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Effect of head phantom size on 10 B and 1 H[ n ,γ] 2 H dose distributions for a broad field accelerator epithermal neutron source for BNCT
Author(s) -
Gupta N.,
Niemkiewicz J.,
Blue T. E.,
Gahbauer R.,
Qu T. X.
Publication year - 1993
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597131
Subject(s) - imaging phantom , neutron , physics , field size , neutron source , monte carlo method , nuclear medicine , dosimetry , gamma ray , linear particle accelerator , absorbed dose , neutron capture , nuclear physics , radiation , optics , beam (structure) , mathematics , medicine , statistics
The effect of head phantom size on the 10 B and 1 H[ n ,γ] 2 H dose distributions for a broad epithermal neutron radiation field generated by an accelerator‐based epithermal neutron source for boron neutron capture therapy (BNCT) have been studied. Also two techniques for calculating the absorbed gamma dose from a measured gamma‐ray source distribution are compared: a Monte Carlo technique, which is well accepted in the BNCT community, and a Point Kernel technique. The count‐rate distribution in the central plane of three rectangular parallelopiped head water phantoms irradiated with an epithermal neutron field was measured with a boron trifluoride (BF 3 ) detector. This epithermal neutron field was produced at the Ohio State University Van de Graaff Accelerator Facility. The 10 B absorbed dose and the gamma‐ray source have the same distribution in the head phantom as the BF 3 count‐rate distribution. The absorbed gamma dose from the measured source distribution was calculated using MCNP , a Monte Carlo code, and QAD ‐ CGGP , a Point Kernel code. The most pronounced effect of phantom size on 10 B absorbed dose was on the dose rate at the depth of maximum dose, d max . An increase in dose rate at d max was observed with a decrease in phantom size, the dose rate in the smallest phantom being larger by a factor of 1.4 than the dose rate in the largest phantom. Also, d max for the phantoms shifted deeper with a decrease in phantom dimensions. The shift between the largest and the smallest phantoms was 6 mm. Finally, the smaller phantoms had lower entrance 10 B dose as a percent of the dose at d max , or better skin sparing. Our calculations for the gamma dose show that a Point Kernel technique can be used to calculate the dose distribution as accurately as a Monte Carlo technique, in much shorter computation times.