Intraoperative computed tomography imaging for dose calculation in intraoperative electron radiation therapy: Initial clinical observations

PLoS One. 2020 Jan 10;15(1):e0227155. doi: 10.1371/journal.pone.0227155. eCollection 2020.

Abstract

In intraoperative electron radiation therapy (IOERT) the energy of the electron beam is selected under the conventional assumption of water-equivalent tissues at the applicator end. However, the treatment field can deviate from the theoretic flat irradiation surface, thus altering dose profiles. This patient-based study explored the feasibility of acquiring intraoperative computed tomography (CT) studies for calculating three-dimensional dose distributions with two factors not included in the conventional assumption, namely the air gap from the applicator end to the irradiation surface and tissue heterogeneity. In addition, dose distributions under the conventional assumption and from preoperative CT studies (both also updated with intraoperative data) were calculated to explore whether there are other alternatives to intraoperative CT studies that can provide similar dose distributions. The IOERT protocol was modified to incorporate the acquisition of intraoperative CT studies before radiation delivery in six patients. Three studies were not valid to calculate dose distributions due to the presence of metal artefacts. For the remaining three cases, the average gamma pass rates between the doses calculated from intraoperative CT studies and those obtained assuming water-equivalent tissues or from preoperative CT studies were 73.4% and 74.0% respectively. The agreement increased when the air gap was included in the conventional assumption (98.1%) or in the preoperative CT images (98.4%). Therefore, this factor was the one mostly influencing the dose distributions of this study. Our experience has shown that intraoperative CT studies are not recommended when the procedure includes the use of shielding discs or surgical retractors unless metal artefacts are removed. IOERT dose distributions calculated under the conventional assumption or from preoperative CT studies may be inaccurate unless the air gap (which depends on the surface irregularities of the irradiated volume and on the applicator pose) is included in the calculations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Breast Neoplasms / diagnostic imaging
  • Breast Neoplasms / radiotherapy*
  • Feasibility Studies
  • Female
  • Humans
  • Intraoperative Period
  • Patient Transfer
  • Preoperative Period
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Radiotherapy, High-Energy / methods*
  • Retroperitoneal Neoplasms / diagnostic imaging
  • Retroperitoneal Neoplasms / radiotherapy*
  • Sarcoma / diagnostic imaging
  • Sarcoma / radiotherapy*
  • Tomography, X-Ray Computed / methods*

Associated data

  • figshare/10.6084/m9.figshare.9248897

Grants and funding

This study was supported by Ministerio de Ciencia, Innovación y Universidades (http://www.ciencia.gob.es) [grant number TEC2013–48251-C2 to JP, VG-V and MJL-C], co-funded by European Regional Development Fund (ERDF), “A way of making Europe” (https://ec.europa.eu/regional_policy/en/funding/erdf); by Ministerio de Ciencia, Innovación y Universidades (http://www.ciencia.gob.es), Instituto de Salud Carlos III (https://www.isciii.es) [grant numbers DTS14/00192 to JP, VG-V and FAC; PI15/02121 to FAC and JC-H; PI18/01625 to JP], co-funded by European Regional Development Fund (ERDF), “A way of making Europe” (https://ec.europa.eu/regional_policy/en/funding/erdf); and by Comunidad de Madrid (http://www.comunidad.madrid) [grant number TOPUS-CM S2013/MIT3024 to JP], co-funded by European Structural and Investment Fund (https://ec.europa.eu/info/funding-tenders/funding-opportunities/funding-programmes/overview-funding-programmes_en). The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades (http://www.ciencia.gob.es) and the Pro CNIC Foundation (https://www.fundacionprocnic.es) [to MD], and is a Severo Ochoa Center of Excellence (SEV-2015-0505). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.