Dosimetric comparison of four target alignment methods for prostate cancer radiotherapy.
OBJECTIVE
The aim of this study was to compare the dosimetric consequences of 4 treatment delivery techniques for prostate cancer patients treated with intensity-modulated radiotherapy (IMRT).


METHODS
During an 8-week course of radiotherapy, 10 patients underwent computed tomography (CT) scans 3 times per week (243 total) before daily treatment with a CT-linear accelerator. Treatment delivery was simulated by realigning a fixed-margin treatment plan on each CT scan and calculating doses. The alignment methods were those based on the following: skin marks, bony registration, ultrasonography (US), and in-room CT. For the last two methods, prostate was the alignment target. The dosimetric effects of these alignment methods on the prostate, seminal vesicles, rectum, and bladder were compared. The average daily minimum dose to 0.1 cm3 was used as the metric for target coverage.


RESULTS
Skin and bone alignments provided acceptable prostate coverage for only 70% of patients, US alignment for 90%, and CT alignment for 100%. CT-based alignment of the prostate provided seminal vesicle (SV) coverage of > or = 69 Gy for all patients; US and bone alignments provided SV coverage of > or = 60 Gy. This SV coverage may be acceptable for early-stage cancer (equivalent SV dose = 55.8 Gy at 1.8 Gy per fraction), but unacceptable for late-stage cancer (SV dose = 75.6 Gy). At 75.6 Gy, the acceptable rate for SV coverage was 40% for skin and bone alignments, 70% for US, and 80% for CT.


CONCLUSIONS
Direct target alignment methods (US and CT) provided better target coverage. CT-guided alignment provided the best and most consistent dosimetric coverage. A larger planning target volume margin is needed for SV coverage when the alignment target is the prostate.
O'Daniel
Jennifer C
JC
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Dong
Lei
L
Zhang
Lifei
L
de Crevoisier
Renaud
R
Wang
He
H
Lee
Andrew K
AK
Cheung
Rex
R
Tucker
Susan L
SL
Kudchadker
Rajat J
RJ
Bonnen
Mark D
MD
Cox
James D
JD
Mohan
Radhe
R
Kuban
Deborah A
DA
D000465:Algorithms; D006801:Humans; D008297:Male; D009068:Movement; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D001743:Urinary Bladder / Q000000981:diagnostic imaging