Dosimetric comparison of intensity-modulated arc radiotherapy and fixed beam dynamic intensity-modulated radiation therapy in nasopharyngeal carcinoma

Abstract

To compare the dosimetric differences of dosiology between intensity-modulated arc radiotherapy (IMAT) and dynamic intensity-modulated radiation therapy (dIMRT) in nasopharyngeal carcinoma. CT data from 25 patients treated in our radiotherapy center were selected randomly for this study. For each patient, the IMAT technique and the fixed beam dIMRT technique were accomplished by the simultaneously integrated boost. Dose volume histogram (DVH) data, isodose distribution, monitor units (MUs) and treatment time were compared in the two techniques. There was no significant difference between the IMAT and the dIMRT in dose received by 95% of target volumes (D(95)) (P>0.05). Overall, the mean dose (D(mean)), maximal dose (D(max)) and volume percentage receiving at least of 107% of the prescribed dose (V(107%)) of planning target volume (PTV) for the IMAT were increased slightly ,compared with the dlMRT (P<0.05). There were no significant differences in dosimetric indices of organs at risk (OARs) including spinal cord,optical nerves,lens and temporomandibular joints in the two techniques (P>0.05). Compared with the dlMRI, the D(max) of brain stem for the IMAT was increased slightly (P<0.05). Similar trends was observed for the D(mean) and dose received by 50% of volume (D(50)) of the left and right parotid glands (P<0.05). Healthy tissue (defined as the volume of the body minus PTV,B-P) irradiated from 800 cGy in the IMAT was higher, and that from 1200-4500 cGy was lower compared with the dlMRI (P<0.05).The average number of MUs was reduced by 62.7% per fraction, and the treatment time was on average reduced by 60.1% per fraction in the IMAT compared with the dlMRI. There is a slight difference in dosiology between the two radiotherapy techniques investigated, but they both meet the clinical requirement. Compared with the dIMRT, the IMAT delivers less irradiation to healthy tissue, uses fewer MUs and takes less time during radiotherapy for nasopharyngeal carcinoma.