Quantifying the effect of eccentric ruthenium plaque placement on tumor volume dose

Jeremy P. M. Flanagan; William H. F. Udovenya; Melvin A. Astrahan; Daniel McKay; Claire Phillips; John D. McKenzie; Roderick O’Day; Lotte S. Fog

doi:10.5114/jcb.2023.133614

eISSN: 2081-2841
ISSN: 1689-832X

Journal of Contemporary Brachytherapy

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6/2023
vol. 15

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abstract:

Original paper

Quantifying the effect of eccentric ruthenium plaque placement on tumor volume dose

Jeremy P. M. Flanagan

^{1, 2}

,

William H. F. Udovenya

¹

,

Melvin A. Astrahan

³

,

Daniel McKay

^{2, 4}

,

Claire Phillips

⁵

,

John D. McKenzie

⁴

,

Roderick O’Day

^{2, 4}

,

Lotte S. Fog

^{4, 6}

Ophthalmology, Department of Surgery, University of Melbourne, Melbourne (Victoria), Australia
Ocular Oncology Research Unit, Centre for Eye Research Australia, Melbourne (Victoria), Australia
Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles (California), USA
Department of Ocular Oncology, Royal Victorian Eye and Ear Hospital, Melbourne (Victoria), Australia
Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne (Victoria), Australia
Alfred Health Radiation Oncology, The Alfred, Melbourne (Victoria), Australia

J Contemp Brachytherapy 2023; 15, 6: 442–447

DOI: https://doi.org/10.5114/jcb.2023.133614

Online publish date: 2023/12/09

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Purpose:
Ruthenium-106 brachytherapy is a common treatment for small to medium-sized uveal melanomas. In certain clinical contexts, plaques may be placed eccentrically to tumor center. The effect of plaque decentration, a common radiation dose measurement in radiotherapy: D_98%, the percentage of the tumor volume receiving at least 98% of the prescribed dose (a commonly used term in radiation oncology), is unknown. We investigated this using two commonly used plaques (CCA and CCB; Eckert & Ziegler, BEBIG GmbH) in silico.

Material and methods:
Using a Plaque Simulator™ (Eye Physics) plaque modelling software, treatment time required to deliver 100 Gy D_98% with central plaque placement was calculated for both plaque models, treating tumors with basal dimensions of 10 mm (CCB plaque only) and 7 mm (CCA and CCB plaques), and a range of thicknesses. D_98% was calculated for plaque-tumor edge distances of 0-5 mm. Additionally, we defined minimum plaque-tumor edge distances, at which D_98% fell by 10% and 5% (safety margins).

Results:
D_98% decreased as plaque-tumor edge distance decreased, i.e. as plaque eccentricity increased. Minor (< 1 mm) plaque decentration caused minimal D_98% changes across tumor thicknesses. Safety margins did not follow a consistent pattern.

Conclusions:
Eccentric plaque placement reduces the radiation dose delivered to choroidal tumors. Both tumor (thickness, diameter) and plaque (size, location) characteristics are important D_98% modulators. Further investigation of the effect of these characteristics and dose to organs at risk is essential.

keywords:

Quantifying the effect of eccentric ruthenium plaque placement on tumor volume dose

Jeremy P. M. Flanagan 1, 2 , William H. F. Udovenya 1 , Melvin A. Astrahan 3 , Daniel McKay 2, 4 , Claire Phillips 5 , John D. McKenzie 4 , Roderick O’Day 2, 4 , Lotte S. Fog 4, 6

brachytherapy, ruthenium, melanoma, eccentric

Jeremy P. M. Flanagan

^{1, 2}

,

William H. F. Udovenya

¹

,

Melvin A. Astrahan

³

,

Daniel McKay

^{2, 4}

,

Claire Phillips

⁵

,

John D. McKenzie

⁴

,

Roderick O’Day

^{2, 4}

,

Lotte S. Fog

^{4, 6}