30P - Stereotactic body radiotherapy using cyberknife versus interstitial brachytherapy in accelerated partial breast irradiation on left-sided breast: A comparison of preliminary clinical result and dosimetric characteristics

Background

Accelerated partial breast irradiation (APBI) is now widely adopted in the treatment with low risk early breast cancer worldwide. Both stereotactic body radiotherapy (SBRT) using Cyberknife (CK) and interstitial brachytherapy (IB) are available for APBI. This study was designed to compare the dosimetric characteristics of organ at risk and the clinical outcome between two different techniques.

Methods

Forty-four patients with left sided early breast cancer treated by APBI in our institute were reviewed. The radiation doses are 30Gy in 5 fractions, in 5 consecutive days using CK and 34Gy in 10 fractions, BID in 5 consecutive days using IB. Dosimetric parameters of OARs were calculated for both techniques and compared. The preliminary clinical outcomes include the local recurrence rate, acute toxicity (CTCAE V5.0) and cosmetic evaluation (Harvard scales) were analyzed.

Results

The median follow up time of CK group and IB group were 19.3 months (range: 4.5∼48.4 months) and 53.5months, respectively. Two patients from IB group had sentinel lymph node micrometastasis in the final pathology report and whole breast irradiation plus regional lymph node irradiation was added subsequently. One patient from IB group had regional lymph node recurrence during follow up and underwent surgery and re-irradiation with stable disease now. Most common acute toxicity was grade 1 radiation dermatitis. Neither radiation pneumonitis nor heart events were noted during the follow up. Multiple small scars left for more than 6 months in a few patients after interstitial brachytherapy. Patients reported cosmetic results according to Harvard scales, with “good” score in most patient of IB group and no cases described as “poor”. Dosimetric parameters of OAR showed the heartV_150cGy of CK and IB was 23.5% and 59.2%. The mean heart dose of CK and IB were 117.1cGy and 215.6cGy.

Conclusions

APBI by SBRT using CK is a non-invasive procedure and has better dose-sparing effect on the heart. There were less risks of wound infection or delayed wound healing when using CK. Since no small scars left on the breast when using CK, better cosmetic outcome is expected.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.