A prospective comparison of adaptive and fixed boost plans in radiotherapy for glioblastoma

Purpose To analyze the efficacy of adaptive radiotherapy (ART) for glioblastoma. Methods Sixty-one glioblastoma patients who received ART were prospectively evaluated. The initial clinical target volume (CTVinitial) was represented by T2 hyperintensity on postoperative MRIs (pre-RT MRI [MRIpre])plus 10 mm. The initial planning target volume (PTVinitial) was the CTVinitial plus a 5-mm margin. The PTVinitial received 40 Gy. An MRI and a second planning CT were performed during radiotherapy (MRImid). Two types of boost CTVs (the resection cavity and residual tumor on enhanced T1-weighted MRI plus 10 mm) were created based on the MRIpre and MRImid (CTVboost-pre and -mid). The boost PTV (PTVboost) was the CTVboost plus 5 mm. Two types of boost plans (fixed and adaptive boost plans in the first and second planning CT, respectively) of 20 Gy were created. The PTV based on the post-RT MRI (PTVboost-post) was created, and the dose-volume histograms of the PTVboost-post in the fixed and adaptive boost plans were compared. Additionally, the conformity indices (CIs) of the fixed and adaptive boost plans were compared. Results The median V95 of the PTVboost-post of the fixed and adaptive boost plans (V95pre and V95mid) were 95.6% and 98.3%, respectively ( P < 0.01). The median V95pre and V95mid of patients after gross total resection (GTR) were 97.4% and 98.8%, respectively ( P = 0.41); in contrast, the median values of patients after non-GTR were 91.9% and 98.2%, respectively ( P < 0.01). The median CIs of the fixed and adaptive boost plans in all patients were 1.45 and 1.47, respectively ( P = 0.31). The median CIs of the fixed and adaptive boost plans in patients after GTR were 1.61 and 1.48, respectively ( P = 0.01); in contrast, those in patients after non-GTR were 1.36 and 1.44, respectively ( P = 0.13). Conclusion ART for glioblastoma improved the target coverage and dose reduction for the normal brain. By analyzing the results according to the resection rate, we can expect a decrease in normal brain dose in patients with GTR and an increase in coverage in those with partial resection or biopsy.