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Dosimetric and Operational Comparison of Two Snout Sizes for Proton Therapy of Breast Cancer with Lymph Node Involvement

Y Zheng

Y Zheng1*, H Singh2 , M Prince2 , (1) Atlantic Health System, Morristown, NJ, (2) Procure Proton Therapy Center, Oklahoma City, OK


SU-I-GPD-T-193 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The treatment volume for breast cancer treatment involving lymph nodes could be very large and requires matching fields for typical proton machines with a maximum snout size of 25 cm in diameter (SNOUT25). Using a larger snout of 30×40 cm2 (SNOUT40) would allow treating the whole volume with one single field. In this study, we investigated whether a SNOUT40 would be advantageous for large field breast cancer treatment in both dosimetry and operation.

Methods: Retrospective planning was performed for 10 breast patients with lymph node involvement using SNOUT40, and compared with the initial planning with SNOUT25 using matching fields. Same beam angles were used for both snout types, with typically two fields for SNOUT40 plans and four fields (two pairs of matching fields for each gantry angle) for SNOUT25. DVH values were compared for target, lung, cord, heart and esophagus. In addition, operational time and cost related to treatment planning, beam delivery, hardware manufacturing, as well as user preference were also compared.

Results: For similar target coverage, treatment plans using SNOUT40 would generate less hot spots in target and spared more lung, cord and esophagus compared to those using SNOUT25 (Fig. 1). While hardware cost was similar for both snout types, treatment planning complexity and patient on couch time were significantly reduced with SNOUT40, which was preferred to use by dosimetrists, therapists and patients.

Conclusion: A larger snout can be beneficial both dosimetrically and operationally and is recommended for proton therapy of breast cancer with lymph node involvement.

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