SPLIT COURSE INTERSTITIAL BRACHYTHERAPY WITH A SOURCE SHIFT - THE RESULTS OF A NEW IRIDIUM IMPLANT TECHNIQUE VERSUS SINGLE COURSE IMPLANTS FOR SALVAGE IRRADIATION OF BASE OF TONGUE CANCERS IN 55 PATIENTS

Between January 1973 and December 1984, 55 patients with prior irradiation of the oropharynx underwent salvage irradiation for recurrent (26 patients) or second cancers (29 patients) of the base of tongue. The initial irradiation had delivered from 45 to 80 Gy to the base of tongue. One of two techniques of Iridium implantation was used for salvage. Single course implants, delivering 60 Gy, were used until June 1981 in a total of 31 patients. After June 1981, split course implants with a source shift were used in 24 patients in the hope of decreasing treatment complications. The first and second course of the split course implants delivered 35 and 30 Gy, respectively, at a 1-month interval. The active lines of the second implant were placed parallel to and between the position of the lines of the first implant. This shift in the source position resulted in a more uniform dose within the treated volume with a 60% reduction in the high dose sleeves. The overall 3-year survival was 19% (28% T less-than-or-equal-to 3 cm). The overall local failure rate was 45.5% (25/55). The difference between the local failure rate after single course implants (52%) and after split course implants (37.5%) was not statistically significative. The response observed after the first course of a split course implant proved to be a reliable indication of the probability of achieving local control after a full course of treatment: 2/14 failures (14%) if the response was greater-than-or-equal-to 75% versus 7/10 (70%) if the response was < 75% (p < 0.01). The only complication noted in the 40 patients achieving immediate local control after either implant technique was mucosal necrosis. The introduction of split course implants was followed by a two and a half fold decrease in the incidence of necrosis: 43% (9/12) in the single course group and 16% (3/19) in the split course group (p = 0.05). Interstitial brachytherapy offers an effective and reasonable option for salvage therapy in patients with recurrent and second cancers occurring in the base of tongue even when the tumor arises in a zone that has previously received high dose irradiation. The use of split course implants with a shift in the position of the active lines at the time of the second implant significantly decreases the risk of radionecrosis.