PATIENT-RELATED FACTORS DETERMINING GEOMETRY OF INTRACAVITARY APPLICATORS AND PELVIC DOSE DISTRIBUTION DURING CERVICAL-CANCER BRACHYTHERAPY

Purpose: The aim of this study was to assess retrospectively the influ ence of the size of cervical cancer brachytherapy applicators (avoids and uterine tandems) on pelvic dose distribution and to analyze the im pact of various patient- and disease-related factors on applicators' g eometry and on dose distribution in particular applications. Methods a nd Materials: The subject of this study were 356 cervical cancer patie nts treated with Selectron LDR as a part of their radical radiotherapy . Analyzed factors included patient age, weight, number of vaginal del iveries, and disease stage. Results: The use of larger vaginal applica tors resulted in lower bladder and rectum doses and in higher point B doses (all p < 0.0001); longer uterine tandems produced lower rectum d oses and higher point B doses (both p < 0.0001). Increasing patient ag e and disease stage resulted in a decreased frequency of use of large ovoids (both p < 0.0001) and of long tandems (age: p = 0.0069, stage: p = 0.004). As a result, higher doses to bladder (age: p < 0.0001, sta ge: p = 0.017) and rectum (age: p = 0.037, stage: p = 0.011) were obse rved. Increasing age also resulted in lower point B doses (p < 0.0001) . Increasing patient weight correlated with less frequent use of long tandems (p = 0.0015) and with higher bladder doses (p = 0.04). Higher number of vaginal deliveries was related to the increase in the use of long tandems (p = 0.002); in patients who had had at least one vagina l delivery, paint B doses were significantly higher (p = 0.0059). In m ultivariate analysis avoid size and uterine tandem length were depende nt on patient age (respectively: p < 0.001 and p = 0.001), disease sta ge (respectively: p = 0.003 and p = 0.008) and on the number of vagina l deliveries (respectively: p = 0.07 and p = 0.008). Doses to critical organs and to points B were dependent on patient age (respectively: p < 0.001,p = 0.011, and p < 0.001) and on disease stage (respectively: p < 0.001, p = 0.004, and p = 0.048). Conclusion: The results of this study allow for identification of some patient- and disease-related f actors influencing pelvic dose distribution in cervical cancer brachyt herapy. This potentially may enable optimization of the dose distribut ion in particular clinical situations. (C) 1997 Elsevier Science Inc.