Clinical outcome after pencil beam scanning proton therapy and dysphagia/xerostomia NTCP calculations of proton and photon radiotherapy delivered to patients with cancer of the major salivary glands

Author:

Walser Marc Andrea1ORCID,Bachmann Nicolas12,Kluckert Jonas1,Köthe A.13,Tully Carson1,Leiser Dominic1,Lomax Antony John13,Bizzocchi Nicola1,Langendijk Johannes Albertus4,Weber Damien C125

Affiliation:

1. Center for Proton Therapy, Paul Scherrer Institute, ETH Domain, CH-5232 Villigen, Switzerland

2. Department of Radiation Oncology, lnselspital, Bern University Hospital, University of Bern, Bern, Switzerland

3. Department of Physics, ETH Zurich, Zurich, Switzerland

4. Department of Radiation Oncology, University of Groningen, Groningen, The Netherlands

5. Department of Radiation Oncology, University Hospital of Zürich, Zürich, Switzerland

Abstract

Objectives The purpose of this study is to report the oncological outcome, observed toxicities and normal tissue complication probability (NTCP) calculation for pencil beam scanning (PBS) PT delivered to salivary gland tumour (SGT) patients. Methods We retrospectively reviewed 26 SGT patients treated with PBSPT (median dose, 67.5 Gy(RBE)) between 2005 and 2020 at our institute. Toxicities were recorded according to CTCAEv.4.1. Overall survival (OS), local control (LC), locoregional control (LRC) and distant control (DC) were estimated. For all patients, a photon plan was re-calculated in order to assess the photon/proton NTCP. Results With a median follow-up time of 46 months (range, 3–118), 5 (19%), 2 (8%), 3 (12%) and 2 (8%) patients presented after PT with distant, local, locoregional failures and death, respectively. The estimated 4 year OS, LC, LCR and DC were 90%, 90%, 87 and 77%, respectively. Grade 3 late toxicity was observed in 2 (8%) patients. The estimated 4 year late high-grade (≥3) toxicity-free survival was 78.4%. The calculated mean difference of NTCP-values after PBSPT and VMAT plans for developing Grade 2 or 3 xerostomia were 3.8 and 2.9%, respectively. For Grade 2–3 dysphagia, the grade corresponding percentages were 8.6 and 1.9%. Not using an up-front model-based approach to select patients for PT, only 40% of our patients met the Dutch eligibility criteria. Conclusion Our data suggest excellent oncological outcome and low late toxicity rates for patients with SGT treated with PBSPT. NTCP calculation showed a substantial risk reduction for Grade 2 or 3 xerostomia and dysphagia in some SGT patients, while for others, no clear benefit was seen with protons, suggesting that comparative planning should be performed routinely for these patients. Advances in knowledge We have reported that the clinical outcome of SGT patients treated with PT and compared IMPT to VMAT for the treatment of salivary gland tumour and have observed that protons delivered significantly less dose to organs at risks and were associated with less NTCP for xerostomia and dysphagia. Noteworthy, not using an up-front model-based approach, only 40% of our patients met the Dutch eligibility criteria.

Publisher

Oxford University Press (OUP)

Subject

Radiology, Nuclear Medicine and imaging,General Medicine

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