Intrafraction Motion of the Prostate During External-Beam Radiation Therapy: Analysis of 427 Patients with Implanted Fiducial Markers
- Department of Radiotherapy, University Medical Center, Utrecht (Netherlands)
Purpose: To analyze the intrafraction motion of the prostate during external-beam radiation therapy of patients with prostate cancer. Methods and Materials: Between August 2001-December 2005, 427 patients with Stage T3Nx/0Mx/0 prostate carcinoma received intensity-modulated radiation therapy treatment combined with position verification with fiducial gold markers. For a total of 11,426 treatment fractions (average, 27 per patient), portal images were taken of the first segment of all five beams. The irradiation time of the technique varied between 5-7 min. From these data, the location of gold markers could be established within every treatment beam under the assumption of minimal marker movement. Results: In 66% of treatment fractions, a motion outside a range of 2 mm was observed, with 28% outside a range of 3 mm. The intrafraction marker movements showed that motion directions were often reversed. However, the effect was small. Even with perfect online position-correction at the start of irradiation, intrafraction motion caused position uncertainty, but systematic errors ({sigma}) were limited to <0.6 mm, and random errors ({sigma}) to <0.9 mm. This would result in a lower limit of 2 mm for margins, in the absence of any other uncertainties. Conclusions: Intrafraction motion of the prostate occurs frequently during external-beam irradiation on a time scale of 5-7 min. Margins of 2 mm account for these intrafraction motions. However, larger margins are required in practice to accommodate other uncertainties in the treatment.
- OSTI ID:
- 21036243
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 69, Issue 2; Other Information: DOI: 10.1016/j.ijrobp.2007.03.029; PII: S0360-3016(07)00511-1; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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