Challenges with Target Volume Delineation for Pelvic Rhabdomyosarcoma in the FaR-RMS Trial: A QUARTET Report

Objectives

Radiotherapy Quality Assurance has been implemented for the FaR-RMS trial (EudraCT number 2018-000515-24) through the SIOPE QUARTET Project, including prospective Individual Case Review (ICR) for all randomized patients. A high rejection rate of target volume contours has been observed for pelvic RMS. We have undertaken to identify areas of uncertainty and variation in primary tumour and nodal target volumes.

Methods

All pelvic RMS patients (n=37) in the FaR-RMS trial submitted to QUARTET, up to 19/02/2024, where reviewers assessed primary tumour or nodal contours as unacceptable variations were identified. The ICR forms, submitted contours and plans were then assessed to identify the most common problem areas.

Results

Unacceptable variations were identified in 16/37 (43%) of Pelvic RMS cases, 69% of which were related to target delineation. Unacceptable variations were related to primary clinical target volume (CTVp) in 36% of these cases, whereas 73% had errors in nodal clinical target volume delineation (CTVn). Delineation errors for CTVn concerned geographical miss (70%), inclusion of excess normal tissue within the CTV (10%) or other reasons (20%). Following reviewer feedback and reassessment, 89% of plans, were considered acceptable.

Conclusion

The delineation of clinical target volume in patients with pelvic RMS represents a challenge for radiation oncologists. Prospective review allows early identification of contouring errors and provides feedback to correct these and refine treatment plans. Given the high proportion of nodal target volume delineation errors, QUARTET is developing a nodal target delineation atlas in collaboration with the EpSSG Radiotherapy Committee.