Dosimetric consequences of seed placement accuracy in permanent breast seed implant brachytherapy

Alexandra Guebert, Michael Roumeliotis, Elizabeth Watt, Tyler Meyer, Sarah Quirk

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: This study quantifies the dosimetric impact of implant accuracy and derives a quantitative relationship relating implant accuracy to target dosimetry. Methods and Materials: A framework was developed to simulate multiple implants for error combinations. Spherical clinical target volumes (CTVs) were modeled with volumes 1.4 cm3, 9.2 cm3, and 20.6 cm3, representing the range seen clinically. Each CTV was expanded 10 mm isotropically to create a planning target volume (PTV). Random and systematic seed placement errors were simulated by shifting needles from their planned positions. Implant errors were simulated over the range of clinically practical errors in permanent breast seed implant. The relative effect on target coverage was evaluated. Regression analysis was performed to derive relationships between CTV dosimetry and the magnitude of implant accuracy. The validity of the clinically used 10 mm PTV margin for each of the CTVs was assessed. Results: Introducing practical implant errors resulted in CTV V90% median (10th and 90th percentile) of 97.7% (85.9% and 100%), 96.2% (86.8% and 99.7%), and 100% (77.8% and 100%) for the typical, large, and small CTV, respectively. All CTVs show similar trends in target coverage. Polynomials were derived relating seed placement accuracy to median (R2 = 0.82) and 10th percentile (R2 = 0.78) CTV V90%.. Conclusions: This work quantitatively describes the relationship between implant accuracy and CTV coverage. Based on simulations, the 10 mm PTV margin is adequate to maintain target coverage. These equations can be used with institutional seed placement accuracy to estimate coverage.

Original languageEnglish (US)
Pages (from-to)664-672
Number of pages9
JournalBrachytherapy
Volume20
Issue number3
DOIs
StatePublished - May 1 2021
Externally publishedYes

Keywords

  • Brachytherapy
  • Brachytherapy uncertainties
  • Breast brachytherapy
  • Optimization
  • Permanent breast seed implant

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Oncology

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