Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_2_3131 - Setup Time and Positioning Accuracy in Breast Radiation Therapy Using Surface Guided Radiation Therapy

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

Setup Time and Positioning Accuracy in Breast Radiation Therapy Using Surface Guided Radiation Therapy
S. Kost, C. S. Shah, P. Xia, and B. Guo; Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): Use of 3D surface imaging for tracking patient position before and during breast radiotherapy (RT) is increasing. However, the impact of surface guided radiation therapy (SGRT) on patient setup accuracy and throughput has yet to be evaluated. Therefore, the objective of this study was to determine setup time and positioning accuracy for breast RT with and without SGRT.

Materials/Methods: A retrospective IRB approved study included 110 patients. Average setup times were determined using recorded time stamps, one entered in the treatment room after confirming patient identity and another recorded at the console immediately prior to delivering the fields. Positioning accuracy was assessed using the number of portal images taken weekly for setup verification. Setup accuracy was also evaluated by comparing projected planning structures to the skin and chest wall (CW) on portal images. Comparisons were performed for four treatment techniques: tangents, tangents using Deep Inspiration Breath Hold (DIBH), and 4-field treatment with and without DIBH.

Results: The setup times with and without SGRT were 4:56 vs. 4:42 (p=0.31), 6:26 vs. 7:14 (p=0.12), 6:17 vs. 4:54 (p=0.01), and 7:07 vs. 6:23 (min:sec) (p=0.30) for tangents, tangents using DIBH, 4-field without DIBH, and 4-field with DIBH treatments respectively. The use of SGRT significantly decreased the number of excess weekly portal images from 0.38 to 0.09 (p=0.03) for tangents and 0.70 to 0.16 (p<0.01) for tangents with DIBH. The difference in excess weekly portal images was not significant for 4-field (0.20 vs. 0.16 using SGRT, p=0.77) or 4-field with DIBH (0.26 vs. 0.58 using SGRT, p=0.17) treatments. As summarized in the table, the mean and maximum distance from the planned skin surface was significantly reduced using SGRT for all treatment techniques. There was no statistically significant differences for the mean and maximum CW deviation with the exception of 4-field plans without DIBH. Here, the maximum distance from the planned CW decreased by 2.3 mm (p=0.01) using SGRT.
Tangents Tangents - DIBH 4-field 4-field - DIBH
Portal image deviation Non-SGRT SGRT Non-SGRT SGRT Non-SGRT SGRT Non-SGRT SGRT
Mean skin surface (mm) 2.91 1.89 (p=0.03) 3.97 1.99 (p<0.01) 3.71 2.47 (p=0.01) 4.00 3.01 (p=0.04)
Max skin surface (mm) 7.21 5.31 (p<0.01) 8.73 5.22 (p<0.01) 7.73 5.50 (p=0.01) 8.17 6.57 (p<0.01)
Mean CW (mm) 2.49 2.66 (p=0.72) 3.30 3.74 (p=0.44) 3.46 2.92 (p=0.26) 3.83 3.52 (p=0.52)
Max CW (mm) 5.86 5.19 p=0.30 6.14 6.58 (p=0.45) 7.59 5.31 (p=0.01) 6.74 6.28 (p=0.44)

Conclusion: No significant increase in treatment time was noted with SGRT, with the exception of 4-field plans without DIBH. The increase is unlikely clinically significant and is also associated with improved setup accuracy when portal imaging is evaluated. SGRT results in better alignment of the skin surface for breast RT and a reduction of the number of portal images required for accurate patient setup for tangential treatments.

Author Disclosure: S. Kost: None. C.S. Shah: Employee; Cleveland Clinic Foundation. Consultant; Impedimed. P. Xia: Employee; Cleveland Clinic. Research Grant; Philips Healthcare. B. Guo: None.

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