Program Information

Use of Patient Geometry Measurements to Predict Dosimetric Gain with VMAT Over 3D for Chestwall and Regional Nodal Radiation

V DUMANE¹*, M HUNT² , E STEINBERGER³ , M KNOLL⁴ , S GREEN⁵ , R BAKST⁶ , (1) THE MOUNT SINAI MEDICAL CENTER, New York, NY,(2) Mem Sloan-Kettering Cancer Ctr, New York, NY, (3) THE MOUNT SINAI SCHOOL OF MEDICINE, New York, NY, (4) THE MOUNT SINAI MEDICAL CENTER, New York, NY, (5) THE MOUNT SINAI MEDICAL CENTER, New York, NY, (6) THE MOUNT SINAI MEDICAL CENTER, New York, NY

Presentations

SU-E-T-342 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To predict the dosimetric gain of VMAT over 3D for the treatment of
chestwall/IMN/supraclavicular nodes using geometric parameters acquired during simulation

Methods:CT scans for 20 left and 20 right sided patients were retrospectively analyzed to
obtain percent ipsilateral lung volume included in the PWT and supraclavicular fields, central lung depth (CLD), maximum lung depth (MLD), separation, chestwall concavity (defined here as the product of CLD and separation) and the maximum heart depth (MHD). VMAT, PWT and P/E plans were done for each case. The ipsilateral lung V20 Gy and mean, total lung V20 Gy and mean, heart V25 Gy and mean were noted for each plan. Correlation coefficients were obtained and linear regression models were built using data from the above training set of patients and then tested on 4 new patients.

Results: The decrease in ipsilateral lung V20 Gy, total lung V20 Gy, ipsilateral lung mean and total lung mean with VMAT over PWT significantly (p<0.05) correlated with the percent volume of ipsilateral lung included in the PWT and supraclavicular fields with correlation coefficient values of r = 0.83, r = 0.77, r = 0.78 and r = 0.75 respectively. Significant correlations were also found between MHD and the decrease in heart V25 Gy and mean of r = 0.77 and r = 0.67 respectively. Dosimetric improvement with VMAT over P/E plans showed no correlation to any of the geometric parameters investigated in this study. The dosimetric gain predicted for the 4 test cases by the linear regression models given their respective percent ipsilateral lung volumes fell within the 95% confidence intervals around the best regression fit.

Conclusion:The percent ipsilateral lung volume appears to be a strong predictor of the dosimetric gain on using VMAT over PWT apriori.

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