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Midline Surface Isocenter: Improved Initial Patient Setup for Breast Cancer Patients

T Reynolds1*, M Ozer1 , (1) MN Oncology, St Paul, MN


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Breast cancer is the most commonly diagnosed cancer. Daily patient setup should be easy to reproduce, efficient and accurate. The process of positioning patient prior to imaging verification involves the use of permanent marks, or tattoos, placed subcutaneously. After aligning on these tattoos, plan specific shifts are applied and the position is verified with kV imaging. Historically, the isocenter was placed close to the planning isocenter in the center of the breast at the depth (Group I). We propose placing the isocenter in more stable position: patient midline on the surface (Group II). The purpose of this study is to compare 3D corrections of patients in Group I versus Group II.

Methods: A total of fifty-two right breast cancer patients (Group I/Group II: 50%/50%) who underwent whole breast radiotherapy followed by boost treatment were randomly selected for this study. Post kV 3D corrections were recorded for the initial fractions of the initial and boost plan. Statistical differences* were evaluated using t-test with significance level of <0.05.

Results: The average magnitudes of the 3D shift vectors (vert/long/lat) for Group II were 0.31±0.19 (0.21±0.17), 0.33±0.29 (0.36±0.23) and 028±0.40 (0.51±0.47) cm for initial plan (boost). For Group I these shifts were larger for initial plan 0.45±0.70, 0.36±0.32 and 0.54±0.61 cm, and significantly larger for boost plan 0.58±0.81*, 0.75±0.73* and 0.52±0.52 cm. In addition, on average 1.5 kV post images were acquired for both groups’ patient setups for initial and boost plans.

Conclusion: This study demonstrates that overall 3D shift corrections for Group II patients were significantly smaller than Group I, especially for the boost patient setup. Midline surface tattoos can be considered to be a more stable, viable option for initial patient setup.


Localization, Linear Accelerator, Breast


TH- External beam- photons: General (most aspects)

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