Assessing the Need for Verification Imaging at Noncoplanar Couch Angles In Proton Therapy for Brain and Head‑and‑Neck Patients
Abstract
Purpose
To evaluate the necessity of verification imaging at couch-angle positions for brain and head-and-neck (HN) patients treated with immobilization masks by analyzing setup accuracy and reproducibility using a year-long retrospective dataset.
Methods
We retrospectively reviewed images and applied couch delta for 28 patients treated with noncoplanar proton therapy plans. The study includes 11 brain and 17 HN patients, who underwent approximately 300 and 500 fractions, respectively. To verify patient alignment, kV image was acquired upon a 6-degree-of-freedom couch that was rotated to the treatment angle. Couch delta was applied when patient realignment exceeded thresholds based on proton plan robustness, 3 mm translational shifts and 2° rotational shifts in any direction. We assessed frequency of couch delta applications to realign patients. Furthermore, we recorded time dedicated to imaging and patient alignment verification.
Results
Our results revealed that patient realignment at couch treatment angles was negligible: 99.3% of brain fractions and 98.5% of HN fractions did not require any adjustment. This indicates that additional verification image between treatment fields is largely unnecessary. Elimination of this step reduces patient imaging dose. In addition, it shortens treatment time by up to 15%, translating into cumulative savings of 26 clinical hours over 12 months on the proton machine schedule.
Conclusion
Verification imaging at couch-angle positions for brain and HN patients treated with immobilization masks is largely unnecessary, as realignment was required in less than 2% of fractions. Based on these findings, our clinical protocol was updated to discontinue verification image between treatment fields for patients who consistently remain within realignment tolerances during their first three fractions. This change reduces unnecessary imaging, minimizes patient dose, and improves treatment efficiency without compromising setup accuracy.