PROSTATE INTRAFRACTION MOTION ASSESSED BY SIMULTANEOUS KILOVOLTAGE FLUOROSCOPY AT MEGAVOLTAGE DELIVERY I CLINICAL OBSERVATIONS AND PATTERN ANALYSIS

Purpose To describe prostate intrafraction motion using kilovoltage fluoroscopy at treatment delivery for a hypo fractionated radiotherapy protocol Methods and Materials Kilovoltage images were acquired during treatment delivery, as well as pre and posttreatment cone-beam computed tomography (CBCT) for each fraction of 30 patients, totaling 571 fractions for analysis We calculated population statistics, evaluated correlation between interfraction and intrafraction motion, evaluated effect of treatment duration, classified whether motion resolved by posttreatment CBCT, and compared motion magnitude on a per patient basis Results The elapsed time between pre- and post-CBCTs was (18 6 +/- 4 5) mm The population mean of motion measured by kilovoltage fluoroscopy was (-0 1, 0 5, 0 6) mm, the systematic was (0 5, 1 3, 1 2) mm, and random was (0 9, 1 9, 2 0) mm in the right left, anterior posterior, and superior inferior axes, respectively The probability of motion Increased with treatment duration, with the mean increasing to (0 0, 1 0, 0 9) mm and the systematic to (0 6, 1 7,1 5) mm when measured using posttreatment CBCT For any motion >= 2mm, approximately 75% did not resolve by posttreatment CBCT Motion magnitude varied considerably among patients, with the probability of a 5 mm displacement ranging from 0 0% to 58 8% Conclusions Time dependency of intrafraction motion should be considered to avoid bias in margin assessment, with posttreatment CBCT slightly exaggerating the true motion The patient specific nature of the intrafraction motion suggests that a patient specific management approach may be beneficial (C) 2010 Elsevier Inc