A novel MRI marker for prostate brachytherapy.
OBJECTIVE
Magnetic resonance imaging (MRI) is the optimal imaging modality for the prostate and surrounding critical organ structures. However, on MRI, the titanium radioactive seeds used for brachytherapy appear as black holes (negative contrast) and cannot be accurately localized. We sought to develop an encapsulated contrast agent marker (ECAM) with high-signal intensity on MRI to permit accurate localization of radioactive seeds with MRI during and after prostate brachytherapy.


METHODS
We investigated several agents with paramagnetic and superparamagnetic properties. The agents were injected into titanium, acrylic, and glass seeds, which were linked together in various combinations and imaged with MRI. The agent with the greatest T1-weighted signal was tested further in a canine prostate and agarose phantom. Studies were performed on a 1.5-T clinical MRI scanner.


RESULTS
The cobalt-chloride complex contrast (C4) agent with stoichiometry (CoCl(2))(0.8)(C(2)H(5)NO(2))(0.2) had the greatest T1-weighted signal (positive contrast) with a relaxivity ratio >1 (r(2)/r(1) = 1.21 +/- 0.29). Acrylic-titanium and glass-titanium seed strands were clearly visualized with the encapsulated contrast agent marker.


CONCLUSIONS
We have developed a novel ECAM that permits positive identification of the radioactive seeds used for prostate brachytherapy on MRI. Preclinical in vitro phantom studies and in vivo canine studies are needed to further optimize MRI sequencing techniques to facilitate MRI-based dosimetry.
Frank
Steven J
SJ
Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA. sjfrank@mdanderson.org
Stafford
R Jason
RJ
Bankson
James A
JA
Li
Chun
C
Swanson
David A
DA
Kudchadker
Rajat J
RJ
Martirosyan
Karen S
KS
D000179:Acrylates / Q000737:chemistry; D000818:Animals; D001918:Brachytherapy / Q000295:instrumentation*; D003035:Cobalt / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry*; D004285:Dogs; D005898:Glass / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D009566:Nitrates / Q000737:chemistry; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*
D000179:Acrylates; D003287:Contrast Media; D009566:Nitrates; D003035:Cobalt; C465446:ethyl nitrate; C018021:cobaltous chloride