ESTRO 2020 Abstract Book

S52 ESTRO 2020

Conclusion The model-based approach, together with technological improvements resulted in two optimization steps that resulted in lower dose to relevant OARs resulting in significant reductions of different aspects of dysphagia. Although the NTCP-models were developed for grade ≥ 2 dysphagia at 6 months after RT, dysphagia decreased at multiple time points. Adding oral cavity sparing to sparing of the PCMsup and supraglottic area further prevented long-term swallowing problems. OC-0107 Quantitative metrics to analyze variations and support best practices in head and neck dose plans L.P. Kaplan 1 , C.R. Hansen 2 , K. Jensen 3 , J. Friborg 4 , E. Samsøe 5 , J. Johansen 4 , M. Andersen 6 , B. Smulders 4 , E. Andersen 5 , M.S. Nielsen 6 , J.G. Eriksen 1 , J.B.B. Petersen 1 , U.V. Elstrøm 1 , A.I.S. Holm 1 , P.S. Skyt 3 , A. Vestergaard 3 , E.L. Lorenzen 2 , M. Nielsen 2 , R.C. Marseguerra 7 , M.H. Morthorst 7 , C. Grau 3 , S.S. Korreman 1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark ; 2 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark ; 3 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark ; 4 Rigshospitalet University Hospital of Copenhagen, Department of Oncology, Copenhagen, Denmark ; 5 Herlev University Hospital, Department of Oncology, Herlev, Denmark ; 6 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark ; 7 Næstved Hospital, Department of Oncology, Næstved, Denmark Purpose or Objective A national guideline for treatment planning in head and neck cancer has continuously been developed, improved and implemented . Due to differences in local TPS, linacs, and specific planning practices, plan quality may still vary between individual planners following the guideline. We analyze inter-planner variations for a group of planners following the guideline, and suggest use of quantitative metrics for further plan exploration. . Material and Methods Planners from seven clinics were asked to create RT plans for the same patient (right-sided oropharyngeal cancer patient with bilateral lymph node target). All were given identical CT and structure data. Plans (66/60/50 Gy) were made locally according to national guidelines (although not under clinical conditions, i.e. reviewing processes and clinical approval of plans was not performed). RT plans were either 1-3 arc VMAT or 9-field co-planar IMRT (PTV margin 3mm). Clinics used different treatment machines and planning systems. Fifteen RT plans were available for analysis. We calculated the following metrics for all plans: clinical dose constraints, D5%, VXGy (X = 10,20,…,70Gy), dose standard deviation for each structure (target or OAR), dose conformality to targets, maximum dose at 1-3cm from targets, dose gradient index, size/number of contiguous cold volumes in targets. Results All plans met the criteria for target coverage and critical OAR (spinal cord, brainstem) dose. For target coverage the plans were very similar, with a max-min span of <3.1Gy (CTV D99% and PTV D98%). There were notable variations in several metrics not related to critical constraints (see examples in fig. 1). DVHs for high-risk PTV (small variation) and contralateral parotid (larger variation) are shown in figure 1. When considering non-critical OAR (mean doses) we saw a group of very similar plans that were notably better than the others (fig.2). These plans achieved lower mean doses for most OAR - it did not seem to be only a case of prioritizing differently between OARs. There were no significant differences in target metrics between the two groups (Mann-Whitney U-test p<0.05). Differences in OAR mean dose correlated with differences in a wide range of dose levels (fig 2 (3)), indicating that constraints 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 The oral cavity Dmean decreased from 48.5 Gy (±15.7) to 40.9 Gy (±17.9) and 27.7 Gy (±16.3) with ST-IMRT, SW-RT and OCS-RT, resp. (P<0.001). The PCMsup D mean decreased significantly from 57.6 Gy (±13.8) to 47.9 Gy (±18.8) and 41.5 Gy (±18.9) with ST-IMRT, SW-RT and OCS-RT, resp. (P<0.001). The prevalence of grade ≥ 2 acute dysphagia significantly decreased in week 3-12 with the introduction of SW-RT compared to ST-IMRT ( Table 1 ) and in week 4-12 with oral cavity sparing versus SW-RT. Both SW-RT and OCS-RT subsequently resulted in significant reductions of grade≥2 and grade≥3 dysphagia after radiotherapy up to 12 months post-RT. Patient-rated swallowing problems reduced with the introduction of SW- RT and OCS-RT, with significantly lower dysphagia scores at most time points during RT and post-RT ( Figure 1 ).