Harvard Medical School Massachusetts General Hospital

Finite range implies reduced integral dose, better conformality Figure from Wikipedia,

 Uncertainty in range has higher consequences Tumor Critical structure Beam Ideal treatment Potential actual treatment Dose to critical structure

 Uncertainty in range has higher consequences Tumor Critical structure Beam Ideal treatment Potential actual treatment Dose to critical structure Patched Beams More robust plan

 In proton therapy, the dose stops within the patient  Good for avoiding dose to sensitive areas  Bad for verifying dose delivery  Protons occasionally interact with nuclei and create a small amount of radioactivity  PET makes it possible to “see” where some of the radioactive particles were made  Detects gamma rays emitted when positrons from the decaying nucleus annihilate with native electrons  Provides 3D images of the radioactivity that can be related to the dose through various means of analysis  Any discrepancies between the measured PET activity and what is expected can be used to improve the therapy

Proton beam from cyclotron sent to patient’s tumor Creates radioactive isotopes that can be imaged

DOSE PET Use of PET for verification of proton therapy

 Positron emitters are produced from nuclear interactions of protons and nuclei  PET cameras detect the photons emitted from the annihilation of the positron and an electron Proton Neutron Positron Electron Photon

 PET makes it possible to “see” the location of the radioactive particles and thus where the therapeutic protons were delivered  Provides 3D images of the radioactivity that can be related to the dose through various means of analysis  e.g., compare PET images with simulations of the expected PET image  Any discrepancies between the measured PET activity and what is expected can be used to improve the therapy Planned dosePET imageSimulated image

 PET monitoring of proton therapy is in the research stage  Scanning phantoms and patients after irradiation to verify analysis techniques  Routine use of PET to monitor and modify proton therapy at MGH has not yet been established  PET has been used at other institutions to successfully alter treatment plans  PET for proton therapy was first proposed in the early 90s  Gradually getting better results as PET cameras improve  Found to be most successful in rigid and bony locations such as the head and the spine  Most critical when the tumor is near a sensitive structure  PET studies so far have found a precision of several millimeters  Would like to reduce the uncertainty to one millimeter

NeuroPET from PhotoDetection Systems The first mobile PET scanner that you can plug and play! Currently being used in patient studies at MGH

 The patient is treated according to their treatment plan  At MGH only patients with head treatments are being scanned  As soon as the beam stops, the mobile NeuroPET scanner is wheeled into the room, while the patient’s bed is repositioned to move into the bore of the scanner  There is no need to move the patient with this technique  The patient’s head is positioned into the scanner and remains there for 20 minutes  In routine use the scan time can be reduced to 5 minutes  The PET data is reconstructed into 3D images that can be compared to the planned dose and/or to Monte Carlo simulations of the expected PET image

The patient is treated according to the prescribed treatment plan Proton beam is on for seconds Patient is moved into PET scanner while still on the treatment bed Positioning takes 1-2 minutes Patient is scanned for 20 minutes Can be reduced to 5 minutes for routine use 3D images are reconstructed and compared to simulations PET Patient treated with proton beam Patient imaged with PET scanner

Comparison 15 O 11 C Simulated PET Dose and PET calculation with nozzle and CT Geant4 Fluence Cross Sections Geant4 Fluence Cross Sections MATLAB Decay Washout Blurrring Normalization MATLAB Decay Washout Blurrring Normalization Monte Carlo Simulation Measured PET In-room PET scan just after irradiation In-room PET List mode raw data In-room PET List mode raw data Reconstruction 3D OSEM PET+CT Reconstruction 3D OSEM PET+CT Patient’s PET scan

Nasal cavity Orbit Brain Treatment planned dose Simulated dose Simulated PET Measured PET

 Incorporate CT scanner into mobile NeuroPET  Already done, will soon be scanning patients at MGH  Better modeling of the signal loss from biological effects  Studying a promising new algorithm  Faster simulations of PET activity  Determination of dose directly from PET image

Includes CT scanner for improved attenuation correction and anatomical registration Soon to be employed for scanning proton therapy patients at MGH