Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_16_3274 - Planning Target Volume Determination of Internal Mammary Nodes in Breast Cancer using 4DCT

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

Planning Target Volume Determination of Internal Mammary Nodes in Breast Cancer using 4DCT
M. Jermoumi, S. M. James, C. L. Ferguson, J. T. Barrett, C. Huh, and A. Al-Basheer; Department of Radiation Oncology, Augusta University, Augusta, GA

Purpose/Objective(s): Accurate planning target definition of the upper internal mammary nodal chain (IMN) in locally advanced breast cancer is necessary to safely deliver comprehensive chest wall and regional nodal irradiation. In this work, we analyzed the appropriate planning target volume based on internal motion of the IMN target using 4DCT planning. In addition, the inter-observer variability of the IMN target contoured by the 2 clinicians was assessed.

Materials/Methods: Ten consecutively treated patients with locally advanced breast cancer were retrospectively enrolled in this study. Each patient was simulated with 4DCT scan and IV contrast. Two board certified radiation oncologist contoured the internal mammary lymph node chain using the data set from the CT average and all 10 respiratory phases according to the RTOG breast cancer atlas. Afterward, the IMN internal motion was determined along all 3 translational directions. Furthermore, the inter-observer delineation variation for the IMN was quantified based on CT average using tumor volume, eccentricity and dice similarity coefficient (DSC) to evaluate the target voxel similarity.

Results: The internal mammary (IM) margin calculated from the difference of the average CT and all ten phases showed significance difference for both observers along superior–inferior, anterior-posterior, and medial-lateral directions (P<0.05). The maximum margin to the IM vessel was 5 mm. High inter-observer variability was shown for target volume and eccentricity feature. For both clinicians, the mean of target volume (SD) were 4.29 cm3 (±1.53) and 2.14 cm3 (±0.53) with p value of 0.005 and the mean of eccentricity were 0.73 (±0.13) and 0.73 ((±0.09) with p value of 0.04. The mean (SD) of the similarity agreement between two manual delineation was 0.65 (±0.16). In seventy percent of cases, the DSC showed good agreement.

Conclusion: We determined a reasonable PTV margin on the IMN nodal chain based on internal motion using 4DCT. When contouring on the average CT, 5 mm margin may be added to the internal mammary nodes volume to account for respiratory motion. To verify the efficacy of the IM margin, phase based review should be used to determine proper coverage. High inter-observer variability was shown for clinical target volume and clinical target shape eccentricity. Dice similarity coefficient showed in overall good agreement.

Author Disclosure: M. Jermoumi: None. S.M. James: None. C.L. Ferguson: None. C. Huh: None.

Mohammed Jermoumi, PhD

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