The personalized remote radiation tracking (PRRT) vest: experimental results

1139 Objectives: Internal radiation therapies are usually personalized by treating to the dose limit of the patient’s main organ at risk (OAR). For Lu-177 DOTATATE, possible OAR are kidneys, bone marrow, liver and spleen, with kidneys the main OAR in a vast majority of patients. We previously introduced the concept of a personalized remote radiation tracking (PRRT) vest to enable customization of Lu-177 DOTATATE therapy for neuroendocrine tumor patients. The goal of the PRRT vest is to enable monitoring of the washout kinetics of Lu-177 DOTATATE from a patient’s OAR without requiring serial visits to a medical center. The monitoring would occur within the comfort of their own home. In this work, we seek to validate our PRRT software tools and personalized detector vest implementation through experimental testing using an in-house built anthropomorphic phantom, where our goal is to estimate washout kinetics for the kidneys within 5%. Methods: We fabricated a 25 cm diameter by 30 cm tall right circular cylinder phantom with anthropomorphic objects representing liver, spleen, right and left kidneys. The phantom inserts were 3D printed and had fill ports to allow additional activity to be added to the different structures without having to disassemble the phantom. A CT scan of the phantom was performed to register the 3D internal organs with a vest-like covering containing a CT visible grid wrapped around the phantom. Simulations were then run to determine the optimal placement of up to 12 small detectors to estimate the washout kinetics for each of the organs/background. A housing to situate 12 detectors around the cylinder was then created based upon the PRRT software results. Each detector was housed in a 14x14x14 mm^3 tungsten alloy box with 3 mm thick sides, an open back to place the sensor and a 4 mm pin-hole in the front plate. Each detector housed a 6x6x3 mm^3 crystal of GAGG coupled to a 6x6 mm^2 MPPC device. The right kidney, left kidney, liver, spleen and background compartments were filled sequentially, with relative activity concentrations of 20, 22, 4.5, 27, 2 for each object, respectively. For these initial experiments, Tc-99m was used in place of Lu-177. Data were collected from all of the sensors after each organ and the background were filled. The sensitivity map between each organ of interest/background and the 12 custom placed detectors was determined from the collected data. The half-lives for the washout kinetics for the right kidney, left kidney, liver, spleen and background were set to 48 hrs, 45 hrs, 65 hrs, 72 hrs and 97 hrs, respectively. Poisson sampling was used for accurate noise modeling of the collected counts for each organ and background. The composite signals for each of the 12 detectors over 21 days were then provided to our PRRT analysis software to estimate the washout kinetics of each individual organ and background from the composite detector signals. Results: Using data from 7, 14 or 21 days of measurements, the estimate of the half-life of the washout from each of the organs and background was always within 4%. Maximum error was 3.8% for the left kidney. Conclusions: Using an in-house built anthropomorphic phantom and our PRRT Vest software tools and experimental protocol, we were able to estimate the washout kinetics for the kidneys, liver, spleen and background to within 4% of the true decay rate for each of the organs of interest validating our simulation and PRRT vest methodologies.