Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_19_3299 - Estimation Geometric Uncertainty of Dynamic Tracking Technique for Lung Cancer

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Estimation Geometric Uncertainty of Dynamic Tracking Technique for Lung Cancer
S. Kito, K. Nihei, Y. Machitori, Y. Suda, M. Kanda, R. Suganami, Y. Nakajima, T. Furuya, S. Hashimoto, and K. Karasawa; Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22, Bunkyo-ku, Tokyo, Japan

Purpose/Objective(s): The target motion should be considered when irradiating to the moving target with patient breathing. Dynamic tracking technique (DTT) which can make the irradiation field move dynamically by synchronizing the target motion have developed to resolve this problem. The purpose of this study is to propose the strategy to evaluate total geometric uncertainty (TGU) of DTT radiotherapy for lung cancers.

Materials/Methods: 17 lung cancer patients that treated by DTT using gimbaled linac were included in this study to evaluate the TGU in each patient. In this study, TGU was evaluated based on the concept of ICRU Report 62, and “Guide to the Expression of Uncertainty in Measurement (GUM)”. TGU calculation of DTT was considered by dividing into two components. One is patient specific uncertainty, and another is institution specific uncertainty. In patient specific uncertainty, residual target displacement (RTD) against centroid of fiducial markers that were estimated from 4DCT analysis in each respiratory phase, and other possible internal errors were included. On the other hand, in institution specific uncertainty, actual tracking error that was directly measured by gimbal tracking log and detected fiducial marker positions in kV X-ray images during treatment, and other possible set-up errors were included. According to the concept of ICRU Report 62 and GUM, our uncertainty calculation protocol were constructed. Finally, TGU in each direction was calculated as follows; TGU = Σμi+2×√Σσi2 , here, i is a content of uncertainty of DTT, μi is systematic uncertainty of i, σi is random uncertainty of i.

Results: Root mean square error (RMSE) of [μ, σ] of RTD for all patients in LR, AP and SI directions were [0.8, 0.6] mm, [0.9, 0.7] mm and [1.4, 1.4] mm, respectively. Also, RMSE of [μ, σ] of actual tracking error for all patients in LR, AP and SI directions were [1.0, 0.4] mm, [1.0, 0.8] mm and [1.8, 1.3] mm, respectively. Average TGUL-R, TGUA-P and TGUS-I were 6.5 ± 0.7 mm, 7.2 ± 1.4 mm, 12.3 ± 2.4 mm, respectively. Table summarizes the calculated results of TGU in each patient.

Conclusion: In this study, the calculation protocol of TGU for DTT based on ICRU Report 62 and GUM has proposed by separating patient specific uncertainty and institution specific uncertainty in each patient. Our proposed method is very helpful to estimate the margin of DTT therapy for lung cancer. Table. The calculated results of TGU by proposed protocol in each patient.
Patient number L - R (mm) A - P (mm) S - I (mm)
1 4.2 - 1.8 3.4 - 3.1 6.5 - 5.5
2 3.0 - 2.7 2.9 - 3.3 5.5 - 7.4
3 5.9 - 0.8 9.3 - 2.2 5.4 - 5.5
4 5.3 - 0.3 3.6 - 2.4 8.5 - 3.0
5 3.1 - 3.6 2.3 - 5.4 12.5 - 3.2
6 4.9 - 3.0 3.9 - 2.8 7.4 - 4.6
7 2.7 - 3.2 3.1 - 3.0 7.3 - 4.1
8 3.3 - 2.4 2.8 - 3.1 3.5 - 6.5
9 3.1 - 3.2 4.3 - 3.6 6.6 - 4.3
10 4.4 - 2.6 3.5 - 4.8 10.8 - 8.7
11 4.4 - 2.1 5.9 - 1.1 3.0 - 7.2
12 3.5 - 2.3 2.6 - 3.8 6.2 - 4.2
13 2.6 - 4.1 3.7 - 2.5 10.3 - 4.9
14 2.8 - 3.2 5.6 - 3.5 8.5 - 4.0
15 2.8 - 4.5 6.3 - 0.5 6.1 - 5.4
16 3.0 - 4.9 6.0 - 1.7 8.6 - 2.8
17 3.6 - 2.2 5.5 - 1.1 6.7 - 4.7
average of TGU range 6.5 7.2 12.3
standard deviation of TGU range 0.7 1.4 2.4

Author Disclosure: S. Kito: None. K. Nihei: None. Y. Machitori: None. R. Suganami: None. T. Furuya: None.

Satoshi Kito, MS

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