Normal Lung Tissue CT Density Changes after Volumetric-Arc Radiotherapy (VMAT) for Lung Cancer

Abstract

Radiation-induced lung injury remains a significant toxicity in thoracic radiotherapy. Because a precise diagnosis is difficult and commonly used assessment scales are unclear and subjective, there is a need to establish quantitative and sensitive grading methods. The lung tissue density change expressed in Hounsfield units (HUs) derived from CT scans seems a useful numeric surrogate. The study aimed to confirm a dose-response effect on HU value changes (ΔHU), their evolution in time, and the impact of selected clinical and demographic factors. We used dedicated, self-developed software to register and analyze 120 pairs of initial and follow-up CT scans of 47 lung cancer patients treated with dynamic arc radiotherapy. The differences in HU values between CT scans were calculated within discretized dose-bins limited by isodose lines. We have proved the dose-effect relationship, which is well described with a sigmoid model. We found the time evolution of HU changes to suit a typical clinical presentation of radiation-induced toxicity. Some clinical factors were found to correlate with ΔHU degree: planning target volume (PTV), V35 in the lung, patient’s age and a history of arterial hypertension, and initial lung ventilation intensity. Lung density change assessment turned out to be a sensitive and valuable method of grading post-RT lung toxicity.

Mechanistic model of radiotherapy-induced lung fibrosis using coupled 3D Agent-Based and Monte Carlo simulations

“…In the ABM-MC model the dose was delivered once at the beginning of the simulation and the parameters were set to the same values as those in the ABM model (notably: phagocytic fraction = 100%, phagocytic index = 1, apoptotic-tosenescent ratio = 0 and bystander threshold = 2). As can be seen from figure 3, both the early and the late components of the DECM (for the ABM-MC model) could be fitted by the equations ( 2) and (3) and are qualitatively in agreement with experimental data [18][19][20][21] . As expected, the DECM increases as a function of the dose and reaches a plateau around 20Gy for the early component and 30Gy for the late component.…”