Electromagnetic tracking in interstitial brachytherapy: A systematic review

Abstract

Brachytherapy is a well-established treatment option for different cancer types. One treatment option, namely temporary afterloading brachytherapy, utilizes an encapsulated radioactive source, which is guided through implanted applicators to pre-defined dwell positions, to deliver highly conformal and concentrated doses to the target volume. However, treatment errors and uncertainties might still occur. The treatment therefore requires a stringent verification on an individual patient level, particularly in the form of applicator reconstruction. Electromagnetic tracking (EMT) is a possible verification option whose application neither relies on direct line of sight nor does it increase the radiation exposure. However, its systematic clinical application is not yet realized. This review will separate the concept of treatment verification through the use of electromagnetic tracking into four focus groups and categorize the relevant papers within said groups. The four focus groups are geometric assessment, applicator reconstruction, patient-individual quality assurance and adaptive treatment planning. The reviewed papers can be mainly sorted into the focus groups of geometric assessment and applicator reconstruction underlining the potential of EMT as an asset for reconstruction and localization. A smaller group of papers can be associated with patient-individual quality assurance where the detection of implant variations such as swaps within the connector cohort or single catheter shifts take center stage. The final focus group, adaptive treatment planning, is sparsely represented, yet the feasibility of an adaptive treatment course can be derived. This review will close with a discussion of possible improvements and illustrate the path ahead to clinical implementation.

Localization of reference points in electromagnetic tracking data and their application for treatment error detection in interstitial breast brachytherapy

“…Its capability to track objects inside the human body, that is in the absence of a line-of -sight, without dose exposure for the patient, and in real-time is a unique characteristic, especially among those imaging techniques available in a typical brachytherapy suite. [1][2][3] iBT is a recognized irradiation technique for various tumor entities including breast, prostate, and gynecological cancers, which is known for its conformal dose distributions and effective healthy tissue sparing. [4][5][6][7] It involves the use of sealed radioactive sources that are brought close to the target volume with surgically inserted or implanted applicators.…”

“…4 EMT allows to determine the geometry of an iBT implant in treatment position and on a fraction-basis by constantly acquiring positional data while being moved through the catheters or hollow needles that comprise the implant during the mandatory check cable run. 1,8,9 The obtained three-dimensional model of the implant is the foundation for the detection of treatment errors and uncertainties, [10][11][12][13][14][15] as well as for increasing accuracy and speed of the implant reconstruction. [16][17][18] Despite the successful use for these applications, EMT faces the problem that, intrinsically, it cannot provide a link to the patient's anatomy.…”

“…Electromagnetic tracking (EMT) can play a pivotal role in patient‐specific, pre‐treatment quality assurance in interstitial brachytherapy (iBT). Its capability to track objects inside the human body, that is in the absence of a line‐of‐sight, without dose exposure for the patient, and in real‐time is a unique characteristic, especially among those imaging techniques available in a typical brachytherapy suite 1–3 . iBT is a recognized irradiation technique for various tumor entities including breast, prostate, and gynecological cancers, which is known for its conformal dose distributions and effective healthy tissue sparing 4–7 .…”

“…It involves the use of sealed radioactive sources that are brought close to the target volume with surgically inserted or implanted applicators 4 . EMT allows to determine the geometry of an iBT implant in treatment position and on a fraction‐basis by constantly acquiring positional data while being moved through the catheters or hollow needles that comprise the implant during the mandatory check cable run 1,8,9 . The obtained three‐dimensional model of the implant is the foundation for the detection of treatment errors and uncertainties, 10–15 as well as for increasing accuracy and speed of the implant reconstruction 16–18 …”

Estimating follow‐up CTs from geometric deformations of catheter implants in interstitial breast brachytherapy: A feasibility study using electromagnetic tracking

“…The geometric information thus obtained is the basis for all applications of EMT in iBT, which range from catheter reconstruction 14,15 to error detection [16][17][18] and treatment verification. [19][20][21] A major drawback is that, unlike (cone-beam) CT imaging, EMT cannot provide information about the anatomic context and hence about the target volume and the critical structures, without which the treatment plan quality cannot be appraised according to GEC-ESTRO recommendations. 11 This is why the clinical decision to trigger a CT rescan and to potentially adapt the treatment should not be solely based on the magnitude of geometric deformation of the implant, but on the dosimetric impact of such deformations on dose quality indices like coverage index, conformity index, and maximum doses to organs at risk.…”