Purpose: Immobilization and daily setup are difficult for patients with head neck cancer (HNC) under external beam therapy (EBRT) due to the large treatment volume involved, sharp dose gradients of the treatment plans, numerous sensitive organs at risk (OAR) and non-rigid nature of the patient anatomy. We analyzed rejected daily CBCT images for patients with these treatments to identify issues in patient setup and immobilization.
Methods: From 2017 to 2021, 1066 patients with HNC underwent 1242 courses of treatments in 27317 fractions at our institution. These patients were immobilized with 5-point masks and mouthpieces, under daily CBCT guidance. All these patients were treated with IMRT or VMAT with 2.5 - 3 mm planning margins using simultaneous integrated boost technique. we categorized the reasons for CBCT rejections from our attending physicians to identify imperfection/failure of immobilization and setup during treatment.
Results: A total of 24214 CBCTs were analyzed. 217 (0.9%) were rejected by the attending physician. Among the rejected images, 39 (17.9%) were due to the misalignment of tongues; 32 (14.7%) due to patient swallowing; 25 (11.5%) due to shoulder misalignments; 24 (11.1%) due to mouthpiece displacements. Misalignments of larynx, hyoid, spinal cord, and eye accounted for 17 (7.8%), 5 (2.4%), 15 (6.9%), 12 (5.5%), respectively. Neck misalignments and patient rotation accounted for 16 (7.3%) of the rejections.
Conclusion: Less than one percent of imperfect setups were identified by physician reviews. Four major issues accounted for more than 50% of the rejected images. Further improvement in patient immobilization and setup are warranted, including the development of automated tools to detect potential issues in immobilization and setup.
Not Applicable / None Entered.