Use of Personalized Ultra-Fractionated Stereotactic Adaptive Radiotherapy for Oligometastatic Lung Adenocarcinoma: Leveraging CT-Guided Online Adaptive Radiotherapy.

Management of oligometastatic non-small cell lung cancer (OM-NSCLC) has changed considerably in recent years, as these patients were found to have better survival with systemic therapy followed by consolidative radiation. Stereotactic body radiotherapy (SBRT), characterized by high doses of radiation delivered in a limited number of fractions, has been shown to have improved local control compared to conventionally fractionated radiation in early-stage lung cancer, but its use in large tumors, ultra-central tumors, or mediastinal nodal regions is limited due to concerns of toxicity to nearby serial mediastinal structures. Recent improvements in image guidance and fast replanning allow adaptive radiotherapy to be used to personalize treatment to the patient's daily anatomy and ensure accurate dose delivery to the tumor while minimizing dose and toxicity to normal. Adaptive SBRT can expand its use into ultra-central tumors that otherwise may not be amenable to SBRT or enable alternative fractionation schedules such as personalized ultra-fractionated stereotactic adaptive radiotherapy (PULSAR) with one-month intervals between fractions. In this case, we report a patient initially presenting with bulky OM-NSCLC of the left lung and mediastinum with an isolated left femur metastasis who was referred for consolidative radiotherapy after systemic therapy. We demonstrate how CT-guided online adaptive radiotherapy to the lung and mediastinum can be used despite the long time interval between treatments. In addition, adaptive plans lead to a substantial decrease in the heart dose, with moderate decreases in other organs compared to non-adaptive plans. This case demonstrates the feasibility of using adaptive radiotherapy for PULSAR of ultra-central OM-NSCLC.