Decreased rates of radiation-induced trismus and lowered mastication structure doses in patients treated for head and neck cancer during the last two decades

Abstract

PurposeTo investigate how absorbed doses to mastication structures in modern radiotherapy (RT) technique for head and neck cancer (HNC) compared to earlier RT techniques and to published trismus tolerance doses. To compare the incidence of radiation-induced trismus by earlier and newer RT techniques. Methods and materialsThis study investigated two HNC patient cohorts treated with RT in 2007-2012 (3D-CRT and/or IMRT; n=121 [Cohort 1]) and 2017-2020 (VMAT; n=124 [Cohort 2]). All patients underwent RT without mastication-structure-sparing intent, had normal mouth-opening ability before RT and were prospectively assessed. Trismus was defined as maximal interincisal opening ≤35 mm at any follow-up (3, 6 and 12 months post RT). The temporo-mandibular joints (TMJs), masseter and medial/lateral pterygoid muscles were delineated on the planning CT:s. Mean doses were compared between cohorts, and evaluated with respect to published trismus tolerance doses. P-values≤0.05 indicated statistical significance. ResultsWithin 12 months post RT, 74/121 (61%) of patients in Cohort 1 had experienced trismus compared to 11/124 (9%) in Cohort 2. Averaged mean doses (±S.D.) for the masseter muscles were 35.2±8.3 Gy in Cohort 1 and 20.2±8.7 Gy in Cohort 2 (p<0.001). Corresponding numbers were 19.1±16.2 and 4.3±4.3 Gy for the TMJs, 53.7±10.1 and 40.2±16.8 Gy for the medial pterygoid muscles, and 29.2±18.7 and 9.2±8.4 Gy for the lateral pterygoid muscles (all p<0.001). Masseter muscle doses were below tolerance doses in 23% of patients in Cohort 1 compared to 90% in Cohort 2. The corresponding numbers were 52% and 96% for the TMJs, 8% and 36% for the medial pterygoid muscles and 72% and 100% for the lateral pterygoid muscles. ConclusionMastication structure mean doses by more recent RT techniques were generally below proposed tolerance doses, with dose reductions of 10-20 Gy compared to earlier techniques. Modern RT without mastication-structure-sparing intent resulted in below 10% of HNC patients experiencing trismus compared to 60% treated with earlier techniques.