Comparison of response of cutaneous Kaposi's Sarcoma in AIDS patients to electron beam radiation therapy versus High Dose Rate Contact Therapy

Purpose: In our department, we have devised a novel method of treating Kaposi's Sarcoma (KS) using High Dose Rate Contact Therapy (HDRCT). The advantages of HDRCT include the following: 1) better conformation of dose distributions to the curved surfaces such as the nose, nasal vestibule or columella, where treatments with electron beams or external photons give either inhomogeneous doses or significant doses to surrounding normal tissues, 2) treatment of intracavitary lesions such as lesions of the hard palate with minimal radiation to the adjacent normal tissue (buccal mucosa) 3) faster dose fall off, 4) availability of optimization techniques. These advantages are especially important in AIDS patients since their tissues usually have decreased tolerance to radiation. Our preliminary data indicated that these KS lesions respond excellently to HDRCT. Thus, it is important to compare the biological effectiveness of HDRCT to standard treatments such as electron beams in treatment of KS lesions. Materials and Methods: HDRCT is performed using parallel afterloading source transfer tubes embedded in flexible bolus material, and radiation is given with a high activity iridium-192 source using Nucletron's MicroSelectron Remote Afterloader. 22 lesions in 4 AIDS patients were treated prospectively with either 6 MeV electrons beam or HDRCT. In each patient, KS lesions of comparable size and thickness were selected for this study to serve as internal controls in terms of clinical status, CD4/CD8 counts, and other effects of antiviral, antifungal or chemotherapy that may influence response and tolerance to radiation treatment. These lesions were then treated concomitantly with either electrons or HDRCT using the same dose fractionation (400 cGy/fraction, given 2x/week) and to the same total dose (1600 cGy). Results: Complete responses were very similar and were over 90% with lesions treated by either electrons or HDRCT. However, at 1200 cGy, there was more skin erythema associated with electron beam use. At completion of treatment, skin erythema and clinical response were practically identical with either modality. At 2 weeks follow-up, erythema associated with the HDRCT had completely faded, whereas it took 4 weeks for erythema to clear in regions treated with electrons. At 6 months follow-up there was no notable difference noted in terms of recurrence (less than 10%) or skin color changes (both were excellent). Conclusion: HDRCT is an effective treatment for Kaposi's Sarcoma, especially for KS lesions occurring in specific sites of the body where conventional radiation with electrons or external photons may give excessive doses or large dose inhomogeneities, therefore, significant acute side effects to the adjacent tissue. We have demonstrated that the biological effectiveness of HDRCT is comparable to conventional radiation and may have less acute side effects