Background: Plastic scintillator detector (PSD) Exradin W1 has shown promising performance in small field dosimetry due to its water equivalence and small sensitive volume. However, few studies reported its capability in measuring fields of conventional sizes. Therefore, the purpose of this study is to assess the performance of W1 in measuring point dose of both conventional IMRT plans and VMAT SRS plans. Methods: Forty-seven clinical plans (including 29 IMRT plans and 18 VMAT SRS plans with PTV volume less than 8 cm3) from our hospital were included in this study. W1 and Farmer-Type ionization chamber Exradin A19 were used in measuring IMRT plans, and W1 and microchamber Exradin A16 were used in measuring SRS plans. The agreement between the results of different types of detectors and TPS was evaluated. Results: For IMRT plans, the average differences between measurements and TPS in high-dose regions were 0.27% ± 1.66% and 0.90% ± 1.78% ( P = 0.056), and were −0.76% ± 1.47% and 0.37% ± 1.34% in low-dose regions ( P = 0.000), for W1 and A19, respectively. For VMAT SRS plans, the average differences between measurements and TPS were −0.19% ± 0.96% and −0.59% ± 1.49% for W1 and A16 with no statistical difference ( P = 0.231). Conclusion: W1 showed comparable performance with application-dedicated detectors in point dose measurements for both conventional IMRT and VMAT SRS techniques. It is a potential one-stop solution for general radiotherapy platforms that deliver both IMRT and SRS plans.
Purpose: A series of practical phantoms were constructed to investigate the accuracy of photon dose calculations performed by the Anisotropic Analytical Algorithm (AAA) in homogeneous and inhomogeneous media. Method and Materials: A total of seven heterogeneous and homogeneous phantoms with solid water (SW) and cork, SW with MapCHECK or MatriXX were constructed to investigate the difference between dose calculated by AAA in Eclipse treatment planning system (TPS) and measured dose using Varian 23 IX LINAC. Ion Chamber was used for point dose measurements and film, MapCHECK, MatriXX were used for 2D dose measurements. A detailed analysis of data computed by the AAA algorithm was carried out and data were compared against measurements. To better appraise the performance of AAA, data obtained from the pencil beam convolution (PBC) algorithm implemented in Eclipse were also added in the comparison. Results: AAA calculation has showed better than PBC in agreement with measurement from both ion chamber and 2D dosimeters. As planar dose evaluation, MapCHECK yielded a pass rate ranging from 88.5% to 95.5% for AAA, and 69.7% to 81.9% for PBC based on 1% difference and 1mm distance to agreement for different phantoms. The film dose distribution showed as well that AAA calculation is better than PBC in agreement with measurements. Generally, the better agreement of AAA than PBC calculation with measurement is more obvious in heterogeneous than homogeneous phantoms. Conclusions: Eclipse TPS dose calculation AAA showed better agreement with dose measurement in both heterogeneous (more significant) and homogeneous phantom than PBC using three different types of 2D dosimetry system and ion chamber. The design of measurements and construction of phantoms represent a simple, efficient, and accurate means for verifying dose calculation algorithms in TPS.
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