Article

Proton therapy for prostate cancer treatment employing online image guidance and an action level threshold.

University of Florida Proton Therapy Institute, Jacksonville, FL 32206, USA.
American journal of clinical oncology (Impact Factor: 2.21). 03/2009; 32(2):180-6. DOI: 10.1097/COC.0b013e3181841f13
Source: PubMed

ABSTRACT The ability to determine the accuracy of the final prostate position within a determined action level threshold for image-guided proton therapy is unclear.
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.
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.
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.

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