Assessment of Volumetric Changes Using Megavoltage-Cone Beam Computed Tomography (MV-CBCT) for Adaptive Radiotherapy in Head and Neck Cancer: A Case Series.

Intensity-modulated radiation therapy (IMRT) has brought about interest in adaptive radiotherapy (ART) due to its benefit of accurately prescribing doses to tumors and sparing normal critical organs. Critical dosimetric errors and geometrical misses can occur due to anatomical changes during radiotherapy. In the present study, five patients with head and neck malignancies undergoing radiation therapy were assessed for changes in primary gross tumor volume (GTVp), nodal gross tumor volume (GTVn), and clinical target volume-high risk (CTV-HR) using weekly megavoltage-cone beam computed tomography (MV-CBCT) scans. All patients had a reduction in GTV and lateral neck diameter (LND). There were reductions in tumor volumes leading to re-planning in the 20th fraction. Daily CBCT can guide the decision on the need for adaptation in patients with tumor volume reduction and with volumes going outside the body.