Abstract
BackgroundTo determine prostate displacement during extreme hypofractionated volume modulated arc radiotherapy (VMAT) using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers.MethodsA total of 150 image pairs were obtained from 30 patients who underwent extreme hypofractionated radiotherapy to a dose of 40 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal x-rays before and after treatment and were used to determine intra-fraction prostate displacement.ResultsThe mean prostate displacements were 0.03 ± 1.23 mm (1SD), 0.18 ± 1.55 mm, and 0.37 ± 1.95 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively. The mean 3D displacement was 2.32 ± 1.55 mm. Only 6 (4%) fractions had a 3D displacement of >5 mm. The average time of treatment delivery for a given fraction was 195 ± 59 seconds.ConclusionsThe mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy delivered via VMAT, continues to be small. Clinical margins typically used in a similar fixed-angle IMRT treatment are adequate. The use of VMAT in further extreme hypofractionation may limit prostatic motion uncertainties that would be otherwise be associated with longer treatment times.
Highlights
To determine prostate displacement during extreme hypofractionated volume modulated arc radiotherapy (VMAT) using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers
The mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy delivered via VMAT, continues to be small
The use of VMAT in further extreme hypofractionation may limit prostatic motion uncertainties that would be otherwise be associated with longer treatment times
Summary
To determine prostate displacement during extreme hypofractionated volume modulated arc radiotherapy (VMAT) using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers. Randomized trials have shown that higher doses of radiotherapy (RT) result in improved biochemical disease free survival, but at the potential cost of increased rectal and urinary toxicity when using traditional 3-dimensional conformal RT (3DCRT) techniques [2,3]. RT techniques such as intensity-modulated radiotherapy (IMRT) have been shown to be able to deliver these increased doses with less toxicity as compared to 3DCRT [3]. As with any radiotherapy treatment, motion, both intra and inter-fraction is a source of uncertainty. Because of this uncertainty, a margin is added to the clinical target volume (CTV) in creating the planning target volume (PTV). Smaller margins may reduce normal tissue toxicity but at the cost of an increased risk of geographical miss [5], while larger margins may maximize tumor control but at the cost of higher normal tissue complications
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