Types of deviation and review criteria in pretreatment central quality control of tumor bed boost in medulloblastoma—an analysis of the German Radiotherapy Quality Control Panel in the SIOP PNET5 MB trial

Purpose In Germany, Austria, and Switzerland, pretreatment radiotherapy quality control (RT-QC) for tumor bed boost (TB) in non-metastatic medulloblastoma (MB) was not mandatory but was recommended for patients enrolled in the SIOP PNET5 MB trial between 2014 and 2018. This individual case review (ICR) analysis aimed to evaluate types of deviations in the initial plan proposals and develop uniform review criteria for TB boost. Patients and methods A total of 78 patients were registered in this trial, of whom a subgroup of 65 patients were available for evaluation of the TB treatment plans. Dose uniformity was evaluated according to the definitions of the protocol. Additional RT-QC criteria for standardized review of target contours were elaborated and data evaluated accordingly. Results Of 65 initial TB plan proposals, 27 (41.5%) revealed deviations of target volume delineation. Deviations according to the dose uniformity criteria were present in 14 (21.5%) TB plans. In 25 (38.5%) cases a modification of the RT plan was recommended. Rejection of the TB plans was rather related to unacceptable target volume delineation than to insufficient dose uniformity. Conclusion In this analysis of pretreatment RT-QC, protocol deviations were present in a high proportion of initial TB plan proposals. These findings emphasize the importance of pretreatment RT-QC in clinical trials for MB. Based on these data, a proposal for RT-QC criteria for tumor bed boost in non-metastatic MB was developed.

GCT-42. CLINICAL CHARACTERISTICS OF LOCALIZED CENTRAL NERVOUS SYSTEM NON-GERMINOMATOUS GERM CELL TUMORS (NGGCT) PATIENTS ENROLLED ON ACNS1123 WITH RELAPSE: A CHILDREN’S ONCOLOGY GROUP (COG) STUDY

ACNS1123 was a Children’s Oncology Group Phase 2 study that was undertaken to determine whether irradiation could be safely reduced without impacting survival in a subgroup of NGGCT patients. Between May 2012-Jan 2017, 107 eligible patients were accrued to Stratum 1 (NGGCT stratum). Sixty-six (61.7%) patients achieved a complete/partial response (CR/PR) to induction chemotherapy and received 30.6Gy whole ventricular field irradiation followed by 54Gy tumor-bed boost achieving a 2-year progression-free survival rate of 89% (95% CI:81%-97%) and overall survival rate of 92% (95% CI:86%- 99%). Eight patients progressed; 6 had a spinal relapse and 2 patients had a local plus spinal relapse. Seven of eight patients had marker elevation at relapse and data was not available in one patient. At diagnosis, location was pineal in six cases, suprasellar in one, and bifocal in one case. Four patients had beta HCGβ and AFP elevation and two each had HCGβ and AFP elevation alone at diagnosis. Only two patients had HCGβ or AFP >1000 (HCGβ 3550 in one patient and AFP of 1340 in another). All eight patients were CR by markers; four had radiographic CR and four had a PR. Five patients had surgery at diagnosis: two had embryonal carcinoma, one germinoma, and two mixed germ cell tumor with malignant elements on histology. A consistent significant risk factor could not be identified to explain excess of spinal failures seen in our cohort.