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ITV Margin Reduction Technique for Abdominal SBRT Treatment

L Jin

L Jin*, J Fan , L Chen , R Price , J Meyer , A Eldib , C Ma , Fox Chase Cancer Center, Philadelphia, PA


SU-I-GPD-T-597 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In the SBRT treatment to lesions situated in liver or pancreas, it has been challenging to give sufficient dose to the target while avoid overdose to adjacent critical structures, especially when an organ motion is prominent as usually seen. A “new” method of reducing ITV margin is developed to ease this challenge as compared to the “old” one often used in our clinic in the past.

Methods: A fiducial is implanted inside the target or near target, and its motion range can be measured on the MIP that is generated from 4D CT data. The “old” method is: a GTV is contoured on the free-breathing CT, and total fiducial motion range on each direction of SI, LR or AP is uniformly added to two ends of the GTV on that direction to make ITV. The “new” method: GTV is contoured on the breath-hold CT which will be fused into the planning CT, i.e. the free-breathing CT, and the new feature of using breath-hold CT allows adding the specific margin to each end of GTV on each direction of SI, LR and AP by comparing fiducial images between one MIP and the breath-hold CT. Detailed formula for calculating ITV margin for the new method is developed, and analyses are performed for seven patients, comparing determined ITV margins for the two methods.

Results: In average, with the “new” method as compared to the “old”, the ITV margin is reduced in SI direction by 42.1%, in LR direction by 35.3% and in AP direction by 37.9%.

Conclusion: With this “new” method, target size can be significantly reduced, which helps dose escalation to the target or dose reduction to critical structures and eventually more effective treatment. More detailed work should be done on, such as comparisons in target volume, dosimetry and treatment effectiveness.

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