Özet:

In our study, it was aimed to compare the volume of accelerated partial breast irradiation in patients diagnosed with early stage breast cancer in CyberKnife target and volume targeted virtual plans (APBI). A virtual plan was created in CyberKnife system for 5 patients who received radiotherapy in our unit, 6 Gy per day for Iris, fixed and multi-leaf collimator (MLC) and 30 Gy in total. Dosimetric parameters for three different collimators were analyzed according to the constraints of the NSABP-39/RTOG 0413 protocol. In the plans, it was ensured that critical organs were protected and PTV received 95% of the prescribed dose. The prescribed dose was defined by a minimum 80% isodose curve. Homogeneity index (HI), conformity index (CI), treatment time (min), monitor unit (MU) and doses received by critical organs were compared. The mean HI values for iris, fixed collimator, and MLC were 1.2- 1.2- 1.19, mean CI values were 1,08-1,06-1,07, mean treatment time was 47,6- 52,2- 25,4 (min) and MU values were found to be 19736,2-2026,.3- 7161,3 on average. Mean MU and duration of treatment were found in the lowest MLC. No significant difference was found for HI, CI. As a result of the comparison of the plans, a significant difference was found for MU and duration of treatment (p< 0,05).ipsilateral breast30 and V15 were found at the lowest MLC.for lung and heartDmax was no significant difference between. As a result, the target volume received the desired dose in each collimator. The contralateral breast and contra-lateral lung doses were the lowest in Iris. Fixed collimator was found to be more suitable for cardiac doses. But these values did not make a significant difference. In the fixed collimator (52,2 min), it may cause difficulties in clinical applications due to the long treatment time. The choice of collimator in breast SBRT applications with CyberKnife may vary depending on tumor size, proximity to critical organs and tumor localization.

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