Investigation of secondary neutron dose for dynamic MLC IMRT delivery

• Published in: Medical physics (Lancaster) 2005-03, Vol.32 (3), p.786-793
• Main Authors: Howell, Rebecca M., Ferenci, Michele S., Hertel, Nolan E., Fullerton, Gary D.
• Format: Article
• Language: eng ; jpn
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1861162

Secondary neutron doses from the delivery of 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 and MLC field sizes of , , and . 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 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 with the MLC 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.