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 II–IIIB 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: BED10 at bladder and rectum reference points were 17.11 ± 12.36 Gy and 13.92 ± 5.71 Gy in Group-1, and 15.69 ± 11.43 Gy and 16.24 ± 5.45 Gy in Group-2, respectively; and BED3 were 33.03 ± 29.67 Gy and 25.01 ± 12.35Gy in Group-1, and 27.00 ± 26.85 Gy and 27.44 ± 11.00 Gy in Group-2, respectively. The HDR BT reference volumes were 233.47 ± 27.30 cm3 and 227.83 ± 32.35 cm3 and corresponding CBED10 at point A with proliferation correction were 76.59 ± 2.31 Gy, and 76.41 ± 2.15 Gy for Group-1 and Group-2, respectively. The CBED10 and CBED3 at point B were 46.38 ± 2.26 Gy and 82.23 ± 0.72 Gy, respectively, for Group-1; and 45.03 ± 2.11 Gy and 82.89 ± 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.