A radiopaque polymer hydrogel used as a fiducial marker in gynecologic-cancer patients receiving brachytherapy.
OBJECTIVE
We assessed a novel Food and Drug Administration-approved hydrogel, synthesized as absorbable iodinated particles, in gynecologic-cancer patients undergoing computed tomography (CT) or magnetic resonance (MR) based brachytherapy after external beam radiation.


METHODS
Nineteen patients underwent CT-guided (n = 13) or MR-guided (n = 6) brachytherapy for gynecologic cancers. Seventy-seven hydrogel injections were placed. The hydrogel material was injected into gross residual disease and/or key anatomic landmarks in amounts ranging from 0.1 to 0.4 mL. The visibility of the tracer was scored on CT and on MR images using a 5-point scoring scale. A Cohen's kappa statistic was calculated to assess interobserver agreement. To assess the unadjusted effects of baseline parameters on hydrogel visibility, we modeled visibility using a linear mixed-effect model.


RESULTS
Injections were without complication. The kappa statistic was 0.77 (95% confidence interval [CI], 0.68-0.87). The volume of hydrogel injected was significantly associated with visibility on both CT (p = 0.032) and magnetic resonance imaging (p = 0.016). We analyzed visibility by location, controlling for amount. A 0.1-cc increase in volume injected was associated with increases of 0.54 (95% CI = 0.05-1.03) in the CT visibility score and 0.83 (95% CI = 0.17-1.49) in the MR visibility score. Injection of 0.4 cc or more was required for unequivocal visibility on CT or MR. No statistically significant correlation was found between tumor type, tumor location, or anatomical location of injection and visibility on either CT or magnetic resonance imaging.


CONCLUSIONS
In this first report of an injectable radiopaque hydrogel, targets were visualized to assist with three-dimensional-based brachytherapy in gynecologic malignancies. This marker has potential for several applications, is easy to inject and visualize, and caused no acute complications.
Department of Radiation Oncology, Dana-Farber Cancer Institute and Brigham and Women's Hospital, Boston, MA.
Ryan J
RJ
Bair
Department of Endodontics, University of North Carolina, Chapel Hill, NC; Department of Biostatistics, University of North Carolina, Chapel Hill, NC.
Eric
E
Bair
Department of Radiation Oncology, Dana-Farber Cancer Institute and Brigham and Women's Hospital, Boston, MA. Electronic address: aviswanathan@lroc.harvard.edu.
Akila N
AN
Viswanathan
D000328:Adult; D001918:Brachytherapy / Q000379:methods*; D003287:Contrast Media; D005260:Female; D057918:Fiducial Markers; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D018365:Neoplasm, Residual; D015588:Observer Variation; D011108:Polymers; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D014057:Tomography, X-Ray Computed
D003287:Contrast Media; D011108:Polymers; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate
Brachytherapy; Fiducial; Radiopaque polymer hydrogel