Dosimetric impact of prostate volume change between CT-based HDR brachytherapy fractions.
OBJECTIVE
The objective is to evaluate the prostate volume change and its dosimetric consequences after the insertion of catheters for high-dose-rate brachytherapy.


METHODS
For 13 consecutive patients, a spiral CT scan was acquired before each of the 2 fractions, separated on average by 20 hours. The coordinates of the catheters were obtained on 3 axial CT slices corresponding to apex, mid portion, and base portion of the prostate. A mathematical expansion model was used to evaluate the change of prostate volumes between the 2 fractions. It is based on the difference in the cube of the average distance between the centroid and catheter positions. The variation of implant dose-volume histograms between fractions was computed for plans produced by either inverse planning based on simulated annealing or geometric optimization.


RESULTS
The average magnitude of either increase or reduction in prostate volume was 7.8% (range, 2-17%). This volume change corresponds to an average prostate radius change of only 2.5% (range, 0.7-5.4%). For 5 patients, the prostate volume increased on average by 9% (range, 2-17%), whereas a reduction was observed for 8 patients by an average of 7% (range, 2-13%). More variation was observed at the prostate base than at mid or apex gland. The comparison of implant dose-volume histograms showed a small reduction of V100 receiving the prescription dose, with an average of 3.5% (range, 0.5-12%) and 2.2% (range, 1-6%) for inverse planning based on our simulated annealing and geometric optimization plans, respectively.


CONCLUSIONS
Small volume change was observed between treatment fractions. This translates into small changes in dose delivered to the prostate volume.
Kim
Yongbok
Y
Department of Radiation Oncology, Comprehensive Cancer Center, University of California-San Francisco, 1600 Divisadero Street, Suite H-1031, San Francisco, CA 94143-1708, USA. kim@radionc17.ucsf.edu
Hsu
I-Chow
IC
Lessard
Etienne
E
Vujic
Jasmina
J
Pouliot
Jean
J
D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009339:Needles / Q000009:adverse effects; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011472:Prostatitis / Q000000981:diagnostic imaging / Q000209:etiology; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed