Development of an online adaptive solution to account for inter- and intra-fractional variations

Purpose: The current IGRT repositioning cannot fully account for the organ deformation and rotation. We introduce a comprehensive solution using gated IMRT with online adaptive replanning to manage both inter- and intra-fractional variations. Methods and materials: The solution includes (1) generating respiration-gated IMRT plans based on 4DCT, (2) acquiring daily gated CT in treatment position prior to the treatment using a diagnostic-quality in-room CT (CTVision, Siemens) with the same gating window as that for the planning CT, (3) performing online repositioning or adaptive replanning based on the gated CT of the day, and (4) delivering the treatment with gating. The entire solution is demonstrated with RT data from 10 selected pancreatic cancer cases. The dosimetric impact of various advanced delivery technologies was investigated. Results: The online adaptive replanning based on the CT of the day combining with gating significantly improves normal tissue sparing during RT for pancreatic cancer. As the complexity of the delivery technology increases from no IGRT to with IGRT, gating and online adaptive replanning, the inter- and intra-fractional variations can be accounted for with increased adequacy. Conclusion: The online adaptive replanning technique based on daily respiration-gated diagnostic-quality CT combined with gated delivery can effectively correct for inter- and intra-fraction variations during radiation therapy.