RECTAL COMPLICATIONS IN PATIENTS WITH CARCINOMA OF THE CERVIX TREATEDWITH CONCOMITANT CISPLATIN AND EXTERNAL-BEAM IRRADIATION WITH HIGH-DOSE-RATE BRACHYTHERAPY - A DOSIMETRIC ANALYSIS

Purpose: This paper reports a dosimetric study of 43 patients treated with a combination of concomitant radiotherapy and chemotherapy (cispl atin) for locally advanced carcinoma of the cervix with the aim of inv estigating the correlation between the radiation dose to the rectum an d the incidence of late rectal complications. Methods and Materials: R adiotherapy consisted of 46 Gy external beam irradiation plus three hi gh dose rate intracavitary treatments given weekly, concurrent with th e last 3 weeks of external beam therapy, to a total dose of 30 Gy to p oint A. Cisplatin 30 mg/m(2) was given weekly throughout the duration of the external beam irradiation. The brachytherapy irradiated volume was reconstructed from the orthogonal treatment radiographs to accurat ely locate the reference points defined by the International Commissio n of Radiation Units and Measurements (ICRU), report 38. The doses cal culated at these points were compared to in vivo dose measurements per formed immediately prior to treatment. Results: The group of patients who were calculated to have received a dose to the rectal reference po int greater than the prescribed point A dose (9/13) had a significantl y greater probability of development of late rectal complications comp ared to the group of patients who were calculated to have received les s than the prescribed point A dose at this rectal point (7/30), p = 0. 003. There was no correlation of rate of complication with the in vivo measured dose in the rectum, stage of disease, or age. At 40 months p ost treatment, the group of patients receiving the higher dose to the rectal reference point had an actuarial rate of serious (Grade 3 and 4 ) rectal complications of 46% compared to a rate of 14% in the remaind er. In terms of survival, the group of patients receiving the higher d ose to the rectal reference point have all survived, whereas the group of patients receiving the lower dose to the rectal reference point ha ve a significantly different rate of survival of 72%, p = 0.046. Concl usion: This investigation has revealed a significant correlation betwe en the dose calculated at the rectal point defined by the ICRU and the incidence of late rectal complications in patients with carcinoma of the cervix undergoing concomitant radiotherapy and chemotherapy. Thus, this rectal reference point appears to be a useful prognostic indicat or of late rectal complications in these patients and we recommend tha t the brachythreapy dose delivered to this rectal point be limited to the dose prescribed to point A for treatment regimens using three frac tions of 8-10 Gy each, limiting the total dose to this point, includin g the external beam component, to 76 Gy. Further study will be require d to determine whether this rule should be applied to patients receivi ng irradiation alone.