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SU‐G‐JeP4‐10: Measurement of Prostate Motion Trajectories During Prostate SBRT Boost Treatments with a Rectafix
Author(s) -
Legge K,
Nguyen D,
Ng J,
Wilton L,
Booth J,
Keall P,
Martin J,
O'Connor D J,
Greer P
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957120
Subject(s) - fiducial marker , truebeam , prostate , medicine , nuclear medicine , prostate cancer , linear particle accelerator , radiology , physics , beam (structure) , cancer , optics
Purpose: To determine prostate motion during SBRT boost treatments with a Rectafix rectal sparing device in place using kV imaging during treatment. Methods: Patients each had three gold fiducial markers inserted into the prostate and received two VMAT boost fractions of 9.5–10 Gy under the PROMETHEUS clinical trial protocol with a Rectafix rectal retractor in place. Two‐dimensional kilovoltage images of fiducial markers were acquired continuously during delivery. Three patients were treated on a Varian Clinac iX linear accelerator (6X, 600 MU/min), where kV images were acquired at 5 Hz during treatment. Seven patients were treated on a Varian Truebeam linear accelerator (10XFFF, 2400 MU/min) where kV images were acquired every 3 seconds. Images were processed off‐line using the Kilovoltage Intrafraction Monitoring (KIM) software after treatment. KIM determines prostate position in three dimensions from 2D kV projections using a probability density model and a pre‐treatment kV arc. The 3D displacement of the prostate was quantified as a function of time throughout each fraction. Results: From all fractions analyzed, it was found that the prostate had moved less than 1 mm in any direction from its initial position 84.6% of the time. The prostate was between 1 and 2 mm from its initial position 14.2% of the time, between 2 and 3 mm of its initial position 0.8% of the time and was greater than 3 mm from its initial position only 0.4% of the time. Conclusion: The amount of prostate motion observed during prostate SBRT boost treatments with a Rectafix device in place was minimal and lower than that observed in non‐Rectafix studies. The Rectafix device reduces rectal dose as well as immobilizing the prostate. Kimberley Legge is the recipient of an Australian Postgraduate Award.