127 - Reduction in Radiation Dose Based on Chemotherapy Response for Rhabdomyosarcoma: A Report from the Children's Oncology Group Soft Tissue Sarcoma Committee

02:15pm - 02:25pm ET

Room 259

Presenter(s)

Brinda Raghavendra, BS - University of North Carolina School of Medicine, Providence, NC

B. Raghavendra¹, W. Xue², Z. Gao², R. Venkatramani³, S. L. Wolden⁴, and D. L. Casey¹; ¹University of North Carolina, Chapel Hill, NC, ²University of Florida, Gainesville, FL, ³Baylor College of Medicine, Texas Children’s Hospital, Houston, TX, ⁴Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s):

For patients with rhabdomyosarcoma (RMS), it remains unknown whether a reduction in radiation therapy (RT) dose to 36 Gy after a complete response to chemotherapy is equally as effective as the standard 50.4-59.4 Gy dose. In this study, we evaluated local control and survival outcomes based on radiation dose in intermediate-risk RMS patients treated on prospective Children’s Oncology Group (COG) protocols.

Materials/Methods:

This study included all local group III intermediate-risk RMS patients on COG protocols ARST0531 and ARST1431 treated with definitive radiotherapy. Protocol guidelines allowed for a cone-down approach after the initial 36 Gy of radiotherapy to account for chemotherapy response, and if a complete response to chemotherapy was observed at the time of radiation planning, the total dose delivered was 36 Gy.

Patients who underwent delayed primary excision were excluded. In total, 393 patients with intermediate-risk RMS were analyzed. Local failure (LF), event-free survival (EFS), and overall survival (OS) were compared in patients who received a reduced RT dose of 36 Gy after a complete response to chemotherapy compared to those who received a total dose of 50.4-59.4 Gy.

Results:

Median follow up was 5 years. In patients who received 36 Gy (n = 16) vs those who received 50.4-59.4 Gy (n = 377), there was no difference in age, gender, race, ethnicity, histology, or tumor size. Patients treated to 36 Gy after a complete response to chemotherapy were more likely to be fusion positive (p=0.0008), have extremity or orbital primaries (and less likely parameningeal or bladder/prostate primaries, p=0.004), and were more likely to be treated with protons compared to photons (p=0.001). There was no difference in local failure by dose received: 5-year LF 12.5% after 36 Gy vs 25.3% after 50.4-59.4 Gy, p=0.24. EFS and OS were improved in patients who had a complete response to chemotherapy and were treated to 36 Gy compared to those who received 50.4-59.4 Gy (5-year EFS 78.8% vs 57.1%, p=0.07 and 5-year OS 100% vs 68.5%, p=0.017).

Conclusion:

For patients with intermediate-risk RMS, local control was not compromised by a reduction in radiation dose to 36 Gy after a complete response to chemotherapy, and survival outcomes were favorable. These results confirm good outcomes among those who achieve a complete response to chemotherapy at the time of radiation planning, and support continued dose reduction to 36 Gy in this setting with the goal of reducing RT-related late effects and improving quality of life.

Acknowledgements:

NCTN Operations Center Grant U10CA180886, NCTN Statistics & Data Center Grant U10CA180899, & St. Baldrick’s Foundation.