| Radiotherapy of nasopharyngeal carcinoma (NPC) is the main treatment method.The conventional intensity-modulated could guarantee the dose of tumor, which is alsogood enough to protect the normal tissues at the same time. But the efficiency ofconventional intensity-modulated radiotherapy(IMRT) was low. More monitor units(MU) and a bunch of time were needed to complete the whole treatment. Recently,volumetric modulated arc therapy(VMAT) has been gradually used in the treatmentof nasopharyngeal carcinoma. One or two arc, few MU were used in the anasopharyngeal carcinoma theraphy, which cost a very short time.The purpose of this study explored the use of VMAT in the treatment of earlynasopharyngeal carcinoma (NPC). VMAT was studied in the early nasopharyngealcarcinoma using the finger cavity ionization chamber, EBT2films and MatriXX, Whichwas made possible used in the treatment of early nasopharyngeal carcinoma.Ten patients who suffered of early nasopharyngeal carcinoma were enrolled in thestudy. They were separated into three groups: IMRT group, single arc and double arcVMAT group. The differences between the target area and the normal tissues werecalculated under the three groups. The differences of MU, delivery times andtreatment times were compared under the therapy apparatus execution plan. Accordingto the different features of the ionization chamber, EBT2films and MatriXX, single anddouble arc VMAT plans were validated respectively in the8patients with earlynasopharyngeal carcinoma. The point dose, one-dimensional profile, isodose map andGamma pass rate were used to analyze the results.In this study, the volume of PTV-G and95%PTV-C reached the prescriptionsdose among the three groups, while the high dose in double arc VMATand IMRTplansare obviously better than the single arc VMAT plans. At the same time, the conformalindex (CI) of double arc VAMTplans was higher than the IMRTplans and the single arcVAMT plans. The normal tissue basically met the program. The does of50%in thethroat,50%bilateral parotid gland in the double arc VMATplans was significantlylower than the groups of IMRT and single arc VAMT plans, which also parralled in theaverage dose. The MUs of both single arc and double arc VAMT plans concerning the execution plan were less than that of IMRT plans. The time of single arc VMAT planswas less than that of IMRT and double arc VMAT plans. This study showed that thedose difference of the actual and the plan measurement in both single arc VMAT anddouble arc VMATplans was less than3%, whose Gamma pass rate was more than90%.This study showed that VAMT in was used in the early nasopharyngeal carcinomaradiotherapy. The quantity of double arc VAMTplans target area and the normal tissueswere better than or close to that of IMRT and single arc VAMT plans. At the same time,the target area may get good CI and uniformity. VMAT could obviously reduce the MU,shorten the treatment time. Meanwhile, the planar dose and point dose results wereclose to the expected ones both in the single and double arc VMAT plans, whichprovided the basis for the early nasopharyngeal carcinoma radiotherapy. |
