Interim Tumor Progression and Volumetric Changes of Surgical Cavities during the Surgery-to-Radiotherapy Interval in Anaplastic Gliomas: Implications for Additional Pre-radiotherapy Magnetic Resonance Imaging

PURPOSE: This study was designed to investigate the incidence of interim disease progression (IPD) and volumetric changes of the surgical cavity (SC) during the surgery-to-radiotherapy interval (SRI), and eventually assess the value of magnetic resonance imaging (MRI) at the time of radiotherapy (RT) planning in newly diagnosed anaplastic gliomas. MATERIALS AND METHODS: Among 195 anaplastic glioma patients who underwent RT, 121 were evaluable with two separate MRIs during SRI. The presence of IPD was determined using the updated Response Assessment in Neuro-Oncology size criteria. In 84 patients who underwent surgical resection, each SC was contoured by a radiation oncologist and the volumetric changes of the SCs were calculated between the two separate MRIs. Daily rate of change in the SC volume was calculated assuming an exponential and linear change. RESULTS: Five of 121 patients (4.13%) demonstrated IPD during SRI, and the incidence was significantly higher in patients undergoing biopsy (vs. surgical resection, 12.9% vs. 1.1%, p=0.015) and in patients with remnant contrast-enhancing tumor after surgery (15.8 vs. 2.0%, p=0.027). The mean daily rate of absolute change in SC was 1.06% (95% confidence interval [CI], 0.89 to 1.23) and 0.89% (95% CI, 0.77 to 1.02) according to the exponential and linear model, respectively. The expected mean volumetric change at 2 weeks were 16.64% (95% CI, 13.77 to 19.52) and 12.51% (95% CI, 10.77 to 14.26), respectively. CONCLUSION: IPD during the SRI is rare in surgically resected anaplastic gliomas. However, pre-RT MRI is essential for accurate RT-target delineation and disease evaluation for patients initiating RT beyond postoperative 2 weeks and undergoing biopsy, respectively.