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Background: In proton therapy, a highly steep distal dose penumbra can be utilized for dose conformity, given the Bragg peak characteristic of protons. However, the location of the Bragg peak in patients (i.e., the beam range) is very sensitive to range uncertainty. Even a small shift of beam range can produce a significant variation of delivered dose to tumor and normal tissues, thus degrading treatment quality and threatening patient safety. This range uncertainty issue, therefore, is one of the important aspects to be managed in proton therapy. Purpose: For better management of range uncertainty, range verification has been widely studied, and prompt gamma imaging (PGI) is considered one of the promising methods in that effort. In this context, a PGI system named the gamma electron vertex imaging (GEVI) system was developed and recently upgraded for application to pencil‐beam scanning (PBS) proton therapy. Here, we report the first experimental results using the therapeutic spot scanning proton beams. Methods: A homogeneous slab phantom and an anthropomorphic phantom were employed. Spherical and cubic planning target volumes (PTVs) were defined. Various range shift scenarios were introduced. Prompt gamma (PG) measurement was synchronized with beam irradiation. The measured PG distributions were aggregated to improve the PG statistics. The range shift was estimated based on the relative change of the centroid in the measured PG distribution. The estimated range shifts were analyzed by range shift mapping, confidence interval (CI) estimation, and statistical hypothesis testing. Results: The range shift mapping results showed an obvious measured range shift tendency following the true shift values. However, some fluctuations were found for spots that had still‐low PG statistics after spot aggregation. The 99% CI distributions showed clearly distributed range shift measurement data. The overall accuracy and precision for all investigated scenarios were 0.36 and 0.20 mm, respectively. The results of one‐sample t‐tests confirmed that every shift scenario could be observed up to 1 mm of shift. The ANOVA results proved that the measured range shift data could be discriminated from one another, except for 16 (of 138) comparison cases having 1–2 mm shift differences. Conclusions: This study demonstrated the feasibility of the GEVI system for measurement of range shift in spot scanning proton therapy. Our experimental results showed that the proton beam can be measured up to 1 mm of range shift with high accuracy and precision. We believe that the GEVI system is one of the most promising PGI systems for in vivo range verification. Further research for application to more various cases and patient treatments is planned. [ABSTRACT FROM AUTHOR]

Purpose: A real‐time solar cell based in vivo dosimetry system (SC‐IVD) was developed using a flexible thin film solar cell and scintillating powder. The present study evaluated the clinical feasibility of the SC‐IVD in electron beam therapy. Methods: A thin film solar cell was coated with 100 mg of scintillating powder using an optical adhesive to enhance the sensitivity of the SC‐IVD. Calibration factors were obtained by dividing the dose, measured at a reference depth for 6–20 MeV electron beam energy, by the signal obtained using the SC‐IVD. Dosimetric characteristics of SC‐IVDs containing variable quantities of scintillating powder (0–500 mg) were evaluated, including energy, dose rate, and beam angle dependencies, as well as dose linearity. To determine the extent to which the SC‐IVD affected the dose to the medium, doses at R90 were compared depending on whether the SC‐IVD was on the surface. Finally, the accuracy of surface doses measured using the SC‐IVD was evaluated by comparison with surface doses measured using a Markus chamber. Results: Charge measured using the SC‐IVD increased linearly with dose and was within 1% of the average signal according to the dose rate. The signal generated by the SC‐IVD increased as the beam angle increased. The presence of the SC‐IVD on the surface of a phantom resulted in a 0.5%–2.2% reduction in dose at R90 for 6–20 MeV electron beams compared with the bare phantom. Surface doses measured using the SC‐IVD system and Markus chamber differed by less than 5%. Conclusions: The dosimetric characteristics of the SC‐IVD were evaluated in this study. The results showed that it accurately measured the surface dose without a significant difference of dose in the medium when compared with the Markus chamber. The flexibility of the SC‐IVD allows it to be attached to a patient's skin, enabling real‐time and cost‐effective measurement. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusion Previous study proposed a method to measure linear energy transfer (LET) at specific points using the quenching magnitude of thin film solar cells. This study was conducted to propose a more advanced method for measuring the LET distribution.This study focuses on evaluating the feasibility of estimating the proton LET distribution in proton therapy. The feasibility of measuring the proton LET and dose distribution simultaneously using a single‐channel configuration comprising two solar cells with distinct quenching constants is investigated with the objective of paving the way for enhanced proton therapy dosimetry.Two solar cells with different quenching constants were used to estimate the proton LET distribution. Detector characteristics (e.g., dose linearity and dose‐rate dependency) of the solar cells were evaluated to assess their suitability for dosimetry applications. First, using a reference beam condition, the quenching constants of the two solar cells were determined according to the modified Birks equation. The signal ratios of the two solar cells were then evaluated according to proton LET in relation to the estimated quenching constants. The proton LET distributions of six test beams were obtained by measuring the signal ratios of the two solar cells at each depth, and the ratios were evaluated by comparing them with those calculated by Monte Carlo simulation.The detector characterization of the two solar cells including dose linearity and dose‐rate dependence affirmed their suitability for use in dosimetry applications. The maximum difference between the LET measured using the two solar cells and that calculated by Monte Carlo simulation was 2.34 keV/µm. In the case of the dose distribution measured using the method proposed in this study, the maximum difference between range measured using the proposed method and that measured using a multilayered ionization chamber was 0.7 mm. The expected accuracy of simultaneous LET and dose distribution measurement using the method proposed in this study were estimated to be 3.82%. The signal ratios of the two solar cells, which are related to quenching constants, demonstrated the feasibility of measuring LET and dose distribution simultaneously.The feasibility of measuring proton LET and dose distribution simultaneously using two solar cells with different quenching constants was demonstrated. Although the method proposed in this study was evaluated using a single channel by varying the measuring depth, the results suggest that the proton LET and dose distribution can be simultaneously measured if the detector is configured in a multichannel form. We believe that the results presented in this study provide the envisioned transition to a multichannel configuration, with the promise of substantially advancing proton therapy's accuracy and efficacy in cancer treatment. [ABSTRACT FROM AUTHOR]