CT-Image based conformal brachytherapy of breast cancer - The significanceof semi-3-D and 3-D treatment planning

Purpose: To compare the conventional 2-D, the simulator-guided semi-3-D and the recently developed CT-guided 3-D brachytherapy treatment planning in t he interstitial radiotherapy of breast cancer. Patients and Methods: In 103 patients with T1-2, N0-1 breast cancer the tum or bed was clipped during breast conserving surgery. Fifty-two of them rece ived boost brachytherapy after 46 to 50 Gy teletherapy and 51 patients were treated with brachytherapy alone via flexible implant tubes. Single, doubl e and triple plane implant was used in 6, 89 and 8 cases, respectively. The dose of boost brachytherapy and sole brachytherapy prescribed to dose refe rence points was 3 rimes 4.75 Gy and 7 times 5.2 Gy, respectively. The posi tions of dose reference points varied according to the level (2-D, semi-3-D and 3-D) of treatment planning performed. The treatment planning was based on the 3-D reconstruction of the surgical clips, implant tubes and skin po ints. Tn all cases the implantations were planned with a semi-3-D technique aided by simulator. In 10 cases a recently developed CT-guided 3-D plannin g system was used. The semi-3-D and 3-D treatment plans were compared to hy pothetical 2-D plans using dose Volume histograms and dose non-uniformity r atios. The values of mean central dose, mean skin dose, minimal clip dose, proportion of underdosaged clips and mean target surface dose were evaluate d. The accuracy of tumor bed localization and the conformity of planning ta rget volume and treated volume were also analyzed in each technique. Results: With the help of conformal semi-3-D and 3-D brachytherapy planning we could define reference dose points, active source positions and dwell t imes individually. This technique decreased the mean skin dose with 22.2% a nd reduced the possibility of geographical miss. We could achieve the best conformity between the planning target volume and the treated volume with t he CT-image based 3-D treatment planning, at the cost of worse dose homogen eity. The mean treated volume was reduced by 25.1% with semi-3-D planning, however, it was increased by 16.2% with 3-D planning, compared to the 2-D p lanning. Conclusion: The application of clips into the tumor bed and the conformal ( semi-3-D and 3-D) planning help to avoid geographical miss. CT is suitable for 3-D brachytherapy planning. Better local control with less side effects might be achieved with these new techniques. Conformal 3-D brachytherapy c alls for new treatment planning concepts, taking the irregular 3-D shape of the target volume into account. The routine clinical application of image- based 3-D brachytherapy is a real aim in the very close future.