S142
Brachytherapy - Physics
ESTRO 2026
comprehensive treatment verification in HDR brachytherapy, utilising their complementary error- trapping capabilities to improve sensitivity and robustness. Material/Methods: The combination of the two systems was evaluated in a solid water phantom containing 14 needles resembling a clinical implant. An inorganic scintillation detector (ISD) comprised of a sub-millimetre cuboid ZnSe:O crystal, coupled to a photodiode via optical fibre, was inserted centrally in its own needle. The FPD was placed beneath the phantom and aligned with the overhead mobile x-ray radiography unit that facilitates implant localisation and registration to ST. To demonstrate the benefits of combining the two systems, clinically relevant errors were introduced, focussing on those that are challenging for each system alone – two such errors are shown here: (i) a 10mm indexer length error which would not be detected by ISD using its derived detector position procedure [2], and (ii) a lateral phantom shift mid- treatment resembling a patient movement that would be flagged as a potential catheter swap by the FPD Each error case was investigated using each detector individually and by combining the two.Figure 1 shows the 10mm indexer-length error. The scintillator dosimetry alone (1a) suggests error-free delivery, while the FPD tracking (1b) correctly identifies this error. Using the scintillator position determined by FPD imaging, the scintillator correctly showed the delivery error (1c).Figure 2 shows the mid-treatment- shift: FPD tracking (2a) shows an apparent dwell position disagreement, potentially interpreted as a catheter-swap error depending on proximity of adjacent needles. Scintillator dosimetry (2b) confirms correct doses, as the ISD moves with the patient, identifying the cause as a patient movement relative to the FPD. The patient-to-FPD registration can be recovered via an updated radiograph. tracking. Results:
The largest differences in applicator position measurements with the surface scanning compared to CT were 0.83 mm, 0.79 mm, 0.71 mm in 𝑡 x, 𝑡 y, 𝑡 z translation and 0.79 °, 0.71 °, 1.02 ° in 𝜃 x, 𝜃 y, 𝜃 z rotation respectively (Figure 2). The standard deviation of repeated surface scanning measurements due to depth image fluctuations was 0.13 mm (translation) and 0.54 ° (rotation).
Conclusion: Surface scanning shows to be a promising technology to accurately position customized skin applicators on the patient during brachytherapy treatments. The developed single camera prototype can provide sub- mm and sub-degree accuracy. A multi-camera approach and more advanced image and point cloud processing can further improve performance for clinical applications. Keywords: surface guidance, skin, HDR Improving HDR brachytherapy treatment verification using a combination of flat-panel detector source tracking and time-resolved scintillator dosimetry Maximilian Hanlon 1,2 , Jordan Wallace 1 , Marjolein Heidotting 3 , Jacob G Johansen 3,4 , Ryan L Smith 2,1 , Rick D Franich 1,2 1 School of Science, RMIT University, Melbourne, Australia. 2 Alfred Health Radiation Oncology, The Alfred, Melbourne, Australia. 3 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 4 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark Proffered Paper 4360 Purpose/Objective: Real-time in vivo dosimetry (IVD) and source tracking (ST) are being performed for routine monitoring of HDR brachytherapy at our clinics with scintillator- based point dosimetry and flat-panel detector (FPD) ST, respectively [1,2]. Both methods have proven valuable for treatment verification but have specific limitations. This phantom study investigates the feasibility of combining the two systems for
Made with FlippingBook - Share PDF online