Pediatric Cancer

PV QA 3 - Poster Viewing Q&A 3

TU_23_3100 - Reduced-Volume Tumor Bed Boost is Not Associated with Inferior Local Control and Survival Outcomes in High-Risk Medulloblastoma

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

Reduced-Volume Tumor Bed Boost is Not Associated with Inferior Local Control and Survival Outcomes in High-Risk Medulloblastoma
L. J. Sudmeier1, S. Tian2, C. Zhang3, N. A. Madden4, Z. S. Buchwald1, B. R. Eaton1, H. K. G. Shu1, I. R. Crocker1, W. J. Curran Jr1, and N. Esiashvili1; 1Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA, 2Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, 3Department of Biostatistics and Bioinformatics Shared Resource, Winship Cancer Institute of Emory University, Atlanta, GA, 4Department of Radiation Oncology, Winship Cancer Institute, Emory University, Atlanta, GA

Purpose/Objective(s): Medulloblastoma is the most common pediatric embryonal tumor. Reduced-dose craniospinal irradiation (CSI) with boost to the tumor bed (TB) has been prospectively evaluated for average-risk patients. For patient with high-risk (HR) disease, the role of limiting boost target volumes in the posterior fossa (PF) to the TB is not well-established. Radiotherapy boost to the entire PF remains the standard of care. We aimed to examine the patterns of failure by boost technique in an exclusively high-risk population.

Materials/Methods: Single institution records for patients with HR medulloblastoma, as defined by the presence of metastatic disease, >1.5cm2 residual disease, or anaplasia, were reviewed. The neuraxis was treated to median dose of 36Gy (range 23.4-45Gy), with boost dose of 54-55.8Gy; boost to additional sites of disease outside of the posterior fossa was at discretion of the treating physician. Anatomically-modified 1cm CTV margins and 3-5mm PTV margins were used in the TB cohort. Marginal failures were those located between 80% to 95% isodose lines. Predictors of local (posterior fossa) control and survival endpoints were analyzed in the univariate setting. Kaplan-Meier methods and Cox proportional hazards were used to assess the impact of radiation boost technique on local control (LC).

Results: 32 patients with HR medulloblastoma were treated with CSI between November 1990 and October 2015, with median follow-up length of 5.12 years (range 0.1-27, IQR 2.6-7.1 years). 22 patients received a boost to the PF, 10 patients received TB boost. The median age at diagnosis was 6.7 years; 65.6% of patients had M+ disease, 43.8% with sub-total resection, and 46.9% had anaplasia. 14 patients had progressive disease (PD) after radiotherapy; 11 patients had a local failure (LF) within the PF (7 in PF group, 4 in TB group). The pattern of failure for the TB group: 1 outside TB, 2 within TB, 1 marginal, 1 isolated LF. The pattern of failure for the PF group: 6 in PF, 1 marginal, 2 isolated LF. Use of TB boost was not associated with inferior LC (HR 0.86, log-rank p = 0.81), progression-free survival (PFS) [HR 1.20, p=0.76] or overall survival (OS) [HR 1.40, p=0.56] in comparison to PF boost. LC rates were 80% vs 88.9% at 12 months, 70% vs 83.3% at 2 years, and 60% vs 64.1% at 3 years (TB vs PF). Pre-radiation PD was linked to inferior LC (HR 17.9, p <0.001) and PFS (HR 33.7, p<0.001), as well as greater risk of distant metastasis (HR 26.81, p<0.001) and worse OS (HR 11, p<0.001). The use of TB boost volume trended towards reduced mean cochlea dose (45.9 vs 50Gy, p=0.06), with an approximately 30% reduction in boost PTV volume (203 vs 299 cm3, p=0.01).

Conclusion: Reduced-volume radiotherapy boost to the tumor bed does not appear to compromise local control or survival outcomes in patients with high-risk medulloblastoma and may reduce the risk of ototoxicity; this requires prospective evaluation.

Author Disclosure: L.J. Sudmeier: None. S. Tian: None. C. Zhang: None. N.A. Madden: None. B.R. Eaton: None. H. Shu: Honoraria; Varian Medical Systems. Speaker's Bureau; Varian Medical Systems. Travel Expenses; Varian Medical Systems. Stock; Medtronics, Apple. Chairman; QIN CTTDWG. Co-Chairman; NCI-QIRT Working Group. I.R. Crocker: None. W.J. Curran: Board Member; ASCO.

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