Abstract
PurposeThis study provides a proof of concept for real‐time 4D dose reconstruction for lung stereotactic body radiation therapy (SBRT) with multileaf collimator (MLC) tracking and assesses the impact of tumor tracking on the size of target margins.MethodsThe authors have implemented real‐time 4D dose reconstruction by connecting their tracking and delivery software to an Agility MLC at an Elekta Synergy linac and to their in‐house treatment planning software (TPS). Actual MLC apertures and (simulated) target positions are reported to the TPS every 40 ms. The dose is calculated in real‐time from 4DCT data directly after each reported aperture by utilization of precalculated dose‐influence data based on a Monte Carlo algorithm. The dose is accumulated onto the peak‐exhale (reference) phase using energy‐mass transfer mapping. To investigate the impact of a potentially reducible safety margin, the authors have created and delivered treatment plans designed for a conventional internal target volume (ITV) + 5 mm, a midventilation approach, and three tracking scenarios for four lung SBRT patients. For the tracking plans, a moving target volume (MTV) was established by delineating the gross target volume (GTV) on every 4DCT phase. These were rigidly aligned to the reference phase, resulting in a unified maximum GTV to which a 1, 3, or 5 mm isotropic margin was added. All scenarios were planned for 9‐beam step‐and‐shoot IMRT to meet the criteria of RTOG 1021 (3 × 18 Gy). The GTV 3D center‐of‐volume shift varied from 6 to 14 mm.ResultsReal‐time dose reconstruction at 25 Hz could be realized on a single workstation due to the highly efficient implementation of dose calculation and dose accumulation. Decreased PTV margins resulted in inadequate target coverage during untracked deliveries for patients with substantial tumor motion. MLC tracking could ensure the GTV target dose for these patients. Organ‐at‐risk (OAR) doses were consistently reduced by decreased PTV margins. The tracked MTV + 1 mm deliveries resulted in the following OAR dose reductions: lung V 20 up to 3.5%, spinal cord D 2 up to 0.9 Gy/Fx, and proximal airways D 2 up to 1.4 Gy/Fx.ConclusionsThe authors could show that for patient data at clinical resolution and realistic motion conditions, the delivered dose could be reconstructed in 4D for the whole lung volume in real‐time. The dose distributions show that reduced margins yield lower doses to healthy tissue, whilst target dose can be maintained using dynamic MLC tracking.
Highlights
Randomized controlled trials have shown that dose escalation in stereotactic body radiation therapy (SBRT) for stage I nonsmall cell lung cancer results in high tumor control (>90% for primal local tumor control).1 A stage I lung tumor typically moves a few millimeters up to a few centimeters due to respiratory motion.2 Assuring dose coverage of the tumor can be accomplished by deep-inspiration breath-hold or respiratory gating strategies,3 at the cost of patient discomfort, longer treatment times, and requiring the patient’s collaboration
This study provides a proof of concept for real-time 4D dose reconstruction for lung stereotactic body radiation therapy (SBRT) with multileaf collimator (MLC) tracking and assesses the impact of tumor tracking on the size of target margins
We have shown that dose can be calculated and accumulated in real-time at 25 Hz for the whole lung volume using a clinical voxel resolution utilizing precalculated dose-influenced data and deformable vector fields (DVFs)
Summary
Randomized controlled trials have shown that dose escalation in stereotactic body radiation therapy (SBRT) for stage I nonsmall cell lung cancer results in high tumor control (>90% for primal local tumor control). A stage I lung tumor typically moves a few millimeters up to a few centimeters due to respiratory motion. Assuring dose coverage of the tumor can be accomplished by deep-inspiration breath-hold or respiratory gating strategies, at the cost of patient discomfort, longer treatment times, and requiring the patient’s collaboration. A stage I lung tumor typically moves a few millimeters up to a few centimeters due to respiratory motion.. The motion can be incorporated into treatment planning, by constructing a planning target volume (PTV) based on an internal target volume (ITV). The ITV is defined as the composite volume of gross target volumes (GTVs), delineated on various phases of a 4DCT reflecting the breathing cycle.. The ITV is defined as the composite volume of gross target volumes (GTVs), delineated on various phases of a 4DCT reflecting the breathing cycle.4 This straight-forward approach guarantees target coverage for the whole breathing cycle (as long as the motion in treatment and imaging sessions coincide), the high-dose volume is unnecessarily large and potentially toxic to surrounding normal tissues. For hypofractionated treatment regimens, moving away from the very conservative ITV-based PTV is expected to reduce toxicity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
