OBJECTIVE: Radiotherapy (RT) outcomes are generally reported based on stage, patient background, and concomitant chemotherapy. This study aimed to investigate the effects of the prescribed dose to gross tumor volume (GTV) and the calculation algorithm on local control in definitive RT for head and neck (H&N) cancers using follow-up images after RT.
METHODS: This study included 154 patients with H&N cancers treated by Volumetric Modulated Arc Therapy at the Kobe City Medical Center General Hospital. Patients were classified into those receiving definitive RT (70 Gy of irradiation) and those not receiving it. Follow-up images were used to categorize the patients into the responders and non-responders groups. In the non-responders group, follow-up images were imported into the treatment planning system, and the contours of the residual or recurrent areas (local failure) were extracted and fused with computed tomography-simulated images for treatment planning. Dose evaluation parameters included maximum dose, dose administered to 1% of the volume, dose administered to 50% of the volume, dose administered to 99% of the volume (D99%), and minimum dose (Dmin) administered to the GTV. The doses to the GTV were compared between responders and non-responders.
RESULTS: D99% exhibited significant differences between local failure and responders and between local failure and non-responders. Dmin showed significant differences between responders and non-responders and between responders and local failure.
CONCLUSIONS: This study emphasizes the importance of verifying dose distribution in all slices of treatment planning, highlighting the need for precise assessment of the dose to the GTV in head and neck cancers.

This study aimed to determine the dosimetric value of flattening filter-free (FFF) beams compared to flattening filter (FF) beams using different algorithms in the treatment planning of thoracic spine stereotactic body radiation therapy (SBRT). A total of 120 plans were created for 15 patients using the Anisotropic Analytical Algorithm (AAA) and the Acuros External Beam (AXB) algorithm with FF and FFF beams at 6 MV and 10 MV energies. Various dosimetric parameters were evaluated, including target coverage, dose spillage, and organs-at-risk sparing of the spinal cord and esophagus. Treatment delivery parameters, such as the monitor units (MUs), modulation factors (MFs), beam-on time (BOT), and dose calculation time (DCT), were also collected. Significant differences were observed in the dosimetric parameters when AXB was used for all energies (P < 0.05). 6 XFFF energy was the best option for target coverage, dose spillage, and organs-at-risk sparing. In contrast, dosimetric parameters had no significant difference when using the AAA. The AAA and AXB calculations showed that the 6 XFFF beam had the shortest DCT. The treatment delivery parameters indicated that 10 XFF beam required the fewest MUs and MFs. In addition, the 10 XFFF beam demonstrated the shortest BOT. For effective treatment of the thoracic spine using SBRT, it is recommended to use the 10 XFFF beam because of the short BOT. Moreover, the AXB algorithm should be used because of its accurate dose calculation in regions with tissue heterogeneity.