Dose Calculation and Treatment Planning for the Brookhaven NCT Facility

Consistency of the calculated to measured fluxes and doses in phantoms is important for confidence in treatment planning for Boron Neutron Capture Therapy at the Brookhaven Medical Research Reactor (BMRR). Two phantoms have been used to measure the thermal and epithermal flux and gamma dose distributions for irradiations at the BMRR and these are compared to MCNP calculations. Since MCNP calculations in phantoms or models would be lengthy if the calculations started each time with fission neutrons from the reactor core, a neutron source plane, which was verified by spectrum and flux measurements at the irradiation port, was designed. Measured doses in phantoms are especially important to verify the simulated neutron source plane. Good agreement between the calculated and measured values has been achieved and this neutron source plane is now used to predict flux and dose information for oncologists to form treatment plans as well as designing collimator and room shielding. In addition, a program using MCNP calculated results as input has been developed to predict reliable flux and dose distributions in the central coronal section of a head model for irradiation by the BMRR beam. Dosimetric comparisons and treatment examples are presented

A Comparison of the Dose-Rbe and the Biological Dosimetry Approaches for Treatment Planning in Bnct

Treatment planning for clinical trials with boron neutron capture therapy (BNCT) is complicated substantially by the fact that the radiation field generated by the activating external neutron beam is composed of several different types of radiation, i.e., fast neutrons, recoil protons from elastic collisions with hydrogen, gamma rays from the reactor and from neutron capture by body hydrogen, protons from nitrogen capture, and the products of the NCT interaction. Furthermore, the relative contribution of each type of radiation varies with depth in tissue. Because each of these radiations has its own RBE, and the RBE of the fast neutron component will not be constant as the neutron spectrum changes with depth, the problem of predicting the severity of the biological effect, in depth, becomes complex indeed. In order to attack this problem, Monte Carlo calculations of dose, checked against benchmark measurements, are employed. Two approaches are then used to assess the severity of the effect. In the first, the effective dose (D[sub EF]) is determined by summing the products of (D[center dot]RBE) for each radiation. The other approach involves placing cells at the location for which the D[sub EF] was calculated. Using a dose-response curvefrom a low-LET radiation, e.g. [sup 137]Cs gamma rays (D[sub [gamma]Ca]), the photon equivalent dose (PED, or D[sub P]) can be determined. If the RBE values used are correct, the D[sub EF] and the D[sub P] should be essentially identical