A real-time method to simultaneously measure linear energy transfer and dose for proton therapy using organic scintillators.

Currently, no detectors are capable of simultaneously measuring dose and linear energy transfer (LET) in real time. In this study, we evaluated the feasibility of exploiting the difference in the response of various organic plastic scintillation detectors to measure LET and dose in therapeutic proton beams. The hypothesis behind this work was that the ratio of the responses of different scintillators exposed to the same proton beam can be used to obtain a LET vs ratio calibration curve that can then be used to infer LET under any other measurement conditions. We first used similar scintillators with different ionization quenching factors. LET values for different irradiation conditions were calculated using a validated Monte Carlo model of the proton beam line. The quenching factors in the Birks equation for different scintillators as a function of LET were obtained from measurements in a 100-MeV pristine proton beam. We then used four different organic scintillation materials - polystyrene (BCF-12), poly (methyl methacrylate), polyvinyltoluene, and a liquid scintillator - for which the LET response varied with regard to not only quenching but also differences in material density and relative stopping power. We simultaneously exposed the four different organic scintillators and a plane-parallel ion chamber to passively scattered proton beams at fluence-averaged LET. Comparisons to the expected values obtained from the Monte Carlo simulations were made on the basis of both dose and LET. The maximum difference in the quenching factor was 20%, resulting in a 5% change in LET with a response ratio over a range of 5 keV/μm. Among all the scintillators investigated, the ratio of PMMA to BCF-12 provided the best correlation with LET values and was therefore used to construct the LET calibration curve. The expected LET values in the validation set were within 2% ± 6%, which resulted in dose accuracy of 1.5% ± 5.8% for the range of LET values investigated in this work. We demonstrated the feasibility of using the ratio of the light outputs of two organic scintillators to simultaneously measure LET and dose in therapeutic proton beams for fluence-averaged LET values from 0.47 to 1.26 keV/μm. Further studies are needed to verify the response for higher LET values and the reproducibility of this method.

Alsanea F ，Therriault-Proulx F ，Sawakuchi G ，Beddar S ... -  《-》

Ionization quenching correction for a 3D scintillator detector exposed to scanning proton beams.

Alsanea F ，Darne C ，Robertson D ，Beddar S ... -  《-》

Ionization quenching in scintillators used for dosimetry of mixed particle fields.

Christensen JB ，Almhagen E ，Stolarczyk L ，Vestergaard A ，Bassler N ，Andersen CE ... -  《-》

Determination of the quenching correction factors for plastic scintillation detectors in therapeutic high-energy proton beams.

Wang LL ，Perles LA ，Archambault L ，Sahoo N ，Mirkovic D ，Beddar S ... -  《-》

Real-time measurement of two-dimensional LET distributions of proton beams using scintillators.

Objective.The linear energy transfer (LET) of proton therapy beams increases rapidly from the Bragg peak to the end of the beam. Although the LET can be determined using analytical or computational methods, a technique for efficiently measuring its spatial distribution has not yet been established. Thus, the purpose of this study is to develop a technique to measure the two-dimensional LET distribution in proton therapy in real time using a combination of multiple scintillators with different quenching.Approach.Inorganic and organic scintillator sheets were layered and irradiated with proton beams. Two-color signals of the CMOS sensor were obtained from the scintillation light and calibration curves were generated using LET. LET was calculated using Monte Carlo simulations asLETtandLETdweighted by fluence and dose, respectively. The accuracy of the calibration curve was evaluated by comparing the calculated and measured LET values for the 200 MeV monoenergetic and spread-out Bragg peak (SOBP) beams. LET distributions were obtained from the calibration curves.Main results.The deviation between the calculated and measured LET values was evaluated. For bothLETtandLETd, the deviation in the plateau region of the monoenergetic and SOBP beams tended to be larger than those in the peak region. The deviation was smaller forLETd. In the obtainedLETddistribution, the deviation between the calculated and measured values agreed within 3% in the peak region, while the deviation was larger in other regions.Significance.The LET distribution can be measured with a single irradiation using two scintillator sheets. This method may be effective for verifying LET in daily clinical practice and for quality control.

Isomura T ，Kamizawa S ，Takada K ，Mori Y ，Sakae T ... -  《-》