Evaluation of a fluorinated 2-nitroimidazole binding to hypoxic cells in tumor-bearing rats by 19F magnetic resonance spectroscopy and immunohistochemistry.

We have examined a hexafluorinated 2-nitroimidazole, CCI-103F, as a probe for hypoxic tumor cells by in vivo 19F magnetic resonance spectroscopy (MRS). Following initial intraperitoneal injections of the drug in tumor-bearing (Dunning R3327-AT1-Matlylu) rats, 19F spectra were obtained on an Otsuka 2.0T Vivospec spectrometer using a 1.5-cm surface coil. Signal at 1- and 2-h time points indicated initial biodistribution of drug in the tumor. At 4 and 8 h, a progressive increase in signal intensity was observed, indicating retention of drug within the tumor. Tumor signal remained detectable in 4 of 10 rats at 24 h, indicating possible nitroreductive bioactivation by hypoxic cells. Immunohistochemistry of these tumors revealed a staining pattern consistent with labeling of hypoxic cells. No detectable 19F signal was found at 24 h for the other rats, indicating complete washout of unbound drug. Immunohistochemical assessment of these tumors revealed some staining for bound drug at the periphery of necrotic zones. 31P-MRS of the tumors showed good correlation with the presence or absence of hypoxia as evaluated by 19F-MRS, T1- and T2-weighted images, and immunohistochemistry. These results provide the groundwork for further studies using this misonidazole analog for noninvasive identification of hypoxic tumor cells in vivo by MRS.

Virtual simulation in the clinical setting: some practical considerations.

Virtual simulation departs from normal practice by replacing conventional treatment simulation with 3-dimensional image data and computer software. Implementation of virtual simulation requires the ability to transfer the planned treatment geometry from the computer to the treatment room in a way which is accurate, reproducible, and efficient enough for routine use. We have separated this process into: (a) immobilization of the patient; (b) establishment and alignment of a practical coordinate system for the patient/couch system; and (c) setup of the patient/couch been addressed by the use of hemi- or full-body foam casts, the second by use of an alignment jig on the treatment couch, and the third with the aid of a patient coordinate system referenced to easily located landmarks. Phantom studies and clinical practice have shown these techniques to be practical and effective within reasonable clinical bounds.

Automatic digital contrast enhancement of radiotherapy films.

The practice of radiotherapy involves the precise geometric localization of both anatomic and non-anatomic structures using radiographs which are typically of very low contrast. Portal and verification films suffer from poor contrast as a result of the dominance of Compton interactions at therapeutic energies, and implant localization films often are degraded by extreme patient thickness (lateral pelvis) or projection of bony structures (head and neck). Automatic contrast enhancement techniques developed and proven for optimization of the display of digitally produced images such as CT have been applied to radiotherapy films to improve contrast and augment readability. This approach has become viable only recently with the advent of high speed, high resolution film digitizers and laser cameras and the evolution of sufficiently powerful computer hardware.

An integrated system for interstitial 192Ir implants.

An efficient system for preparing, afterloading, and removing interstitial 192Ir strands has been developed. Use of the system reduces the risk of personnel exposure and eliminates some patient discomfort. The system is "integrated" in that all aspects of the implantation process are considered, from source preparation to source removal. Strand preparation is facilitated by an "assembly line" process using shielded equipment. Components include a handling block for measuring and cutting active strands, a mirror, and a transport container. Afterloading and removal techniques use quick release devices and several forms of afterloading tubing and catheters, each terminated by a Luer lock adapter. Both blind-end and through-and-through implants are possible. Each 192Ir strand, threaded through an injection cap that mates with the Luer lock adapter, is quickly inserted into its tubing or catheter and locked into place. No crimping is required and no additional positioning of the sources is needed. Strand removal is easily accomplished by unlocking and removing the injection cap. The strands receive no mechanical damage and can be reused after appropriate cleaning. More than 100 cases have been performed without incident. Applications include head/neck, breast, and template and non-template vaginal wall treatments.