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Evaluating the Impact of Respiratory Motion On Proton Breast Treatment

X Wang

X Wang1*, H Cao2 , N Yue1 , M Zhang1 , (1) Rutgers-Cancer Institute of New Jersey, Rutgers-Robert Wood Johnson Medical School, New Brunswick, NJ, (2) Radiation Oncology Center of Renji Hospital, Shanghai, China


SU-I-GPD-T-102 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Proton therapy is beneficial to left-sided breast patient with significant heart and lung sparing. The treatment is commonly delivered with free breathing. In literature, no evaluation has been performed regarding the dosimetric effect of respiratory motion in proton breast treatment. This project is aimed to fill in this blank.

Methods: 5 left sided breast patients’ 4DCT images were acquired with Varian RPM. Double scattering proton plans following RTOG3510 protocol were generated for each patient on CT-average. Two treatment plans were compared: 1-field plan with only one en face field, and 2-field plan with equally weighted one en face and one AP field. Then the same plan was recalculated on 10 individual breathing phases’ images. The delivered dose was simulated by deforming each phase’s dose back to CT-average and then summing up utilizing Varian Velocity. PTV D90 and lung V20 were compared between the planned and delivered dose distribution for evaluation.

Results: The 2-field plan generally showed better PTV coverage and lung sparing. Out of 5 patients with similar breathing amplitude in RPM, 4 patients showed breast movement of less than 7mm, while 1 patient showed breast movement of 13 mm. The differences in PTV D90 and lung V20 between planned and delivered dose were less than 2% for 4 patients with smaller breast motion. For the patient with 13 mm breast motion, the PTV D90 and lung V20 variation was -28.9% and -11.9% for 1-field plan and -23.5% and -9% for 2-field plan. Differences in PTV D90 and lung V20 showed significant correlation with breast motion.

Conclusion: The results showed that for patients with breast motion less than 7 mm, free breathing CT would be sufficient. For larger breast motion, the dosimetry should be evaluated. In general, 2-field plan showed slightly better lung sparing and robustness to respiratory motion.

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