Dataset Information

Cleaning the dose falloff in lung SBRT plan.

ABSTRACT:

Purpose

To investigate a planning technique that can possibly reduce low-to-intermediate dose spillage (measured by R50%, D2cm values) in lung SBRT plans.

Materials and methods

Dose falloff outside the target was studied retrospectively in 102 SBRT VMAT plans of lung tumor. Plans having R50% and/or D2cm higher than recommended tolerances in RTOG protocols 0813 and 0915 were replanned with new optimization constraints using novel shell structures and novel constraints. Violations in the RTOG R50% value can be rectified with a dose constraint to a novel shell structure ("OptiForR50"). The construction of structure OptiForR50% and the novel optimization criteria translate the RTOG goals for R50% into direct inputs for the optimizer. Violations in the D2cm can be rectified using constraints on a 0.5 cm thick shell structure with inner surface 2cm from the PTV surface. Wilcoxon signed-rank test was used to compare differences in dose conformity, volume of hot spots, R50%, D2cm of the target in addition to the OAR doses. A two-sided P-value of 0.05 was used to assess statistical significance.

Results

Among 102 lung SBRT plans with PTV sizes ranging from 5 to 179 cc, 32 plans with violations in R50% or D2cm were reoptimized. The mean reduction in R50% (4.68 vs 3.89) and D2cm (56.49 vs 52.51) was statistically significant both having P < 0.01. Target conformity index, volume of 105% isodose contour outside PTV, normal lung V20, and mean dose to heart and aorta were significantly lowered with P < 0.05.

Conclusion

The novel planning methodology using multiple shells including the novel OptiForR50 shell with precisely calculated dimensions and optimizer constraints lead to significantly lower values of R50% and D2cm and lower dose spillage in lung SBRT plans. All plans were successfully brought into the zone of no RTOG violations.

SUBMITTER: Desai D

PROVIDER: S-EPMC7856511 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Publications

Cleaning the dose falloff in lung SBRT plan.

Desai Dharmin D Narayanasamy Ganesh G Bimali Milan M Cordrey Ivan I Elasmar Hisham H Srinivasan Senthamizhchelvan S Johnson Ellis Lee EL

Journal of applied clinical medical physics 20201207 1

<h4>Purpose</h4>To investigate a planning technique that can possibly reduce low-to-intermediate dose spillage (measured by R50%, D2cm values) in lung SBRT plans.<h4>Materials and methods</h4>Dose falloff outside the target was studied retrospectively in 102 SBRT VMAT plans of lung tumor. Plans having R50% and/or D2cm higher than recommended tolerances in RTOG protocols 0813 and 0915 were replanned with new optimization constraints using novel shell structures and novel constraints. Violations i ...[more]

PMID: 33285036

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Project description: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.The 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.Real-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 V20 up to 3.5%, spinal cord D2 up to 0.9 Gy/Fx, and proximal airways D2 up to 1.4 Gy/Fx.The 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.

Dataset Information

Cleaning the dose falloff in lung SBRT plan.

Purpose

Materials and methods

Results

Conclusion

Publications

Cleaning the dose falloff in lung SBRT plan.

Similar Datasets

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