ESTRO 2023 - Abstract Book

S69

Saturday 13 May

ESTRO 2023

OC-0108 The influence of tumor volume on the risk of distant metastases in head and neck cancer J. Kjems 1 , K.E. Håkansson 2 , C.A. Kristensen 2 , J.G. Eriksen 3 , M.H. Kristensen 3 , A.I.S. Holm 4 , J. Overgaard 3 , C.R. Hansen 5 , R. Zukauskaite 5 , J. Johansen 5 , I.R. Vogelius 2 , J. Friborg 2 1 Copenhagen University Hospital, Rigshospitalet , Department of Oncology, Copenhagen, Denmark; 2 Copenhagen University Hospital, Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 3 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 5 Odense University Hospital, Department of Oncology, Odense, Denmark Purpose or Objective Metastatic disease is the most significant factor for survival in cancer. In most circumstances, distant metastasis (DM) in head and neck cancer is non-curable. The current TNM staging system is insufficient to predict the risk of DM and identifying high-risk patients may facilitate interventions to reduce this risk. We hypothesize that the risk of DM in head and neck cancer can be determined using a multivariate model including pre-treatment total tumor volume. Materials and Methods The study includes patients from three large head and neck cancer centers with localized pharyngeal and laryngeal squamous cell carcinomas treated with primary radiotherapy from 2008-2017. Patients were identified in the Danish Head and Neck Cancer (DAHANCA) database, which has a coverage of close to 100%. Patient-specific, tumor-specific and treatment-specific data were extracted and verified from patient file review. Tumor volume (Gross Tumor Volume, GTV) was extracted from local treatment planning systems (TPS) and represented the total volume of the primary tumor and nodal metastases at time of primary treatment planning. Results We included 2,865 patients, of which 305 (11%) developed DM. The risk of DM was assessed in a multivariate model (Cox proportional hazard regression) based on 2,708 patients controlled for pre-selected clinical values: age, gender, center, subsite incl. p16-status for oropharyngeal carcinoma, stage (UICC/AJCC-8), differentiation grade, smoking and GTV. The GTV was binned into four groups by volume (cm3): small [0-10), medium [10-25), large [25-50), and very large [50+). The analyses were performed on p16-positive oropharyngeal squamous cell carcinoma (OPSCC, N = 1,006) and all other sites separately (N = 1,702). Very large tumor volume was significantly associated with the risk of DM in both patient populations (Figure 1 and 2), hazard ratio (HR) 10.0 (p<0.001) for patients with p16-positive OPSCC and HR 4.2 (p<0.001) in other pharynx and larynx carcinomas (excl. p16-positive OPSCC). Analyzing all patients together in a combined model (N = 2,708), stage, tumor differentiation, and GTV were significantly associated with the risk of DM. In the combined model HRs for tumor volume were 2.0 (medium GTV, p = 0.01), 2.1 (large GTV, p<0.01) and 5.3 (very large GTV, p<0.001).

Conclusion Tumor volume is an independent factor strongly associated with the risk of DM. Adding total tumor volume from TPS to a predictive model is important in identifying subgroups of head and neck cancer patients at high risk of DM. OC-0109 Functional dose to the parotid gland: a new regional based dose metric in NTCP models for xerostomia M.I. van Rijn - Dekker 1 , P. van Luijk 1 , E. Schuit 2 , A. van der Schaaf 1 , J.A. Langendijk 1 , R.J. Steenbakkers 1 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 2 University Medical Center Utrecht, Julius Center for Health Sciences and Primary Care, Utrecht, The Netherlands Purpose or Objective Despite improvements, HNC patients still experience xerostomia due to RT-induced salivary gland damage. The parotid gland’s (PG) stem cells, concentrated in the gland’s main ducts (stem cell rich (SCR) region), play a critical role in the PG’s response to radiation. However, treatment optimization requires dose metrics accounting for the relative contributions of dose to this SCR region and dose to the remainder of the gland (non-SCR region) to the risk of xerostomia. This study aimed to develop such dose metric: the functional dose. Subsequently, NTCP models including additional contributions of other risk factors were constructed using multivariable logistic regression analyses. Materials and Methods Treatment and toxicity data of 1,013 HNC patients treated with definitive RT was obtained from our prospective data registration program. Xerostomia was measured with the EORTC QLQ-H&N35, the Groningen Radiotherapy-Induced Xerostomia questionnaire and the CTCAE version 4. For xerostomia endpoints associated with PG dose, functional dose (D func ) to the PG was defined as D func,PG = D mean,SCR + r * D mean,non-SCR . In our cohort for weighting factor r = 3.6, D func,PG corresponds to D mean,PG . This reflects the difference in volume between the SCR and the non-SCR region. A value of r < 3.6 indicates an enhanced contribution of D mean,SCR to the risk of xerostomia. The value of r for which D func,PG was the best predictor for xerostomia endpoints,