S643
Clinical – Head & neck
ESTRO 2026
followed by adjuvant chemotherapy, whereas IMPT patients typically underwent neoadjuvant chemotherapy followed by CRT. IMPT significantly reduced mean doses to OOI (Mean reduction: 39Gy oral cavity, 8Gy superior pharyngeal constrictor muscle (PCM), 20Gy middle PCM, 30Gy inferior PCM, 32Gy contralateral and 19Gy ipsilateral parotid gland, and 28 and 20Gy submandibular glands). Significant dose reductions were also observed compared with VMAT plans using multiple organ-sparing strategies implemented after 2018. These dosimetric advantages translated into substantially fewer acute and late side effects, including xerostomia, taste loss, dysphagia, mucositis, and feeding-tube dependence (Fig 1). Compared with photons, TTB decreased with IMPT by 55% (W1–W7), 54% (W7–W12), 72% (W12–M6), and 67% (M6–M24), yielding an overall 64% reduction in cumulative toxicity (Fig 2).
perspectives. Focused follow up and integration of patient-reported outcomes are crucial for personalized survivorship care. Keywords: health related quality of life, survivorship
Mini-Oral 3978
Proton therapy significantly reduces acute and late side effects in nasopharyngeal cancer: results from a prospective cohort study Makbule Atasoyu 1 , Tineke W.H. W.H. Meijer 1 , Johanna G.M. van den Hoek 1 , Stefan Both 1 , Edwin Oldehinkel 1 , Hans H.G. Verbeek 1 , Gyorgy B. Halmos 2 , Sjoukje F. Oosting 3 , Roel J.H.M. Steenbakkers 1 , Johannes A. Langendijk 1 1 Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands. 2 Department of Otorhinolaryngology, Head and Neck Surgery, University of Groningen, University Medical Center Groningen, Groningen, Netherlands. 3 Department of Medical Oncology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands Purpose/Objective: To evaluate whether Intensity Modulated Proton Therapy (IMPT) reduces acute and late radiation- induced side effects in patients with nasopharyngeal carcinoma (NPC) compared to photon-based techniques. Material/Methods: In this prospective study 181 NPC patients treated with curative-intent radiotherapy (RT), with or without (neo)adjuvant and concurrent chemotherapy (CRT), were included. Between 2007 and 2017, all patients received photon-based RT (IMRT/VMAT). From 2018 onward, 143 of 145 eligible patients (99%) were treated with IMPT, selected using a model-based approach: 133 for expected reductions in xerostomia and dysphagia, and 10 for anticipated reductions in neurological side effects. Side effects were prospectively assessed at baseline (T0), weekly during treatment (W1–W7), at 5 weeks post-treatment (W12), and during follow-up up to 24 months (M6–M24). To quantify the overall treatment burden, a Total Toxicity Burden (TTB) metric was developed, defined as the weighted sum of all recorded side effects, with weights based on grade and duration. The area under the TTB curve (TTB-AUC) represents the cumulative side effect burden from T0 to M24. Two groups were compared in terms of organs of interest(OOI) doses and side effects. Results: Baseline characteristics were comparable between the IMPT and photon cohorts. For stage III–IV disease, photon-treated patients more often received CRT
Conclusion: IMPT significantly reduces both acute and late side effects in NPC patients compared with photon-based RT. The transition to less toxic chemotherapy regimens may also have contributed to the lower toxicity rates. Nevertheless, the consistent dose– response relationship supports that reduced radiation exposure to critical organs plays a major role, highlighting the importance of normal tissue sparing and supporting the broader adoption of IMPT in curative NPC treatment. Keywords: nasopharyngeal carcinoma, proton therapy, toxicity
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