High-dose-rate brachytherapy with external beam radiotherapy in the treatment of carcinoma of cervix: dosimetric and radiobiologic analysis

Abstract

Purpose: The aim of this study was to find out equivalency between two high-dose-rate (HDR) fractionation schemes, relevance to the International Commission on Radiation Units and Measurements report-38 (ICRU-38) reference volume with respect to point A dose and other ICRU reference points in two-dimensional (2D) planning.Methods and Materials: Forty-nine patients having carcinoma of cervix of stages IIÀIIIB treated with external beam radiotherapy plus HDR brachytherapy (BT) were analysed. The external beam radiotherapy dose of 45 Gy/25 fractions delivered in 5 weeks followed by HDR BT delivered either in two fractions with 9.5 Gy per fraction (Group-1) or in three fractions with 7.5 Gy per fraction (Group-2) to point A. ICRU-38 recommendations were followed to determine reference volume with respect to Manchester dose point A, and biologically effective dose (BED) at different points.Results: BED 10 at bladder and rectum reference points were 17.11 AE 12.36 Gy and 13.92 AE 5.71 Gy in Group-1, and 15.69 AE 11.43 Gy and 16.24 AE 5.45 Gy in Group-2, respectively; and BED 3 were 33.03 AE 29.67 Gy and 25.01 AE 12.35Gy in Group-1, and 27.00 AE 26.85 Gy and 27.44 AE 11.00 Gy in Group-2, respectively. The HDR BT reference volumes were 233.47 AE 27.30 cm 3 and 227.83 AE 32.35 cm 3 and corresponding CBED 10 at point A with proliferation correction were 76.59 AE 2.31 Gy, and 76.41 AE 2.15 Gy for Group-1 and Group-2, respectively. The CBED 10 and CBED 3 at point B were 46.38 AE 2.26 Gy and 82.23 AE 0.72 Gy, respectively, for Group-1; and 45.03 AE 2.11 Gy and 82.89 AE 0.44 Gy, respectively, for Group-2.Conclusion: No significant differences were found in the results of two HDR fractionation schemes. ICRU reference volume with respect to point A dose correlates with tumour control and is a good pre-treatment predictor in 2D planning. Neither ICRU bladder and rectum reference points nor trapezoid points showed correlation with complications. The trapezoid points did not also show any correlation with loco-regional control.

Clinical Investigations Effectiveness of two different HDR brachytherapy regimens with the same BED value in cervical cancer

“…Details of the dose calculations and treatment planning are described elsewhere [22–24]. In brief, orthogonal radiographs were taken for all the ICBT insertions individually.…”