Abstract—Orthogonal ray imaging is a new low-dose imaging technology under study aimed at assist external-beam radiotherapy (EBRT) treatments. It consists in detecting radiation scattered in the patient and emitted perpendicularly to the incident beam. Such radiation can be collected by positioning a multi-sliced, collimator-based, 1D detector system parallel to the beam axis, hence collecting such orthogonal rays, or by using a pinhole-like detector system positioned above or below the patient. This system can potentially be useful for on-board imaging, or real-time EBRT monitoring. In terms of prostate cancer irradiation, the use of implanted fiducial markers allows a more precise verification of the gland position relative to the bony anatomy. The prostate target normally exhibits intra- and interfraction motion induced by the daily variation in rectal and bladder filling. In order to solve this issue, three gold fiducial markers are inserted into the prostate. In the present study, the imaging capability provided by utilizing X-rays escaping the patient/fiducial markers orthogonally in respect to the incoming beam direction is studied by GEANT4 simulation. The results allow concluding that the signal provided by such X-rays is highly coincident with the position of the gold fiducial markers, even in situations where these have been deviated by as little as 3.0 mm.

Index Terms—Image-guided radiotherapy, OrthoCT, Monte Carlo simulation, Gold fiducial markers, Prostate cancer

Cite: Ana Luísa Lopes, Hugo Simões, Carolina Travassos, and Paulo Crespo, "Patient Compton Scattered Radiation for Monitoring Prostate Radiotherapy with Gold Fiducial Markers: A Simulation Study," International Journal of Pharma Medicine and Biological Sciences, Vol. 6, No. 3, pp. 77-82, July 2017. doi: 10.18178/ijpmbs.6.3.77-82