Sequential evaluation of prostate edema after permanent seed prostate brachytherapy using CT-MRI fusion.
OBJECTIVE
To analyze the extent and time course of prostate edema and its effect on dosimetry after permanent seed prostate brachytherapy.


METHODS
Twenty patients scheduled for permanent seed (125)I prostate brachytherapy agreed to a prospective study on postimplant edema. Implants were preplanned using transrectal ultrasonography. Postimplant dosimetry was calculated using computed tomography-magnetic resonance imaging (CT-MRI) fusion on the day of the implant (Day 1) and Days 8 and 30. The prostate was contoured on MRI, and the seeds were located on CT. Factors investigated for an influence on edema were the number of seeds and needles, preimplant prostate volume, transitional zone index (transition zone volume divided by prostate volume), age, and prostate-specific antigen level. Prostate dosimetry was evaluated by the percentage of the prostate volume receiving 100% of the prescribed dose (V(100)) and percentage of prescribed dose received by 90% of the prostate volume (D(90)).


RESULTS
Prostate edema was maximal on Day 1, with the median prostate volume 31% greater than preimplant transrectal ultrasound volume (range, 0.93-1.72; p < 0.001) and decreased with time. It was 21% greater than baseline at Day 8 (p = 0.013) and 5% greater on Day 30 (p < 0.001). Three patients still had a prostate volume greater than baseline by Day 30. The extent of edema depended on the transition zone volume (p = 0.016) and the preplan prostate volume (p = 0.003). The median V(100) on Day 1 was 93.6% (range, 86.0-98.2%) and was 96.3% (range, 85.7-99.5%) on Day 30 (p = 0.079). Patients with a Day 1 V(100) >93% were less affected by edema resolution, showing a median increase in V(100) of 0.67% on Day 30 compared with 2.77% for patients with a V(100) <93 % on Day 1.


CONCLUSIONS
Despite the extreme range of postimplant edema, the effect on dosimetry was less than expected. Dose coverage of the prostate was good for all patients during Days 1-30. Our data indicate that postimplant dosimetry on the day of implant is sufficient for patients with good dose coverage (Day 1 V(100) >93%).
Department of Radiation Oncology, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada.
Daniel
D
Taussky
Lyn
L
Austen
Ants
A
Toi
Ivan
I
Yeung
Theresa
T
Williams
Shannon
S
Pearson
Michael
M
McLean
Gregory
G
Pond
Juanita
J
Crook
D000368:Aged; D001918:Brachytherapy / Q000009:adverse effects* / Q000295:instrumentation; D004487:Edema / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology; D006207:Half-Life; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011467:Prostate / Q000473:pathology; D011469:Prostatic Diseases / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed