Effect of post-implant edema on prostate brachytherapy treatment margins.
OBJECTIVE
To determine if postimplant prostate brachytherapy treatment margins calculated on Day 0 differ substantially from those calculated on Day 30.


METHODS
Thirty patients with 1997 American Joint Commission on Cancer clinical stage T1-T2 prostatic carcinoma underwent prostate brachytherapy with I-125 prescribed to 144 Gy. Treatment planning methods included using loose seeds in a modified peripheral loading pattern and treatment margins (TMs) of 5-8 mm. Postimplant plain radiographs, computed tomography scans, and magnetic resonance scans were obtained 1-4 hours after implantation (Day 0). A second set of imaging studies was obtained at 30 days after implantation (Day 30) and similarly analyzed. Treatment margins were measured as the radial distance in millimeters from the prostate edge to the 100% isodose line. The TMs were measured and tabulated at 90 degrees intervals around the prostate periphery at 0.6-cm intervals. Each direction was averaged to obtain the mean anterior, posterior, left, and right margins.


RESULTS
The mean overall TM increased from 2.6 mm (+/-2.3) on Day 0 to 3.5 mm (+/-2.4) on Day 30. The mean anterior margin increased from 1.2 mm on Day 0 to 1.8 mm on Day 30. The posterior margin increased from 1.2 mm on Day 0 to 2.8 mm on Day 30. The lateral treatment margins increased most over time, with mean right treatment margin increasing from 3.9 mm on Day 0 to 4.7 mm on Day 30.


CONCLUSIONS
Treatment margins appear to be durable in the postimplant period, with a clinically insignificant increase from Day 0 to Day 30.
Reed
Daniel R
DR
Radiation Oncology, Arizona Oncology Services, Phoenix, AZ 85260, USA.
Wallner
Kent
K
Ford
Eric
E
Mueller
Amy
A
Merrick
Gregory
G
Maki
Jeffrey
J
Sutlief
Steven
S
Butler
Wayne
W
D001918:Brachytherapy / Q000009:adverse effects*; D004487:Edema / Q000209:etiology / Q000473:pathology*; D006801:Humans; D008297:Male; D011467:Prostate / Q000473:pathology; D011469:Prostatic Diseases / Q000209:etiology / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage