• Paul J Keall, Michael Chang, Stanley Benedict, Howard Thames, S Sastry Vedam, and Peck-Sun Lin.
• Radiation Physics Division, Department of Radiation Oncology, Stanford University, 875 Blake Wilbur Drive, Stanford, CA 94305, USA. Paul.Keall@stanford.edu
• Int. J. Radiat. Oncol. Biol. Phys. 2008 Aug 1; 71 (5): 1547-52.

PurposeTo experimentally and theoretically investigate the temporal effects of respiratory-gated and intensity-modulated radiotherapy (IMRT) treatment delivery on in vitro survival.Methods And MaterialsExperiments were designed to isolate the effects of periodic irradiation (gating), partial tumor irradiation (IMRT), and extended treatment time (gating and IMRT). V79 Chinese hamster lung fibroblast cells were irradiated to 2 Gy with four delivery methods and a clonogenic assay performed. Theoretical incomplete repair model calculations were performed using the incomplete repair model.ResultsTreatment times ranged from 1.67 min (conformal radiotherapy, CRT) to 15 min (gated IMRT). Survival fraction calculations ranged from 68.2% for CRT to 68.7% for gated IMRT. For the same treatment time (5 min), gated delivery alone and IMRT delivery alone both had a calculated survival fraction of 68.3%. The experimental values ranged from 65.7% +/- 1.0% to 67.3% +/- 1.3%, indicating no significant difference between the experimental observations and theoretical calculations.ConclusionThe theoretical results predicted that of the three temporal effects of radiation delivery caused by gating and IMRT, extended treatment time was the dominant effect. Care should be taken clinically to ensure that the use of gated IMRT does not significantly increase treatment times, by evaluating appropriate respiratory gating duty cycles and IMRT delivery complexity.

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