Title

SU‐E‐T‐691: On the Use of Multiple Beam Angles to Minimize the Impact of High Density Fiducial Markers in the Prostate Proton Radiotherapy

Document Type

Conference Proceeding

Publication Date

1-1-2011

Journal

Medical Physics

Volume

38

Issue

6

DOI

10.1118/1.3612653

Abstract

Purpose: Fiducial markers are commonly used in prostate radiotherapy to improve accuracy of target localization. However, in proton therapy, since the proton range is sensitive to the material it travels through, under‐dose to the prostate has been reported in conventional passive scattering treatment and 3D‐modulation based intensity modulated proton therapy (IMPT), in the presence of high density fiducial markers inside the prostate. This study investigated the ability of using multiple beam angles to minimize the dosimetric impact of fiducial markers in 3D‐modulation and distal edge tracking (DET) based IMPT. Methods: CT images of a typical prostate patient with three gold markers (3mm by 1mm, density = 19.3 g/cc) were used in this study. 2‐field lateral and 4‐field box type 3D‐modulation proton treatment plans as well as DET plans with evenly spaced 18, 10, and 6 beam angles were generated to deliver 70Gy to 95% of the PTV. Geant4 Monte Carlo code was used for dose calculation. The plan was performed on images with fiducial markers artificially removed. Then the delivered dose distribution was calculated with fiducial markers present in the patient. The dose distributions between the planed and delivered were then compared to evaluate the efficacy of using multiple beam angles to minimize the dosimetric deviations. The tumor control probability (TCP) was also used to quantify the dose variation. Results: The preliminary result shows all the 3D‐modulation and DET plans yielded equivalent PTV coverage. The planned and delivered D98% of prostate was 68.68Gy vs. 68.32Gy in 18‐field DET, 67.83Gy vs. 65.53Gy in 10‐field DET, and 67.82Gy vs. 58.19Gy in 2‐field 3D‐Modulation. No significant dose change to rectum and bladder was observed. Conclusions: With high density fiducial markers present in the target, multiple beam angles are recommended in proton treatment plans to avoid significant under‐dose to the target. © 2011, American Association of Physicists in Medicine. All rights reserved.

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