Normal tissue complication probability during proton therapy for head & neck cancer patients
OC-0110
Abstract
Normal tissue complication probability during proton therapy for head & neck cancer patients
Authors: van Weerd , Eva(1)*;Jacobs , Jenneke(1);Hutschemaekers , Stefan(1);Kroesen , Michiel(1);Klaver , Yvonne(1);Rodrigues , Myra(1);Werz , Hans-Joerg(1);Keskin-Cambay , Fatma(1);de Jong , Martin(1);Wiggenraad , Ruud(1);Hoogeman , Mischa(1);Habraken , Steven(1);van Vulpen , Marco(1);Zindler , Jaap(1)[j.zindler@erasmusmc.nl];
(1)Holland Proton Therapy Center, Radiotherapy, Delft, The Netherlands;
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Purpose or Objective
In the Netherlands, proton therapy (PT) is standard of care for patients with head & neck cancer (HNC) if the risk of xerostomia, dysphagia, and/or tube feeding dependence can be lowered compared to photon radiotherapy with 10%, 10%, and 5%, respectively. It is currently unknown whether the pretreatment predicted Normal Tissue Complication Probability (NTCP) remains stable throughout the PT course if anatomy changes due to tumor regression or weight loss occur. In this study we investigated the stability of NTCP during adaptive PT in HNC.
Material and Methods
All HNC patients who completed PT for HNC between January and October 2019 were selected for this study. Patients were treated with a simultaneous integrated boost of 70 GyRBE on the macroscopic tumor and 54.25 GyRBE on the elective neck areas in 35 fractions, using scenario-based robust treatment planning and subsequent evaluation. Repeat CTs were acquired weekly during the treatment course. The dose distribution was recalculated on each weekly CT to evaluate target coverage and organs at risk (OARs) dose. If clinical constraints were exceeded in the dose recalculation, the treatment plan was adapted. For every individual patient the average OAR dose and NTCP on all repeated CTs were compared with the OAR dose and NTCP on the planning-CT. Then the average OAR doses and NTCPs for all patients were calculated.
Results
Sixteen patients completed PT. Seventy repeat CTs were acquired and used for dose recalculation and NTCP assessment. For 8 patients, in total 11 plan adaptations were performed. In the next table the mean difference in OAR and NTCP dose with respect to baseline for the whole population is presented. During the course of PT, 4 of 16 (25%) patients had an increase of at least 3% in the risk of xerostomia, 0 of 16 (0%) patients of dysphagia, and 0 of 16 (0%) patients of tube feed dependence. The maximum dose variation in the contralateral parotid gland was 3,2 Gy.
Conclusion
The average difference of OAR dose and NTCP on the repeated CTs versus the planning-CT was small (<1 Gy and <1.5% respectively). On an individual patient basis larger variations occured, especially for xerostomia. Therefore regular PT dose recalculation and adaptation with special focus on contralateral parotid gland dose is necessary to maintain NTCP stability for all patients during the course of PT.
[1] Robust Intensity Modulated Proton Therapy (IMPT) Increases Estimated Clinical Benefit in Head and Neck Cancer Patients. van Dijk LV, Steenbakkers RJ, ten Haken B, van der Laan HP, van ''t Veld AA, Langendijk JA, Korevaar EW. PLoS One. 2016 Mar 31;11(3):e0152477.