Abstract
Introduction: Radiation Therapy Oncology Group (RTOG) report #0813 and 0915 recommends using D2cm and R50% as plan quality metrics for evaluation of normal tissue sparing in stereotactic body radiation therapy (SBRT) of lung lesion. This study introduces dose falloff gradient (DFG) as a tool for analyzing the dose beyond the planning target volume (PTV) extending into normal tissue structures. In ascertaining the impact of PTV size and SBRT planning techniques in DFG, this study questions the independence of the RTOG recommended metrics. Materials and Methods: In this retrospective study, 41 RapidArc lung SBRT plans with 2 or 3 complete or partial arcs were analyzed. PTV volumes ranged between 5.3 and 113 cm3 and their geographic locations were distributed in both lungs. 6MV, 6 MV-FFF, 10 MV, or 10 MV-FFF energies were used. RTOG-0915 metrics conformity index, homogeneity index, D2cm, R50%, and HDloc were evaluated. DFG was computed from the mean and maximum dose in seven concentric 5 mm wide rings outside the PTV. DFG was investigated against the volume of normal lung irradiated by 50% isodose volume. Treatment plans with alternate energy and couch rotations were generated. Results: The dose falloff beyond PTV was modeled using a double exponential fit and evaluated for relationship with intermediate lung dose. Photon energy and beam configuration had a minimal impact on the dose falloff outside. The product of normalized D2cm and R50% was estimated to have a slowly varying value. Conclusions: Dose falloff outside PTV has been studied as a function of radial distance and ascertained by intermediate dose to normal lung. DFG can serve as a complementary plan quality metric.
Document Type
Article
Publication Date
7-2018
Digital Object Identifier (DOI)
https://doi.org/10.4103/jmp.JMP_38_18
Repository Citation
Narayanasamy, Ganesh; Desai, Dharmin; Maraboyina, Sanjay; Penagaricano, Jose; Zwicker, Robert; and Johnson, Ellis Lee, "A Dose Falloff Gradient Study in RapidArc Planning of Lung Stereotactic Body Radiation Therapy" (2018). Radiation Medicine Faculty Publications. 16.
https://uknowledge.uky.edu/radmed_facpub/16
Notes/Citation Information
Published in Journal of Medical Physics, v. 43, issue 3, p. 147-154.
© 2018 Journal of Medical Physics | Published by Wolters Kluwer - Medknow
This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution‑NonCommercial‑ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non‑commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.