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Considerations for Further Pulmonary Toxicity Reduction with 4DCT Derived Functional Avoidance Intensity Modulated Proton Therapy

J Dougherty

J Zhang1*, Y Vinogradskiy2 , E Castillo1 , A Faught2 , C Stevens1 , I Grills1 , T Guerrero1 , (1) Beaumont Health System, Royal Oak, MI, (2) University of Colorado School of Medicine, Aurora, CO,


SU-F-605-4 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 605

Purpose: With the advent of 4DCT based functional image-guided radiotherapy for lung cancer, CT ventilation images have been translated into clinical usage for functional avoidance radiotherapy. The purpose of this study is to evaluate the potential dosimetric gains for functional avoidance with Intensity Modulated Proton Therapy (IMPT).

Methods: Functional ventilation images were created using a prior published algorithm based on deformable registration and underlying CT density characteristics. 4DCT data from patients enrolled in a prospective functional avoidance clinical trial are re-planned with robustness optimized IMPT(3.5% and 5mm) and compared with VMAT. Dose degradation due to proton spot arrangement and breathing motion was studied by evaluating dynamic dose accumulation based on 4DCT with an in-house built interplay Python script. Patient tumor excursion was estimated by both weekly 4DCBCT and simulation 4DCT. Dosimetric parameters were compared between IMPT and VMAT. Both pencil beam and MC dose algorithms were evaluated. Dose re-painting (layer) method was applied to increase target coverage on the IMPT plans and decrease the motion interplay effect.

Results: The CTV target coverage was adequate for all IMPT plans (D95>60Gy). Compared with VMAT, IMPT plans have a relative dose reduction to most of the OARs (P<0.05), including functional mean lung dose (-4.4Gy), fV20 (-5.1%), and fV5 (-39.7%). Compared with pencil beam method, MC engine has a significant regional dose difference of 28% of the total prescription.

Conclusion: We perform one of the first studies to investigate IMPT for functional avoidance thoracic RT. We found that IMPT was able to further spare healthy functional lung tissue with layer repainting technique to avoid excess dose to normal structures while maintaining satisfying target coverage. Studies have shown that the risk of pulmonary complications can be reduced with functional radiotherapy; our data demonstrate that even further toxicity reductions are possible with IMPT.

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