• Michael B Altman, Michelle A Stinauer, Desler Javier, Brett D Smith, Lauren C Herman, Matthew L Pytynia, Bulent Aydogan, Charles A Pelizzari, Steven J Chmura, and John C Roeske.
• Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60657, USA. mbaltman@uchicago.edu
• Int. J. Radiat. Oncol. Biol. Phys. 2009 Nov 15; 75 (4): 1240-6.

PurposeTo experimentally validate how temporal modification of the applied dose pattern within a single fraction of radiation therapy affects cell survival.Method And MaterialsUsing the linear-quadratic model, we have previously demonstrated that the greatest difference in cell survival results from comparing a temporal dose pattern delivering the highest doses during the middle of a fraction and the lowest at the beginning and end ("Triangle") to one with the lowest doses at the middle and the highest at the beginning and end ("V-shaped"). Also, these differences would be greatest in situations with low alpha/beta and large dose/fraction and fraction length. Two low (WiDr, PC-3) and one high (SQ-20B) alpha/beta cell lines were irradiated in six-well plates with 900 cGy over 20 min (900 cGy/20 min), one each with a Triangle and V-shaped dose pattern. WiDr cells were subjected to the same experiments with first 180 cGy/20 min, then 900 cGy/5 min. Cell survival was assessed using the clonogenic assay.ResultsAt 900 cGy/20 min, irradiation with a V-shaped pattern resulted in an increased survival compared with use of a Triangle pattern of 21.2% for WiDr (p < 0.01), 18.6% for PC-3 (p < 0.025), and 4.7% for SQ-20B cells (p > 0.05). For WiDr cells at 180 cGy/20 min, this increase reduced to 2.7% (p > 0.05) and to -0.8% (p > 0.05) at 900 cGy/5 min.ConclusionsThese results verify the assertions of the modeling study in vitro, and imply that the temporal pattern of applied dose should be considered in treatment planning and delivery.

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