CHICAGO--In feasibility testing, a custom-designed high-dose-rate contact radiation therapy technique destroyed Kaposi's sarcoma on the hard palate in less time than conventional external beam radiotherapy and with less severe side effects.
The technique was developed at New York Hospital and Cornell University Medical Center by Drs. James Wong, Lourdes Nisce, and Dattareyudu Nori.
Dr. Wong, director of Radiation Oncology Research, described the new technique at the annual meeting of the Radiological Society of North America (RSNA).
Kaposi's sarcoma of the hard palate, a common presentation in individuals with AIDS, usually is treated by external beam radiotherapy. Despite receiving doses as low as 180 cGy to 200 cGy per fraction for a maximum dosage of 2,600 cGy, AIDS patients who undergo external beam radiotherapy often suffer severe mucositis and xerostomia secondary to their decreased tolerance to radiation.
By concentrating radiation on the tumor itself, the oral high-dose-rate contact therapy minimizes these adverse side effects while raising radiation dose, Dr. Wong said.
This new form of therapy is delivered by means of a flexible surface applicator that has been shielded with lead on the underside and along the lateral edges, in order to protect the tongue, buccal mucosa, and parotid gland from exposure to radiation.
Patient Bites Down on Device
Afterloading source tubes that will deliver the radiation are embedded in bolus material, which is attached to the applicators and secured in place with thermoplastic. The applicators are placed in a patient's mouth while the thermoplastic is still warm so that the patient can bite down on the device and push the bolus material up against the Kaposi's sarcoma lesion on the palate.
Radiation using a high-activity iridium-192 source is administered through the afterloading source tubes, which are positioned so that the center of the radiation source is 0.5 cm from the mucosal surface.
A mean dose of 400 cGy per fraction is administered twice a week for a total initial treatment dose of 1,600 cGy. "Sometimes at the end of treatment, we may not see complete response after this regimen. We wait another two to four weeks, and usually the tumor disappears. If it doesn't, we give another course of 1,600 cGy," Dr. Wong explained.
Treatment Takes 20 Minutes
Treatment with the oral high-dose-rate contact technique is quick; it takes only five minutes to prepare the device and 15 minutes to administer the radiation therapy.
The new contact treatment causes minimal damage to normal tissue. Dr. Wong has calculated that Kapo-si's sarcoma at the contact surface receives the full dosage of radiation, but because of the lead shielding beneath and at the sides of the device, the tongue receives only 22% of the maximum dosage; the nearest portion of buccal mucosa receives 35% of the maximum dosage; buccal mucosa further away from the contact region receives less than 10% of the dosage; and the parotid gland receives 8% to 11%.
As a result, patients treated with this novel device experience no changes in taste, have only minor mucositis and xerostomia, and require no analgesics, narcotics, or special diets following treatment, he said.
