ESTRO 2020 Abstract book

S55 ESTRO 2020

acceptable. In clinical practice, medical physicists (MPs) perform a first plan quality assessments during planning and then radiation oncologists (ROs) perform it for plan approval. Here we investigate inter-observer variability in scoring of Pareto-optimal plans, including differences 15 head and neck cancer patients, treated with a three- level SIB technique, were selected for the study. Three to five plans were evaluated per patient by 5 ROs and 4 MPs from the same department. Each observer independently evaluated all plans available for a patient in a single session, i.e. all 3-5 plans were available in the clinical TPS. Scoring was blinded, i.e. observers did not know how the plans were generated. Plan scores were given from 1-7 (1- 2: unacceptable, 3-5: acceptable, if failure to improve quality in further planning, 6-7: acceptable, no further planning needed). For all patients, the plan database contained the clinically delivered plan (CLIN) and 2-4 Pareto-optimal plans, generated automatically with an in- house algorithm for automated a priori Multi-Criteria Optimization (MCO). Together with the clinical team, this algorithm was first configured to generate clinically favourable Pareto-optimal plans according to the department’s protocol and tradition. For each patient, the plan generated with that configuration (MCOa) was added to the database. Next, 20 sub-optimal configurations (x=b,c,d, …) were then performed and for each patient, the database was complemented with 1 or 3 of such MCOx plans. Results Overall, for 60%, 27%, and 13% of the patients, MCOa, CLIN and MCOx plans where ranked as best plan. In 20%, 27% and 40% of the patients, all observers, all ROs and all MPs choose the same plan as the best for treatment. Table1 shows the scores for all investigated 65 plans and all 9 observers, including mean scores. Mean scores of ROs and MPs were 4.7±1.3 and 5.5±1.0 for MCOa plans, 3.9±1.3 and 4.6±1.4 for CLIN plans and 3.5±1.4 and 3.8±1.4 for MCOx plans. Differences between the optimal autoplanning configuration MCOa plans and corresponding CLIN plans and between MCOa and MCOx plans were statistically significant (p<0.05). Interobserver variations (1 SD) in absolute scores were 1.1, 1.0, 0.9 (All, ROs, MPs). Correlation between ROs’ and MPs’ scores was moderate with R 2 =0.67 (Fig. 1). between MPs and ROs. Material and Methods

Conclusion On average, MCOa plans resulted better than CLIN plans and MCOx plans. However, large inter-observer differences in plan scores were observed with moderate correlation between scores of medical physicists and radiation oncologists. This can result in suboptimal plan quality in the usual workflow of physicists who plan for clinicians, and in selecting a Pareto-optimal plan using Pareto Navigation. OC-0106 Stepwise model-based treatment plan optimization to prevent head and neck cancer. H. Langendijk 1 , L. Van den Bosch 1 , A. Van den Hoek 1 , E. Oldehinkel 1 , T. Meijer 1 , R. Kierkels 1 , D. Scandurra 1 , A. Wolter 1 , D. Mulder 1 , H. Van der Laan 1 , S. Both 1 , A. Van der Schaaf 1 , R. Steenbakkers 1 1 UMCG University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands Purpose or Objective In 2007, prospective data collection started for all head and neck (HNC) patients treated with radiotherapy (RT). Physician- and patient-rated outcome measures were systemically collected at fixed time points. These data were used to develop and validate NTCP-models for dysphagia. The DVH-parameters in the NTCP-models were subsequently used to reduce dysphagia by using them as optimization parameter in treatment planning (NTCP- guided optimization). This approach resulted in a shift from standard IMRT (ST- IMRT) with sparing of the parotid glands only, towards swallowing-sparing RT (SW-RT with either IMRT or VMAT) with additional sparing of the superior pharyngeal constrictor muscle (PCMsup) and supraglottic area. Based on a new NTCP-model, further optimization was obtained with oral cavity sparing RT (OCS-RT) with additional sparing of the oral cavity, using either VMAT or IMPT. The aim of this study was to test the hypothesis that dysphagia was significantly reduced by these two NTCP-guided treatment plan optimizations. The primary endpoint for these NTCP-models was grade ≥ 2 dysphagia at 6 months after RT. Material and Methods In total 1118 patients were included of which 201 were treated with ST-IMRT (2007-2011), 704 with SW-RT (2012- 2017) and 213 with OCS-RT (2018-2019). Assessments were made at baseline, weekly during RT and at fixed time points after RT ( Table 1 ). Physician-rated toxicity was scored according to the CTCAEv4.0 and patient-rated dysphagia with the EORTC QLQ-HN35. Univariable and multivariable logistic and linear regression analysis was performed whenever appropriate. Results

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