The cumulative dose received by circulating blood during a linear, sequential total body irradiation is illustrated. The dose cloud moves continuously in one direction, while blood voxels move sinusoidally along the patient’s length.
The total dose received by each blood voxel in a serial TBI treatment is shown for treatment times ranging from 10 to 60 min. Dose heterogeneity is maximum for short treatment times and long perfusion periods. However, clinically relevant parameters (e.g., 20 min treatment time and 125 s perfusion period) result in clinically acceptable heterogeneity (i.e., ). Error bars refer to standard deviation. The maximum and minimum dose values are also indicated on the plots.
The EUD is plotted for various values of mean lethal dose and perfusion period. Dose heterogeneity reduces the EUD, particularly for relatively fast (i.e., 10 min) treatment times. EUD, however, remains within 10% for virtually all scenarios with treatment times . Radiosensitive cell types exhibit greater EUD compromise than radioresistant types.
EUD is plotted as a function of perfusion period for the range of treatment times studied. Data for radiosensitive cell types are shown with , as the EUD is compromised most for these cells. Long perfusion periods, coupled with short (i.e., 10 min) treatment times, compromise the EUD by 10%–30%. However, all perfusion periods show only modest declines in EUD for treatment times of 20 min or longer.
Dose delivered to discrete blood voxels is plotted in (a) for treatment interrupted at the midpoint of a 20 min treatment delivery. The effect of these intrafraction treatment gaps on EUD is plotted in (b). Data were modeled for 10 and 20 min treatment durations with 5 and 2 min perfusion periods as indicated in (b). The EUD is affected by different degrees depending on other treatment parameters and is not compromised for the 20 min treatment duration with a 2 min perfusion period.
The dose per fraction received by circulating blood cells undergoing sequential TBI over six fractions is shown in (a). The error bars represent the standard deviation. Maximum and minimum dose for each perfusion period is also shown. In (b), the EUD is shown to be virtually unaffected by circulation using the fractionated protocol.
The total dose received by individual blood voxels is shown, with varying levels of random circulatory dispersion introduced via the “dispersion scale.” Figures (a), (b), and (c) show the dose distributions for dispersion scales of 1, 5, and 20. In (d), the EUD is displayed and demonstrates that under most clinically relevant conditions, it remains within 10% of the prescribed dose.
The statistical distribution of doses received by blood cells is shown for 10, 20, and 30 min treatment times. A uniform tomotherapy treatment delivery was modeled by setting the FFV to 0.05. A binomial probability distribution was used to predict the total dose received by individual blood cells. The EUD and mean dose are reported and remain within 10% of the prescription dose (2.0 Gy) for all treatment times studied.
The statistical distribution of blood cells is shown for a nonuniform tomotherapy delivery model. In this model, the full dose FFV is 0.05 and the reduced dose FFV is 0.01. Organ-sparing dose levels of 1.5 and 1.0 Gy were modeled. The mean dose to all blood voxels is reduced, as expected, to 1.91 and 1.83 Gy for the 1.5 and 1.0 reduced dose levels, respectively. The corresponding EUDs are 1.86 and 1.78 Gy.
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