On‐line monitoring of radiotherapy beams: Experimental results with proton beams

Abstract

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 beam's range, monitoring dose, and determining tissue composition. The prototype imaging system consists of 12 pairs of cylindrical BGO detectors shielded in lead. Each crystal was 1.9 cm in diameter, 5.0 cm long, and separated by 0.5 cm from other detectors in the row. These are arranged in two rows, 60 cm apart, with the proton beam and tissue phantoms half-way between and parallel to the detector rows. Experiments were conducted with 150 MeV continuous and macro-pulsed proton beams which had beam currents ranging from 0.14 nA to 1.75 nA. The production and decay of short-lived isotopes, 15O and 14O, was studied using 1 min irradiations with a continuous beam. These isotopes provide a significant signal on short time scales, making on-line imaging possible. Macro-pulsed beams, having a period of 10 s, were used to study on-line imaging and the production and decay of long-lived isotopes, 13N, 11C, and 18F. Decay data were acquired and on-line images were obtained between beam pulses and indicate that range verification is possible, for a 150 MeV beam, after one beam pulse, to within the 1.2 cm resolution limit of the imaging system. The dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. Over 80% of the initial positron-emitting activity is from 15O while the remainder is primarily 11C, 13N, 14O with traces of 18F, and 10C. Radioisotopic imaging may also be performed along the beam path by fitting decay data collected after the treatment is complete. Using this technique, it is shown that variations in elemental composition in inhomogenous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals that 14O is created well beyond the Bragg peak, apparently by secondary neutrons.

Reaction and proton-removal cross sections ofLi6,Be7Warner1, Cârstoiu2, Brown3 et al. 2006Phys. Rev. CSelf Cite412370View full textAdd to dashboardCite

“…Proton and heavy ion radiotherapy is now utilized in the treatment of cancer [10]. These beams produce nuclear fragments, including short-lived isotopes such as 11 C, and these can contribute significant dosage.…”

Experimental verification of the utility of positron emitter nuclei generated by photonuclear reactions for X-ray beam monitoring in a phantom

“…The human body comprises carbon, nitrogen, oxygen, and hydrogen, and the main composition is carbon and oxygen. 22 For 16 O and 12 C nuclei, positron emitter nuclei of 15 O and 11 C are generated by X ray beams of energies exceeding 15.7 and 18.7 MeV, respectively. These are summarized in the following equations.…”

“…[12][13][14][15][16] For high-energy photon treatment, the use of PET-CT at 50 MV was proposed; and experimental results [17][18][19][20] and Monte Carlo calculation results were also reported for in-beam PET imaging. 21 The purpose of this article is to show that 15 O and 11 C positron emitter nuclei can be detected using a commercial PET-CT in the photonuclear reaction with X-ray energy as low as 21 MV. Furthermore, the PET-CT image obtained from such activity can provide the area of X-ray beam irradiation in a phantom.…”

Magnetic confinement of radiotherapy beam-dose profiles

“…This might also have applications in the PET imaging of β + emitters produced in proton-beam [12] or heavy-ion beam radiotherapy. Related to this is the possibility of using magnetic confinement in selected brachytherapy treatments where, again, one might be dealing with high-energy hence long-range charged, radioactivedecay particles (β − , β + , or α's).…”