Investigation of adaptive radiotherapy technique for the treatment of nasopharynx cancer

Intensity-modulated radiotherapy is the primary treatment for nasopharynx cancer and its success depends on correct application.Changes in size-and-position that can occur at the target during treatment can cause undesirable consequences; inability to deliver defined dose to the target and protect healthy tissues.This condition is important in radiotherapy of tumors that are close to vital organs, such as nasopharynx-cancer.Adaptive radiotherapy(ART) technique is a method that minimizes dosimetric differences that may occur between planned and applied treatment by considering changes in radiotherapy area. The aim of this study is to investigate the dosimetric effects and applicability of ART for 20-nasopharynx-cancer patients. Changes in the volumes-and-doses of target and healthy tissues identified on the first computed tomography(CT) images of patients were observed in the first group with 11 and 21.fractions control CTs, in the second group with 17.fraction control CTs.For all patients, volume and dose changes of target and healthy tissue volumes identified in adaptive and non-adaptive radiotherapy treatments were compared.The dosimetric effects of ART were investigated for both groups. GTVs were found to be 9.27±6.10, 8.51±5.70 ve 7.67±5.51 cm3 for 1.,11. and 21.fractions in the first group; 22.77±18.42 ve 20.27±17.82 cm3 for 1. and 17.fractions in the second group, respectively.Contralateral-parotid doses were found to be 9.27% lower in the first group and 5.37% lower in the second group with ART. It was concluded that ART is effective in reducing parotid doses, the most appropriate time for its application is between the 17-21.fractions of the treatment, and patient-based evaluation of treatment is required.