Time course of prostatic edema post permanent seed implant determined by magnetic resonance imaging.
OBJECTIVE
To quantify the time course of postimplant prostatic edema magnitude and spatial isotropy using serial magnetic resonance imaging (MRI).


METHODS
Forty patients with histologic diagnosis of prostate cancer received an iodine-125 seed implant (Day 0) and consented to 1.5-T MRI on Days -1, 0, 14, and 28. Seeds of strength 0.39mCi were placed in a modified peripheral loading pattern to deliver 145Gy to the target volume. MR images consisted of 3-4mm thick axial slices with no gap. The image sets were anonymized and randomized to minimize contouring bias, then contoured by a single radiation oncologist. Contours were reoriented about their center of mass to align the prostate long axis with the superior-inferior (S-I) direction; prostate volumes and dimensions in the left-right (L-R), anterior-posterior (A-P), and S-I directions through the center of mass were calculated.


RESULTS
The average relative edema volume was 1.18±0.14 (1standard deviation) on Day 0 and 1.01±0.15 on Day 30. Between Days 0 and 30, the edema resolved linearly with time on average. Average relative edema dimensions on Day 0 in the L-R, A-P, and S-I directions were 1.01±0.07, 1.11±0.09, and 1.08±0.13, respectively.


CONCLUSIONS
As measured using MRI, the average edema magnitude for our study population was ∼20% on Day 0 and resolved linearly with time to ∼0% on Day 30. The edema exhibited spatial anisotropy, the prostate expanding on Day 0 by ∼10% in each of the A-P and S-I directions and by ∼0% in the L-R direction.
Sloboda
Ron S
RS
Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada. ron.sloboda@cancerboard.ab.ca
Usmani
Nawaid
N
Pedersen
John
J
Murtha
Albert
A
Pervez
Nadeem
N
Yee
Don
D
D000368:Aged; D001918:Brachytherapy / Q000009:adverse effects* / Q000379:methods; D004487:Edema / Q000209:etiology* / Q000473:pathology; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011467:Prostate / Q000473:pathology / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology* / Q000473:pathology; D011879:Radiotherapy Dosage; D013997:Time Factors
D007457:Iodine Radioisotopes