Development of 4D Monte Carlo Dose Calculation Program by Using Posture-deformed Mesh Phantoms and its Potential Application to Real-time Dose Monitoring System

Unlike in other medical procedures that involve radiations, medical staffs in image-guided interventional radiography procedures remain inside the imaging room, and for required cases, they even stay close to the patients, causing relatively high doses by scattered radiation [1]. Severe radiation injuries to interventional radiologists, especially in lens and skin, have been extensively reported by may literatures [2-6]. Occupational radiological protection issues in interventional procedures are recently being more highlighted with the increase in the number of interventions and their diversity and complexity. In most cases for regular monitoring, the doses to medical staffs are evaluated by passive dosimeters, usually by TLD-type dosimeter, and in other limited cases for dose optimizations, active personal dosimeters are used, which can provide immediate alert for high dose rate and time variation of doses. However, both passive and active dosimeters cannot provide dose values for specific organs, and thus for more accurate estimations for organ absorbed and effective doses and for more precise dose optimizations, advanced computational dose calculations should be performed and the relations between the measured value and organ absorbed or effective doses should be investigated [1]. Regarding this, a real-time computational dose monitoring system was developed by Badal et al. [7], which calculated organ doses of a medical staff in realtime by continuously adjusting the position of the detailed human phantom from the Virtual Family [8] according to the data obtained from Kinect device. This system, however, used the phantom only in standing posture without considering the effects by posture. To investigate of the influence of posture to dose values, various researchers have developed phantoms in different postures, mostly constructed by manually deforming voxel or boundary representation (BREP) phantoms [9-11]. Xu et al. [12] obtained rather realistic posture data from motion capture system and directly applied obtained data by replacing joint areas of BREP phantoms by spherical hinges. Very recently, Yeom et al. [13] developed phantoms in five different postures by deforming mesh-type reference computational phantoms (MRCPs), which are the most advanced form of computational phantoms for radiation dose calculations. Although there were some discrepancies in dose values, all these previous studies concluded that non-standing phantoms can yield significantly different dose values from those for standing phantoms. While the doses for static postures were extensively investigated, the method to calculate doses for moving posture was not yet been developed. In the present study, a Geant4-based 4D Monte Carlo dose calculation program was developed to automatically deform the posture of mesh phantom and directly calculate doses for the deformed phantom. The developed program was then used to calculate organ absorbed doses for dynamic posture data obtained from a motion capture system. In addition, feasibility study was conducted to investigate its potential application to real-time dose monitoring system.