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

  1. Ophthalmology, Department of Surgery, University of Melbourne, Melbourne (Victoria), Australia
  2. Ocular Oncology Research Unit, Centre for Eye Research Australia, Melbourne (Victoria), Australia
  3. Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles (California), USA
  4. Department of Ocular Oncology, Royal Victorian Eye and Ear Hospital, Melbourne (Victoria), Australia
  5. Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne (Victoria), Australia
  6. Alfred Health Radiation Oncology, The Alfred, Melbourne (Victoria), Australia
J Contemp Brachytherapy 2023; 15, 6: 442–447
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: D98%, 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 D98% 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. D98% was calculated for plaque-tumor edge distances of 0-5 mm. Additionally, we defined minimum plaque-tumor edge distances, at which D98% fell by 10% and 5% (safety margins).

Results:
D98% decreased as plaque-tumor edge distance decreased, i.e. as plaque eccentricity increased. Minor (< 1 mm) plaque decentration caused minimal D98% 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 D98% modulators. Further investigation of the effect of these characteristics and dose to organs at risk is essential.

keywords:

brachytherapy, ruthenium, melanoma, eccentric

 
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