Calculating equivalent dose received from a patient undergoing nuclear medicine procedure by merge phantoms tool and GAMOS/Geant4 6.0.0 software

e-RPT: Ecuadorian radioactive particle tracking. Proposal and evaluation of a low-budget RPT system with GEANT4

Radioactive Particle Tracking (RPT) is a non-invasive measurement technique used to reconstruct the Lagrangian particle field inside a fluid flow. This technique tracks the trajectories followed by radioactive particles that move along the fluid, and it is based on the counts registered by radiation detectors that are placed strategically around the boundaries of the system. The aim of this paper is to develop a low-budget RPT system proposed by the Departamento de Ciencias Nucleares of the Escuela Politécnica Nacional and to generate a GEANT4 model of it for optimizing its design. This system is based on the usage of the minimum amount of radiation detectors required to track a tracer and on the innovative idea of calibrating them with moving particles. To achieve this, energy and efficiency calibrations were performed with a single NaI detector, and their results were compared with the results generated with a GEANT4 model simulation. As a result of this comparison, another methodology was proposed to add the effects of the electronic detector chain in the simulated results by a Detection Correction Factor (DCF) without further C++ coding in GEANT4. Next, the NaI detector was calibrated for moving particles. For this purpose, a single NaI was used in different experiments to analyze the influence of particle velocity, data acquisition systems, and radiation detector position along the x-axis, y-axis, and z-axis. Finally, these experiments were simulated in GEANT4 to improve the digital models. Particle positions were reconstructed based on the generation of Trajectory Spectrum (TS) which gives a specific count rate for each particle position as it moves on the x-axis. The magnitude and shape of TS were compared with DCF corrected simulated data and experimental results. This comparison showed that the variation of detector position along the x-axis changed the shape of TS, while the variation of the location along the y-axis and z-axis reduced the sensitivity of the detector. The existence of an effective zone of the detector location was identified. At this zone, the TS shows high changes in the count rate for low changes of particle position. Based on the overhead of the TS, it was demonstrated that this RPT system must employ at least 3 detectors to have capabilities to predict particle positions.

Using a 'vector rotation' technique and 'parallel geometry' utility to calculate the equivalent dose rate from a patient undergoing nuclear medicine procedures

A dose calculation for a person who has been in contact with a patient undergoing Nuclear medicine procedures can be performed by using Merged Phantom Tool (MPT). In this study, we are upgrading the MPT to help users easily merge phantoms at any axis and with any angle using the "vector rotation" technique. The segmented structure information of the contact's phantom is also included in the calculation using the GEANT4 "parallel geometry" utility. The calculation is applied to a case of a male cancer patient lying on a bed who has used I-131, and a caregiver standing beside the patient. The equivalent dose to the thyroid of the caregiver is calculated at 0.3, 0.5, 0.8 and 1m away from the patient, as the caregiver is standing near the patient's abdomen, chest and neck area. The results show that the dose to the thyroid of the contact greatly depends on his standing position and that there are clear differences between the results calculated with the point source and those calculated with the patient source. In summary, using activity distributions in the patient's body as well as the right communication circumstance helps to calculate the optimal dose for people who have been in contact with patients.

ADDING TWO NEW CONTACT CIRCUMSTANCES TO 'MERGED PHANTOM TOOL' AND A TECHNIQUE TO CONVERT STRUCTURE INFORMATION SEGMENTED BY THE CARIMAS SOFTWARE INTO GEANT4 GEOMETRY

Two new contact circumstances called 'stand-lie' and 'front-rear' are implemented to the merged phantom tool. To allow more flexibility for users when they calculate the dose for a volume of interest (VOI) with arbitrary geometry, an optional utility to convert segmented structure information from the CARIMAS software into parallel geometry of GEANT4 is provided. The effective dose for a person who has been in contact with a male patient being treated for thyroid cancer with 131I is calculated for four circumstances: opposite, side by side, stand-lie and front-rear. The biggest dose is the 'opposite' circumstance and the smallest one is the 'stand-lie' circumstance. Using the dose distribution in the patient's body and applying the right circumstance should be done to optimise the dose calculation for the contact person.