Short-lived positron emitters in beam-on PET imaging during proton therapy

Abstract

The only method for in vivo dose delivery verification in proton beam radiotherapy in clinical use today is positron emission tomography (PET) of the positron emitters produced in the patient during irradiation. PET imaging while the beam is on (so called beam-on PET) is an attractive option, providing the largest number of counts, the least biological washout and the fastest feedback. In this implementation, all nuclides, independent of their half-life, will contribute. As a first step towards assessing the relevance of short-lived nuclides (half-life shorter than that of (10)C, T1/2 = 19 s) for in vivo dose delivery verification using beam-on PET, we measured their production in the stopping of 55 MeV protons in water, carbon, phosphorus and calcium The most copiously produced short-lived nuclides and their production rates relative to the relevant long-lived nuclides are: (12)N (T1/2 = 11 ms) on carbon (9% of (11)C), (29)P (T1/2 = 4.1 s) on phosphorus (20% of (30)P) and (38m)K (T1/2 = 0.92 s) on calcium (113% of (38g)K). No short-lived nuclides are produced on oxygen. The number of decays integrated from the start of an irradiation as a function of time during the irradiation of PMMA and 4 tissue materials has been determined. For (carbon-rich) adipose tissue, (12)N dominates up to 70 s. On bone tissue, (12)N dominates over (15)O during the first 8-15 s (depending on carbon-to-oxygen ratio). The short-lived nuclides created on phosphorus and calcium provide 2.5 times more beam-on PET counts than the long-lived ones produced on these elements during a 70 s irradiation. From the estimated number of (12)N PET counts, we conclude that, for any tissue, (12)N PET imaging potentially provides equal to superior proton range information compared to prompt gamma imaging with an optimized knife-edge slit camera. The practical implementation of (12)N PET imaging is discussed.

Proton therapy treatment monitoring with in-beam PET: Investigating space and time activity distributions

“…As it is clear from the figures, the best fit function includes the contributions of 11 C, 15 O, 10 C, 8 B where, as expected, the fist two isotopes are the most abundant ones. The presence of these 4 isotopes is also reported in other experiments where 55 MeV protons impinging on a PMMA phantom and an ad-hoc experimental setup for time analysis are used [27]. From Fig.…”

INSIDE in-beam positron emission tomography system for particle range monitoring in hadrontherapy

“…As can be observed, the d value for the in-spill data is comparable with the interspill one within 0.4 mm. The lower value of the slope for the in-spill profile can be explained by the contribution of the long positron range of short-lived βþ emitters, 45,46 such as 12 N, and the contributions of prompt photons. 16 In the following part, we report on the results obtained for the second set of measurements with the PMMA phantoms A and B.…”

In-beam tests of a PET demonstrator (LAPD) for hadrontherapy beam ballistic control: data comparison to Geant4 Monte-Carlo predictions

“…Protons of 55 MeV, hitting of PMMA target, were first simulated. The goal was to compare the Geant4 predictions to the experimental results obtained by Dendooven et al [15], reported in the table I. The relative difference between Geant4 and the experimental results are shown on figure 12, for the Binary Cascade (BIC) and the BIC High Precision (BIC AllHP) models.…”