Proton therapy for prostate cancer treatment employing online image guidance and an action level threshold.
OBJECTIVE
The ability to determine the accuracy of the final prostate position within a determined action level threshold for image-guided proton therapy is unclear.


METHODS
Three thousand one hundred ten images for 20 consecutive patients treated in 1 of our 3 proton prostate protocols from February to May of 2007 were analyzed. Daily kV images and patient repositioning were performed employing an action-level threshold (ALT) of > or = 2.5 mm for each beam. Isocentric orthogonal x-rays were obtained, and prostate position was defined via 3 gold markers for each patient in the 3 axes.


RESULTS
To achieve and confirm our action level threshold, an average of 2 x-rays sets (median 2; range, 0-4) was taken daily for each patient. Based on our ALT, we made no corrections in 8.7% (range, 0%-54%), 1 correction in 82% (41%-98%), and 2 to 3 corrections in 9% (0-27%). No patient needed 4 or more corrections. All patients were treated with a confirmed error of < 2.5 mm for every beam delivered. After all corrections, the mean and standard deviations were: anterior-posterior (z): 0.003 +/- 0.094 cm; superior-inferior (y): 0.028 +/- 0.073 cm; and right-left (x) -0.013 +/- 0.08 cm.


CONCLUSIONS
It is feasible to limit all final prostate positions to less than 2.5 mm employing an action level image-guided radiation therapy (IGRT) process. The residual errors after corrections were very small.
Vargas
Carlos
C
University of Florida Proton Therapy Institute, Jacksonville, FL 32206, USA. c2002@ufl.edu
Falchook
Aaron
A
Indelicato
Daniel
D
Yeung
Anamaria
A
Henderson
Randall
R
Olivier
Kenneth
K
Keole
Sameer
S
Williams
Christopher
C
Li
Zuofeng
Z
Palta
Jatinder
J
D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009367:Neoplasm Staging; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy