Quantification of β⁺activity generated by hard photons by means of PET

Abstract

Positron emission tomography (PET) as a method for quality assurance in radiotherapy is well investigated in the case of therapy with carbon ion beams and successfully applied at the Heavy Ion Medical Accelerator at Chiba (HIMAC), Japan, and the Gesellschaft für Schwerionenforschung (GSI), Germany. By measuring the beta(+) activity distribution during the irradiation (in-beam PET), valuable information on the precision of the dose deposition can be obtained. To extend this efficient technique to other radiation treatment modalities may be worthwhile. For example, since positron emitters are generated by high-energy photons with energies above 20 MeV due to (gamma, n) reactions (predominantly (11)C and (15)O in tissue), in-beam PET seems to be feasible for radiation therapy with high-energy photons as also shown in Geant4 simulations. Quantitative results on the activation of tissue-equivalent materials at hard photon beams were obtained by performing off-beam PET experiments. Homogeneous PMMA phantoms as well as inhomogeneous phantoms were irradiated with high-energy bremsstrahlung. After the irradiation the distributions of the generated positron emitters in the phantoms were measured using a conventional PET scanner. Furthermore, the depth-dose distributions were determined by means of optically stimulated luminescence detectors. In the experiments an activity per dose comparable to that produced in a typical patient irradiation with carbon ions could be achieved for 34 MV bremsstrahlung. In addition, a high contrast in the PET images for materials with different density and stoichiometry could be detected. Thus, further research concerning the development of in-beam PET seems to be worthwhile.

In vivoproton range verification: a review

“…However, since for carbon therapy, particle fluence is 20 times smaller than for proton therapy, the total activity produced within an irradiated volume will be only half for carbon therapy (Parodi and Enghardt 2000). An increasing interest has been devoted to PET imaging in the last few years, not only of protons and carbon ions but also of 3 He (Fiedler et al 2006), 7 Li (Priegnitz et al 2008), 16 O (Inaniwa et al 2008) and even photons (Moeckel et al 2007). 4.4.5.…”

In-Beam and Off-Beam PET Measurements of Target Activation by Megavolt X-Ray Beams

“…Phantom irradiations similar to those presented in [18] were performed. A high-energy bremsstrahlung beam was generated at ELBE by impinging electrons with an energy up to 40 MeV and a beam current up to 150 A on an aluminum bremsstrahlung target of 18 m thickness and used to irradiate various phantoms.…”

“…In the case of off-beam PET, only decay could be detected. As described in [18], the off-beam PET measurements were performed over 60 min. in listmode without septa (i.e.…”

Dose reduction in computed tomography: the effect of eye and testicle shielding on radiation dose measured in patients with beryllium oxide-based optically stimulated luminescence dosimetry

“…The reader ("BeOmax") has been developed by a group of two of the coauthors (M. S., J.H.) [13][14][15][16]. BeOs feature a linear dose response of between about 5 µGy and up to more than 5 Gy.…”