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Significant dose can be lost by extended delivery times in IMRT with x rays but not high-LET radiations
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10.1118/1.3425792
/content/aapm/journal/medphys/37/6/10.1118/1.3425792
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/37/6/10.1118/1.3425792

Figures

Image of FIG. 1.
FIG. 1.

Cell survival versus dose data for PC-3 cells exposed to x rays (panel a) and neutrons (panel b) at the different durations of overall delivery time of all the six subfractions: 0–60 min for x rays and 0–120 min for neutrons. The time-dependent variability in the x-ray response is substantially reduced in the neutron response, at similar levels of surviving fraction. Panel c (x rays) and panel d (neutrons) present these same data as surviving fraction versus time for each total dose delivered.

Image of FIG. 2.
FIG. 2.

Cell survival versus dose data for HGL21 cells exposed to x rays (panel a) and neutrons (panel b) at the different durations of overall delivery time of all the six subfractions: 0–60 min for x rays and 0–120 min for neutrons. The time-dependent variability in the x-ray response is reduced in the neutron response, at similar levels of surviving fraction. Panel c (x rays) and panel d (neutrons) present these same data as surviving fraction versus time for each total dose delivered.

Image of FIG. 3.
FIG. 3.

Predicted responses calculated from the parameter values in Table I, of PC-3 cells to the six-segment irradiation with either x rays (panels a and c) or neutrons (panels b and d), as a function of either dose (panels a and b) or overall irradiation time (panels c and d). These diagrams show the loss of effectiveness of at least 5% dose equivalent as the six-segment x-ray irradiation is protracted beyond 30 min duration, and that this loss is reduced substantially by utilizing high-LET irradiation.

Image of FIG. 4.
FIG. 4.

Predicted responses calculated from the parameter values in Table I, of HGL21 cells to the six-segment irradiation with either x rays (panels a and c) or neutrons (panels b and d), as a function of either dose (panels a and b) or overall irradiation time (panels c and d). These diagrams show the loss of effectiveness of at least 5% dose equivalent as the six-segment x-ray irradiation is protracted beyond 30 min duration, and that this loss is reduced substantially by utilizing high-LET irradiation.

Image of FIG. 5.
FIG. 5.

Increase in surviving fraction of PC-3 (panel a) and HGL21 (panel b) cells for a 2 Gy x-ray dose protracted out to 1 h and a similarly effective neutron dose extended out to 2 h, calculated from the parameters in Table I. The neutron responses demonstrate a considerably lessened effect of dose protraction compared with the x-ray responses.

Tables

Generic image for table
TABLE I.

Parameters in the incomplete-repair model fitted separately to the x-ray data and neutron data for each cell line. 95% confidence intervals are shown in parentheses. Note that although values for neutrons are given which minimize the sum of squared errors in the nonlinear regression, these values are technically indeterminate as indicated by their infinite confidence intervals.

Generic image for table
TABLE II.

Parameters in the incomplete-repair model fitted to all the data (x ray and neutron simultaneously) for each cell line. 95% confidence intervals are shown in parentheses.

Generic image for table
TABLE III.

Percent increase in the isoeffective dose per fraction, caused by example treatment protractions, calculated using the parameters in the incomplete-repair model fitted separately to the x-ray data and neutron data for each human cell line (see Table I). This analysis assumes that the number of fractions would be kept constant, and the fraction size would be increased to compensate for loss of effectiveness. Normal type: X rays; italic type: Neutrons.

Generic image for table
TABLE IV.

Percent increase in the isoeffective total dose (given in multiple equal fractions) caused by example treatment protractions, calculated using parameters in the incomplete-repair model fitted separately to the x-ray data and neutron data for each human cell line (see Table I). This analysis assumes that the fraction size would be kept constant and the number of fractions would be increased to compensate for loss of effectiveness. Normal type: X rays; italic type: Neutrons.

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/content/aapm/journal/medphys/37/6/10.1118/1.3425792
2010-05-06
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Significant dose can be lost by extended delivery times in IMRT with x rays but not high-LET radiations
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/37/6/10.1118/1.3425792
10.1118/1.3425792
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