Trial lecture title: The scientific evidence and practical implications of the acquisition of variable number of views during mammography or tomosynthesis screening.
The ordinary opponents are:
- First opponent: Professor Sophia Zackrisson, Lund University, Sweden
- Second opponent: Professor Ioannis Sechopoulos, Radboud University Medical Center, Nijmegen, The Netherlands
- Leader of the evaluation committee: Professor Trine B. Haugen, Faculty of Health Sciences, OsloMet
The leader of the public defence is Professor Kaare Magne Nielsen, OsloMet.
The main supervisor is Professor Solveig Hofvind, Faculty of Health Sciences, OsloMet. The co-supervisor is Professor Peter Hogg, University of Salford.
Abstract
Breast cancer is the most common type of cancer among women in the world, and also in Norway. BreastScreen Norway offers mammographic screening to all women aged 50–69 years in Norway, and the screening examination includes two mammograms of each breast.
Compression force is applied to the breast during the examination to reduce the thickness of the breast, separate breast structures, minimise movement blur and thereby increase image quality and reduce the radiation dose.
However, the breast compression may lead to uncomfortable or painful experiences for the women. The Norwegian guidelines recommends applying a compression force between 108–177 Newton (N).
The guidelines are based on expert opinions and "best practice", however, optimal values for breast compression are not known.
Breast compression parameters
In this thesis, I investigated how breast compression was used in BreastScreen Norway.
The aim was to generate knowledge about breast compression parameters and radiation dose used at the breast centres in BreastScreen Norway, whether women attending consecutive screens receives similar breast compression, and whether similar breast compression is used between the screening techniques standard digital mammography (DM) and digital breast tomosynthesis (DBT).
We defined breast compression parameters as compression force, compression pressure (kilopascal, kPa), compressed breast thickness (mm). The work was performed in the period 2015–2019, solely using data from BreastScreen Norway.
First study
First, we retrospectively collected information about compression forces used between and within breast centres among 17,951 women attending screening at fourteen breast centres in BreastScreen Norway, January–March 2014.
We observed a larger variation in compression force between the breast centres (<56N) than between mammography x-ray machines (<18N) within the breast centres.
Second study
In the second study, we used the same study sample and variables, in addition to information about compressed breast thickness and radiation dose. We explored the correlation between quartiles of compression force and compressed breast thickness, and radiation dose.
We found that the radiation dose increased by quartiles of compression force and compressed breast thickness, where the highest values of compression force and compressed breast thickness had the highest dose.
Third study
In the third study, we investigated whether women who attends consecutive screening examinations in BreastScreen Norway receives similar breast compression.
We retrospectively analysed the compression force, compression pressure and compressed breast thickness among 25,143 women attending four consecutive screening examination in two counties during January 2007 and March 2016.
We observed increased mean values of compression force (<9.0N), compression pressure (<1.4kPa) and compressed breast thickness (<2.3mm) from first to consecutive screening examinations, when adjusting for breast volume, fibroglandular volume, the women’s age, breast centre and calendar year.
Fourth study
Finally, in the fourth study we used data from a randomised controlled trial; the Tomosynthesis Trial in Bergen (To-Be-trial), performed as a part of BreastScreen Norway.
We compared the compression force, compression pressure, compressed breast thickness and mean glandular dose (MGD) used for 11,056 women screened with DM versus 10,673 women screened with DBT in the trial during 2016 and 2017.
Women screened using DM received higher compression force (+4.7N), compression pressure (+1.0kPa), and compressed breast thickness (in medio-lateral oblique view, +0.3mm) than women screened using DBT, when adjusting for age, quartiles of breast volume and quartiles of fibroglandular volume.
Findings
With today’s guidelines for breast compression, we observed that breast compression varied between and within breast centres, for the same women when they attended consecutive screening examinations and between DM and DBT in BreastScreen Norway.
Our findings call for attention to the practice of breast compression in mammographic screening.
Today’s guidelines for breast compression should be revised with a goal of establishing evidence-based guidelines for breast compression.
The guidelines should be developed as a partnership between radiologists, medical physicists and radiographers, and women within the screening program.
