Open AccessAn analytical expression for R50% dependent on PTV surface area and volume: a lung SBRT comparison
Author(s) -
Desai Dharmin D.,
Johnson E. L.,
Cordrey Ivan L.
Publication year - 2020
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.13026
Subject(s) - volume (thermodynamics) , nuclear medicine , expression (computer science) , mathematics , medicine , physics , computer science , programming language , quantum mechanics
In stereotactic body radiation therapy (SBRT), R50% is a common metric for intermediate dose spill and is defined in RTOG 0915 as the ratio of 50% isodose cloud volume (IDC50%) to the planning target volume (PTV). By coupling sound physical principles with the basic definition of intermediate dose spill, we derive an exact analytical expression for R50% for the case of a spherical volume. This expression for R50% depends on three quantities: the surface area of PTV (SA PTV ), the volume of PTV (V PTV ), and the dose gradient Δr. Validity of our analytical expression for R50% was confirmed via direct comparison to peer‐reviewed, multi‐institutional, diverse clinical data. The comparison of our R50% values computed from our analytical expression to the clinical data yielded an average percent difference of 3.8 ± 4.5%.