Dosimetric evaluation of prostate rotations and their correction by couch rotations.
OBJECTIVE
To investigate the dosimetric effect of prostate rotations and limited on-line corrections by couch rotations (<or=3 degrees ) for prostate, seminal vesicles and organs at risk.


METHODS
For 5 patients IMRT plans were made, treating the prostate plus base of the seminal vesicles. Realistic and idealised dose distributions were considered, the latter demonstrating extreme effects for rotations and their corrections. Translation errors were assumed to be corrected on-line. For each patient 20 treatments with different rotation errors were simulated: 20 systematic errors were generated and 20 times 35 random deviations were superimposed to simulate day-to-day variations. Using a research module of PLATO-RTS treatments with rotation errors, with and without on-line corrections, were simulated.


RESULTS
The largest dosimetric effect of rotation errors and corrections was found for the seminal vesicles with idealised dose distribution: coverage improved from 92.6% (range 89.9-96.0%) to 95.9% (94.7-98.1%). The gain for the idealised prostate was less: 95.9% (94.4-97.0%) to 97.5% (95.5-98.4%). For the femoral heads the dose increase could be as large as 12.2% (6.2-19.3%).


CONCLUSIONS
On-line correction of rotations can improve target coverage slightly. For organs at risk at a large distance from the isocentre the result can be a significant increase in dose.
van Herten
Yvonne R J
YR
Department of Radiation Oncology, University of Amsterdam, The Netherlands. Y.R.vanHerten@amc.uva.nl
van de Kamer
Jeroen B
JB
van Wieringen
Niek
N
Pieters
Bradley R
BR
Bel
Arjan
A
D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012399:Rotation; D012669:Seminal Vesicles / Q000528:radiation effects; D014057:Tomography, X-Ray Computed