Investigating the necessity of adaptive radiotherapy in tomotherapy of head and neck cancer patients.

Background: Anatomical variations that occur during radiation therapy in head and neck cancer (HNC) patients can lead to significant dosimetric changes. The purpose of this study is to evaluate dosimetric and volume changes in key anatomical structures for different treatment sites in HNC patients, and to determine the percentage of patients who need adaptive radiotherapy (ART) per treatment site.

Methods: A total of 1,740 megavoltage computed tomography (MVCT) images from 58 HNC patients treated with helical tomotherapy (HT) were exported to the PreciseART™ (Accuray) software. Volume changes in the planning target volume (PTV) and the organs at risk (OARs) in the planning stage and the first and last fractions of treatment were calculated. The differences between the values of actual accumulated and initial plan doses were used to determine which patients benefit ART.

Results: The average volume changes between the planning stage and the first fraction were 3.93%, 4.49%, and 6.46% for the PTV, brainstem, and spinal cord, respectively, for all patients. However, the average volume changes between the first and last fractions of treatment were relatively small and included 0.84%, 3.62%, and 1.19% for the PTV, brainstem, and spinal cord, respectively. The average dose changes between the initial planned dose and the actual cumulative dose in the last fraction were in the range of 10.43-30.81%; 4.66-11.61%; 3.73-9.97%; and - 0.17-5.40% for the brainstem, left parotid, right parotid, and spinal cord, respectively, for all patients. A maximum of 10.53%, 28.57%, and 18.18% of patients with oral cavity, larynx, and nasopharyngeal cancers, respectively, needed ART. Patients with salivary gland cancers did not need ART.

Conclusion: Although monitoring the volume and dose changes of the tumor and OARs during the course of radiation therapy is important, not all patients need ART. Criteria such as weight loss and rapid tumor shrinkage should be considered when selecting candidate patients for ART. The time interval between CT simulation and the first fraction also plays an important role in the difference in the volume and dose to organs during the course of radiation therapy.