Proceedings Article | 16 March 2011
J. Gillam, C. Lacasta, I. Torres-Espallardo, C. Candela Juan, G. Llosá, P. Solevi, J. Barrio, M. Rafecas
KEYWORDS: Photons, Reconstruction algorithms, Image restoration, Gamma radiation, Beam analyzers, Tissues, Sensors, Tumors, Positron emission tomography, Polymethylmethacrylate
Hadron therapy, a subject of study by the ENVISION project, promises to provide enhanced accuracy in the
treatment of cancer. The Bragg-peak, characteristic of the hadron-beam structure provides larger dose to the
tumor while being able to spare surrounding tissue - even tissues in the beam-path, beyond the tumor-site.
However, increased dose gradients require more precise treatment, as small beam misalignment can result in dose
to healthy, often delicate, surrounding tissue. The requirement for accuracy necessitates imaging during therapy,
yet the lack of a transmitted beam makes this difficult. The particulate beam interacts with the target material
producing neutrons, positron emitting isotopes and a broad spectra of gamma radiation. Photons from positron-annihilation
allow in-beam PET to provide on-line measurements of dose deposition during therapy. However,
ib-PET suffers from low statistics and lost projections due to low sensitivity and detector constraints respectively.
Instead, Compton imaging of gamma radiation is proposed to provide on-line monitoring for hadron therapy.
Compton imaging suffers similarly from low statistics, especially, as is the case here, when incident energy is
unknown. To surmount this problem, a method of Compton image reconstruction is proposed and tested using
simulated data, which reconstructs incident energy along with the spatial variation in emission density. Through
incident energy estimation, a larger range of measurements are available for image-reconstruction - greatly
increasing the sensitivity of the system. It is shown in this preliminary study that, even with few statistics, a
reasonable estimate of the beam path is calculable.
