Abstract
Radiation dosimetry for Neutron Capture Therapy (NCT) has been performed since 1959 at Thermal Neutron Irradiation Facility (TNIF) of the three-megawatt light-water cooled Brookhaven Medical Research Reactor (BMRR). In the early 1990s when more effective drug carriers were developed for NCT, in which the eye melanoma and brain tumors in rats were irradiated in situ, extensive clinical trials of small animals began using a focused thermal neutron beam. To improve the dosimetry at irradiation facility, a series of innovative designs and major modifications made to enhance the beam intensity and to ease the experimental sampling at BMRR were performed; including (1) in-core fuel addition to increase source strength and balance flux of neutrons towards two ports, (2) out of core moderator remodeling, done by replacing thicker D2O tanks at graphite-shutter interfacial areas, to expedite neutron thermalization, (3) beam shutter upgrade to reduce strayed neutrons and gamma dose, (4) beam collimator redesign to optimize the beam flux versus dose for animal treatment, (5) beam port shielding installation around the shutter opening area (lithium-6 enriched polyester-resin in boxes, attached with polyethylene plates) to reduce prompt gamma and fast neutron doses, (6) sample holder repositioning to optimize angle versus distance for a single more » organ or whole body irradiation, and (7) holder wall buildup with neutron reflector materials to increase dose and dose rate from scattered thermal neutrons. During the facility upgrade, reactor dosimetry was conducted using thermoluminescent dosimeters TLD for gamma dose estimate, using ion chambers to confirm fast neutron and gamma dose rate, and by the activation of gold-foils with and without cadmium-covers, for fast and thermal neutron flux determination. Based on the combined effect from the size and depth of tumor cells and the location and geometry of dosimeters, the measured flux from cadmium-difference method was 4 - 7 % lower than the statistical mean derived from the Monte-Carlo modeling (5% uncertainty). The dose rate measured by ion chambers was 6 - 10 % lower than the output tallies (7% uncertainty). The detailed dosimetry that was performed at the TNIF for the NCT will be described. « less
Highlights
The thermal neutron beam which has a spectrum of energy at < 0.5 eV was primarily generated for use in the clinical trial of Neutron Capture Therapy (NCT), a non-invasive therapeutic process for treating locally invasive malignant tumors [4]
When the thermal neutron beam was used in NCT to treat deeply-seated tumors, results from clinical trial were disappointing primarily due to the weak penetration of thermal neutrons
Through the improved thermal beam and experimental apparatus at the irradiation port, extensive clinical trials on rats and mice were able to be conducted especially in the 1990’s when effective medical carriers and therapeutic protocols were developed for the brain tumor and skin cancer treatment
Summary
The more penetrating epithermal neutron beam, which has a spectrum of higher energy between 0.5 eV and 10 keV, was generated to treat deeply seated cancer cells, such as brain tumors within the cranium [5]. The tumor treatment on patients using the thermal neutron beam (1959–1994) the epithermal neutron beam (1994–1999) at BMRR was a continuing effort of those made in 1954–1959 at Brookhaven Graphite Research Reactor [6], where a. When treating subjects with tumors at shallow sites, such as eye melanoma and skin cancer [8], the NCT by thermal neutrons had notable success. This suggests the necessity of generating two neutron beams at different energy levels for cancer treatment. The NCT for tumor treatment on animals had been successfully continued at BMRR up to its decommissioning in 1999
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