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WE‐G‐BRA‐02: Model for Time‐Dependent Radiation‐Induced Lung Disease Risk Based on Systematic Image‐Based Scoring and Monte‐Carlo Dose Calculations
Author(s) -
Lee S,
Stroian G,
Seuntjens J,
El Naqa I
Publication year - 2011
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 - 10.1118/1.3613407
Subject(s) - nuclear medicine , radiation therapy , dosimetry , monte carlo method , medicine , radiation treatment planning , radiology , mathematics , statistics
Purpose: To construct an analytical model for radiation‐induced lung injury (RILD) risk using computed tomography (CT) image analysis correlated to Monte Carlo (MC) dose calculations along with investigation of the modelˈs post‐RT dependency. Methods: The extent of RILD was segmented on the difference CT image between a planning CT image and registered post‐RT diagnostic CT image. Radiation dose was calculated using the anisotropic analytical algorithm (AAA) and MC methods. The segmented RILD was spatially correlated with the dose distribution to generate a dose‐response curve for each of 39 follow‐up studies from 12 subjects. The response curves were grouped into 6 follow‐up periods with 3 months intervals according to the time elapsed since the completion of RT. For each period, a probit function derived from the Lyman‐Kutcher‐Burman (LKB) model was fit to the patient data with the two adjustable parameters: TD50 (dose at 50% chances of complication) and m (steepness of the curve). Results: TD50 demonstrated a monotonic increase from its initial level (73 Gy/77 Gy for AAA/MC dose) to its peak (130 Gy/116 Gy) at 9∼12 months post‐RT after which it fell to 85 Gy/80 Gy beyond 15 months post‐ RT. The change in TD50 occurred coincidently with the decrease in the proportion of injured lung volume, demonstrating the association between TD50 and the severity of RILD. The value of m significantly decreased in time from its initial values (0.51/0.55) to 0.24/0.25 beyond 15 months post‐RT. This suggests a transition in the dose‐response from a linear‐no‐threshold to nonlinear‐threshold type behavior. Replacement of AAA calculation by MC did not yield a significant difference in the fitting parameters. Conclusions: Time‐dependent results from the analytical modeling of RILD dose response indicates the transition from early to late radiation effects and the necessity to incorporate a temporal factor into the current time‐static RILD risk models.