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Abstract
We use a rectal balloon for prostate immobilization during intensity modulated radiotherapy (IMRT) prostate treatment. To improve the accuracy of our prostate planning target volume, we have measured prostate displacements using computed tomography (CT)‐CT fusion on patients that previously received gold seed implants. The study consists of ten patients that were scanned twice per week during the course of IMRT treatment. In addition to biweekly scans, breathing studies were performed on each patient to estimate organ motion during treatment. The prostate displacement in the anterior‐posterior and the lateral direction is minimal, on the order of measurement uncertainty (~1mm). The standard deviation of the superior‐inferior (SI) displacements is 1.78 mm. The breathing studies show that no organ displacement was detected during normal breathing conditions with a rectal balloon.PACS number(s): 87.53.–j, 87.90.+y
Highlights
The goal of intensity modulated radiotherapyIMRTis to minimize the dose to normal tissue surrounding the clinical target volumeCTV
We present prostate displacement measurements associated with a rectal balloon to identify immobilization uncertainties expected for our IMRT treatment setup
The largest prostate displacements were observed in the superior-inferiorSIdirection
Summary
The goal of intensity modulated radiotherapyIMRTis to minimize the dose to normal tissue surrounding the clinical target volumeCTV. The planning target volumePTVis defined to include the CTV and associated treatment uncertainties, which include, but are not limited to imaging, patient setup and organ motion. Radioopaque markers, gold seeds, computed tomographyCT-CT fusion, and CT chamfer matching are examples of methods used to determine the prostate position relative to fixed bony landmarks. Within these studies, the largest motion was observed to be in the anterior-posteriorAPdirection and to a lesser extent in the superior-inferiorSIdirection. Values of A/P shifts range fromϪ0.9-mm mean, 1.7-mm standard deviationtoϪ5.4-mm mean, 6.2-mm standard deviation. The range in S/I shifts wereϪ0.2-mm mean, 3.2-mm standard deviationtoϪ5.9-mm mean, 5.0-mm standard deviation. In the case of patients treated in the prone position, the bladder effect was correlated with both AP and SI movement. A current summary of setup errors and organ motion results is found in Antolak et al.
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