Three-dimensional (3D) dose distribution measurements of proton beam using a glass plate

Abstract

The measurements of the three-dimensional (3D) dose distribution of proton beams in water are critical for proton therapy for quality assessment (QA). Although ionization chambers are commonly used for this purpose, such measurements take a long time to calculate precise 3D dose distribution.To solve this problem, we measured 3D dose distributions using a glass plate. We placed a 1-mm thick float glass plate on the upper inside of a black box with a water tank set above the float glass plate outside the black box and irradiated the proton beam to the water tank from the upper side. The attenuated proton beam by water in the tank was detected by the float glass plate and a scintillation image was formed in the plate. The image was reflected by a first-surface mirror set below the float glass plate and detected by a cooled charge-coupled device (CCD) camera from the side. We changed the water depths in the tank and measured the scintillation images at each depth. Then we calculated the 3D scintillation images from the measured images by stacking them in the depth direction. Measurements were made for 71.2-and 100-MeV proton pencil beams and a spread-out Bragg peak (SOBP) using the imaging system. From the images, we successfully formed 3D scintillation images without quenching. The depth profiles measured from the scintillation images showed almost identical distribution with those measured by the ionization chamber within a maximum difference less than 5%. The lateral profiles were also almost identical within width differences less than 2 mm. We conclude that our proposed method is promising for the 3D dose distribution measurements of proton beams.

Three-dimensional dose-distribution measurement of therapeutic carbon-ion beams using a ZnS scintillator sheet

“…Although the ZnS scintillator yielded smaller LET dependence (quenching effect) than the Gd scintillator for carbon ions, it still required small corrections (maximum of approximately 20%) to obtain the correct 3D dose distributions for carbon ions. Previous studies reported that, for a proton beam with a lower LET, 3D dose distributions showed good agreement with those obtained using a float glass plate that had no quenching effect [ 26 , 27 ]. The float glass provides the advantage of a light output—approximately 20 times higher than that of silica glass, which does not undergo proton quenching [ 28 ].…”

“…The depths indicated the water-equivalent depths (WEDs), which included the bottom wall of the tank (11.6 mm of PMMA) and the black aluminum plate (0.6 mm) above the scintillator. Each 3D image was created from the corresponding measured 2D image using ImageJ [ 26 ]. To compensate the quenching effect (brightness reduction due to a higher LET), correction factors were multiplied to the brightness of the images at each depth.…”

Utilizing Pencil Beam Scan Dynamics and a Scintillation Screen to produce 3D Dose Distribution of Proton Beams

“…In proton therapy, validation of dose distribution is vital to verifying the irradiation system can treat patients and deliver the prescribed plan, particularly due to the significant dose deposition at the Bragg peak. There has been an interest in measuring precise three-dimensional (3D) dose profile of proton beams and scintillation and radioluminescence imaging has shown promising methods of acquiring volumetric dose distributions [1][2][3]. Optical imaging inherently provides two-dimensional (2D) dose profiles and require reconstruction methods to produce a 3D dose distribution.…”

“…Optical imaging inherently provides two-dimensional (2D) dose profiles and require reconstruction methods to produce a 3D dose distribution. Some methods include multiple acquisitions of 2D radioluminescence slices of the dose profile [1] or imaging the scintillation projection dose profiles from orthogonal views with multiple cameras [3].…”

Three-dimensional (3D) optical imaging of electron beam and X-rays from medical linear accelerators (LINAC) using a plastic scintillator plate in water

“…One high-resolution and cost-effective method to measure 3D optical images is to stack measured 2D optical images perpendicular to the beam direction. In this method of measuring 3D optical images of radiation, a scintillator plate such as a plastic scintillator [19], float glass [20], or ZnS(Ag) [21] has been used in the imaging to measure the cross sections of beams. The depths of these cross sections were changed by adding water in a container set above the scintillators [19][20][21].…”