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Demonstration of a Planning Scheme for Emission Guided Radiation Therapy (EGRT) in a Metastatic Breast Cancer Patient

Q Fan

Q Fan1,2*, A Nanduri2, J Yang3, T Yamamoto4, B Loo3, E Graves3, L Zhu1, S Mazin2, (1) Georgia Institute of Technology, Atlanta, GA, (2) Reflexion Medical, Burlingame, California, (3) Stanford University, Palo Alto, CA, (4) UC Davis School of Medicine, SACRAMENTO, CA

SU-F-500-6 Sunday 4:00PM - 6:00PM Room: 500 Ballroom

Purpose: Emission guided radiation therapy (EGRT) is a new modality that uses PET emissions in real-time for direct tumor tracking during radiation delivery. Radiation beamlets are delivered along PET lines of response (LOR's) by a fast rotating ring therapy unit consisting of a Linac and PET detectors. The feasibility of tumor tracking has been demonstrated previously. In this work, we develop a planning scheme for EGRT to accomplish sophisticated intensity modulation based on an intensity modulated radiation therapy (IMRT) plan while preserving tumor tracking.

Methods: To incorporate the IMRT plan into EGRT treatment, we sample EGRT's detection and delivery space into 3D parallel sinogram space. Planning modulation is achieved via generating an LOR response probability distribution in the same sinogram space, which accounts for attenuation correction, PET activity normalization, and a modified IMRT plan. The IMRT plan is optimized for a planning target volume that encompasses the tumor motion. Evaluation studies are performed on a 4D digital patient as well as a clinical breast cancer patient with moving tumors in the lung. The Linac dose delivery is simulated using a Monte Carlo algorithm. Emission data are obtained using GATE and a commercial PET scanner.

Results: Compared with the 3D IMRT treatment which covers the same PTV based on the same IMRT plan, EGRT achieves a 15.1%, 15.2% relative increase in dose to 95% of the gross tumor volume (GTV) and a 31.8%, 20.7% increase to 50% of the GTV for the digital and clinical patients, respectively. The organs at risk doses are kept similar or lower for EGRT in both cases, with tumor tracking preserved.

Conclusion: With the capabilities of incorporating planning modulation and accurate tumor tracking, EGRT has the potential to enable a practical and effective implementation of 4D biologically guided radiation therapy for planning and delivery.

Funding Support, Disclosures, and Conflict of Interest: This work is supported by Georgia Institute of Technology new faculty startup fund, RefleXion Medical and the National Cancer Institute (R43CA153466). SRM, ASN and LZ have financial interest in RefleXion Medical. BWL receives speaking honoraria from Varian and research support from Varian, Philips, and RaySearch Labs.

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