Pediatric Cancer

PV QA 3 - Poster Viewing Q&A 3

TU_23_3095 - Primary Site Irradiation using Proton Therapy in Young Children with Medulloblastoma

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Primary Site Irradiation using Proton Therapy in Young Children with Medulloblastoma
A. S. Grewal1, Y. Li2, M. J. Fisher2, J. Minturn2, J. Belasco2, P. Phillips2, T. Kang2, R. A. Lustig1, and C. E. Hill-Kayser1; 1Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 2Children's Hospital of Philadelphia, Philadelphia, PA

Purpose/Objective(s): Radiotherapy is often deferred in very young children with medulloblastoma, with use of more intense chemotherapy and stem cell rescue regimens; however, posterior fossa (PF) radiation has been shown to improve overall survival and event free survival compared to adjuvant chemotherapy alone. The role of primary site irradiation (PSI) to the tumor bed compared to conformal PF radiation remains unknown; PSI performed with proton therapy provides significant sparing of normal brain compared to X-ray based PF radiotherapy. This study was performed to assess the overall survival, recurrence free survival, patterns of failure, and clinical toxicity for children aged 5 and under who received PSI using proton therapy.

Materials/Methods: From 2010 to 2017, 14 patients with newly diagnosed medulloblastoma treated at one institution received primary site irradiation to the tumor bed alone after detailed discussion regarding treatment options. All patients received surgery upfront, followed by chemotherapy and radiation therapy. Median age was 3 years (range, 1-5 years), and the male to female ratio was 1:1. Primary site radiation doses ranged from 50.4Gy to 54Gy.

Results: With a median follow-up of 54 months, four patients have relapsed: three within the CNS outside of the posterior fossa, and one within the tumor bed after subtotal resection. All relapses occurred within 28 months after the completion of radiation therapy. Seven-year overall survival and recurrence free survival for this cohort of patients were 86% and 71%, respectively. All 14 patients received proton beam therapy, utilizing either double scatter or pencil beam scanning planning depending on treatment era. Target volumes included tumor bed and residual disease with a 1 cm margin, and additional margin for set-up error and internal motion. The median maximum dose and D50% received by the brainstem were 55.2Gy (range, 40.6-56.4Gy) and 48.2 Gy (range, 4.3-55.5Gy), respectively. Median maximum dose to the cochlea and D50% to the temporal lobes were 12.2Gy (range, 0.01-54.4Gy) and 0.47Gy (0.02-19.4Gy), respectively. One patient experienced significant tumor regrowth within 10 months of completion of radiation, autopsy showed live tumor and necrosis near and within the brainstem, with relation to radiation unknown; however, no other clinical toxicities were observed in this group of patients.

Conclusion: Primary site irradiation to tumor bed in young children allows for significant sparing of brain tissue from radiation. Rates of overall survival and relapse free survival in this series are similar to those reported when the entire posterior fossa is treated in older children and higher than those reported in series of younger children treated with chemotherapy alone. No definitive clinical toxicities were seen in these patients. This approach should be further investigated in young children with medulloblastoma.

Author Disclosure: A.S. Grewal: None. Y. Li: None. J. Minturn: None. T. Kang: None. C.E. Hill-Kayser: Employee; University of Pennsylvania.

Amardeep Grewal, MD

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