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| Home > Publications database > Ion Beam Tracking: Pin-pointing the location ofthe Bragg peak real-time in Patients |
| Report | DKFZ-2019-02784 |
2019
EFOMP
Abstract: The main argument for the use of ion beams (protons or carbon ions) in radiotherapy is their ability to lower the depositeddose to surrounding healthy organs, because of the Bragg peak. However, due to the steep dose gradient at the distal edgeof the Bragg peak, uncertainties in the determination of ion range can have a profound impact on organs adjacent to the tumor.Incorrect range predictions may cause an overshoot or undershoot of the Bragg peak respectively lowering the tumordose or increasing the delivered dose to adjacent organ.Clinically the uncertainty in the range predictions is accounted for by adding a margin around the tumor to address all possibleshifts of the Bragg peak. We thus voluntarily irradiate nearby healthy organs to guarantee that the cancer gets full dose,which can lead to severe side effects for the patient. In addition, ion beam treatment directions are often selected that avoidplacing the sharp falloff of the Bragg peak near or directly on the edge of an adjacent healthy organ that is sensitive to radiation.In order to maximize the benefit of ion beam therapy, it would be desirable to verify real-time the range in patients. Thestate-of-the-art for in-vivo range verification methods was reviewed by Knopf 1, where technologies such as implantablemarkers, radiography, prompt gamma imaging, positron emission tomography (PET) and MRI were presented and discussed.Prompt gamma imaging (PGI) has become the most promising technique for real-time in-vivo range verification, offeringan instantaneous snap-shot of the location of the Bragg peak in the patient and not being affected by biological washout ororgan motion. PGI was initially proposed in 2003 by Stichelbaut 2 at the PTCOG meeting, for online verification of the ionrange. The first experimental evaluation of PGI was performed on a 38 MeV proton beam in 2007 3, using CsI(Tl) scintillatoras the primary detector of the prompt gammas. Since 2007, several research groups have tried to develop PGI technologyfor use with 1) proton beams using cyclotrons 4-8 and 2) ion beams using synchrotrons 9-10. The critical aspect for a successfulapplication of PGI in patients is the efficient detection of the secondary prompt gamma radiation leaving the body relative tothe large background signal coming from scattered photons and neutron activated gammas. Most PGI systems are photoncounting systems that integrate the photon signal arriving at the detector 5, while others use energy (prompt gamma spectroscopy,PGS 4) or timing (prompt gamma timing, PGT 7) to separate the prompt gammas from the background.Ongoing radiation oncology medical physics research in Heidelberg focuses on developing novel PGS imaging technologiesto allow real-time Bragg peak verification in patients for protons, Helium, Carbon and Oxygen ion beams available at theHeidelberg Ion Therapy (HIT) facility. The HIT facility uses a synchrotron to accelerate ions for therapy, which generates approximatelycontinuous radiation. In order develop PGS for the HIT facility a dedicated trigger was developed to time-stampeach ion entering the room, with timing resolution of less than 1 ns. The PGS system being developed in Heidelberg, willbe composed of a 1) trigger to time stamp each ion entering the room, 2) a primary detector composed CeBr3 scintillatorwith approximately 1.5-3.0% energy resolution in the MeV range of the emitted prompt gammas and 3) a BGO Comptonsuppression system to reduce the background continuum. The goal of the novel PGS being developed at the HIT facility forions is to allow real-time verification of the Bragg peak location in the patient.
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