The data table of a 1cm dose equivalent per fluence to estimate the effective dose equivalents conservatively from external photon beams were given by ICRP. However these data were calculated with single energy photon beams; therefore, it must be careful when for applying the data to photon beams with spectral distributions. In this paper, we calculated the 1cm dose equivalent per unit exposure for spectral photon beams by means of a Monte Carlo simulation, and ascertained the suitability of the usual method which estimates dose equivalents by means of ICRP data corresponding to the effective energy of the spectral beam. Consequently, the 1cm dose equivalent per unit exposure calculated for primary X-ray beams and for scattered photon beams from an irradiated body were in good agreement with the ICRP data corresponding to the effective energies of each beam. However, those calculated for X-rays transmitted through a lead shield showed a considerably lower value than ICRP data corresponding to their effective energies.
We studied the physical and technical situation of total body irradiation (TBI) for long SAD and a 6MV X-rays. In principle this paper consists of the following : Physical characteristics of 6MV X-rays; Basic TBI dosimetry; Dose distribution in the phantom; Compensating method for inhomogeneity; Practical TBI technique; In vivo dosimetry of the oesophagus. For TBI, it is very important to have uniformity of the three-dimensional dose distribution in the whole body. TBI technique is performed by AP/PA opposing fields, bilateral opposing fields and four fields (combined AP/PA and bilateral opposing fields). As a result of measured dose distribution in the phantom, four fields with compensators is the best TBI technique, which indicating unaccuracy dose of ±10%. It is impossible to deliver a dose uniformity of ±10% for bilateral fields. For TBI dosimetry, it needs to measure for the phantom size needs to be measured to achieve the full scattering conditions, but the phantom size for dosimetry is practically suitable for use of a minimum dimension of 30×30×30cm^3. Compensating methods are used to give homogeneous dose to different thick bodys and inhomogenities. We use tissue-equivalent bolus and compensator such as lead or copper. For in vivo measurement, expected dose ratio in the oesophagus is 0.947±0.044 for four fields, 0.994±0.025 for AP/PA fields, and 0.987±0.077 for the bilateral fields. The unaccuracy of irradiation doses are less than 5% for various TBI. In the future, TBI technique should be established the best irradiated method that the uncertainty dose is delivred within ±5%.
In Tokai University Hospital ever since 1982, TBI for bone marrow transplantation has been performed by the moving couch method. In this method, the patient is irradiated from the opposite direction of A-P and P-A in a comfortable supaine position as is. This technique has been well studied and greatly improved. For example, the moving speed of the couch is automatically varied depending on the dose rate deviation of the electron linear accelerator, function having variable speed with the dose rate (VSDR). Another function in variable speed with division (VSDV). In addition it has a self-recording function for the actual condition for the dose and couch movement. In such small areas as the eyes and gonad, the shielding effect cannot be effectively used. For the lungs, but it is able to shield and compensate to a sufficient extent. It applied to actual treatment resulting from data obtained from the measurements using a phantom. During the irradiation we must check the reproducibility of the systems which are dose rate, couch position, and so on. This is one reasonable concept of the dose monitor.
Moving beam technique in performing total body irradiation (TBI), which sweeps the X-ray beam completely over the whole body axis, is a useful technique for small treatment room in our hospital. However, homogenous dose distributions for patient cannot be obtained without changing the output during gantry rotation. We developed a method for obtaining a homogenous dose distribution by changing the software of the control unit of the linac without any change in the construction of the machine. The change of output/degree and /or the field width at each gantry angle can be automatically calculated by our method, the result, homogenous dose of ±3% at the reference plane was obtained in treating a useful length of 200cm. From this study, though the results are still preliminary, our method might be promising in performing TBI.
A trend toward hospital computerization is accelerated and clinical work computerization are adopted in many hospitals to contribute to the improvement of medical work and become useful for service of patients. Total hospital information system (HIS) based on order-entry system (GUNMAS) is going on smoothly to date. In HIS of GUNMAS, in vivo nuclear medicine examinations system are involved in physiological and radiological examination system which include plain X-P, MRI, ECG, and so on, because in vivo nuclear medicine examination subjects to a person as well as the order physiological or radiological examinations. In contrast, in vitro nuclear medicine examination system is involved in clinical laboratory system. The medical physician selects the necessary item such as examination's name, purpose and the order on CRT, and then, the date of scintigraphy is reserved. While the reception of samples for in vitro nuclear medicine examination is performed to feed of patient's number into HIS (GUNMAS). In the field of in vivo nuclear medicine ordering system, GUNMAS is connected to the Nuclear Medicine Computer System through a computer system which includes reporting and data base functions. Ordering and reporting for in vivo nuclear medicine examination can be done by these two computer systems. The introduction of HIS (GUNMAS) is useful to save labor and rationalize the clinical work, which contribute to better service for patients.