Session Item

Purpose: Reported brachytherapy incidents affecting a large number of patients raise relevant concerns about safety and treatment verification. The clinical acceptance of the methods currently available for estimating the delivered dose in BT is limited due to the absence of adequate commercial systems, large uncertainties, and laborious methods. Time-resolved measurements using imaging panels (IPs) can overcome several of the current technical limitations. However, considerable efforts are necessary to implement such technology in clinical practice.  This talk will provide an overview of current developments, main challenges, uncertainties and clinical trials using source tracking. In addition, we will present results obtained using an IP for source tracking aiming to evaluate the sensitivity of the panel and the possibility to combine source tracking with anatomical information.

Materials/Methods: A 3D printed pelvic phantom (Figure 1), based on a brachytherapy prostate patient, was made with 4 holes for the insertion of tissue-mimicking inserts, a “rectum” (cavity for the insertion of an ultrasound probe), and a template for needle insertion allowing several implant configurations. Two radiopaque markers (spheres with d ≈ 1mm) were placed at the back of the phantom to register CT coordinates and IP measurements. Different arrangements were tested with 4 tissue-mimicking inserts (cortical bone, inner bone, muscle, solid water, and adipose tissue). Different needle arrangements (4 – 9 needles) dwell times (0.3 – 1s) and interdwell distances (1 – 5 mm) were used to verify the IP sensitivity. In addition, IP acquisitions were performed using 0.139 and 0.278 mm spatial resolution and acquisition rates up to 33 fps.

Results: source movements <1mm are detected comparing consecutive frames whilst dwell positions are identified when the source dwells for at least 2 consecutive frames. Therefore, the acquisition rate should be at least 2 to 3 times higher than the desired measurement uncertainty.  All dwell positions were identified (figure 2) with acquisition rates ≥ 20 fps with and standard deviation (k=1) around 0.02 s. Higher acquisition rates (> 9 fps) require a lower spatial resolution, which didn’t affect source tracking capabilities. Radiopaque markers were clearly visible in both planning CT and IP measurements. Results obtained with different tissue-mimicking inserts showed differences in imaging intensity >10%. In addition, the ultrasound probe is visible in the IP images providing another geometric reference related to the patient anatomy.

Conclusion: The evaluated IP has submillimeter accuracy and acquisition rates (≥20 fps) allowing dwell time measurements with an accuracy superior to 0.1s.  IP acquisitions include geometric information (e.g. ultrasound sound probes) that can be related to the patient anatomy. In addition, the evaluated IP is sensitive to the material composition and could allow the use of patient anatomy as a reference.