Investigating the Temporal Effects of Respiratory-Gated and Intensity-Modulated Radiotherapy Treatment Delivery on In Vitro Survival: An Experimental and Theoretical Study

Keall, Paul J.; Chang, Michael; Benedict, Stanley; Thames, Howard; Vedam, S. Sastry; Lin, Peck-Sun

doi:10.1016/j.ijrobp.2008.03.047

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Volume 71, Issue 5 , Pages 1547-1552, 1 August 2008

Investigating the Temporal Effects of Respiratory-Gated and Intensity-Modulated Radiotherapy Treatment Delivery on In Vitro Survival: An Experimental and Theoretical Study

Paul J. Keall, Ph.D.
- Department of Radiation Oncology, Stanford University, Stanford, CA
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA
- Reprint requests to: Paul J. Keall, Ph.D., Radiation Physics Division, Department of Radiation Oncology, Stanford University, 875 Blake Wilbur Drive, Room G-233, Stanford, CA 94305-5847. Tel: (650) 723-5549; Fax: (650) 498-5008
Michael Chang, M.D.
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA
Stanley Benedict, Ph.D.
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA
- Department of Radiation Oncology, University of Virginia, Charlottesville, VA
Howard Thames, Ph.D.
- Department of Biomathematics, The University of Texas M. D. Anderson Cancer Center, Houston, TX
S. Sastry Vedam, Ph.D.
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA
- Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX
Peck-Sun Lin, Ph.D.
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA

Received 5 November 2007; received in revised form 10 March 2008; accepted 28 March 2008. published online 21 May 2008.

Purpose

To experimentally and theoretically investigate the temporal effects of respiratory-gated and intensity-modulated radiotherapy (IMRT) treatment delivery on in vitro survival.

Methods and Materials

Experiments 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.

Results

Treatment 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.

Conclusion

The 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.

Respiratory gating, IMRT, In vitro survival, Incomplete repair model