Prompt gamma measurements for locating the dose falloff region in the proton therapy

Abstract

The location of the distal falloff in the proton therapy is an important but often uncertain parameter as different tissue elements are traversed by the beam. A multilayered collimator system has been constructed as a practical means to locate the dose ends by measuring prompt gammas. The collimator is designed to moderate and capture fast neutrons and to prevent unwanted gammas from reaching the scintillation detector. The system has been studied using Monte Carlo technique and has been tested in the beam energy range of 100–200MeV. Measurements clearly indicated correlations between the gamma distributions and the distal falloff regions.

Determination of Optimal Energy Window for Measurement of Prompt Gammas from Proton Beam by Monte Carlo Simulations

“…2 shows the experimental setup to measure the distribution of the prompt gammas at the National Cancer Center (NCC, Korea). The prompt gamma scanning system developed in a previous study 4,5) was used to scan the distribution of the prompt gammas in a water phantom (20 cm x 20 cm x 30 cm), while a 150 MeV pencil-type proton beam was delivered to the center of the phantom. The beam current was roughly 2 nA, and each scanning point was measured for 10 sec.…”

“…4,5) The scanning system measures only the rightangled or 90° prompt gammas to determine the distribution of the 'origins' of the prompt gammas along the beam passage in the patient. It was found, however, that a significant amount of high energy spallation neutrons are also generated from the protons in the medium, and that the resulting background gammas significantly affect the measurement.…”

Imaging particle beams for cancer treatment

“…Initial studies have found a good correlation between dose delivery and prompt-gamma emission, 9,10 and small shifts in the Bragg peak position can be detected by measuring prompt-gamma emission during treatment. 11,12 Recent studies have also shown that the intensities of the characteristic prompt-gamma spectral lines from individual elements are directly proportional to the concentration of the elements in tissue, 13 so prompt-gamma imaging could provide a path to spectroscopic analysis of irradiated tumors and healthy tissues.…”

Investigation of optimized prompt gamma detection strategy for real-time Bragg Peak tracking in proton radiation therapy

“…The emitted positrons annihilate with electrons of the tissue to produce pairs of coincident 511 keV gamma photons [3]- [4]. Another is called prompt gamma (PG) imaging [5]- [7], which relies on the measurement of single gamma photons promptly emitted from some excited tissue nuclei following their decays from the excited states to their ground states. The PET-based range verification technique has been adopted for the post-treatment quality control [8], but it still has some limitations.…”