SU‐FF‐J‐24: Functional Planning for Tomotherapy‐Based Stereotactic Body Radiotherapy (SBRT) for Peripheral Lung Tumors

Purpose: To investigate the impact of incorporating hyperpolarized heliume‐3 (HP He‐3) MRI ventilation images to Tomotherapy‐based stereotactic body radiation therapy (SBRT) planning for peripheral lung tumors. Method and Materials: CT and HP He‐3 MRI ventilation images of 6 subjects were co‐registered for segmentation. Highly functional lungs (HFL) were defined as the 70‐percentile hyperventilation lungs and less functional lungs (LFL) were subsequently calculated. A cylinder‐shaped artificial object was created in peripheral lungs to mimic planning‐target‐volume (PTV). Two Tomotherapy‐based IMRT plans, a anatomical plan (Plan 1) and a functional plan (Plan 2), were designed with SBRT‐type prescription (60Gy in 5 fractions) and normal tissue constrains. The following dosimetric parameters were compared between two plans: total lung V₂₀ (TLV20), highly functional lungs V20 (HFLV20), less functional lungs V20 (LFLV20), mean total lung dose (MTLD), mean highly functional lung dose (MHFLD), mean less functional lung dose (MLFLD), max dose to organs at risk (OARs) and conformality index (CI). Results: Compared to Plane 1, Plan 2 significantly reduced HFLV₂₀ (median reduction 2.1%, range 0.7–2.9%, p‐value=0.031), TLV₂₀ (median reduction 1.6%, range 0.5–2.1%, p‐value=0.031), MHFLD (median reduction 0.8Gy, range 0.4–1.0Gy, p‐value=0.031), and MTLD (median reduction 0.7Gy, range 0.1–1.0Gy, p‐value=0.031). There was no significant difference in LFLV₂₀ and MLFLD (p‐value is 0.438 and 0.156 respectively). Dose constrains for OARs were satisfied in all plans and max doses to OARs were not significantly changed in Plan 2 (p‐values range: 0.063–0.563). CI was generally reduced in Plan 2 (median reduction 0.02) but the difference is insignificant (p‐value=0.125). Conclusions: The incorporation of HP He‐3 MRI ventilation information to the Tomotherapy‐based SBRT planning for peripheral lung cancer improved the sparring of radiation dose to highly functional lungs and can potentially preserve more highly functional lungs. Conflict of Interest: Dr. Paul W. Read serves as a consultant for Tomotherapy Inc.