4705 was enacted in 1985. Since then, the revised version of JIS Z 4705 has been published in October of 1993.
Furthermore, product liabil i ty act was enacted June 22,1994, issued July 1,1994 and was enforced July 1,1995.
This papers ummarizes the revision of JIS Z 4705 (1993) and the product liability act.

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