eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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vol. 12
Original paper

Biological dose summation of external beam radiotherapy for the whole breast and image-guided high-dose-rate interstitial brachytherapy boost in early-stage breast cancer

Georgina Fröhlich
1, 2
Norbert Mészáros
1, 3
Viktor Smanykó
Csaba Polgár
1, 3
Tibor Major
1, 3

Centre of Radiotherapy, National Institute of Oncology, Budapest, Hungary
Faculty of Natural Sciences, Eötvös Loránd University, Budapest, Hungary
Department of Oncology, Faculty of Medicine, Semmelweis University, Budapest, Hungary
J Contemp Brachytherapy 2020; 12, 5: 462–469
Online publish date: 2020/10/30
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To develop an alternative method for summing biologically effective doses of external beam radiotherapy (EBRT) with interstitial high-dose-rate (HDR) brachytherapy (BT) boost in breast cancer. The total doses using EBRT boost were compared with BT boost using our method.

Material and methods
Twenty-four EBRT plus interstitial HDR-BT plans were selected, and additional plans using EBRT boost were created. The prescribed dose was 2.67/40.05 Gy to whole breast and 4.75/14.25 Gy BT or 2.67/10.7 Gy EBRT to planning target volume (PTV) boost. EBRT and BT computed tomography (CT) were registered twice, including fitting the target volumes and using the lung, and the most exposed volume of critical organs in BT were identified on EBRT CT images. The minimal dose of these from EBRT was summed with their BT dose, and these EQD2 doses were compared using BT vs. EBRT boost. This method was compared with uniform dose conception (UDC).

D90 of PTV boost was significantly higher with BT than with EBRT boost: 67.1 Gy vs. 56.7 Gy, p = 0.0001. There was no significant difference in the dose of non-target and contralateral breast using BT and EBRT boost. D1 to skin, lung, and D0.1 to heart were 58.6 Gy vs. 66.7 Gy (p = 0.0025), 32.6 Gy vs. 50.6 Gy (p = 0.0002), and 52.2 Gy vs. 58.1 Gy (p = 0.0009), respectively, while D0.1 to ribs was 44.3 Gy vs. 37.7 Gy (p = 0.0062). UDC overestimated D1 (lung) by 54% (p = 0.0001) and D1 (ribs) by 28% (p = 0.0003).

Based on our biological dose summation method, the total dose of PTV in the breast is higher using BT boost than with EBRT. BT boost yields lower skin, lung, and heart doses, but higher dose to ribs. UDC overestimates lung and ribs doses.


breast cancer, dose summation, integrated biological doses, boost, interstitial brachytherapy

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