Online

ESTRO 2020

Session Item

Saturday
November 28
10:30 - 11:30
Physics Stream 2
Proffered papers 6: Novel treatment planning strategies
1204
Proffered Papers
Physics
11:20 - 11:30
Quantitative metrics to analyze variations and support best practices in head and neck dose plans
Laura Patricia Kaplan, Denmark
OC-0107

Abstract

Quantitative metrics to analyze variations and support best practices in head and neck dose plans
Authors: Bob Smulders (Rigshospitalet University Hospital of Copenhagen, Department of Oncology, Copenhagen, Denmark), Anne Vestergaard (Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark), Elo Andersen (Herlev University Hospital, Department of Oncology, Herlev, Denmark), Maria Andersen (Aalborg University Hospital, Department of Oncology, Aalborg, Denmark), Ulrik Vindelev Elstrøm (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Jesper Grau Eriksen (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Jeppe Friborg (Rigshospitalet University Hospital of Copenhagen, Department of Oncology, Copenhagen, Denmark), Cai Grau (Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark), Christian Rønn Hansen (Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark), Anne Ivalu Sander Holm (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Kenneth Jensen (Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark), Jørgen Johansen (Rigshospitalet University Hospital of Copenhagen, Department of Oncology, Copenhagen, Denmark), Laura Patricia Kaplan (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Stine Sofia Korreman (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Ebbe Laugaard Lorenzen (Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark), Romain Cyril Marseguerra (Næstved Hospital, Department of Oncology, Næstved, Denmark), Morten Hjartdal Morthorst (Næstved Hospital, Department of Oncology, Næstved, Denmark), Martin Skovmos Nielsen (Aalborg University Hospital, Department of Oncology, Aalborg, Denmark), Morten Nielsen (Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark), Jørgen Breede Baltzer Petersen (Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Eva Samsøe (Herlev University Hospital, Department of Oncology, Herlev, Denmark), Peter Sandegaard Skyt (Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark)
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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 not given equal time and weight by all planners during optimization. Number of fields had no influence.

Figure1Figure2
Conclusion

The national guidelines generally resulted in high plan quality, meeting all clinical constraints. Using the additional quantitative metrics, we saw notable inter-planner variation. . Although plans were not made under strict audit-conditions, this study demonstrates the potential for interplanner variations within clinical acceptability and under a guideline, and methods for quantifying these variations. Systematic application of quantitative metrics during planning should be investigated as a method of supporting dissemination of best practices in treatment planning.