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Medical Physics / Volume 37 / Issue 6 / RADIATION BIOLOGY

Med. Phys. 37, 2457 (2010); http://dx.doi.org/10.1118/1.3425792 (9 pages)

Significant dose can be lost by extended delivery times in IMRT with x rays but not high-LET radiations

Michael C. Joiner, Nagaraju Mogili, Brian Marples, and Jay Burmeister

Department of Radiation Oncology, Wayne State University, Detroit, Michigan 48201

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(Received 13 June 2009; accepted 11 April 2010; revised 15 March 2010; published online 6 May 2010)

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Purpose: To experimentally simulate IMRT delivery using two human cell models in vitro and test the hypothesis that a loss in effective dose resulting from the prolongation of megavoltage x-ray treatment delivery time would be greatly reduced in corresponding IMRT simulations using higher-LET radiation.
Methods: The effect of prolonging the delivery time of a treatment fraction was investigated in vitro using human PC-3 prostate and HGL21 glioblastoma tumor cell lines. Cells were irradiated with x rays from a conventional linear accelerator or with neutrons from a clinical d(48.5)+Be radiotherapy beam and maintained at 37 °C throughout. The delivery time for six closely spaced doses, simulating six multiple-port segments, was varied from acute to 60 min for x-ray irradiation, and acute to 120 min for neutron irradiation. Cell survival was measured following summed doses for the six segments of 0.5–6 Gy for x rays and 0.16–2 Gy for neutrons, covering the most likely range of dose per fraction used in clinical radiotherapy.
Results: Prolonging x-ray delivery time (from initiation of segment 1 to initiation of segment 6) from 5 to 45 min resulted in a loss in effective total dose (in equivalent 2 Gy multifraction treatments) of 5.6% in the PC-3 cell line and 11.7% in the HGL21 cell line. More clinically common prolongations of 5–30 and 5–15 min resulted in effective dose reductions of 3.8% and 1.7% for PC-3, and 7.3% and 2.9% for HGL21. A loss of less than 0.5% in effective dose was observed for prolongations up to 45 min of similarly effective neutron irradiation of PC-3 and HGL21 cells.
Conclusions: Prolonged delivery times of photon fractions could have a significant impact on treatment outcome especially for tumors with a low α/β ratio and short repair halftime. These effects are significant at delivery times commonly associated with IMRT and are variable with cell type. X-ray IMRT should therefore always be planned to minimize dose-fraction delivery time. However, if IMRT treatments are delivered with high-LET radiation, this considerably reduces the dependence of the biological effect on fraction delivery time even out to 2 h.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

This work was partly supported by funds from the Wayne State University Medical Physics Graduate Program and by the Department of Radiation Oncology, Wayne State University Medical School.

Article Outline

  1. INTRODUCTION
  2. METHODS AND MATERIALS
    1. Cell lines and culture
    2. Irradiations
    3. Experimental design
    4. Assay of radiation effect
  3. RESULTS
  4. DISCUSSION
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3425792

KEYWORDS and PACS

Keywords

biological effects of neutrons, biological effects of X-rays, biological organs, cellular effects of radiation, dosimetry, physiological models, radiation therapy, tumours, dose protraction, loss of effectiveness, incomplete repair, IMRT, simulation, neutrons

PACS

  • 87.53.Bn

    Dosimetry/exposure assessment

  • 87.59.-e

    X-ray imaging

  • 87.53.Jw

    Therapeutic applications, including brachytherapy

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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