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Clinical Trial
. 2010 Jun 10:5:52.
doi: 10.1186/1748-717X-5-52.

Planning target volume margins for prostate radiotherapy using daily electronic portal imaging and implanted fiducial markers

David Skarsgard  1 , Pat Cadman, Ali El-Gayed, Robert Pearcey, Patricia Tai, Nadeem Pervez, Jackson Wu
Affiliations
Clinical Trial

Planning target volume margins for prostate radiotherapy using daily electronic portal imaging and implanted fiducial markers

David Skarsgard et al. Radiat Oncol. .

Abstract

Background: Fiducial markers and daily electronic portal imaging (EPI) can reduce the risk of geographic miss in prostate cancer radiotherapy. The purpose of this study was to estimate CTV to PTV margin requirements, without and with the use of this image guidance strategy.

Methods: 46 patients underwent placement of 3 radio-opaque fiducial markers prior to prostate RT. Daily pre-treatment EPIs were taken, and isocenter placement errors were corrected if they were > or = 3 mm along the left-right or superior-inferior axes, and/or > or = 2 mm along the anterior-posterior axis. During-treatment EPIs were then obtained to estimate intra-fraction motion.

Results: Without image guidance, margins of 0.57 cm, 0.79 cm and 0.77 cm, along the left-right, superior-inferior and anterior-posterior axes respectively, are required to give 95% probability of complete CTV coverage each day. With the above image guidance strategy, these margins can be reduced to 0.36 cm, 0.37 cm and 0.37 cm respectively. Correction of all isocenter placement errors, regardless of size, would permit minimal additional reduction in margins.

Conclusions: Image guidance, using implanted fiducial markers and daily EPI, permits the use of narrower PTV margins without compromising coverage of the target, in the radiotherapy of prostate cancer.

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Figures

Figure1
Figure1
Isocenter placement errors (in cm) relative to DRR on pre-treatment EPIs (gray circles; n = 736 fractions), along a): S-I and A-P axes, and b): S-I and L-R axes. Ellipse shows 95% confidence intervals for CTV coverage in each direction.
Figure 2
Figure 2
Isocenter placement errors (in cm) relative to DRR on during-treatment EPIs (gray circles; n = 530 fractions), along a): S-I and A-P axes, and b): S-I and L-R axes. Outer box shows PTV margins used in the study; inner ellipse shows 95% confidence intervals for CTV coverage in each direction.
Figure 3
Figure 3
Isocenter placement errors (in cm) on during-treatment EPIs (gray circles; n = 530 fractions), relative to the expected pre-treatment isocenter position, along a): S-I and A-P axes, and b): S-I and L-R axes. Ellipse shows 95% confidence intervals for CTV coverage in each direction.
See this image and copyright information in PMC

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