Geometric and dosimetric evaluations of an online image-guidance strategy for 3D-CRT of prostate cancer

Qiuwen Wu, Giovanni Ivaldi, Jian Liang, David Lockman, Di Yan, Alvaro Martinez

Research output: Contribution to journalArticlepeer-review


Purpose: To evaluate an online image-guidance strategy for conformal treatment of prostate cancer and to estimate margin-reduction benefits. Methods and Materials: Twenty-eight patients with at least 16 helical computed tomography scans were each used in this study. Two prostate soft-tissue registration methods, including sagittal rotation, were evaluated. Setup errors and rigid organ motion were corrected online; non-rigid and intrafraction motion were included in offline analysis. Various clinical target volume-planning target volume (CTV-PTV) margins were applied. Geometrical evaluations included analyses of isocenter shifts and rotations and overlap index. Dosimetric evaluations included minimum dose and equivalent uniform dose (EUD) for prostate and gEUD for rectum. Results: Average isocenter shift and rotation were (dX,dY,dZ,θ) = (0.0 ± 0.7,-1.1 ± 4.0,-0.1 ± 2.5,0.7°± 2.0°) mm. Prostate motion in anterior-posterior (AP) direction was significantly higher than superior-inferior and left-right (LR) directions. This observation was confirmed by isocenter shift in perspectives AP (1.8 ± 1.8 mm) and RL (3.7 ± 3.0 mm). Organ motion degrades target coverage and reduces doses to rectum. If 2% dose reduction on prostate D99 is allowed for 90% patients, then minimum 3 mm margins are necessary with ideal image registration. Conclusions: Significant margin reduction can be achieved through online image guidance. Certain margins are still required for nonrigid and intrafraction motion. To further reduce margin, a strategy that combines online geometric intervention and offline dose replanning is necessary.

Original languageEnglish
Pages (from-to)1596-1609
Number of pages14
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number5
Publication statusPublished - Apr 1 2006


  • 3D conformal radiation therapy
  • Image registration
  • Image-guided radiation therapy
  • Margins
  • Prostate cancer

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation


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