“Real-time gated proton therapy with a reduced source to imager distance: Commissioning and quality assurance”
Introduction (extract): Real-time gated proton therapy (RGPT) is a motion management technique unique to the Hitachi particle therapy system. It uses pulsed fluoroscopy to track an implanted fiducial marker. The marker positional tolerance can be defined such that the proton beam is only turned on for a small fraction of the breathing cycle. This effectively reduces the internal target volume (ITV) structure and thus the doses to the normal tissues as well. Unlike surface tracking technology, RGPT relies on implanted marker position which is a truer representation of tumor position. National Cancer Centre Singapore (NCCS) has recently performed has started treating prostate and liver cancers with RGPT since September 2023.
Methods (extract): As part of commissioning, NCCS measured fiducial marker tracking fidelity. This measures the visibility and the tracking fidelity of all the clinical fiducial markers under different water equivalent thickness (WET) to determine the maximum WET for which marker tracking is still feasible. Apart from testing the marker suitability for RGPT, this measurement ensures the matching and tracking algorithm for irregularly shaped markers is functional. We perform measurements on two different markers, namely 0.28 x 10 mm2 and 0.4 x 10 mm2 Gold Anchor markers which are used in our clinic. These markers can attach firmly to the tissue and reduce the odds of marker migration and it can be inserted in ball or rod shapes based on clinical preference.
Results (extract): The 0.4 x 10 mm2 Gold Anchor fiducial markers inserted in a rod and ball shape manner can be tracked reliably up to 20 cm and 30 cm of plastic water thickness respectively. The smaller 0.28 x 10 mm2 marker inserted in a ball shape manner can be tracked up to 25 cm of plastic water thickness.
Discussion (extract): 0.4 x 10 mm2 Gold Anchor marker has been chosen for clinical use with RGPT.