ESTRO 2020 Abstract book

S59 ESTRO 2020

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.

and CVD events, adjusted for age and calendar year at planning CT. Results Data from 14,034 patients were included. The mean age at the planning CT was 58 years (SD=11). Twenty-eight percent of the patients had a CAC score of >0 (Table 1). Over a median follow-up time of 52 months (IQR: 27-82), 8.2% of the patients (n=1148) were admitted to the hospital for CVD events and 93 patients (0.7%) died from this disease. After adjustment for age and calendar year at planning CT, the incidence of CVD events increased with higher CAC scores (CAC 1-10 HR=1.3, 95%CI:1.0-1.5; CAC 11-100 HR=1.7, 95%CI:1.5-2.1; CAC 101-400 HR=2.2, 95%CI:1.7-2.7; CAC >400 HR=3.7, 95%CI:2.9-4.6).

Conclusion CAC detected on the radiotherapy planning CT is strongly associated with an increased risk of CVD events. This finding is relevant for breast cancer patients since early identification of high risk patients enables switching to less cardiotoxic breast cancer treatment (e.g. adaptation of radiotherapy target volumes or technique, chemotherapy dose reduction). Also, patients can adopt targeted cardio- preventive interventions (e.g. lifestyle changes, pharmaco-prevention, close monitoring for early detection of cardiotoxicity). Hence, the burden of CVD in breast cancer survivors can be reduced and better overall survival rates can be achieved. OC-0110 Normal tissue complication probability during proton therapy for head & neck cancer patients E. Van Weerd 1 , J. Jacobs 1 , S. Hutschemaekers 1 , M. Kroesen 1 , Y. Klaver 1 , M. Rodrigues 1 , H. Werz 1 , F. Keskin- Cambay 1 , M. De Jong 1 , R. Wiggenraad 1 , M. Hoogeman 1 , S. Habraken 1 , M. Van Vulpen 1 , J. Zindler 1 1 Holland Proton Therapy Center, Radiotherapy, Delft, The Netherlands 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 Gy RBE on the macroscopic tumor and 54.25 Gy RBE 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.

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. OC-0111 Patient-reported acute diarrhea in a cervical cancer patient cohort correlates with dose to rectum D. Reijtenbagh 1 , J. Godart 1 , J. Mens 1 , S. Heijkoop 1 , W. Heemsbergen 1 , M. Hoogeman 1,2 1 Erasmus MC, Radiation Oncology, Rotterdam, The Netherlands ; 2 HollandPTC, Medical Physics & Informatics, Delft, The Netherlands Purpose or Objective Patient-Reported Outcomes Measures (PROMs) are an increasingly important tool to record the patient’s individual perception of toxicity. Understanding the relations between dosimetric parameters and PROMs could help to optimize the treatment. However, these relations are poorly described for cervical cancer patients and the spatial information of dose distributions is usually not included in the analysis. In this study patient-reported acute diarrhea symptoms are evaluated specifically, and their relationship with dosimetric parameters of the bowelbag and rectum, as well as spatial information, is investigated. Material and Methods In this prospective study, 103 locally-advanced cervical cancer (LACC) patients treated according to an IMRT/VMAT