High-Dose Contact RT Feasible in KS on the Hard Palate

CHICAGO--In feasibility testing, a custom-designed high-dose-rate contactradiation therapy technique destroyed Kaposi's sarcoma on the hard palatein less time than conventional external beam radiotherapy and with lesssevere side effects.

The technique was developed at New York Hospital and Cornell UniversityMedical Center by Drs. James Wong, Lourdes Nisce, and Dattareyudu Nori.

Dr. Wong, director of Radiation Oncology Research, described the newtechnique at the annual meeting of the Radiological Society of North America(RSNA).

Kaposi's sarcoma of the hard palate, a common presentation in individualswith AIDS, usually is treated by external beam radiotherapy. Despite receivingdoses as low as 180 cGy to 200 cGy per fraction for a maximum dosage of2,600 cGy, AIDS patients who undergo external beam radiotherapy often suffersevere mucositis and xerostomia secondary to their decreased toleranceto radiation.

By concentrating radiation on the tumor itself, the oral high-dose-ratecontact therapy minimizes these adverse side effects while raising radiationdose, Dr. Wong said.

This new form of therapy is delivered by means of a flexible surfaceapplicator that has been shielded with lead on the underside and alongthe lateral edges, in order to protect the tongue, buccal mucosa, and parotidgland from exposure to radiation.

Patient Bites Down on Device

Afterloading source tubes that will deliver the radiation are embeddedin bolus material, which is attached to the applicators and secured inplace with thermoplastic. The applicators are placed in a patient's mouthwhile the thermoplastic is still warm so that the patient can bite downon the device and push the bolus material up against the Kaposi's sarcomalesion on the palate.

Radiation using a high-activity iridium-192 source is administered throughthe afterloading source tubes, which are positioned so that the centerof the radiation source is 0.5 cm from the mucosal surface.

A mean dose of 400 cGy per fraction is administered twice a week fora total initial treatment dose of 1,600 cGy. "Sometimes at the endof treatment, we may not see complete response after this regimen. We waitanother 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; ittakes only five minutes to prepare the device and 15 minutes to administerthe 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 receivesthe full dosage of radiation, but because of the lead shielding beneathand at the sides of the device, the tongue receives only 22% of the maximumdosage; the nearest portion of buccal mucosa receives 35% of the maximumdosage; buccal mucosa further away from the contact region receives lessthan 10% of the dosage; and the parotid gland receives 8% to 11%.

As a result, patients treated with this novel device experience no changesin taste, have only minor mucositis and xerostomia, and require no analgesics,narcotics, or special diets following treatment, he said.