Author: Lili Chen, Ahmed A. Eldib, Chang Ming Charlie Ma 👨🔬
Affiliation: Fox Chase Cancer Center 🌍
Purpose: Specialized adaptive radiotherapy (ART) systems have been developed and clinically implemented, which are either cost-ineffective such as MR-linacs or inflexible in workflow such as the Ethos system, affecting their widespread clinical use. This work investigates a new workflow that integrates ART into the routine IGRT workflow seamlessly.
Methods: The new workflow uses the same treatment simulation and planning process as in routine IGRT. During a treatment session, the patient will be set up and CBCT imaged, and the patient’s anatomy will be compared with the planned dose distribution to decide whether ART is needed. If so, new contours and treatment plans will be generated. Independent dosimetry verification will be performed before and after the dose delivery. Two novel strategies make the new workflow more effective and efficient: (1) the use of pre-selected isodose lines rather than the planning contours to match the patient anatomy, which can improve the target localization accuracy, thus reducing the need for re-planning, and (2) the use of direct-aperture optimization and MLC leaf adjustment to improve planning efficiency (in seconds) and plan quality over the scheduled plan.
Results: With Ethos one must go through the entire ART workflow including re-contouring and re-planning even if the patient has minimal anatomy changes. The new workflow allows efficient IGRT treatment and only initiates ART when necessary. Our results showed that strategy (1) significantly improved the target localization accuracy and reduced the necessity of re-planning from 36.7% to 19.4% for 98 prostate fractions, and strategy (2) significantly improved heterogeneity index and conformity index for the target and dose-volume parameters for lung, liver, kidney, bladder and rectum for 15 patients.
Conclusion: The new workflow integrates ART into routine IGRT on existing CBCT-lincs, which can significantly improve the effectiveness and efficiency of IGRT/ART with the use of two novel strategies.