A Dosimetric Comparison Of Brachial Plexus Deemed As/not As Dose-limiting Structure In Patients With Nasopharyngeal Carcinoma Treated With Intensity-modulated Radiation Therapy

Purpose: To evaluate whether dose constraints placed on the brachialplexus (BP) could result in a dosimetric benefit for nasopharyngeal carcinoma(NPC) treated with intensity-modulated radiation therapy (IMRT).Methods and Materials: Planning CT images for30NPC patients treatedwith definitive IMRT were retrieved from patient database and transferred to theplanning system software. Targets and the BP as well as other critical structureswere delineated retrospectively. Two separate IMRT plans for each patient weredesigned: one did not use any restrictions for the BP(Plan-1), and the otherconsidered the BP a critical structure for which a maximum dose limit of≤66Gy was set (Plan-2). Different doses were prescribed to different planning targetvolumes (PTVnx, PTVnd, PTV1, and PTV2) with curative intent,according totheir risk levels. A higher priority was given to the targets if the target coverageand dose constrain for the BP could not be achieved simultaneously.Results: No significant differences were found in conformity index (CI), homogeneity index(HI), maximum dose to the PTVs, minimum dose to thePTVs, percentage of the volume of the PTVnx and PTVnd receiving more than110%of the prescribed dose,and percentage of the volume of the PTVsreceiving95%and＞93%of the prescribed dose, between the two plans. Doseconstraints resulted in significant reductions in the maximum dose, mean dose,V45, V50, V54, V60, V66, and V70where Vx represented percentage of thevolume of the BP which received dose exceeding x Gy. For N0-1and N2-3diseases, there was significant difference in the maximum dose to the BPbetween the two plans. Similar results were also found in V45, V60and V66.No significant differences were found in the magnitude of dosimetric gain ineach parameter obtained with dose constraints between N0-1andN2-3diseases.Conclusions: Dose constraints for the BP in NPC patients during IMRTtreatment planning session could significantly decrease its irradiated volumesand radiation dose without compromising adequate dose delivery to the targets.