Program Information
Time Evolution of Radiation-Induced Lung Injury After Stereotactic Proton Therapy
C Grassberger*, G Sharp , F Fintelmann , H Paganetti , H Willers , Massachusetts General Hospital, Boston, MA
Presentations
SU-E-J-247 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Quantitative metrics to assess patient-specific radiation-induced lung injury have the potential to guide individualization of therapy and be early indicators of recurrence. Here we investigate computed tomography (CT) density changes in normal lung after stereotactic Proton Therapy.
Methods: Participants in a phase-I clinical trial for stereotactic body radiation therapy (SBRT) with protons are analyzed on a rolling basis. The dataset includes 9 patients with 34 CT images to date. Follow-up images are registered to the planning CT using deformable image registration and the change in CT density is correlated to the dose to examine the time-evolution of Hounsfield Unit (HU) changes after large doses of proton radiation.
Results: The lung density observed on the follow-up images increases significantly with dose for all dose levels above 5 Gy(RBE) (p<0.001) for 8/9 patients. The change per unit dose [HU/Gy] varies significantly among the patients, from 0.1 (for the one patient without significant correlation) to 5.7 ΔHU/Gy(RBE). The current population average of ΔHU/Gy(RBE) is 2.1, i.e. a 1 Gy(RBE) increase in dose leads on average to a 2.1 HU increase in CT density. The slope of the dose-response curve is constant for all timepoints investigated (from 3-24+ months). Additionally a pronounced non-linearity in the dose response curve is noted for long follow-up times (>18 months).
Conclusion: CT density changes have a robust correlation with proton dose, quantitatively similar to photon dose, and may allow estimation of a patient’s intrinsic radiosensitivity after proton therapy. The stability of the correlation with time however diverges from what is known about CT response after photon irradiation. This could have important implications for clinical decision-making during proton therapy for lung cancer, especially for scheduling of follow-up CT/PET imaging and diagnosis of recurrence.
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