To test the efficacy of a simple, robust-inspired intensity modulated radiotherapy (IMRT) planning strategy for lung radiotherapy designed to reduce lung dose and escalate tumor dose using realistic dose accumulation tools.
A deformable image registration tool was used to plan and accumulate dose over all phases of the breathing cycle for conventional and robust-inspired IMRT strategies of eight nonsmall cell lung cancer patients exhibiting peak-to-peak respiratory motion with amplitudes ranging from 1 to 2 cm in the craniocaudal direction. The authors’ robust-inspired plans were designed to have smaller beam apertures based on target location during exhale, combined with edge-enhanced intensity maps to ensure target coverage during inspiration. For these, a new planning target volume defined as the rPTV was generated from a 5-mm isotropic expansion of the clinical target volume (CTV) on end-exhale combined with a boost volume, set to 110% of the prescription dose. Plans were evaluated in terms of (i) lung sparing and (ii) dose escalation for mean lung dose (MLD) isotoxicity. CTV and planning target volumes (PTV) coverage and lung dose were compared to the conventional IMRT approach.
Robust-inspired plans showed potential lung dose reductions in seven out of eight patients. For non-GTV lung, percent reductions of 3%–14% in MLD and 6%–15% in V20 were observed. For seven of eight cases, the robust-like approach yielded increased accumulated doses to CTV. Isotoxicity studies for MLD showed increased dose to the CTV and the rPTV, in the range of 104%–118% and 95%–114% of prescription dose, respectively.
A 4D dose calculation based on deformable image registration was used to evaluate a robust-inspired planning strategy for lung radiotherapy. This method offers notable reductions to lung dose while improving tumor coverage through the use of reduced geometric margins combined with edge enhancements.
The authors would like to thank RaySearch Laboratories for their financial contribution and technical support, including Dr. Henrik Rehbinder and Ms. Anna Lundin. We would also like to thank Mr. James Stewart for his technical support. This research was funded in part by an unrestricted grant from RaySearch Laboratories. The authors would also like to thank Dr. Emily Heath and Dr. Timothy Chan for their insightful and helpful discussions on robust optimization. The authors report no conflicts of interest in conducting the research. This study was supported in part by RaySearch Laboratories. Dr. Henrik Rehbinder and Ms. Anna Lundin hold shares in RaySearch.
II. METHODS AND MATERIALS
II.D. IMRToptimization and dose accumulation
II.F. Dose accumulation
III.A. Lung sparing
III.B. Dose escalation: MLD isotoxicity
- Intensity modulated radiation therapy
- Radiation therapy
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