Premium
Toward optimal organ at risk sparing in complex volumetric modulated arc therapy: An exponential trade‐off with target volume dose homogeneity
Author(s) -
Tol Jim P.,
Dahele Max,
Doornaert Patricia,
Slotman Ben J.,
Verbakel Wilko F. A. R.
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4862521
Subject(s) - nuclear medicine , medicine , radiation therapy , head and neck , radiology , surgery
Purpose: Conventional radiotherapy typically aims for homogenous dose in the planning target volume (PTV) while sparing organs at risk (OAR). The authors quantified and characterized the trade‐off between PTV dose inhomogeneity (IH) and OAR sparing in complex head and neck volumetric modulated arc therapy plans.Methods: Thirteen simultaneous integrated boost plans were created per patient, for ten patients. PTV boost (B) /elective (E) optimization priorities were systematically increased. IH B and IH E , defined as (100% − V95%) + V107%, were evaluated against the average of the mean dose to the combined composite swallowing and combined salivary organs (D‐OAR comp ). To investigate the influence of OAR size and position with respect to PTV B/E , OAR dose was evaluated against a modified Euclidean distance (DM B /DM E ) between OAR and PTV.Results: Although the achievable D‐OAR comp for a given level of PTV IH differed between patients, excellent logarithmic fits described the D‐OAR comp /IH B and IH E relationship in all patients (mean R 2 of 0.98 and 0.97, respectively). Allowing an increase in average IH B and IH E over a clinically acceptable range, e.g., from 0.4% ± 0.5% to 2.0% ± 2.0% and 6.9% ± 2.8% to 14.8% ± 2.7%, respectively, corresponded to a decrease in average dose to the composite salivary and swallowing structures from 30.3 ± 6.5 to 23.6 ± 4.7 Gy and 32.5 ± 8.3 to 26.8 ± 9.3 Gy. The increase in PTV E IH was mainly accounted for by an increase in V107, by on average 5.9%, rather than a reduction in V95, which was on average only 2%. A linear correlation was found between the OAR dose to composite swallowing structures and contralateral parotid and submandibular gland, with DM E ( R 2 = 0.83, 0.88, 0.95). Only mean ipsilateral parotid dose correlated with DM B ( R 2 = 0.87).Conclusions: OAR sparing is highly dependent on the permitted PTV B/E IH. PTV E IH substantially influences OAR doses. These results are relevant for clinical practice and for future automated treatment‐planning strategies.