Balancing Dose and Toxicity in Central NSCLC SBRT: Insights into Organ Motion and the IRV Framework

Using an internal organ at risk volume (IRV) framework may offer a way to mitigate treatment-related injury during stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC). In this project, we examined: (1) distinctions in clinical presentation between tumors situated centrally and peripherally, (2) how the IRV strategy behaves in central disease, (3) the extent of positional and volumetric organ motion, and (4) the normal tissue complication probabilities (NTCPs) that arise from these factors. Two datasets were reviewed: patients treated with SBRT for localized NSCLC (n = 78), and a subgroup evaluated specifically for motion analysis (n = 35). When comparing tumor locations, central lesions required larger planning target margins, received lower biologically effective doses, delivered greater doses to lung tissue, and showed poorer locoregional tumor control. Motion of the bronchial structures was more pronounced in men and in taller individuals, while patients with elevated body mass index (BMI) demonstrated reduced esophageal volume variation. A retrospective, non-optimized application of the IRV method resulted in more than a 10% absolute NTCP increase for the bronchial tree in three patients. These observations reinforce the importance of improving planning techniques to balance effective dose intensification with acceptable toxicity in central tumors. Organ motion and shape changes may be more substantial in males and taller patients, and less evident in those with higher BMI. As emerging research further separates central tumor subtypes for tailored treatment, the IRV approach may be useful in refining risk estimation.