Abstract
Proton radiography and tomography have long promised benefit for proton therapy. Their first suggestion was in the early 1960s and the first published proton radiographs and CT images appeared in the late 1960s and 1970s, respectively. More than just providing anatomical images, proton transmission imaging provides the potential for the more accurate estimation of stopping-power ratio inside a patient and hence improved treatment planning and verification. With the recent explosion in growth of clinical proton therapy facilities, the time is perhaps ripe for the imaging modality to come to the fore. Yet many technical challenges remain to be solved before proton CT scanners become commonplace in the clinic. Research and development in this field is currently more active than at any time with several prototype designs emerging. This review introduces the principles of proton radiography and tomography, their historical developments, the raft of modern prototype systems and the primary design issues.
Highlights
Despite a history going back over 50 years,[1] proton radiography and tomography have been slow to reach the clinic.[2]
It turns out that the use of protons instead of X-rays for transmission imaging has some disadvantages. These include the need for large expensive equipment to produce proton beams and the limitations on image quality arising from the multiple scattering of protons
The radiotherapist is confronted with the problem of determining the energy of the incident protons necessary to produce the high ionization at just the right place, and this requires knowing the variable-specific ionization of the tissue through which the protons must pass
Summary
AQUA, Advanced Quality Assurance; CMOS APS, complementary metal oxide semi-conductor active pixel sensor; CsI : Tl, thallium-doped caesium iodide scintillator; CSUSB, California State University, San Bernadino; INFN, Istituto Nazionale di Fisica Nucleare; FNAL, Fermilab National Accelerator Laboratory; LLU, Loma Linda University; NaI : Tl, thallium-doped sodium iodide scintillator; NIU, Northern Illinois University; PRaVDA, Proton Radiotherapy Verification and Dosimetry Applications; PRIMA, PRoton IMAging; Sci-Fi, scintillating fibre hodoscope; UCSC, University of California Santa Cruz; x-y (or x-u-v) SiSDs, two-plane (or three-plane) silicon strip detectors; YAG : Ce, cerium-doped yttrium aluminium garnet scintillator. Since there will be statistical variations in penetration depth within the range telescope itself (residual range straggling) this will contribute extra uncertainty on the estimate of WEPL While this is true, a calorimeter will always possess a finite energy resolution.[50] In consequence, the superiority of any particular RERD over another cannot be established based on such a general criterion. A calorimeter will always possess a finite energy resolution.[50] In consequence, the superiority of any particular RERD over another cannot be established based on such a general criterion Another factor that affects precision of WEPL estimated in a range telescope is the water-equivalent thickness, D, of the
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