Evolution of Proton Radiotherapy Brainstem Constraints on the Pediatric Proton/Photon Consortium Registry.

Correia, Dora; Indelicato, Daniel J; Paulino, Arnold C; Ermoian, Ralph; Mihalcik, Stephen; Perkins, Stephanie M; Hill-Kayser, Christine; Mangona, Victor S; Lee, Jae; Chang, John Han-Chih; Laack, Nadia N; Kwok, Young; Perentesis, John; Vatner, Ralph; Dave, Ronak; Gallotto, Sara L; Lawell, Miranda P; Bajaj, Benjamin V M; Allison, Keith W; Perry, Alisa; ... (2024). Evolution of Proton Radiotherapy Brainstem Constraints on the Pediatric Proton/Photon Consortium Registry. (In Press). Practical radiation oncology Elsevier 10.1016/j.prro.2024.05.013

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INTRODUCTION

Increasing concern that brainstem toxicity incidence after proton radiotherapy (PRT) might be higher than with photons led to a 2014 XXXX (XX) landmark paper identifying its risk factors and proposing more conservative dose constraints. We evaluated how practice patterns changed among the XXXX (XXXX).

METHODS

This prospective multicenter cohort study gathered data from patients under age 22 enrolled on the XXXX, treated between 2002-2019 for primary posterior fossa brain tumors. After standardizing brainstem contours, we garnered dosimetry data and correlated those meeting the 2014 proton-specific brainstem constraint guidelines by treatment era, histology, and extent of surgical resection.

RESULTS

A total of 467 patients with evaluable PRT plans were reviewed. Median age was 7.1 years (range: <1-21.9), 63.0% (n=296) were male, 76.0% (n=357) were white, and predominant histologies were medulloblastoma (55.0%, n=256) followed by ependymoma (27.0%, n=125). Extent of resection was mainly gross total resection (GTR) (67.0%, n=312), followed by subtotal resection (STR) or biopsy (20.0%, n=92). The XX brainstem constraint metrics most often exceeded were the goal D50% of 52.4 GyRBE (43.3%, n=202) and maximal D50% of 54 GyRBE (12.6%, n=59). The compliance rate increased after the new guidelines (2002-2014: 64.0% vs. 2015-2019: 74.6%, p=0.02), except for ependymoma (46.3% pre vs. 50.0% post guidelines, p=0.86), presenting lower compliance (48.8%) in comparison to medulloblastoma/PNET/pineoblastoma (77.7%), glioma (89.1%), and ATRT (90.9%) (p<0.001). Degree of surgical resection did not affect compliance rates (GTR/NTR 71.0% vs. STR/biopsy 72.8%, p=0.45), even within the ependymoma subset (GTR/NTR 50.5% vs. STR/biopsy 38.1%, p=0.82).

CONCLUSION

Since the publication of the XX guidelines, the pediatric proton community has implemented more conservative brainstem constraints in all patients except those with ependymoma, irrespective of residual disease after surgery. Future work will evaluate if this change in practice is associated with decreased rates of brainstem toxicity.

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