Abstract
C4 (cobalt dichloride-N-acetylcysteine [1% CoCl2:2% NAC]) is a novel magnetic resonance imaging contrast marker that facilitates visualization of implanted radioactive seeds in cancer brachytherapy. We evaluated the toxicity of C4. Rats were assigned to control (0% CoCl2:NAC), low-dose (0.1% CoCl2:2% NAC), reference-dose (C4), and high-dose (10% CoCl2:2% NAC) groups. Agent was injected into the left quadriceps femoris muscle of the rats. Endpoints were organ and body weights, hematology, and serum chemistry and histopathologic changes of tissues at 48 hours and 28 and 63 days after dosing. Student's t tests were used. No abnormalities in clinical signs, terminal body and organ weights, or hematologic and serum chemistry were noted, and no gross or histopathologic lesions of systemic tissue toxicity were found in any treatment group at any time point studied. At the site of injection, concentration-dependent acute responses were observed in all treatment groups at 48 hours after dosing and were recovered by 28 days. No myofiber degeneration or necrosis was observed at 28 or 63 days in any group. In conclusion, a single intramuscular dose of C4 produced no acute or chronic systemic toxicity or inflammation in rats, suggesting that C4 may be toxicologically safe for clinical use in cancer brachytherapy.
Highlights
The current standard of care after brachytherapy for localized prostate cancer includes an image-guided quality assurance check of the radioactive seed placement and anticipated dose distribution
Neutrophil and monocyte counts were slightly elevated in the treatment groups relative to the control group at 48 hours, the increased values remained within the normal reference range, and these values had recovered to control levels by 28 days and 63 days after injection (Table 1)
None of these findings indicate a clinically meaningful adverse effect, because all differences remained within the normal reference range and the mean corpuscular volume had returned to control levels at 28 days after dosing
Summary
The current standard of care after brachytherapy for localized prostate cancer includes an image-guided quality assurance check of the radioactive seed placement and anticipated dose distribution. Magnetic resonance imaging (MRI), on the other hand, is ideal for visualizing soft tissues [1, 2] but requires a positive-contrast marker to identify the seeds [3]; MRI is increasingly being viewed as an excellent imaging tool for posttreatment quality assurance [4, 5]. Previous studies have shown that C4 does not affect anisotropy or volumetric dosimetry when placed adjacent to radioactive seeds, nor does it alter the T1 positive-contrast signal after exposure to high doses of radiation [6]. Whether leakage of the C4 solution from the capsules after prostate brachytherapy would potentiate systemic inflammatory effects or produce acute or chronic toxicity is unknown. The purpose of this study was to evaluate the potential inflammatory toxicity of C4 in the target organs and systemically. An experimental model in which C4 is injected into the quadriceps femoris muscle of rats, which would allow evaluation of local tissue tolerance and recovery from of any damage, and accurate assessment of local and systemic inflammation was used
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