Interfractional Variation of Radiation Target and Adaptive Radiotherapy for Totally Resected Glioblastoma

This study aimed to evaluate the effects of volume adapted re-planning for radiotherapy (RT) after gross total resection (GTR) for glioblastoma. Nineteen patients with glioblastoma who underwent GTR and postoperative RT were analyzed. The volumes of the surgical cavity on computed tomography (CT) obtained one day after GTR (CT0), the first RT simulation CT (sim-CT1), and the second simulation CT for the boost RT plan (sim-CT2) were compared. The boost RT plan was based on the surgical cavity observed on the sim-CT2 (boost RTP2) and was compared with that based on the surgical cavity observed on the sim-CT1 (boost RTP1). The volume reduction ratios were 14.4%-51.3% (median, 29.0%) between CT0 and sim-CT1 and -7.9%-71.9% (median, 34.9%) between sim-CT1 and sim-CT2 (P < 0.001). The normal brain volumes in boost RTP1 were significantly reduced in boost RTP2, especially at high dose levels. Target volume in sim-CT2 which was not covered with the boost RTP1, developed in five cases (26.3%). The surgical cavity volume was reduced following surgery in patients with glioblastoma who underwent GTR. The application of volume-adapted re-planning during RT could decrease the irradiated volume of normal brain and prevent a target miss for boost RT.