eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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5/2021
vol. 13
 
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abstract:
Original paper

Radiobiological evaluation of organs at risk for electronic high-dose-rate brachytherapy in uveal melanoma: a radiobiological modeling study

Timothy J. Waldron
1
,
Bryan G. Allen
1
,
Edward Pennington
1
,
Culver Boldt
2
,
Yusung Kim
1

1.
Departments of Radiation Oncology, Carver College of Medicine, The University of Iowa, Iowa City, Iowa, USA
2.
Departments of Ophthalmology, Carver College of Medicine, The University of Iowa, Iowa City, Iowa, USA
J Contemp Brachytherapy 2021; 13, 5: 563–574
Online publish date: 2021/10/29
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Introduction
The objective of this study was to examine feasibility of single- or hypo-fraction of high-dose-rate (HDR) electronic brachytherapy (eBT) in uveal melanoma treatment.

Material and methods
Biologically effective doses (BED) of organs at risk (OARs) were compared to those of iodine-125-based eye plaque low-dose-rate brachytherapy (125I LDR-BT) with vitreous replacement (VR). Single- or hypo-fractionated equivalent physical doses (SFEDs or HFEDs) for tumor were calculated from tumor BED of 125I LDR-BT using linear-quadratic (LQ) and universal survival curve (USC) models. BED OARs doses to retina opposite the implant, macula, optic disc, and lens were calculated and compared among SFED, HFED, and 125I LDR-BT. Electronic BT of 50 kVp was considered assuming dose fall-off as clinically equivalent to 125I LDR-BT. All OARs BEDs were analyzed with and without silicone oil VR.

Results
For a single-fraction incorporating VR, the median/interquartile range of LQ (USC)-based BED doses of the retina opposite the implant, macula, optic disc, and lens were 16%/1.2% (33%/4%), 35%/19.5% (64%/17.7%), 37%/19% (75%/17.8%), and 27%/7.9% (68%/23.2%) of those for 125I LDR-BT, respectively. SFED tumor values were 29.8/0.2 Gy and 51.7/0.5 Gy when using LQ and USC models, respectively, which could be delivered within 1 hour. SFED can be delivered within 1 hour using a high-dose-rate eBT. Even four-fraction delivery of HFED without VR resulted in higher OARs doses in the macula, optic disc, and lens (135 ~ 159%) than when using 125I LDR-BT technique. A maximum p-value of 0.005 was observed for these distributions.

Conclusions
The simulation of single-fraction eBT, including vitreous replacement, resulted in significantly reduced OARs doses (16 ~ 75%) of that achieved with 125I LDR-BT.

keywords:

electronic brachytherapy, episcleral plaque, uveal melanoma, biologically equivalent dose, vitreous replacement

 
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