(Dr. Nolan Hertel, advisor)
"Development of a Boron-Neutron-Capture-Enhanced Fast-Neutron Therapy Beam "
The combination of fast neutron therapy and boron neutron capture therapy is currently under investigation at several fast neutron therapy centers worldwide. This treatment method, termed boron neutron capture enhanced fast neutron therapy (BNCEFNT) utilizes a boron containing drug to selectively increase the dose to the target tumor. BNCEFNT may be useful in the treatment of some radioresistant brain tumors, such as glioblastoma multiforme.
A neutron therapy beam for boron neutron capture enhanced fast neutron therapy has been developed for the existing Fermilab Neutron Therapy Facility. This beam produces a significant dose enhancement due to the the boron neutron capture reaction. The beam was developed by designing a filter and collimator system using the Monte Carlo radiation transport code, MCNPX. The MCNPX code was benchmarked against depth-dose measurements of the standard treatment beam. The new BNCEFNT beam is filtered with 18.3-cm of low carbon steel and is collimated with steel.
Measurements of the dose enhancement of the new BNCEFNT beam were performed with paired tissue equivalent ion chambers. One of the ion chambers has boron incorporated in the wall of the chamber to measure the dose due to boron neutron capture. The measurement of the dose enhancement of the BNCEFNT beam is 17.0 +/- 2.7% per 100-ppm10B for a 20-cm diameter beam and 10.4 +/- 1.7% per 100-ppm 10B for a 10-cm diameter beam. The dose rate of the new beam is reduced to 4.4% of the dose rate of the standard treatment beam.
A conceptual design that overcomes the reduced dose rate is also presented. This design uses a tungsten collimator placed near the patient, with a 1.5-cm tungsten filter just upstream of the collimator. Using partial moderation of the patient with graphite a percent dose enhancement of 15% can be attained with good collimation, for field sizes as small as 5x5 cm2, without a reduction in dose rate.