Comparison of the temporomandibular joint, constructor pharyngeal muscle and parotis doses with different techniques in radiotherapy of HEAD and neck cancers

Objective: Dosimetric comparison of conventional linac-based intensity modulated radiotherapy (S-IMRT) and Helical Tomotherapy based intensity modulated radiotherapy (HT-IMRT) treatment techniques in oropharyngeal cancers with dose distribution at the target volume in terms of protection of critical organs, especially temporomandibular joint and constrictor pharyngeal muscle. This is the aim of this thesis. Method: In this retrospective study, computer tomography sections, target volumes and contours of critical organs of 13 patients diagnosed with oropharyngeal cancer are included. For each patient, 26 treatment plans were designed with sIMRT and HT-IMRT techniques, with 2 Gy doses per fraction and a total dose definition of 60, 66, and 70 Gy. Dosimetric evaluation and comparison of techniques were made in accordance with dose volume histogram (DVH), homogeneity index (HI) and conformity index (CI) parameters. The results of all treatment plans, target volumes and dosimeric parameters of critical organs were evaluated statistically. In addition, treatment times for each technique were compared. For all plans, the volume percent value of the 5, 10, 15 and 20 Gy dose taken by the healthy tissue outside the target was analyzed. Results: In terms of PTV, the HT-IMRT technique gave more successful results than the sIMRT technique. HI was within the acceptable limits for all techniques, but HT-IMRT techniques were found to be more suitable for CI. The duration of treatment was found to be higher in the HT-IMRT technique compared to the sIMRT technique. In VSD (healthy tissue volume) analysis, the sIMRT technique was found to be superior to the HT-IMRT technique. Conclusion: HT-IMRT plans and sIMRT treatment plans have been found to provide viable results for oropharyngeal cancer patients. HT-IMRT plans are more advantageous in terms of critical organ dose compared to sYART plans. The results obtained should be considered with re-irradiation strategies in mind. Keywords: IMRT, Oropharyngeal Cancer, Radiotherapy, Tomotherapy