Anisotropy characterization of I-125 seed with attached encapsulated cobalt chloride complex contrast agent markers for MRI-based prostate brachytherapy.
We have developed a novel MRI marker for prostate brachytherapy. The purpose of this study was to evaluate the changes in anisotropy when cobalt chloride complex contrast agent encapsulated contrast agent markers (C4-ECAM) were placed adjacent to an iodine-125 (I-125) titanium seed, and to verify that the C4-ECAMs were visible on magnetic resonance imaging (MRI) after radiation exposure. Two C4-ECAMs were verified to be MRI visible in a phantom before radiation exposure. The C4-ECAMs were then attached to each end of a 12.7-U (10-mCi) I-125 titanium seed in a polymer tube. Anisotropy was measured and analyzed with the seed alone and with attached C4-ECAMs by suspending thermoluminescent dosimeters in a water phantom in 2 circles surrounding the radioactive source with radius of 1 or 2 cm. A T1-weighted MRI evaluation of C4-ECAMs was then performed after exposure to the amount of radiation typically delivered during 1 month of prostate brachytherapy. Measured values of the anisotropy function F(r, θ) for the I-125 seed with and without the C4-ECAMs were mutually statistically indistinguishable (standard error of the mean <4.2%) and agreed well with published TG-43 values for the bare seed. As expected, the anisotropy function ϕ(an)(r) for the 2 datasets (with and without C4-ECAMs) derived from the measured F(r, θ) did not exhibit statistically measurable difference. Both datasets showed agreement with the published TG-43 ϕ(an)(r) for the bare seed. The C4-ECAMs were well visualized by MRI after 1 month of radiation exposure. There were no changes in anisotropy when the C4-ECAMs were placed next to an I-125 radioactive seed, and the C4-ECAMs were visualized after radiation exposure.
Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. sjfrank@mdanderson.org
Steven J
SJ
Frank
Ramesh C
RC
Tailor
Rajat J
RJ
Kudchadker
Karen S
KS
Martirosyan
R Jason
RJ
Stafford
Andrew M
AM
Elliott
David A
DA
Swanson
David
D
Sing
Jonathan
J
Choi
Firas
F
Mourtada
Geoffrey S
GS
Ibbott
D016880:Anisotropy; D001918:Brachytherapy / Q000379:methods*; D003035:Cobalt; D003287:Contrast Media; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D019275:Radiopharmaceuticals
D003287:Contrast Media; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D003035:Cobalt; C018021:cobaltous chloride