ESTRO 2024 - Abstract Book

S4903

Physics - Quality assurance and auditing

ESTRO 2024

Department of Oncology, Belfast, United Kingdom. 7 The Royal Marsden NHS Foundation Trust, The GI Unit, Sutton, United Kingdom. 8 Leeds Cancer Centre, University of Leeds, Department of Clinical Oncology, Leeds, United Kingdom. 9 Weston Park Cancer Centre, University of Sheffield, Department of Clinical Oncology, Sheffield, United Kingdom. 10 Royal Surrey Cancer Centre, Department of Clinical Oncology, Guildford, United Kingdom. 11 Oxford University Hospital NHS Foundation Trust, Department of Oncology, Oxford, United Kingdom. 12 Iridium Netwerk, University of Antwerp, Department of Radiation Oncology, Wilrijk, Belgium. 13 The Institute of Cancer Research, Clinical Trials and Statistics Unit, London, United Kingdom. 14 University Hospital Zürich, University of Zürich, Department of Radiation Oncology, Zürich, Switzerland

Purpose/Objective:

The CRUK/16/020/EORTC 1702-LCG-ROG HALT trial is a randomised, multi-centre, phase II/III trial which aims to determine whether in patients with driver mutation-positive advanced Non-Small Cell Lung Cancer (NSCLC), the use of stereotactic body radiotherapy (SBRT) to ≤ 5 sites of oligoprogressive disease (OPD) with the continuation of tyrosine kinase inhibitor (TKI) improves progression-free survival (PFS) compared with continuation of TKI alone. Prospective individual case reviews (ICR) were required for all patients prior to treatment initiation This study describes the interim results of ICR for 54 patients accrued into the SBRT arm and assesses the compliance level to the study protocol.

Material/Methods:

Submissions were assessed using the trial RT QA (Radiotherapy Quality Assurance) guidelines and graded as Per Protocol (PP), Acceptable (A) or Unacceptable (UA) for for outlining and planning compliance by the radiotherapy trials quality assurance groups. The dosimetric consequence of contouring inaccuracy was assessed by comparing the protocol-defined dose-constraints for the unacceptable vs. corrected delineations.

Results:

Fifty-four out of the 73 patients randomized to the SBRT arm had their submissions (total submissions including re submissions: n=89) evaluated for this interim analysis (Fig.1). A total of 75 lesions were treated, with the lung being the most common (77%), followed by bone (9%) and liver (6%). The most frequently used schedules were 40 Gy in 8 fractions (n=19) and 45 Gy in 5 fractions (n=19) followed by 52 Gy in 8 fractions (n=12). Protocol compliance for outlining at first submission was as follows: 30 (34%) PP, 33 (37%) A and 22 (25%) UA. Planning compliance at first submission was as follows: 24 (27%) PP, 39 (44%) A, 3 (3%) UA (Fig.1). After corrections, only 2 cases had to be further resubmitted, one for outlining and one for planning failure. All UA variations were corrected prior to treatment initiation. Fifteen out of 22 UA (68%) submissions contained a failed structure delineation within 2 cm of the PTV, three (14%) at the border and three (14%) outside 2 cm (Fig.1). In total 51 structure delineations were deemed unacceptable, of which 27 (53%) were within 2 cm of the PTV. The most frequently failed delineations were for the heart (n=6), great vessels (n=6), target volumes (n=5) and bronchial tree (n=5). The majority of the structures close to the PTV had point dose constraints. Of the 5 unacceptable target volume contours, subsequent correction following the ICR caused a change in PTV coverage between 0 - 46.61% (Table 1). In 52 (58%) submissions, there was mention of compromises