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
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
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.