Consideration of lung dose changes when establishing lung cancer treatment plans according to tumor changes

Purpose: The purpose of this study was to determine if treatment dose to the lungs can be considered in the initial treatment planning according to change in tumor size during treatment.Methods: Lung dose was evaluated in 26 patients who underwent re-planning CT (reCT) due to changes in tumor size during lung cancer treatment with intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT). Relevant parameters were V5, V10, V20, V30, V40, and mean lung dose. Results: Dose parameters to most lungs followed a normal distribution, but there were no statistically significant results for changes in lung dose after reCT. Patients with only lungs surrounding the tumor tended to have a 7.6% decrease in mean bilateral lung dose (MBLD) as tumor volume decreased. In contrast, patients with ribs and vertebrae within the target region showed a 5.9% increase in MBLD. Mean dose to the bilateral lungs before and after reCT increased (positively correlated) with high-density material in the planned target volume (PTV).Conclusions: This study found a correlation of radiological dose to the lungs to presence of high-density material in the PTV. In such patients, reducing lung dose in the initial treatment plan is expected to reduce radiation side effects.