Citation: Australasian Physical and Engineering Sciences in Medicine. 2019, 42(1), 400-1
Author: Schnuerer R. (Roland.schnuerer@cockcroft.ac.uk); Yap J.S.L. (Jacinta.yap@cockcroft.ac.uk); Zhang H. (Hao.zhang@cockcroft.ac.uk); Welsch C.P. (carsten.welsch@cockcroft.ac.uk); Szumlak T. (szumlak@agh.edu.pl); Kacperek A. (andrzej.kacperek@nhs.net)
Abstract: Introduction Online beam monitoring in medical accelerators is essential in assuring patient's safety as well as high quality and efficacy of cancer treatment. In clinical practice for proton therapy, currently used ionization chambers are interceptive devices, degrading both the beam profile and its energy spread. Therefore, a new noninterceptive approach of online beam monitoring is highly desirable. Method The Vertex Locator (VELO) detector is a multi-strip silicon detector used in the LHCb experiment at CERN. The semi-circular design and position of its sensitive silicon detector offers a non-invasive way to measure the beam intensity through a precise measurement of the beam halo without interfering with the beam core. The adapted standalone VELO detector is integrated at the 60 MeV proton therapy beamline at the Clatterbridge Cancer Centre (CCC), UK. Synchronised with a Faraday Cup and the RF cyclotron frequency, the quality of the beam monitor is assessed by measuring the beam current at different dose rates and by monitoring the beam halo profile at different positions along the beamline. Results The integration zone of the VELO detector is after the double scattering foils, range shifter and modulation wheel. The detector can move along 15 cm along the beamline. The beam current is measured for the dose rate of 10 Monitor Units (MU)/min to 60 MU/min at position 0 cm, 8 cm and 15 cm each. Also, 2D and 3D beam profile measurements are presented for non-skewed and skewed beams. The results are benchmarked against GEANT4 simulations. Conclusion The full setup optimized for implementation in the proton beam line at CCC is described. The capability of VELO as a beam monitor is assessed by measuring the beam current at different dose rates and by monitoring the beam profile. Further measurements in other proton therapy facilities with scanning systems are desirable.
