Objective To explore the differences in volume and doses to clinical target volumes (CTVs) and organs at risk (OARs) with and without adaptive treatment plans by using deformable image registration technology.Methods Ten patients with head and neck cancer were selected for this retrospective study.Each patient’s original treatment plan was generated using the Eclipse treatment planning system(Varian,Inc.). Verification CT scans were performed during the third week of treatment. The verification CT images were registered with the original CT images using the Eclipse rigid registration tool simulating daily patient treatment alignment. Then, deformable image registrations (Velocity, Inc.) were performed between the two CT image sets,and the CTVs and major OARs were transferred from the original CT images to the verification CT images. The original treatment plan was then copied into the verification CT image set to calculate the radiation dose reflecting the most recent anatomic changes. Verification plan doses were evaluated by a radiation oncologist,who determined whether an adaptive treatment plan was required.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 the doses that would have been delivered if the adaptive plans were not used.All dosimetric data were extracted using the Eclipse Application Programming Interface tool,which was developed in house to access the Eclipse database.Results Body contours were different after 3 weeks of treatment.Mean volumes of all CTVs were reduced(P≤0.04), and the volumes of left and right parotid glands decreased(P≤0.004). There were no significant differences in the volumes of brainstem and oral cavity(P≥0.14) between the original and verification CT scans.The spinal cord had a mean 8.7%decrease in volume(P=0.04). Mean doses of CTVs were all decreased(P≤0.04), whereas the mean doses of the right parotid and oral cavity were increased (P=0.03). Conclusion Verification CT scans and adaptive planning are required during the course of proton therapy for patients with head and neck cancer to identify anatomic and dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues.Our results indicate that deformable image registration can serve as an essential tool for current proton treatment. Objective To explore the differences in volume and doses to clinical target volumes (CTVs) and organs at risk (OARs) with and without adaptive treatment plans by using deformable image registration technology. Methods Ten patients with head and neck cancer were selected for this retrospective study . The Each patient’s original treatment plan was generated using the Eclipse treatment planning system (Varian, Inc.). Verification CT scans were performed during the third week of treatment. The verification CT images were registered with the original CT images using the Eclipse rigid registration tool Then, deformable image registrations (Velocity, Inc.) were performed between the two CT image sets, and the CTVs and major OARs were transferred from the original images to the verification CT images. The original treatment plan was then copied into the verification CT image set to calculate the radiation dose reflecting the most recent anatomic change s. Verification plan doses were evaluated by a radiation oncologist, who determined whether an adaptive treatment plan was required. 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 the doses that would have been delivered if the adaptive plans were not used. All dosimetric data were extracted using the Eclipse Application Programming Interface tool, which was developed in house to access the Eclipse database. Results Body contours were different after 3 weeks of treatment. There were no significant differences in the volumes of brainstem and oral cavity (P ≧ 0.14) between the original (P ≦ 0.14) and the volumes of left and right parotid glands decreased and verification CT scans. The spinal cord had a mean of 8.7% decrease in volume (P = 0.04). Mean doses of CTVs were all decreased (P ≦ 0.04), whereas the mean doses of the right parotid and or al cavitywere additionally (P = 0.03). Conclusion Verification CT scans and adaptive planning are required during the course of proton therapy for patients with head and neck cancer to identify anatomic and dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues .Our results that that deformable image registration can serve as an essential tool for current proton treatment.