Performance of Novel Plastic Vessel Design with Enhanced Sealing Mechanism for Use In Water Calorimetry for Radiation Dosimetry
Abstract
Purpose
Water calorimetry enables measurement of absolute absorbed dose to water, but its practical implementation depends strongly on vessel design and adequate isolation of the sensitive volume. This work presents the development and initial evaluation of a new parylene-coated plastic water calorimetry vessel intended to improve mechanical robustness, sealing reliability, and reproducibility compared with earlier designs. The focus is on assessing relative dosimetric performance against a calibrated glass-vessel based calorimeter standard.
Methods
A novel cylindrical calorimeter vessel design was made from Lucite and coated with parylene-C. Two measuring thermistors were affixed inside a ceramic tube spanning the diameter to provide stability. The traditional neck-and-stopper seal was replaced by a double-valve mechanism to completely isolate the inside of the vessel from outer environment. The high purity water inside the vessel was saturated with ultra-pure hydrogen gas. Measurements were performed using a 6 MV photon beam with a nominal delivered dose of 4 Gy per 40s run. Glass-vessel measurements comprised 100 runs (10 sets of 10 runs) over a 10-week period, while plastic-vessel measurements were similarly acquired, with 11-12 runs per set.
Results
For the calibrated glass vessel, the mean absorbed dose measured was 2.557Gy with a standard error of the mean (SEM) of 0.29%, which is consistent within uncertainty with the 2.563Gy predicted dose. Measurements with plastic yielded an SEM of 0.39% (thermistors in this vessel were uncalibrated, so no dose information obtained). Relative to glass, coated plastic vessel showed good stability and reproducibility. Following rigorous testing, double valve-sealing technology of plastic-vessel showed superior performance to traditional glass stoppers.
Conclusion
The new parylene-coated Lucite vessel demonstrates promising mechanical and dosimetric performance and stability over a continuous 10-week calorimetric study, with improved sealing and structural rigidity. This work will help lead the way to robust, accurate, and cost-effective plastic-based calorimetry vessels.