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A Multi-Institutional Study of Independent Dose Verification Using a New Clarkson Method That Accounts for Lateral Scatter in Inhomogeneous Media

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S Jinno

S Jinno1*, H Tachibana2 , S Moriya3 , N Mizuno4 , R Takahashi5 , T Kamima5 , S Ishibashi6 , M Sato1 , (1) Komazawa University, Setagaya, Tokyo, (2) National Cancer Center, Kashiwa, Chiba, (3) University of Tsukuba, Tsukuba, Ibaraki, (4) St. Luke's International Hospital, chuo, Tokyo, (5) Cancer Institute Hospital of Japanese Foundation of Cancer Research, Koto, Tokyo, (6) Sasebo City General Hospital, Sasebo, Nagasaki


SU-F-FS2-8 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: Four Seasons 2

Purpose: We designed and developed a lateral scatter corrected Clarkson (L-Clarkson) to take into account the effects of the lateral dimension of the heterogeneity. We also conducted a multi-institutional study to evaluate the effectiveness of the L-Clarkson for breast and lung plans including stereotactic body radiotherapy (SBRT).

Methods: In L-Clarkson, a two-dimensional (2D) image on a reference point was reconstructed from CT images using affine transformation with several parameters (gantry angle, collimator angle and couch angle). Subsequently, radiological path length was computed using the reconstructed 2D image from the reference point to the edge of the MLC or Jaw at each pie sector to calculate tissue maximum radio (TMR) and phantom scatter factor (Sp). Finally, dose was calculated using the TMR, the Sp and other factors such as collimator scatter factor, wedge factor and inverse square law’s factor. This study was performed in four institutions. Eclipse (AAA, PBC), Pinnacle3 (AC) and Xio (Superposition) were used as treatment planning system (TPS). Comparison in dose between the TPS and the standard Clarkson (S-Clarkson)/L-Clarkson were performed using the confidence limits (CLs, Mean ± 2SD) for breast and lung including lung SBRT.

Results: The results of CLs for total fields showed -0.4 ± 2.7 % (CL of the S-Clarkson: 3.8 ± 3.1 %), -1.6 ± 4.8 % (0.6 ± 5.5 %) and -0.5 ± 5.2 % (4.5 ± 5.5 %) for breast, lung with large field and lung SBRT, respectively. The L-Clarkson enabled us to consider the effect of missing tissue and the tumor surrounding lung and showed better agreement compared to the S-Clarkson.

Conclusion: Our new Clarkson algorithm could reduce the systematic and random deviations in the sites including inhomogeneous media. A simple action level of the range from -5% to 5% would be applicable in secondary check.

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