Reduction of head and neck lymphedema by placing dose limiting rings in the anterior and posterior regions of the neck for treating early nasopharyngeal carcinoma using intensity-modulated radiotherapy: A dosimetric perspective.

Objective To establish an optimal limiting dose for dose limiting rings placed in the anterior and posterior regions of the neck for reducing head and neck lymphedema under intensity-modulated radiation therapy(IMRT) for early nasopharyngeal carcinoma(NPC) from a dosimetric perspective. Method Fifteen newly diagnosed early-stage nasopharyngeal carcinoma patients who underwent CT localization for radiotherapy at the Cancer Hospital of Guangzhou Medical University from January to September 2022 were included in the study. Each case was designed with five sets of radiotherapy plans. Plan A consisted of conventional unlimited-field plans, while Plans B-E consisted of limited-field plans with dose constraints set at 20, 18, 16, and 14 Gy, respectively, with the remaining parameters consistent with Plan A. The impact on target coverage and organ-at-risk constraints was evaluated through variance analysis and pairwise multiple comparisons using a randomized block design to determine the optimal dose limits. Results The gradient of 16Gy was determined as the optimal dose limiting cutoff point for achieving the balance between target coverage and organ limiting dose. Compared with the conventional plan, The plans with the placement of a cervical anterior and posterior dose limiting ring (16Gy) did not change the target dose coverage (P > 0.05), but only yielded a slight change in the homogeneity index (P < 0.05). It did not cause any changes of the dosage in the inner ear, mandible, and brainstem (all P > 0.05), but lead to statistically significant reductions in the oral cavity, throat, and thyroid (all P < 0.05). It caused a slight increase of the dose in the parotid gland and spinal cord (both P < 0.05), but the increased dose was anyhow within the tolerance range. Conclusion The dosimetric investigation determines an optimal dose limit cutoff point for the cervical anterior and posterior dose limiting rings. It is expected to provide a design method for IMRT plans to reduce head and neck lymphedema after radiotherapy for early NPC. [ABSTRACT FROM AUTHOR]