Prostate volume determination: differential volume measurements comparing CT and TRUS.
OBJECTIVE
To compare the differences in prostate volume assessed by computerized tomography (CT), step-section transrectal ultrasound (TRUS-step), and TRUS with ellipsoid-formula volume calculation (TRUS-ellipsoid).


METHODS
Thirty-one patients with localized prostate cancer treated with combined external conformal radiotherapy and high dose rate brachytherapy, who had prostate volumes evaluated using CT, TRUS-step and TRUS-ellipsoid according to our clinical routine for dose planning. The measurements were collected retrospectively based on actual dose-plans.


RESULTS
The prostate volume was on average 34 cc (range 18-60 cc) according to CT, 28 cc (range 12-57 cc) and 24 cc (range 13-44 cc) according to TRUS-step and TRUS-ellipsoid, respectively. The differences between the lengths measured were most pronounced with a mean length of 4.5 cm (range 3.0-6.0 cm) defined by CT as compared to 3.6 cm (range 3.0-5.0 cm) and 3.6 cm (range 2.8-5.0 cm) when defined by TRUS-step and TRUS-ellipsoid, respectively.


CONCLUSIONS
CT defined volumes are 30% larger than volumes defined with TRUS-step. This is probably due to uncertainty in defining the apex of the prostate and thereby the length of the prostate using CT. When defining target in radiotherapy, it is important to be aware of the differences in volumes depending on the technique used.
Kälkner
Karl Mikael
KM
Department of Oncology, Radiumhemmet, Karolinska University Hospital, Stockholm, Sweden. karl.kalkner@karolinska.se
Kubicek
Gregory
G
Nilsson
Josef
J
Lundell
Marie
M
Levitt
Seymour
S
Nilsson
Sten
S
D006801:Humans; D008297:Male; D009929:Organ Size; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography / Q000379:methods*