'Line' Constraints Optimization for Improved Dose Distribution in Locally Recurrent Nasopharyngeal Carcinoma Using Knowledge-Based Planning.

IntroductionTo investigate the efficacy of a knowledge-based planning (KBP) model in optimizing dose distribution, and identify the inter-institutional variation in radiotherapy of recurrent nasopharyngeal carcinoma (rNPC).MethodsA total of 70 rNPC patients treated with intensity-modulated radiotherapy (IMRT) were recruited to build a KBP model. Following model refinement, 36 patients were retrospectively enrolled for dosimetric comparison between manually optimized and KBP-generated plans. Ten experienced physicists from six different institutions were engaged to independently design manual plan for a representative case, to assess inter-institutional variations, and differences between KBP and manual plans.ResultsThe refined KBP model provided significant reduced dose in brainstem D(1cc) (the dose received by the "hottest"1 cm(3) volume, 41.14 +/- 8.51 Gy vs 38.48 +/- 8.60 Gy, P < 0.001) and spinal cord D(1cc) (17.48 +/- 9.38Gy vs 12.23 +/- 6.56Gy, P < 0.001). In addition, The mean dose (D(mean)) of brainstem, spinal cord, mandible, parotid, temporomandibular joint and inner ear were statistically decreased (P < 0.05). In validation cohort, KBP model eliminated the hotspot (0.57 +/- 0.01% vs 0.00 +/- 0.00%, P < 0.001), improved target homogeneity (HI: 0.06 +/- 0.00 vs 0.08 +/- 0.00, P < 0.001), and performed superior to the manual plans in sparing organs. While all institutions achieved comparable target coverage, manual plans exhibited substantial variability in sparing brainstem. KBP implementation reduced inter-institutional dose disparities for brainstem (46.30 +/- 10.08 Gy vs 41.80 +/- 5.80 Gy, P = 0.041) and spinal cord (26.08 +/- 7.06 Gy vs 18.19 +/- 1.98 Gy, P = 0.002). Additionally, planning efficiency increased by 48.7% (39 vs 76 min).ConclusionsThis KBP framework optimized rNPC reirradiation from three dimensions: 1) Enhanced OARs' protection; 2) Improved target homogeneity; 3) Improved the multi-institutional consistency and efficiency of planning. These advancements established a clinically actionable paradigm for precision reirradiation.