Sparing the contralateral submandibular gland without compromising PTV coverage by using volumetric modulated arc therapy

BACKGROUND Salivary gland function decreases after radiation doses of 39 Gy or higher. Currently, submandibular glands are not routinely spared. We implemented a technique for sparing contralateral submandibular glands (CLSM) during contralateral elective neck irradiation without compromising PTV coverage. METHODS Volumetric modulated arc therapy (RapidArc™) plans were applied in 31 patients with stage II-IV HNC without contralateral neck metastases, all of whom received elective treatment to contralateral nodal levels II-IV. Group 1 consisted of 21 patients undergoing concurrent chemo-radiotherapy, with elective nodal doses of 57.75 Gy (PTVelect) and 70 Gy to tumor and pathological nodes (PTVboost) in 7 weeks. Group 2 consisted of 10 patients treated with radiotherapy to 54.45 Gy to PTVelect and 70 Gy to PTVboost in 6 weeks. All clinical plans spared the CLSM using individually adapted constraints. For each patient, a second plan was retrospectively generated without CLSM constraints ('non-sparing plan'). RESULTS PTV coverage was similar for both plans, with 98.7% of PTVelect and 99.2% of PTVboost receiving ≥95% of the prescription dose. The mean CLSM dose in group 1 was 33.2 Gy for clinical plans, versus 50.6 Gy in 'non-sparing plans' (p < 0.001). In group 2, mean CLSM dose was 34.4 Gy for clinical plans, and 46.8 Gy for non-sparing plans (p = 0.002). CONCLUSIONS Elective radiotherapy to contralateral nodal levels II-IV using RapidArc consistently limited CLSM doses well below 39 Gy, without compromising PTV-coverage. Future studies will reveal if this extent of dose reduction can reduce patient symptoms.