What if a tumor is significantly enlarged just before stereotactic body radiation therapy? A case report and review of the literature.

Stereotactic body radiation therapy (SBRT) plays an important role in early stage non-small cell lung cancer. Tumor growth before radiotherapy planning (RTP) or during SBRT has been reported in lung cancer patients; however, little is known of growth during the period in-between (i.e. after RTP but before SBRT). An 83-year-old man referred to our hospital and diagnosed with medically inoperable non-small cell lung cancer was noted to have significant tumor progression on day 1 of cone beam computed tomography just before the planned SBRT delivery. Because of uncertainty of the underlying etiology and unfamiliarity with this phenomenon, we made a clinical decision to arrange re-simulation and revise our treatment to conventional fractionated radiotherapy (CFRT). After an initial response, distant metastases occurred eight months after CFRT. The patient received best supportive care and was under hospice care at the last follow-up (27 months after CFRT). We report a case with significant tumor growth just before planned SBRT. Optimal management in this scenario requires further investigation.