SU-E-J-34: Influence of Prone versus Supine Patient Position on Localization with Image Guided Radiotherapy of Prostate Cancer

Medical Physics
N ShethC Yang

Abstract

To retrospectively assess the influence of prone versus supine patient position on setup shifts and target margins for image guided radiotherapy (IGRT) of prostate cancer. Ninety prostate cancer patients were treated at our institution between September 2006 and June2011 with IGRT utilizing daily megavoltage cone beam; 52 patients were prone receiving 1577 fractions and 38 supine receiving 1035 fractions. Patients were setup to skin tattoos, imaged with megavoltage cone beam, then moved to treatment position by the alignment of three intraprostatic fiducials with lateral, longitudinal, and vertical shifts. The magnitude of the daily shift is root sum of squares of the translations. Patients positioned prone had a mean daily shift magnitude 1.4 mm greater than supine: 7.5 ± 4.0 mm vs. 6.1 ± 2.9 mm (p ≪ 0.001). The mean magnitude of the daily shift for prone vs. supine respectively were 3.7 ± 3.1 mm vs. 2.6 ± 2.3 mm laterally, 3.5 ± 3.0 mm vs. 3.3 ± 2.6 mm longitudinally, and 3.9 ± 3.5 mm vs. 3.1 ± 2.4 mm vertically. The percentage of daily shifts within our intuition's planning target volume (PTV) margin (7 mm posterior and 10 mm for all other directions) for prone vs. supine respectively were 97.3% vs. 99.5% laterally, 97.1%...Continue Reading

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