Tumor regression dynamics with external radiotherapy in cancer cervix and its implications

BACKGROUND: To study the external radiotherapy (EXTRT) regression patterns in cancer of the cervix. AIMS: Evaluate EXTRT tumor regression doses (TRD) for 50% (TRD₅₀), 80% response (TRD₈₀), normalized dose response gradient (g₅₀) and slope (slope₅₀) with clinical outcome. SETTINGS AND DESIGN: Patients, treated solely with radiotherapy and enrolled for other prospective studies having weekly tumor regressions recorded were considered. MATERIAL AND METHODS: Seventy-seven patients received 50Gy of EXTRT at 2 Gy/fraction followed by 18Gy of high-dose rate intracavitary brachytherapy at 6 Gy/fraction. Loco-regional regressions were assessed clinically at weekly intervals during EXTRT to generate EXTRT dose-response curves. STATISTICAL ANALYSIS USED: Student's t test, logistic regression, Kaplan Meier and Cox's proportional hazard model. Scatter plots were fitted using cubic fit. RESULTS: Age (P=0.052) and absence or presence of gross residual tumor (AGRT and PGRT respectively) following EXTRT (P<0.001) were the only determinants for complete response (CR) at 1 month following completion of radiotherapy. EXTRT tumor regression sigmoid curves obtained for various patient characteristics differed only for those with AGRT and PGRT with differences in TRD50, (P<0.001); TRD₈₀ (P<0.001) and slope₅₀ (P=0.001). Response status to EXTRT was a prognosticator for loco-regional disease free survival (LDFS) (AGRT vs. PGRT; P=0.046). On multivariate analysis, both TRD₅₀ and TRD₈₀ emerged as significant predictors for tumor status at end of EXTRT while TRD₈₀ was the sole determinant of LDFS. CONCLUSION: Extent of tumor regression to EXTRT is an important predictor for treatment outcome in cancer cervix as evident from TRD₅₀ and TRD₈₀ values of EXTRT tumor regression curves.