Hurdles in radiation planning for glioblastoma: Can delayed-contrast enhanced computed tomography be a potential solution?

Objective Conformal radiation is the standard of care in treatment of glioblastoma. Although co-registration of magnetic resonance imaging (MRI) with early contrast enhanced computed tomography (CECT) is recommended for target delineation by consensus guidelines, ground realities in developing countries often result in availability of less-than-ideal MR sequences for treatment planning. Purpose of this study is to analyze the impact of incorporation of delayed-CECT sequences for radiation planning in glioblastomas, as an adjunct or alternative to MRI. Methods Case records of all patients of glioblastoma treated at our center between 2011 and 2014 were retrospectively evaluated. Gross treatment volumes were delineated on T1 contrast MRI (m-GTV), early CECT (e-GTV) and delayed CECT (d-GTV); volumetric comparisons were made using repeated measures analysis of variance and pair-wise analysis. Results Although 96% of registered patients underwent postoperative MRI, only 38% of them had desirable sequences suitable for co-registration. Median duration between acquisition of postoperative MRI and surgery was 45 days (range, 33-60), whereas that between MRI and treatment-planning CT was 5 days (range, 1-10). Statistically significant differences (P < 0.0001) were obtained between mean volumes of e-GTV (41.20cc), d-GTV (58.09cc) and m-GTV (60.52cc). Although the mean GTV increased by 46% between early CECT and MRI, the difference was only 4% between delayed CECT and MRI. Conclusion Delayed CECT is superior to early CECT for co-registration with MRI for target delineation, especially when available MR sequences are less-than-ideal for treatment planning, and can be considered as the most appropriate adjunct as well as an alternative to MRI, compared to early CECT.