ESTIMATION OF MEAN BONE MARROW DOSES TO WESTERN AND JAPANESE ADULT AND CHILD IN ROTATIONAL PANORAMIC RADIOGRAPHY BY MEANS OF MONTE CARLO METHOD

• Published in: Shika Hoshasen Vol. 26; no. 4; pp. 310 - 320
• Main Author: HAYAMI, Akimune
• Format: Journal Article
• Language: Japanese
• Published: Japanese Society for Oral and Maxillofacial Radiology 1986
• ISSN: 0389-9705; 2185-6311
• DOI: 10.11242/dentalradiology1960.26.310

One of the latent somatic risks to low level radiation dose is leukemia. Radiation induced leukemia is apparently produced by irradiation of active bone marrow. The average radiation dose to the active bone marrow is an important index of the somatic risks. This index is known as the mean bone marrow dose. The purpose of this study was to estimate the individual mean bone marrow dose to Western and Japanese adult and child in order to obtain the basic data for risk calculations of panoramic radiography using Monte Carlo method. In this study, the mathematical phantom of five years child designed by Hwang and of adult designed by Snyder were used. The phantom consists of three parts (head, trunk, leg) and three regions (skeletal, lung and soft tissue). The density assigned to the skeletal region (bone plus marrow), lung and the remainder of the phantom are 1.5, 0.3 and 1.0gcm-3 respectively. In the skelton, bone and marrow are assumed to be mixed homogeneously. The interaction between photon and phantom took into consideration photoelectric absorption, coherent and incoherent scattering. The atomic form factor and the scattering function for electron binding corrections to coherent and incoherent scattering were considered. The photon histories of 500, 000 according to the x-ray photon spectrum were pursued. The spectrum according to single phase, tube voltage, target angle of x-ray tube and total filtration were generated by computer simulation. The x-ray photon data used here are for the target angle of 16 degrees and for the total filtrations of 1, 2, 3 and 4mm Al eq., at an increment of 10kV steps of tube voltage between 60 and 90kV. The mean bone marrow dose is determined considering the energy deposited in the skelton, the weighting factor for the active marrow in the skeleton, the ratio of the mass energy absorption coefficient for the active marrow to the skelton, the excess dose factor due to photo-electrons and the total mass of the active marrow. Following conclusions were obtained. 1) Examples of the mean bone marrow dose are ranged about 30 to 100μGy according to the race, adult or child and radiographic factors. 2) Concerning mean bone marrow dose in panoramic radiography, more than 90% of whole absorbed energy in bone marrow are absorbed in the head and neck parts and remainder is very small. 3) The mean bone marrow dose increases as an increase of tube voltage when other radigraphic factors remains constant. 4) The complicated problems related to the dosimetry of low energy and dose of x-rays could be avoided. In the case of Japanese child, special care must be taken about justification and optimisation, because the mean bone marrow dose was suggested grater than that of Japanese adult.