On the importance of quality assurance (QA) for COMS eye plaque Silastic inserts: A guide to measurement methods, typical variations, and an example of how QA intercepted a manufacturing aberration

Courtney C. Oare, Christopher L. Deufel, Jordan McCauley Cutsinger, Tania De La Fuente Herman, Clara Ferreira

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: Eye plaques are widely used for ocular melanoma and provide an effective alternative to enucleation with adequate tumor control. A COMS plaque utilizes a Silastic insert for precise positioning of the radioactive seeds with respect to the scleral surface of the eye; however, due to manufacturing variability, the insert may unintentionally increase or decrease the distance between the sources and tumor. The purpose of this work is to provide guidance in measuring and identifying outliers in Silastic inserts. The importance of regular quality assurance (QA) is illustrated in an experience where a systematic problem was detected and the manufacturer's 22-mm mold was corrected. Methods: A detailed description of the molds and manufacturing process used to produce Silastic inserts is provided, including photographs of the process steps. The variability in Silastic insert production was evaluated by measuring the thickness of 124 Silastic inserts. An estimate of how the observed Silastic thickness discrepancies impact the dose to the tumor and critical eye structures was performed using homogeneous dose calculations. A standard QA protocol was developed to guide the clinical user. Results: Thickness of the measured Silastic inserts ranged from 1.22 to 2.67 mm, demonstrating variation from the 2.25 mm standard. Six of the 22-mm inserts were outliers (Δthickness >3 standard deviations) and were excluded from the statistics. The outliers were investigated with the help of the manufacturer, who discovered that a systematic error was accidentally introduced into the 22-mm mold. Conclusions: Due to manufacturing errors or variability, the Silastic inserts used in COMS eye plaques may be thicker or thinner than the design standard. Such variations may impact tumor control or increase the risk of normal tissue side effects. A standardized QA program is recommended to detect variations and communicate unusual findings to the manufacturer.

Original languageEnglish (US)
Pages (from-to)72-82
Number of pages11
JournalJournal of Applied Clinical Medical Physics
Volume22
Issue number8
DOIs
StatePublished - Aug 2021

Bibliographical note

Funding Information:
We would like to thank Jacob Trachsel from Trachsel Dental Inc. for many helpful conversations with regards to Silastic manufacturing and for welcoming us into their fabrication studio to learn about and photograph the Silastic manufacturing process.

Publisher Copyright:
© 2021 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine

Keywords

  • LDR brachytherapy
  • Silastic
  • eye plaque
  • quality assurance
  • uveal melanoma

PubMed: MeSH publication types

  • Journal Article

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