DOSE-VOLUME HISTOGRAM ANALYSIS OF HIGH-DOSE-RATE INTRACAVITARY BRACHYTHERAPY FOR UTERINE CERVIX CANCER

Purpose: We retrospectively analyzed the relationship between dose dis tribution and local control using a dose-volume histogram (DVH) in pat ients with cancer of the uterine cervix treated by definitive radiothe rapy including intracavitary brachytherapy. Methods and Materials: Twe nty-five patients with squamous cell carcinoma of the uterine cervix w ho underwent definitive radiotherapy between August 1987 and April 199 4 were selected for the present study, They included 15 patients with local control and 10 patients with local recurrence. In principle, the se patients were treated with 50 Gy of external beam pelvic radiothera py and a paint A dose of 24 Gy, in four fractions, of intracavitary br achytherapy. The DVHs of tumor volumes were calculated by superimposin g three-dimensional (3D) dose distributions on computed tomography (CT ) images taken before brachytherapy. Results: Differential DVHs reveal ed a tendency for the portion of the total tumor volume to which the d elivered dose was low to be larger in patients with local recurrence, The tumor volumes and the absolute dose volumes of which the absorbed dose was less than 24 Gy [DV (<24 Gy)] were significantly larger in pa tients with local recurrence than those in local control patients (p = 0.02 and 0.03, respectively), The percent DV (<24 Gy) was not signifi cantly different in the two groups, In patients with larger tumor volu me, the absolute DV (<24 Gy) was also larger and a strong linear corre lation was noted between them. Conclusions: The analysis of dose distr ibution of brachytherapy using DVH was useful to evaluate the quality of dose distribution quantitatively, The absolute dose volume was cons idered more important than the percent dose volume for evaluation of t he clinical outcome. Our study suggested that unfavorable dose distrib ution for the tumor volume in brachytherapy was one of the reasons of poor local control in patients with large tumor volume.