The authors aimed to illustrate the potential dose differences to clinical target volumes (CTVs) and organs-at-risk (OARs) volumes after proton adaptive treatment planning was used.

The records of 10 patients with oropharyngeal cancer were retrospectively reviewed. Each patient's treatment plan was generated by using the Eclipse treatment planning system. Verification computed tomography (CT) scan was performed during the fourth week of treatment. Deformable image registrations were performed between the 2 CT image sets, and the CTVs and major OARs were transferred to the verification CT images to generate the adaptive plan. We compared the accumulated doses to CTVs and OARs between the original and adaptive plans, as well as between the adaptive and verification plans to simulate doses that would have been delivered if the adaptive plans were not used.

Body contours were different on planning and week-4 verification CTs. Mean volumes of all CTVs were reduced by 4% to 8% ( ≤ .04), and the volumes of left and right parotid glands also decreased (by 11% to 12%,  ≤ .004). Brainstem and oral cavity volumes did not significantly differ (all  ≥ .14). All mean doses to the CTV were decreased for up to 7% ( ≤ .04), whereas mean doses to the right parotid and oral cavity increased from a range of 5% to 8% ( ≤ .03), respectively.

Verification and adaptive planning should be recommended during the course of proton therapy for patients with head and neck cancer to ensure adequate dose deliveries to the planned CTVs, while safe doses to OARs can be respected.