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Investigation of secondary neutron dose for 18 MV dynamic MLC IMRT delivery
Author(s) -
Howell Rebecca M.,
Ferenci Michele S.,
Hertel Nolan E.,
Fullerton Gary D.
Publication year - 2005
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 - 10.1118/1.1861162
Subject(s) - collimated light , neutron , dosimetry , monte carlo method , fluence , field size , multileaf collimator , neutron flux , physics , nuclear medicine , materials science , optics , nuclear physics , beam (structure) , linear particle accelerator , irradiation , medicine , mathematics , laser , statistics
Secondary neutron doses from the delivery of 18 MV conventional and intensity modulated radiation therapy (IMRT) treatment plans were compared. IMRT was delivered using dynamic multileaf collimation (MLC). Additional measurements were made with static MLC using a primary collimated field size of 10 × 10cm 2and MLC field sizes of 0 × 0 , 5 × 5 , and 10 × 10cm 2 . Neutron spectra were measured and effective doses calculated. The IMRT treatment resulted in a higher neutron fluence and higher dose equivalent. These increases were approximately the ratio of the monitor units. The static MLC measurements were compared to Monte Carlo calculations. The actual component dimensions and materials for the Varian Clinac 2100 ∕ 2300 C including the MLC were modeled with MCNPX to compute the neutron fluence due to neutron production in and around the treatment head. There is excellent agreement between the calculated and measured neutron fluence for the collimated field size of 10 × 10cm 2with the 0 × 0cm 2MLC field. Most of the neutrons at the detector location for this geometry are directly from the accelerator head with a small contribution from room scatter. Future studies are needed to investigate the effect of different beam energies used in IMRT incorporating the effects of scattered photon dose as well as secondary neutron dose.