Acoustic Localization of Bragg Peak Proton Beams for Hadrontherapy Monitoring

Abstract

Hadrontherapy makes it possible to deliver high doses of energy to cancerous tumors by using the large energy deposition in the Bragg-peak. However, uncertainties in the patient positioning and/or in the anatomical parameters can cause distortions in the calculation of the dose distribution. In order to maximize the effectiveness of heavy particle treatments, an accurate monitoring system of the deposited dose depending on the energy, beam time, and spot size is necessary. The localized deposition of this energy leads to the generation of a thermoacoustic pulse that can be detected using acoustic technologies. This article presents different experimental and simulation studies of the acoustic localization of thermoacoustic pulses captured with a set of sensors around the sample. In addition, numerical simulations have been done where thermo-acoustic pulses are emitted for the specific case of a proton beam of 100 MeV.

Keywords: Bragg peak; acoustic localization; hadrontherapy; piezoelectric ceramic; thermoacoustic.

Figure 1

Scheme for obtaining the time of arrival (TOA).

Figure 2

(a) The distance between the initial position for the algorithm and the real position of the source is shown on the abscissa axis, while the axis of the ordinates shows the distance between the signal reconstructed by the algorithm and the real position of the source; (b) The reconstructed positions for each of the 10,000 simulations are shown together with the real position (black).

Figure 3

Bragg peak for different energies. (a) The deposition of the dose varies according to the energy of the proton. The maximum of the Bragg peak varies according to the energy; (b) The relationship Range–Energy for protons in water is shown.

Figure 4

(a) Bragg curves with an initial energy of 100 MeV protons in water. The line represents the dose contribution from the fraction of protons that have nuclear interactions; (b) Pressure for a sensor located 4 cm from the Bragg peak on the axis of symmetry of the emission.

Figure 5

(a) The emitter and receiver are located as close as possible to each other to calibrate the motors; (b) The first position for measurements of sound speed and location; (c) System of generation and capture of signals.

Figure 6

Volume proposed to evaluate the localization algorithm. In this case, four sensors (black points) have been situated on the sides of the cube. Inside, three events will be simulated in different positions. The positions of the sensors and sources are shown in Table 1. This figure shows the point source (blue point).

Figure 7

The positions of sources 1, 2, and 3 are shown in red, blue, and black, respectively. The dotted line is a fitting line to the results.

Figure 8

Calculation time with an Intel i5 processor for different sensors and volume.

Figure 9

This figure shows the configuration of the receiver positions. The source is represented by a sphere (white) that is inside the volume generated by the sensors (cylinders of grey color with black tip) whose route is shown with the black lines and the conical red marks. In this figure, a smaller volume is represented inside the tank for its correct visualization.

Figure 10

The figure shows the process of detecting the signal from the correlation between the emitted and received signal. (a) The signal generated in the simulation, shown in black, is emitted by the transmitter. The captured signal for point 1 is shown in red; (b) The arrival time can be extracted from the maximum value of the correlation of signals.