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Biomedical subjects

T K Ho

Publications and source records attributed to T K Ho.

7 recordsLinked to original sources
PubMed1991

Palladium 103 ophthalmic plaque radiotherapy.

We compared the ocular radiation distribution of palladium 103 (103Pd) vs iodine 125 (125I) ophthalmic plaques sewn to 12 human donor eyes. We then performed preoperative comparative simulations on the first seven patients to be treated with palladium 103 plaque therapy for choroidal melanoma. The in vitro experiment involved palladium 103 seeds placed into a Silastic seed holder, which was affixed into standard 14-mm gold eye plaques. Then the plaques were sewn onto 12 human donor eyes so as to approximate either the nasal (six eyes) or temporal (six eyes) equator. Three sets of two thermoluminescent dosimeters were used to quantify the amount of radiation delivered by the episcleral plaques. Thermoluminescent dosimeters were sewn to the sclera in three locations: on the center of the cornea, on the sclera beneath the macula, and at the equator in a position opposite the plaque. This experiment was then repeated with iodine 125 seeds and thermoluminescent dosimeters. After the plaques were adjusted to equalize their activity (plaque strength), the palladium 103 plaques were found to deliver less radiation to the three target points. Comparative clinical dosimetry also reflected this difference. Preoperative simulations comparing equal doses to the tumors' apex revealed that the palladium 103 ophthalmic plaques delivered more radiation to the tumor and less radiation to most normal ocular structures.

Brachytherapy↗
PubMed1990

Intraocular radiation blocking.

Iodine-based liquid radiographic contrast agents were placed in normal and tumor-bearing (Greene strain) rabbit eyes to evaluate their ability to block iodine-125 radiation. This experiment required the procedures of tumor implantation, vitrectomy, air-fluid exchange, and 125I plaque and thermoluminescent dosimetry (TLD) chip implantation. The authors quantified the amount of radiation attenuation provided by intraocularly placed contrast agents with in vivo dosimetry. After intraocular insertion of a blocking agent or sham blocker (saline) insertion, episcleral 125I plaques were placed across the eye from episcleral TLD dosimeters. This showed that radiation attenuation occurred after blocker insertion compared with the saline controls. Then computed tomographic imaging techniques were used to describe the relatively rapid transit time of the aqueous-based iohexol compared with the slow transit time of the oil-like iophendylate. Lastly, seven nontumor-bearing eyes were primarily examined for blocking agent-related ocular toxicity. Although it was noted that iophendylate induced intraocular inflammation and retinal degeneration, all iohexol-treated eyes were similar to the control eyes at 7 and 31 days of follow-up. Although our study suggests that intraocular radiopaque materials can be used to shield normal ocular structures during 125I plaque irradiation, a mechanism to keep these materials from exiting the eye must be devised before clinical application.

Animals↗
PubMed1989

Thermoradiotherapy of choroidal melanoma. Clinical experience.

Thermoradiotherapy (TRT) was used to treat 18 patients with choroidal melanoma. Techniques and clinical observations using a plaque-type device capable of delivering microwave hyperthermia to intraocular tumors are described. Iodine-125 plaque irradiation (48-88 Gy to apex), together with microwave hyperthermia (46 degrees-52.5 degrees C to base), were given to patients during one brachytherapy session. Since October 1985, 15 medium and 3 large-sized tumors were treated. Clinical observations include partial clearing of six vitreous opacities as well as three retinal detachments noted before treatment. Objective measurements of improved visual acuity were noted in seven of the nine cases. All tumors responded to treatment, but one tumor had regrowth and the eye was enucleated. These data suggest that a microwave plaque can be used to deliver hyperthermia to human choroidal melanomas. Within the range of the follow-up period, no side effects that might preclude the use of this hyperthermia system for choroidal melanoma treatment were noted.

Choroid Neoplasms↗
PubMed1978

Opiate properties of SKF 525A.

SKF 525A, a classical inhibitor of microsomal drug-metabolizing enzymes, is structurally similar to the diphenylpropylamine analgesics, and certain reported effects in animals resemble those produced by opiate drugs. In an opiate radioreceptor assay, SKF 525A was 50 times less potent than methadone in the absence of sodium and 10 times less potent in the prescence of sodium. The nature of the sodium effect indicates SKF 525A to have less opiate agonist character than does methadone. In mice, 2 mg of SKF 525A given intraperitoneally induced less profound analgesia on a hot plate (44 degrees C) than did 0.1 mg of methadone. Analgesia by SKF 525A was prevented by pretreatment of the mice with naloxone. In rats, 50 microgram of SKF 525A given intracerebroventricularly was analgesic.

Analgesia↗