(Thursday, 7/18/2019) 7:30 AM - 9:30 AM
Room: Stars at Night Ballroom 2-3
Purpose: To investigate the association between local lung ventilation change and radiation dose for patients treated with photon or proton radiotherapy.
Methods: Ten (four photon, six proton) patients who received two courses (<1 yr apart) of lung radiotherapy (first prescription 50.4-72 Gy) where no lung reducing surgery was performed following radiation were retrospectively identified. Three of the ten patients experienced radiation pneumonitis (RP) after their first course of treatment. The 3D ventilation map for each course was calculated via the Jacobian of the deformable image registration matrix based on exhalation and inhalation images from the 4D-CT. Rigid registration of the healthy lungs of the first and second treatment courses was used to co-register the 3D-ventilation values before and after the first treatment. Local ventilation change was then calculated. The voxelized dose distribution was obtained from the treatment plan of the first course. The ventilation and dose maps were down sampled to a 5mm grid using 3D-cubic interpolation to match the setup and registration uncertainties prior to analysis.
Results: 53.2±7.8 % and 50.3±9.4 % of the healthy lung showed a decrease in ventilation post irradiation for proton and photon patients, respectively. The mean value of ventilation change among all patients was -0.01±0.27. The three patients who experienced lung toxicities after treatment had larger lung volumes with substantial ventilation degradation (>0.5) across all dose levels. The volume percentage of healthy lung receiving 20±5 Gy with substantial ventilation degradation was 4.88±2.70 % and 1.08±0.98 % for patients with RP and non-RP, respectively.
Conclusion: Preliminary results show that only minor associations of the dose distribution to ventilation change were observed for both photon and proton patients. Patients with lung toxicities had poorer ventilation post irradiation, compared to patients without lung toxicities. Further studies are being conducted to include a larger patient cohort.
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