Utility of Interval Imaging During Focused Radiation Therapy for Residual Cystic Craniopharyngiomas.

BACKGROUND: In the present study, we investigated the changes in cyst volume detected on interval computed tomography (CT) in patients undergoing radiation therapy (RT) for residual cystic craniopharyngioma after surgery. METHODS: We performed a retrospective analysis of CT scans performed halfway during the course of RT for residual cystic craniopharyngioma from January 2005 to January 2018 to assess the incidence of cyst expansion requiring additional intervention. The possible risk factors for cyst expansion during RT were also analyzed. RESULTS: A total of 33 patients (23 males) with a median age of 15 years (interquartile range 8-21 years) who had undergone surgical excision (n = 30) or aspiration (n = 3) of cystic craniopharyngiomas, followed by stereotactic (n = 25) or conformal (n = 8) RT were included. The extent of reduction in tumor volume after surgery was 66.5% ± 17.9% (range, 20.6%-88.9%). Of the 33 patients, 6 (18.2%) experienced a median increase in cyst volume of 11.1 mL (interquartile range, 9.1-12.1 mL; range, 6.3-40 mL) that was beyond the initial planned target volume (PTV) and necessitated additional intervention. Of the 6 patients in whom the cyst showed an increase in volume, 4 underwent cyst aspiration followed by repeat planning of RT and 2 underwent repeat planning of RT alone without additional surgical intervention. In 5 of these 6 patients, the increase in cyst volume was asymptomatic. Younger age (P = 0.002) and a larger residual cyst wall (P = 0.009) were risk factors for early cyst expansion. CONCLUSIONS: Cyst expansion will occur in nearly one fifth of patients with cystic craniopharyngioma during the course of RT. As nearly all these expansions are asymptomatic, interval CT scans midway through RT are essential to avoid geographic miss of the tumor.