Estimation and evaluation of a CT image based on electromagnetic tracking data for adaptive interstitial multi-catheter breast brachytherapy

Type: MA thesis

Status: finished

Date: July 1, 2020 - January 7, 2021

Supervisors: Andreas Maier

The second leading cause of death worldwide is cancer. In 2018 9.6 million people died of cancer [1]. Additionally, in 2018 24.2% of the cancer incidences in women were breast cancer [2]. Common therapies for breast cancer are chemotherapy, surgery, and radiation therapy [3]. There are two options for radiation therapy: whole breast irradiation and the accelerated partial breast irradiation [4]. One well-established possibility to apply accelerated partial breast irradiation is the interstitial multi-catheter brachytherapy (iBT), a treatment technique that uses γ-radiation from enclosed radioactive sources positioned very close to the tissue to be irradiated [5]. In order to guide the radiation source there, multiple plastic catheters are inserted surgically and remain within the body throughout the course of the treatment (typically five days). A CT scan, the so-called planning CT (PCT), serves as a basis for treatment planning.
At the University Hospital Erlangen, the standard protocol for iBT consists of nine treatment fractions of 3.8 Gy per fraction, administered within five consecutive days. To date, the treatment plan remains unchanged throughout this period and hence does not account for interfractional changes. However, in a study assessing the need for treatment adaptation in the course of the treatment it was found that 4% of the patients would have benefitted from replanning [6]. In our workflow, the only measure to ensure the correct position of the catheter implant is a follow-up CT (FCT) after the fourth fraction. However, this exposes the patient to additional dose and therefore cannot be performed prior to every fraction.
The aim of this Master’s thesis is to develop a CT estimation (estCT) based on the data from the PCT and a dose-free electromagnetic tracking system. The first step is calculating the deformation vector field from the EMT data acquired immediately after the PCT (without moving the patient in between) and the EMT data acquired immediately after the FCT. In a second step, this deformation field is used to warp the PCT to yield the estCT. The estCT can then be compared to the FCT as a ground truth.
If the estCT could accurately “reproduce” the FCT, this method would allow describing interfractional changes of the catheter geometry without additional dose exposure. Since EMT measurements are easy and fast to conduct at any time point in the course of the treatment, estCTs could be acquired prior each treatment fraction. Finally, these estCTs can be evaluated dosimetrically to trigger patient-specific changes to the treatment plan, which would mean an essential step towards adaptive brachytherapy.
Master’s Thesis Description
[1] World Health Organization: “Cancer”, 2018,, (Date last accessed 2018-06-19)
[2] BRAY, Freddie, et al. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA: a cancer journal for clinicians, 2018, 68. Jg., Nr. 6, S. 394-424.
[3] WAKS, Adrienne G.; WINER, Eric P. Breast cancer treatment: a review. Jama, 2019, 321. Jg., Nr. 3, S. 288-300.
[4] STRNAD, Vratislav, et al. Practical handbook of brachytherapy. UNI-MED Verlag, Bremen-London-Boston, 2014, S. 166-183.
[5] NJEH, Christopher F.; SAUNDERS, Mark W.; LANGTON, Christian M. Accelerated partial breast irradiation (APBI): a review of available techniques. Radiation Oncology, 2010, 5. Jg., Nr. 1, S. 90.
[6] KALLIS, Karoline, et al. Is adaptive treatment planning in multi-catheter interstitial breast brachytherapy necessary?. Radiotherapy and Oncology, 2019, 141. Jg., S. 304-311