Shahbazian H, Bakhshali R, Shamsi A, Bagheri A. Dosimetric analysis of breast cancer tumor bed boost: An interstitial brachytherapy vs. external beam radiation therapy comparison for deeply seated tumors.
Brachytherapy 2019;
19:264-274. [PMID:
31787575 DOI:
10.1016/j.brachy.2019.10.008]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/23/2019] [Accepted: 10/24/2019] [Indexed: 10/25/2022]
Abstract
PURPOSE
To dosimetrically compare interstitial brachytherapy (MIBT) vs. EBRT (3DCRT and high-energy electron beams) for deep-seated tumor bed boosts (depth ≥4 cm) in early-stage breast cancer.
METHODS AND MATERIALS
Planning CTs of fifteen left-side breast cancer patients previously treated with MIBT boost chosen for this study. MIBT, 3DCRT (three-field technique), and enface high-energy electron (15-18 MeV) plans retrospectively generated on these images. To minimize intrapatient target contour inconsistency, due to a technical limitation for transferring identical contours from brachytherapy to EBRT planning system, spherical volumes delineated as hypothetical CTVs (CTV-H) (depth ≥4 cm with considering the geometry of the brachytherapy implant) instead of original lumpectomy cavities (which had irregular contours). In EBRT, PTV-H=CTV-H+5 mm. To account for beam penumbra, additional PTV-H to beam-edge margins added (3DCRT = 5 mm; electron = 10 mm). Included organs at risk (OARs) were ipsilateral breast, skin, ribs, lung, and heart. Prescribed dose-fractionations were 12 Gy/3fractions (MIBT) and 16 Gy/8fractions (EBRT) (BED = 24 Gy, breast cancer Alpha/Beta = 4 Gy). Biologically equivalent DVH parameters for all techniques compared.
RESULTS
Mean CTV-H depth was 6 cm. Normal breast V25%-V100%; skin V10%-V90%; rib V25%-V75%; lung V5%-V25%; heart V10%; mean lung dose; ribs/lung Dmax were lower in MIBT vs. 3CDRT. MIBT reduced breast V25%-V125%; skin V25%-V125%; rib V25%-V75% and V100%; lung V25%-V90%; heart V10%-V50%; skin/ribs/lung Dmax compared to electrons. In contrast, breast V125%-V250% and V175%-V250% were increased in MIBT vs. 3DCRT and electron plans, respectively. Electron plans had the minimum mean heart dose.
CONCLUSIONS
From a dosimetric point of view, in deeply-seated lumpectomy beds, MIBT boost better protects OARs from exposure to medium and high doses of radiation compared to 3DCRT and high energy electron beams (except more ipsilateral breast hot spots).
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