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

Abstract

Purpose 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). Results D 90 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. D 1 to skin, lung, and D 0.1 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 D 0.1 to ribs was 44.3 Gy vs. 37.7 Gy ( p = 0.0062). UDC overestimated D 1 (lung) by 54% ( p = 0.0001) and D 1 (ribs) by 28% ( p = 0.0003). Conclusions 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.

Comparison of Breast Cancer Radiotherapy Techniques Regarding Secondary Cancer Risk and Normal Tissue Complication Probability – Modelling and Measurements Using a 3D-Printed Phantom

“…As a boost after external beam radiotherapy, only Fröhlich et al. ( 79 ) combined interstitial multicatheter brachytherapy (3 × 4.75 Gy) with tangential beam WBI (15 × 2.67-Gy accelerated fractionation), showing that brachytherapy achieved a higher dose to the target with equal sparing of OARs in comparison to percutaneous treatment of both series, which is consistent with our observations, albeit for a normally fractionated dose concept.…”

Determining Combined Modality Dosimetric Constraints by Integration of IMRT and LDR Prostate Brachytherapy Dosimetry and Correlation with Toxicity

“…Fröhlich et al used deformable image registration to combine volumetric modulated arc therapy and high-dose rate (HDR) brachytherapy dose contributions for 25 patients with intermediate- and high-risk prostate cancer. 34 The authors demonstrated superior BED of brachytherapy boost versus external beam boost but did not examine clinical toxicity. Moulton et al summed 4-field 3D conformal dose distributions with HDR for 118 patients with prostate cancer and found significant correlations between dose strata and GI toxicity such as rectal bleeding and stool frequency.…”

Unresectable bulky chest wall recurrent breast cancer controlled with CT-guided interstitial high-dose-rate brachytherapy and external beam radiotherapy with adjuvant hormonal therapy – case report

“…In patients with bulky unresectable tumors, EBRT alone may not provide adequate loco-regional control [14]. Fröhlich et al [15] demonstrated that EBRT plus ISBT after breast surgery allowed for delivery of higher doses compared with EBRT alone.…”