Treatment of extraprostatic cancer in clinically organ-confined prostate cancer by permanent interstitial brachytherapy: is extraprostatic seed placement necessary?
OBJECTIVE
Successful treatment with ultrasound-guided transperineal interstitial permanent prostate brachytherapy (TIPPB) relies on effective radiation coverage of intraprostatic and clinically occult extraprostatic cancer. This study examines prostatectomy findings as they relate to treatment of extraprostatic extension (EPE) of cancer and TIPPB techniques and dosimetry.


METHODS
A total of 313 prostatectomy specimens from patients with clinical tumor classification T1-T2b adenocarcinomas, serum prostate-specific antigen <20 ng/mL, and Gleason score <8 were whole mounted and evaluated for intraprostatic cancer volume and extraprostatic radial distance, area of perforation, and cancer density. From these data, extraprostatic cancer volume is calculated and used to estimate extraprostatic tumor control probabilities using the linear quadratic radiobiological model and Poisson statistics. TIPPB dose-gradient characteristics at the prostate periphery are examined.


RESULTS
Intraprostatic cancer volume ranges from 0 to 38 cc, whereas extraprostatic cancer volume ranges from 0 to 4.6 cc (mean 0.06 cc). The radial distance of EPE ranges from 0 to 4.4 mm (mean 0.18 mm). The ratio of extraprostatic to intraprostatic cancer volume ranges from 0% to 18% (mean 0.4%).


CONCLUSIONS
Only small amounts of clinically occult extraprostatic cancer were identified in the majority of specimens with EPE. Tumor control probability calculations suggest that this volume of cancer may be treated effectively with TIPPB. Treatment of this cancer possibly is achieved with an intraprostatic implant, but treatment of all cancers identified in this study suggests that some extraprostatic seed placement is desirable.
Davis
B J
BJ
Division of Radiation Oncology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
Haddock
M G
MG
Wilson
T M
TM
Rothenberg
H J
HJ
Bostwick
D G
DG
Herman
M G
MG
Pisansky
T M
TM
D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D001918:Brachytherapy / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008297:Male; D009361:Neoplasm Invasiveness; D009364:Neoplasm Recurrence, Local; D009367:Neoplasm Staging; D010502:Perineum / Q000000981:diagnostic imaging; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D011881:Radiotherapy, Computer-Assisted; D012189:Retrospective Studies; D016896:Treatment Outcome; D014463:Ultrasonography