High dose rate brachytherapy versus electron boost for tumor bed after breast conserving therapy
OC-0016
Abstract
High dose rate brachytherapy versus electron boost for tumor bed after breast conserving therapy
Authors: Janna Bryantseva1, Sergei Novikov1, Irina Akulova1, Julia Melnik1, Sergei Kanaev1
1N.N. Petrov National Medical Research Center Oncology, radiotherapy, St Petersburg, Russian Federation
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Purpose or Objective
To perform dosimetric comparison of interstitial
high dose rate brachytherapy (HDRB) and electron boost to the tumor bed after
breast conserving therapy.
Material and Methods
In 62
patients with stage IA-IIIA breast cancer (pT1N0M0-pT2N2M0) HDRB was used to
deliver a boost to the tumor bed. In all the cases preimplantation CT with
markers on the scar and nipple was used for planning of the procedure. Tumor
bed was determined by markers that were implanted during surgery with
consideration of the tumor localization determined on pre-surgery staging CT. Insertion of the needles was performed under
CT navigation. Postimplant CT was used for final planning with inverse and
graphical optimization. Pre-implantation
CT images were used for additional virtual planning of electron boost to the
tumor bed. All brachytherapy and electron plans were compared according to the
following dosimetric parameters: V90 (%) – percentage of PTV receiving 90% of
prescribed dose;); Dmean – mean dose at organ at risk; Dmax – maximum dose in
the organ at risk (heart, left main coronary artery and its descending branch,
ipsilateral lung, breast, skin and subcutaneous tissue, liver).
Results
The use of HDRB it possible to more accurately irradiate the bed of a remote tumor than additional electron beam irradiation: the mean value of D90 using HDRB was 93.1% (69.1%-118%), while D90 was lower than 80% in only 8 patients; when using electrons, D90 was below 90% in 43.5% of cases, and in 10 patients below 70% with an average D90 value of 86.2% (47.6%-104%). The HDRB allows reducing the radiation load on the organs at risk: the myocardium and coronary vessels, especially during left-side localization of the process. Dmed for these structures is reduced from 3% when using electrons to 2.2% when using HDRB for myocardium, from 7.3% to 3.4% for the main trunk of the left coronary artery, from 12.1% to 6.9% for anterior descending branch of the left coronary artery; on the ipsilateral lung Dmax when using the electron beam was 69.8% (4.7%-104.5%), and when using VDB decreased to 26.8% (4.7%-76.7%), Dmed decreased from 6.5% (0.5%-19.3%) to 2.3% (0.8%-10.8%).
Conclusion
The use of brachytherapy, compared with the use of an electron beam,
improves the accuracy of irradiation of the tumour bed and significantly reduce
radiation dose to the organs at risk:
main trunk of the left coronary artery, descending branch of the left
coronary artery, ipsilateral lung, skin and subcutaneous tissue.