ESTRO 2023

Session Item

Sunday

May 14

15:15 - 16:15

Business Suite 3-4

QA and auditing

Chair: , Belgium

Session Type: Poster Discussion

Track: Physics

Journey:

Final analysis of the benchmark case RTQA procedure for the EORTC 1420 ‘Best of’ trial (NCT02984410)

Daniel Portik, The Netherlands

Presentation Number: PD-0577

Abstract

Abstract Title:

Final analysis of the benchmark case RTQA procedure for the EORTC 1420 ‘Best of’ trial (NCT02984410)

Authors:

Daniel Portik¹, Enrico Clementel¹, Coreen Corning¹, Ridwan Oyebayo Olaniran², Joanna Kazmierska³, Esat Mahmut Ozsahin⁴, Warren Grant⁵, Milan Tomsej⁶, Laure Vieillevigne⁷, Christian Simon⁸, Vincent Gregoire⁹, Nick Reynaert¹⁰, Nicolaus Andratschke¹¹

¹European Organisation for Research and Treatment of Cancer (EORTC) Headquarters, RTQA, Brussels, Belgium; ²European Organisation for Research and Treatment of Cancer (EORTC) Headquarters, Statistics, Brussels, Belgium; ³Greater Poland Cancer Center, Radiotherapy, Poznan, Poland; ⁴Centre Hospitalier Universitaire Vaudois (CHUV), Radiation Oncology, Lausanne, Switzerland; ⁵Gloucestershire Hospitals NHS Foundation Trust, Radiotherapy, Gloucester, United Kingdom; ⁶Centre de Radiothérapie du Hainaut, Radiotherapy, Charleroi, Belgium; ⁷Institut Claudius Regaud (ICR), Institut Universitaire du Cancer de Toulouse-Oncopole (IUCT-O), Medical Physics, Toulouse, France; ⁸Centre Hospitalier Universitaire Vaudois (CHUV), Otolaryngology - Head and Neck Surgery, Lausanne, Switzerland; ⁹Centre Léon Bérard, Radiation Oncology, Lyon, France; ¹⁰Institut Jules Bordet, Radiophysics and MRI Physics Laboratory, EORTC RTQA Chair, Brussels, Belgium; ¹¹University Hospital Zürich, Radiation Oncology, EORTC RTQA Chair, Zürich, Switzerland

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Purpose or Objective

The EORTC 1420 ‘Best of’ trial aims to assess swallowing function after trans-oral surgery versus radiotherapy in head and neck cancer (RT). RT participating sites had to complete a benchmark case (BC) procedure by delineating and planning a specific patient case according to study protocol. Our objective was to analyse interobserver variability (IOV) in contouring and planning in the complete BC dataset.

Material and Methods

A total of 43 sites participated in the BC procedure. Each site’s treatment plan was sent for expert review for protocol compliance and approval. For each site, the submitted structure set (Sub-SS) was compared to a set of gold standard structures (GS-SS) created by consensus between the RTQA experts. IOV was evaluated by measuring mean conformity index (CI) and maximum Hausdorff Distance (HD) between Sub-SS and GS-SS. Dose-volume parameters for targets and OAR were extracted from the approved plan using both Sub-SS and GS-SS and compared.

Results

Forty-two of the 43 sites (97.67%) completed the procedure. Due to delineations 32 sites had to resubmit Sub-SS at least once before approval, while only 9 had to resubmit RT plans. Lowest CI indexes and highest HD were measured in OAR not usually delineated, such as the swallowing structures (Fig. 1). Sites successfully created acceptable target volumes coverages, only 5/42 sites having minor deviations attributable to treatment planning system differences.

The OAR most affected by delineation IOV, when applying site doses to GS-SS, were the Brainstem PRV and Cervical Esophagus where we observed a dose difference of >4 Gy (Table 1). While within OAR protocol limits, this variation resulted in unacceptable PTV coverages with GS-SS (6/42 sites).

Organs at Risk/Target Volumes	Mean Dose (Gy)	Mean dGS*** (Gy)	Mean diff.
Brainstem PRV	18.37	26.88	-8.51
Brainstem	13.64	16.51	-2.87
Cervical Esophagus	14.35	18.51	-4.16
Parotid Left	5.24	5.25	-0.01
Parotid Right	24.34	24.63	-0.30
CPI*	51.83	48.17	3.65
Submandibular Left	7.50	8.18	-0.68
Submandibular Right	55.31	54.94	0.38
Oral Cavity - PTV	27.05	29.08	-2.03
Larynx	22.12	22.04	-1.08
Mandible	65.93	66.16	-0.24
PCM**	33.42	33.20	0.22
Spinal Cord PRV	35.1	38.56	-3.45
Thyroid	22.72	23.35	-0.63
Prophylactic PTV	98.05	94.64	3.41
Therapeutic PTV	97.97	95.11	2.86

*CPI - Cricoid pharyngeal Inlet; **PCM - pharyngeal constrictor muscles; *** dGS – doses from submitted RT plans applied to GS-SS

Conclusion

Our analysis highlights that delineations remain the major cause of BC rejection. Especially delineation of newly introduced OAR or target volumes were responsible for unacceptable variations. Although protocol compliant OAR doses were achieved, significant PTV dose trade-offs were observed and could be corrected. This underlines the need for individual case review, as further improvement in dose distribution can be achieved beyond protocol compliance.