On‐line monitoring and PET imaging of the positron‐emitting activity created in tissue by proton radiotherapy beams

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135054/1/mp8193.pd

Generation of GeV protons from 1 PW laser interaction with near critical density targets

The propagation of ultra intense laser pulses through matter is connected with the generation of strong moving magnetic fields in the propagation channel as well as the formation of a thin ion filament along the axis of the channel. Upon exiting the plasma the magnetic field displaces the electrons at the back of the target, generating a quasistatic electric field that accelerates and collimates ions from the filament. Two-dimensional Particle-in-Cell simulations show that a 1 PW laser pulse tightly focused on a near-critical density target is able to accelerate protons up to an energy of 1.3 GeV. Scaling laws and optimal conditions for proton acceleration are established considering the energy depletion of the laser pulse.Comment: 26 pages, 8 figure

Accelerating Protons to Therapeutic Energies with Ultra-Intense Ultra-Clean and Ultra-Short Laser Pulses

Proton acceleration by high-intensity laser pulses from ultra-thin foils for hadron therapy is discussed. With the improvement of the laser intensity contrast ratio to 10-11 achieved on Hercules laser at the University of Michigan, it became possible to attain laser-solid interactions at intensities up to 1022 W/cm2 that allows an efficient regime of laser-driven ion acceleration from submicron foils. Particle-In-Cell (PIC) computer simulations of proton acceleration in the Directed Coulomb explosion regime from ultra-thin double-layer (heavy ions / light ions) foils of different thicknesses were performed under the anticipated experimental conditions for Hercules laser with pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half maximum (FWHM), focused to a spot size of 0.8 microns (FWHM). In this regime heavy ions expand predominantly in the direction of laser pulse propagation enhancing the longitudinal charge separation electric field that accelerates light ions. The dependence of the maximum proton energy on the foil thickness has been found and the laser pulse characteristics have been matched with the thickness of the target to ensure the most efficient acceleration. Moreover the proton spectrum demonstrates a peaked structure at high energies, which is required for radiation therapy. 2D PIC simulations show that a 150-500 TW laser pulse is able to accelerate protons up to 100-220 MeV energies.Comment: 26 pages, 6 figure

On-line monitoring and PET imaging of the positron-emitting activity created in tissue by proton radiotherapy beams.

Proton radiotherapy is a powerful tool in the local control of cancer. The advantages of proton radiotherapy over gamma-ray therapy arise from the phenomenon known as the Bragg peak. This phenomenon enables large doses to be delivered to well-defined volumes while sparing surrounding healthy tissue. To fully realize the potential of this technique the location of the high dose volume must be controlled very accurately. An imaging system was designed and tested to monitor the positron-emitting activity created by the beam as a means of verifying the beams range and determining tissue composition. Design studies of the detection system are presented, the data acquisition system used is described and the results of on-line experiments with proton beams are presented. The depth-distribution of positron-emitting activity created by proton radiotherapy beams was imaged on-line using this system. Decay data was acquired and imaged between beam pulses and after the irradiation. Over 80% of the initial positron-emitting activity is from \sp{15}O which has a half-life of 122 seconds. The residual range of the treatment beam below the energy threshold for producing \sp{15}O is 0.3 cm. Consequently, the end of the activity distribution and the location of the Bragg peak are well correlated in homogenous tissue. The results show that the range of a 150 MeV proton radiotherapy beam may be verified after a single beam pulse to within a detectors width of the imaging system. The integrated total dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. It is also shown that in some situations the width of the plateau region of a Spread-Out Bragg Peak (SOBP) may be inferred from the fall of activity at the distal end of the distribution. Radioisotopic imaging may be performed along the beam path if decay data is collected after the treatment is completed. It is shown that using this technique, variations in elemental composition in inhomogenous treatment volumes may be identified and used to locate anatomical landmarks. Radioisotopic imaging also reveals that \sp{14}O is created well beyond the Bragg peak, apparently by secondary neutrons.Ph.D.Applied SciencesBiomedical engineeringHealth and Environmental SciencesMedical imagingNuclear physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130527/2/9732128.pd