A novel and fast method for proton range verification using a step wedge and 2D scintillator

Abstract

Purpose: To implement and evaluate a novel and fast method for proton range verification by using a planar scintillator and step wedge. Methods: A homogenous proton pencil beam plan with 35 energies was designed and delivered to a 2D flat scintillator with a step wedge. The measurement was repeated 15 times (3 different days, 5 times per day). The scintillator image was smoothed, the Bragg peak and distal fall off regions were fitted by an analytical equation, and the proton range was calculated using simple trigonometry. The accuracy of this method was verified by comparing the measured ranges to those obtained using an ionization chamber and a scanning water tank, the gold standard. The reproducibility was evaluated by comparing the ranges over 15 repeated measurements. The sensitivity was evaluated by delivering to same beam to the system with a film inserted under the wedge. Results: The range accuracy of all 35 proton energies measured over 3 days was within 0.2 mm. The reproducibility in 15 repeated measurements for all 35 proton ranges was AE0.045 mm. The sensitivity to range variation is 0.1 mm for the worst case. This efficient procedure permits measurement of 35 proton ranges in less than 3 min. The automated data processing produces results immediately. The setup of this system took less than 5 min. The time saving by this new method is about two orders of magnitude when compared with the time for water tank range measurements. Conclusions: A novel method using a scintillator with a step wedge to measure the proton range was implemented and evaluated. This novel method is fast and sensitive, and the proton range measured by this method was accurate and highly reproducible.

LET response variability of Gafchromic EBT3 film from a Co calibration in clinical proton beam qualities

“…Prior to any film measurements, the WET was measured and benchmarked for all slabs of Solid Water ® individually as well as in groups horizontally aligned within the beamline. The WET was assessed for nominal proton beam energies of 125 and 163 MeV using a pull‐back range technique, which is an established method that has been used for beam range verification . The range of the beam in water was measured using an IBA Zebra multilayer ionization chamber (MLIC) and OmniPro Incline software.…”

Technical Note: Using dual step wedge and 2D scintillator to achieve highly precise and robust proton range quality assurance

“…As shown in Fig. (a), the reproducibility on the same day is within 0.1 mm, which is already much better than the results from our preliminary work . This improved reproducibility is due to the strict selection of images captured by a single frame, which successfully removes the effect of the interframe dead time.…”

“…The basic methods for range derivation have previously been described . A brief overview of the method is given here, with a focus on the new dual step wedge for measuring all 97 clinical energies at our facility.…”

“…Figure (b) shows a sample image captured by the scintillator after the 153.5 MeV proton beam passes through the step wedge. The “Bragg peaks” as indicated by the ellipses were used to calculate the absolute proton range using a simple trigonometric method . In Fig.…”

“…Recently, a highly efficient and accurate method using a dual step wedge and a 2D scintillator to measure proton range was introduced by our group . In this technical note, as a follow‐up of the previous work, we used a new dual step wedge that can measure all 97 clinical beams at our center, with ranges varying from 4 to 32 cm.…”