The care and management of patients with indication for intracavitary 3D brachytherapy

Abstract

This paper evaluates the differences between two types of normalization of 3D intracavitary brachytherapy (3D-BT) treatment plans for malignant cervical lesions. Immediately after the end of the treatment, intracavitary irradiation was continued, three fractions with 7.5 Gy per session, using High Dose Rate (HDR) brachytherapy and 3D imaging. Tree plans were made, one for the 3 cm diameter vaginal applicator and two for the vaginal applications where 2.6 cm diameter intracavitary applicators were used. Treatment plans were made using the dedicated software Eclipse-BrachyVision version 10.0.42, manufacturer Varian Medical Systems. Dose Calculation Model-Linear source and step size 0.50 cm. The normalization was done in the first phase at the surface of the applicator, at the prescription line. The next normalization was by volume. We present the results of the two normalizations. The data obtained from the 2 normalization methods was entered into an Excel spreadsheet. We took into account the dose prescribed for EBRT, the number of fractions, the dose/fr, the dose prescribed for 3D-BT and the dose absorbed by the OAR in 2 cm. We also took into account the isodose obtained for 90%, 100% and 150% of the volume of interest. In the first optimization, the absorbed dose was between 7.45–8 Gy. We also tracked BED and EQD2 in the spreadsheet. Results: In the second optimization, on the target volume, we obtained for the plan with a cylinder with a diameter of 3 cm (Ф = 3 cm), 90% of the IR volume the dose of 7.5 Gy. For Ф = 2.6 cm, of the IR volume with a dose of 7.5 Gy and for the last plane also with Ф = 2.6 cm, of the IR2 volume with a dose of 7.5 Gy. Calculated data for EQD2 in the three planes with normalization to the line on the applicator surface resulted in higher doses for OARs compared to EQD2 data from volume optimization. The volume of interest according to EQD2 calculations in the first optimization had 77.8 Gy and in the second optimization it had 78.4 Gy. After volume optimization, we achieved 78.4 Gy for all three brachytherapy fractions and the 25 EBRT fractions, the rectum totaling a dose of 67.1 Gy and the bladder 77.5 Gy. With the volume-optimized plans, we obtained a coverage between V90% = D100%.