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 positron emission tomography (PET) lines of response (LORs) by a fast rotating ring therapy unit consisting of a linear accelerator (Linac) and PET detectors. The feasibility of tumor tracking and a primitive modulation method to compensate for attenuation have been demonstrated using a 4D digital phantom in our prior work. However, the essential capability of achieving dose modulation as in conventional intensity modulated radiation therapy (IMRT) treatments remains absent. In this work, the authors develop a planning scheme for EGRT to accomplish sophisticated intensity modulation based on an IMRT plan while preserving tumor tracking.
The planning scheme utilizes a precomputed LOR response probability distribution to achieve desired IMRT planning modulation with effects of inhomogeneous attenuation and nonuniform background activity distribution accounted for. Evaluation studies are performed on a 4D digital patient with a simulated lung tumor and a clinical patient who has a moving breast cancer metastasis in the lung. The Linac dose delivery is simulated using a voxel-based Monte Carlo algorithm. The IMRT plan is optimized for a planning target volume (PTV) that encompasses the tumor motion using the MOSEK package and a Pinnacle3™ workstation (Philips Healthcare, Fitchburg, WI) for digital and clinical patients, respectively. To obtain the emission data for both patients, the Geant4 application for tomographic emission (GATE) package and a commercial PET scanner are used. As a comparison, 3D and helical IMRT treatments covering the same PTV based on the same IMRT plan are simulated.
3D and helical IMRT treatments show similar dose distribution. In the digital patient case, compared with the 3D IMRT treatment, EGRT achieves a 15.1% relative increase in dose to 95% of the gross tumor volume (GTV) and a 31.8% increase to 50% of the GTV. In the patient case, EGRT yields a 15.2% relative increase in dose to 95% of the GTV and a 20.7% increase to 50% of the GTV. The organs at risk (OARs) doses are kept similar or lower for EGRT in both cases. Tumor tracking is observed in the presence of planning modulation in all EGRT treatments.
As compared to conventional IMRT treatments, the proposed EGRT planning scheme allows an escalated target dose while keeping dose to the OARs within the same planning limits. With the capabilities of incorporating planning modulation and accurate tumor tracking, EGRT has the potential to greatly improve targeting in radiation therapy and enable a practical and effective implementation of 4D radiation therapy for planning and delivery.
This work is supported by Georgia Institute of Technology new faculty startup fund, RefleXion Medical, and the National Cancer Institute (R43CA153466). S.R.M., A.S.N. and L.Z. have financial interest in RefleXion Medical. B.W.L. receives speaking honoraria from Varian and research support from Varian, Philips, and RaySearch Labs. The authors thank Sue Wallace, Michael Kaus, Ying Xiong, Hari Gopalakrishnan, and Matthieu Bal from Philips Radiation Oncology Systems for providing a Pinnacle3 workstation and technical support. The authors thank Frédéric Tessier and the National Research Council of Canada for providing the VMC++ software, and CliQr Technologies for providing cloud computing resources. The authors would also like to thank Paul Segars, Youngho Seo, Xun Jia, Norbert Pelc, David Townsend, Charles Pelizzari, Chin-Tu Chen, Ralph Weichselbaum, Paul Keall, and James Welsh for generous help and useful discussions.
II.A. The proposed EGRT treatment
II.A.1. System geometry and radiation delivery
II.A.2. EGRT treatment scheme
II.B. The proposed EGRT planning scheme
II.B.1. The overall scheme
II.B.2. PET activity normalization and attenuation correction
II.B.3. Modified IMRT plan
II.C. EGRT simulation workflow
II.D. Performance evaluation
II.D.1. Digital XCAT patient
II.D.2. Clinical patient
III.A. Digital XCAT patient
III.B. Clinical patient
- Intensity modulated radiation therapy
- Positron emission tomography
- Computed tomography
Data & Media loading...
Article metrics loading...
Full text loading...