Sep 12 – 17, 2021
University of Birmingham
Europe/London timezone

Upstream MLC leaf position detection in complex radiotherapy fields

Sep 13, 2021, 5:25 PM
Teaching and Learning Building (University of Birmingham)

Teaching and Learning Building

University of Birmingham

Edgbaston Campus University of Birmingham B15 2TT UK
talk Medical Applications of Position Sensitive Detectors Medical Applications of Position Sensitive Detectors 1


Mr Jordan Pritchard (University of Bristol)


Multileaf collimators (MLC) are an integral component in modern radiotherapy as they dynamically shape the MV photon treatment field and therefore need to be closely monitored to ensure correct treatment delivery. Currently, MLC leaves are calibrated to ±1 mm every 3 months, however leaves can drift beyond this during calibration dates and treatment verification only occurs post-treatment. MAPS detectors are radiation hard for photon and electron irradiation, have high readout speeds and low attenuation which makes them ideal upstream radiation detectors. Previously, we reported on leaf position reconstruction for single leaves using the Lassena, a 12x4 cm2, three side buttable MAPS suitable for clinical deployment. Sobel filter-based methods were used for edge reconstruction. It was shown that correspondence between reconstructed and set leaf position was excellent and resolutions ranged between 60.6±8 and 109±12 μm for a single central leaf with leaf extensions ranging from 1 to 35 mm using 0.3 sec of treatment beam time. Here, we report on leaf edge reconstruction using Sobel filter-based methods in complex leaf configurations, as in clinical use with extensions ranging up to 120 mm. The Lassena detector was placed in the treatment field of an Elekta Agility LINAC with MLC leaves of width 0.5 cm extended into the field creating various leaf configurations. Results show that leaf positions can be reconstructed with resolutions between 78±7 and 149±14 μm at the iso-centre using 0.15 sec long treatment segments. These resolutions significantly exceed current calibration standards.

Title Mr
Institute University of Bristol
Nationality British
Your name Jordan Pritchard

Primary authors

Mr Jordan Pritchard (University of Bristol) Dr Jaap Velthuis (University of Bristol) Dr Lana Beck (University of Bristol) Ms Yutong Li (University of Bristol) Dr Chiara De Sio (University of Bristol) Dr Richard Hugtenburg (University of Bristol)

Presentation materials