Interstitial rotating shield brachytherapy for prostate cancer.
OBJECTIVE
To present a novel needle, catheter, and radiation source system for interstitial rotating shield brachytherapy (I-RSBT) of the prostate. I-RSBT is a promising technique for reducing urethra, rectum, and bladder dose relative to conventional interstitial high-dose-rate brachytherapy (HDR-BT).


METHODS
A wire-mounted 62 GBq(153)Gd source is proposed with an encapsulated diameter of 0.59 mm, active diameter of 0.44 mm, and active length of 10 mm. A concept model I-RSBT needle/catheter pair was constructed using concentric 50 and 75 μm thick nickel-titanium alloy (nitinol) tubes. The needle is 16-gauge (1.651 mm) in outer diameter and the catheter contains a 535 μm thick platinum shield. I-RSBT and conventional HDR-BT treatment plans for a prostate cancer patient were generated based on Monte Carlo dose calculations. In order to minimize urethral dose, urethral dose gradient volumes within 0-5 mm of the urethra surface were allowed to receive doses less than the prescribed dose of 100%.


RESULTS
The platinum shield reduced the dose rate on the shielded side of the source at 1 cm off-axis to 6.4% of the dose rate on the unshielded side. For the case considered, for the same minimum dose to the hottest 98% of the clinical target volume (D(98%)), I-RSBT reduced urethral D(0.1cc) below that of conventional HDR-BT by 29%, 33%, 38%, and 44% for urethral dose gradient volumes within 0, 1, 3, and 5 mm of the urethra surface, respectively. Percentages are expressed relative to the prescription dose of 100%. For the case considered, for the same urethral dose gradient volumes, rectum D(1cc) was reduced by 7%, 6%, 6%, and 6%, respectively, and bladder D(1cc) was reduced by 4%, 5%, 5%, and 6%, respectively. Treatment time to deliver 20 Gy with I-RSBT was 154 min with ten 62 GBq (153)Gd sources.


CONCLUSIONS
For the case considered, the proposed(153)Gd-based I-RSBT system has the potential to lower the urethral dose relative to HDR-BT by 29%-44% if the clinician allows a urethral dose gradient volume of 0-5 mm around the urethra to receive a dose below the prescription. A multisource approach is necessary in order to deliver the proposed (153)Gd-based I-RSBT technique in reasonable treatment times.
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Quentin E
QE
Adams
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Jinghzu
J
Xu
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Elizabeth K
EK
Breitbach
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Xing
X
Li
Medical Physics Unit, McGill University, 1650 Cedar Ave, Montreal, Quebec H3G 1A4, Canada.
Shirin A
SA
Enger
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
William R
WR
Rockey
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Yusung
Y
Kim
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Xiaodong
X
Wu
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Ryan T
RT
Flynn
D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D057785:Catheters; D004867:Equipment Design; D005682:Gadolinium / Q000627:therapeutic use; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D008297:Male; D009010:Monte Carlo Method; D009339:Needles; D009532:Nickel; D017671:Platinum Compounds; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011835:Radiation Protection; D011868:Radioisotopes / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012007:Rectum / Q000528:radiation effects; D013997:Time Factors; D014025:Titanium; D014521:Urethra / Q000528:radiation effects; D001743:Urinary Bladder / Q000528:radiation effects
D007496:Iridium Radioisotopes; D017671:Platinum Compounds; D011868:Radioisotopes; C040654:titanium nickelide; D009532:Nickel; D005682:Gadolinium; D014025:Titanium