Author: Andrew Huang, Jonathan Huang, Andrew S Kennedy, Ellie Grace Kong, Ajay Zheng 👨🔬
Affiliation: New York Proton Center, Centennial Medical Center, Executive Medical Physics Associates, Sarah Cannon Cancer Institute, Belmont University 🌍
Purpose:
Lung stereotactic body radiotherapy (SBRT) is the standard of care for early-stage lung cancer. Respiratory phase gating can be applied to mitigate motion-induced effects. The purpose of this study was to explore the clinical benefits of gating for lung SBRT. For most of 20 lung tumor patients and various gating windows, doses to normal tissue could be reduced by gating simulation. These pretreatment results are useful for the risk assessment and therefore could be used to select patients and optimal gating windows.
Methods:
Volumetric modulated arc therapy (VMAT) treatment plans with variable gantry rotations for 6 MV photons were developed using 4D computed tomography (4DCT) acquired on a GE discovery CT. We investigated the potential of the respiratory gating to reduce the motion-induced inaccuracy of dose delivery in lung stereotactic body radiotherapy. For 20 patients with lung tumors, we investigated treatment plans for a gating window (GW) including three breathing phases around the maximum exhalation phase, GW40–60. We analyzed the target volume, lung, esophagus, ascending aorta and heart doses for 1) the plans based on average CT from all phases and 2) those on average CT from GW40-70. The risk model for radiation pneumonitis (RP) has been used to estimate the toxicity to lungs.
Results:
We found four-phase GW40–70 seems optimal. When the plans generated using GW40-70 were compare with those using all phases, the PTV coverage is similar, and doses to ascending aorta, bronchus, chestwall/rib, esophagus, great vessels, liver and spinal cord are reduced in GW40-70. The NTCP of RP is strongly correlated with the tumor volume (P<0.001) and heart dose (P=0.01). The NTCP of RP is relatively lower in GW40-70 than all phases.
Conclusion:
Gating has the potential to reduce lung and esophageal toxicity for lung SBRT. The pretreatment toxicity risk analysis facilitates patient selection for gating.