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Evaluation of daily online set-up errors and organ displacement uncertainty during conformal radiation treatment of the prostate

¹ Department of Medical Physics, Grand River Regional Cancer Center, 835 King Street West, Kitchener, ² Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, ³ Radiation Treatment Program, Grand River Regional Cancer Center, 835 King Street West, Kitchener, Ontario, Canada

View larger version (27K): [in this window] [in a new window]   Figure 1. Distribution of gold seed marker displacement relative to the isocentre over the entire study for all 118 patients.(a) Anteroposterior: anterior ("–"), posterior ("+") direction. (b) Left-right: left ("–"), right ("+") direction. (c) Superoinferior: superior ("–"), inferior ("+") direction.

View larger version (17K): [in this window] [in a new window]   Figure 2. Cumulative frequency distribution of seed marker displacement relative to the isocentre for 118 patients in the anterior, posterior, left, right, superior and inferior directions.

View larger version (15K): [in this window] [in a new window]   Figure 3. Scatter plot of the individual patient systematic error as a function of the random error for the seed marker displacement relative to the isocentre for 118 patients. The seed marker systematic error for a patient was calculated by averaging all of the seed marker displacements over all fractions, and the standard deviations are the random errors.(a) Anterior ("–")/posterior ("+") direction, Pearson correlation coefficient, r = –0.22. (b) Left ("–")/right ("+") direction, Pearson correlation coefficient, r = 0.05. (c) Superior ("–")/inferior ("+") direction, Pearson correlation coefficient, r = 0.05.

View larger version (19K): [in this window] [in a new window]   Figure 4. Cumulative frequency distribution of the set-up error for 20 selected patients in the anterior, posterior, left, right, superior, and inferior directions. The isocentre set-up error is the bony anatomy mismatch between the simulated digitally reconstructed radiograph and the daily electronic portal image.

View larger version (20K): [in this window] [in a new window]   Figure 5. Cumulative frequency distribution of prostate displacement relative to the pelvis for the 20 selected patients in the anterior, posterior, left, right, superior, and inferior directions.

View larger version (15K): [in this window] [in a new window]   Figure 6. Scatter plots of bony landmarkvs seed marker displacement. All displacements are relative to the isocentre. (a) Anterior ("–")/posterior ("+") direction, Pearson correlation coefficient, r = 0.78. (b) Left ("–")/right ("+") direction, Pearson correlation coefficient, r = 0.83. (c) Superior ("–")/inferior ("+") direction, Pearson correlation coefficient, r = 0.59. (d) The systematic displacement in the anteroposterior (AP), left-right (L-R) and superoinferior (SI) directions; r = 0.87, 0.76 and 0.60 in AP, L-R and SI directions, respectively. (e) The random errors in the AP, L-R and SI directions; r = 0.83, 0.92 and 0.55 in AP, LR and SI directions, respectively.

View larger version (16K): [in this window] [in a new window]   Figure 7. The systematic isocentre set-up error and prostate displacement for the 20 selected patients in the anteroposterior, left-right and superoinferior directions. The error bars indicate one standard deviation (1 SD). (a) Anterior ("–")/posterior ("+") direction. (b) Left ("–")/right ("+") direction. (c) Superior ("–")/inferior ("+") direction.

View larger version (17K): [in this window] [in a new window]   Figure 8. A comparison of the cumulative frequency distribution for set-up errors and prostate displacement in 20 selected patients. (a) Anteroposterior directions; (b) left and right directions; and (c) superoinferior directions.

View larger version (17K): [in this window] [in a new window]   Figure 9. Scatter plots of prostate displacement relative to pelvisvs bone anatomy displacement relative to the isocentre. (a) Anterior ("–")/posterior ("+") direction, Pearson correlation coefficient, r = –0.03. (b) Left ("–")/right ("+") direction, Pearson correlation coefficient, r = –0.16. (c) Superior ("–")/inferior ("+") direction, Pearson correlation coefficient, r = –0.27. (d) The systematic displacement in the anteroposterior (AP), left-right (L-R) and superoinferior (SI) directions; r = 0.15, –0.12 and –0.34 in the AP, L-R and SI directions, respectively. (e) The random error in the AP, LR and SI directions; r = 0.38, 0.35 and 0.31 in the AP, L-R and SI directions, respectively.

View larger version (24K): [in this window] [in a new window]   Figure 10. Prostate displacement(corrected for set-up errors) and set-up errors over the entire course of treatment for three randomly selected patients in the anteroposterior (AP), left-right (L-R) and superoinferior (SI) directions.