Multivariate analysis of prognostic parameters using interstitial thermoradiotherapy (IHT-IRT): tumor and treatment variables predict outcome.

PURPOSE

From January 1986 to October 1991, 90 patients with localized tumors were treated in a Phase I/II trial using low-dose 192Ir brachytherapy (IRT) plus interstitial 915 MHz microwave (MW) hyperthermia (IHT) and external beam radiotherapy (ERT). Tumors were classified as locally advanced primary (class 1: 27), recurrent (class 2: 40), metastatic (class 3: 10) and persistent (class 4: 13) lesions. The treatment sites included tumors of the head and neck (62), pelvis (26), and others (2). The mean cuboidal tumor volume was 63 cm3 (range: 8-288 cm3). Most recurrent and metastatic lesions (48) had received prior treatment including ERT.

METHODS AND MATERIALS

The treatment protocol prescribed two heating sessions (each 60 min) at 41-44 degrees C before and after IRT. One hundred sixty-one IHT sessions were evaluated. Invasive thermal data were recorded at an average of 18 sites throughout the implant volume. Several thermal variables were analyzed (e.g., averaged parameters: Tmaxav, Tmean, Tminav; index parameters: T10, T50, T90). The study was evaluated with a minimum follow up (FU) of one year. Median follow-up was 19 months.

RESULTS

At 3 months FU, a complete response (CR) was observed in 59 of 90 (66%) patients. At 12 months FU, local control (LC) was achieved in 54 of 84 (64%) evaluable patients. Ten patients developed a local and 14 a regional recurrence (REC) after achieving a CR and/or LC. At last FU, a total of 31 (34%) patients were still alive and 28 (31%) patients had relapse-free survival. For all 90 patients, the median overall survival was 20 months and the median relapse-free survival was 17 months. Overall and relapse-free survival was significantly longer for primary and persistent lesions as compared to recurrent and metastatic lesions (p = 0.002; p < 0.001). Totally 22 (24%) patients experienced acute or subacute side-effects (Grade 1: 12 patients; Grade 2: eight patients; Grade 3: two patients).

CONCLUSION

Univariate logistic regression analysis revealed significant dependencies of CR, LC and REC upon tumor parameters as well as radiation and thermal parameters. The overall and relapse free survival was associated with tumor and radiation parameters. The multivariate analysis revealed two independent predictors of CR: tumor volume and minimum tumor temperature variables. We conclude, that IHT-IRT is a safe and effective treatment. The results provide important implications for planning HT-RT studies and for defining quality assurance (QA) criteria and thermal performance standards in HT studies.