Abstract
Fundamental and clinical studies on supervoltage roentgenography using Mitsubishi 6 Mev linac were carried out. We called this roentgenography as linacgraphy. Linacgraphy is important not only for radiotherapeutic collimation but also for radiographic diagnosis.
Following mechanical device for taking linacgraphy was characteristic.
(1) The effective energy for the X-ray which is deduced from a measurement of halfa value layer with iron was 1.8 Mev. (2) Coil and magnet system for accelerated electron beam was installed to make small X-ray focal spot. (3) Loss time after switch on photography was only 0.1 second and exposure time was within one second. (4)Electronics timer in which every 0.05 second is graded between 0 to 1 second showed good reproduction. (5) A. F. C. (Automatic Frequency Control) worked well by the adjustment not only in the therapeutic dose range (300-200R/min/m) but also in the photographic dose range(80-30R/min/m). (6) The acryl plate of 0.5cm thickness was marked with lead at every 1cm on the isocentral plane. This plate was used for field collimation and correction. (7) Cassette holder was available at the bed to take linacgraphy on the vertical and horizontal direction.
Following studies on the photosensitive materials were performed. From the standpoint of contrast and sharpness (grain) of the linacgram and exposured dose cn the human body, two combinations of screens and film showed good results. (1) The Kyokko GS screens and industrial X-ray film (Fuji No.100 or Sakura RR Type). (2) The Kyokko GF screens and medical X-ray film (Fuji KX or Sakura New Y type). Resolution was determined by Burger phantom experiments and showed best result at film density: 1.6. Finally we decided following condition as one standard for taking linacgraphy. Exposure time: 0.3 to 0.5 second, exposured dose on the film: 150mR (medical), 230mR (industrial). Clinically, the irradiation field was corrected by the help of mark on the linacgram for field collimation. In linacgraphy of the head and neck region, the nasal sinuses, pharynx, oral cavity, larynx were clearly shown without any superimposed bony shadow. Also, lung field which is superimposed with clavicle, ribs, heart and diaphragm on the conventional chest film were well revealed on the linacgram. Highly radioopaque lung on the conventional chest film demonstrated the interior structure if air is kept in the lung. Since linacgraphy of head and neck region and chest have these characteristic advantages, it was found to be most useful for the radiographicc diagnosis. of malignant tumor. In the abdominal region, pneumo-gastrointestinal and pneumoperitoneal linacgraphy and air cysto-linacgraphy were adopted. Abdominal masses and tumors were clearly contrasted with air or gas
