A strategy to correct for intrafraction target translation in conformal prostate radiotherapy: Simulation results
Flow diagram of the treatment scenarios investigated in this study. The treatment-beam aperture and monitor units were continuously updated based on the information from a patient-positioning system. For the purposes of the study, the internal motion shift was assumed to be constant throughout the treatment—a worst case scenario from a dosimetric point of view. The required information for the geometric and dosimetric correction, not generally available at treatment, is the target position with time and the planning target volume from planning.
Representative CT slices and beam view demonstrating the beam alignment (a) at the time of simulation and (b) at the time of treatment in the presence of posterior/left internal motion. The target at the time of simulation is blue, and at the time of treatment is yellow. In (b), the original blue target is overlaid to demonstrate the magnitude of the change in internal position.
Isodose curves for a representative patient (a) without internal motion of the target and (b) with a simulated lateroposterior internal motion internal shift. The target is shaded blue in both cases, with the white outline showing the position of the target in the opposite figure for comparison. Note the shift of the PTV and isodose lines with respect to the bony anatomy in the two figures.
Dose-volume histograms (DVHs) after motion correction for a representative patient showing 36 sampled internal motion shifts of vector lengths (a) , (b) , (c) , and (d) . Each sample is represented by a dashed line. The solid lines are the DVH curves in the absence of internal motion.
Average dose-volume histogram (DVH) changes relative to the prescription dose (Rx) of after motion correction for (a) the planning target volume (PTV), (b) rectum, (c) periprostatic rectum, (d) bladder, and (e) right femoral head. Error . volume-dose relative change ( of volume of region of interest). change of mean dose. target volume.
Dose-volume histogram changes by magnitude of internal motion corrected by dynamic compensation. Number of patients: 25. Isotropic internal motion samples per offset: 36. Total number of internal motion samples (4 offsets): 3600. The prescription dose (Rx) is .
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