In order to improve dose distributions at NIRS's 70MeV proton eye treatment beam course, we introduced finer bar ridge filters, and examined the effects of range compensators. The pitch of new bar ridge filters was 5mm in contrast to 15mm pitch of old ones. A NC machine recently available enabled this refinement. The spread out Bragg peak (SOBP) widths were 10,15,20 and 30mm. The new ridge filters improved the field uniformity considerably. In the ridge filter design we assumed parallel beam condition in which the mono energetic proton should proceed in parallel with the central axis, and bar ridges only changes the proton ranges. We searched empirically for the optimum wobbler radius in view of field flatness and depth dose distribution. Range shifter and compensator did not affect the field flatness and depth dose distribution at the optimum condition thus searched. We measured dose distribution in a phantom using a compensator of stairs shape, which fairly modulated the beam. A 50% isodose line almost coincided with the compensator shape, and these results suggested that improvements of dose distributions should be possible using compensators. However width between 50% and 80% isodose lines depended on the thickness of phantom. This might be due to scattering in the compensator and suggests that it is necessary to calculate dose distribution taking account of such effects.

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The bone contrast on chest radiographs obtaind with computed radiography (CR, hereafter) is not decreased enough compaired with that for screen/film combination, even if we use a high tube voltage. This may be because the Exporsure Data Recognizer which can normalize the density and contrast of the chest images is performed. In order to increase the diagnostic accuracy for the lung disease, we propose to use a copper additional filter to decrease the bone contrast.
Consequently, in order to have satisfied the bone contrast and the patient expousure dose, additional 0.3mm copper filter and effective energy was 59.3 keV or more were required of the tube voltage of 140kV. Further, the effective energy of 140kV tube voltage with a 0.7mm copper, which is the maximum thickness of the additional filter within 50 m seconds in exporsure time, was 68keV.
Concluding these results, optimum range of additional copper filter is from 0.3mm to 0.7mm in chest high voltage radiography using CR. The bone contrast decreases sufficiently, if we use X-rays which have effective energy within this range. Our method is also useful to reduce patient dose.

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The present study investigated the possibility of using PLD (photoluminescence dosimetry) for clinical radiotherapy of absorbed dose. The main parameters which provide desirable dosimetric properties of PLD in high energy x-rays for radiotherapy, such as linearity, fading, and random uncertainty, were studied and the following conclusions were reached. There is good linearity of PLD response to absorbed dose. The PLD response is independent of the x-ray energy and depth in the water phantom. PLD has unique properties, such as a small response dispersion among PLD glasses, reproducibility of measurements, and extremely low fading. Additionally, PLD has a high spatial resolution. It is suitable for exact dose measurement, especially for an extremely small field and/or in the high dose gradient region. Moreover, there is no need for a complicated washing process of PLD glass and PLD can be used to irradiate a bare glass in a water phantom. The PLD system is found to be a suitable dosimeter system for clinical radiotherapy.

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