Abstract
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% (P ≤ .04), and the volumes of left and right parotid glands also decreased (by 11% to 12%, P ≤ .004). Brainstem and oral cavity volumes did not significantly differ (all P ≥ .14). All mean doses to the CTV were decreased for up to 7% (P ≤ .04), whereas mean doses to the right parotid and oral cavity increased from a range of 5% to 8% (P ≤ .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.
Highlights
There has been substantial growth in the use of proton therapy in the treatment of cancer in the past decade [1]
Numerous reports have documented the theoretical advantages of proton therapy over photon therapy for head and neck malignancies [2, 3], and clinical results achieved with proton beams have been promising [4]
Wang et al [19] found that patients with head and neck cancer could have anatomic structure changes during the course of radiation therapy (RT) owing to the shrinkage of the tumor or lymph nodes or to body weight loss; it was found that gross tumor volume (GTV) can be reduced by as much as 70% [20]
Summary
There has been substantial growth in the use of proton therapy in the treatment of cancer in the past decade [1]. Owing to its ability to create sharp distal falloff of proton beams within tissue, this technologically advanced form of particle therapy has substantial advantages over conventional photon therapy by reducing unnecessary radiation doses to organs at risk (OARs) and other healthy tissues. Because changes in patient anatomy (such as weight loss) may occur during treatment, the planned radiation doses to clinical target volumes (CTVs) and OARs can change significantly, as protons have a very defined and finite range for targeting and RT dose deposition. Numerous studies have been performed by using deformable dose accumulation methods on prostate and head and neck cancer treatments with photonbased intensity-modulated RT planning [7, 8] and adaptive strategies [6, 9], respectively. Because of the inherent sharp falloff in the distal range of a Bragg peak, small changes in anatomy can cause a large dosimetric deviation in target coverage and/or OARs
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