1085 - A Phase II Single-arm Study of Total Body Irradiation With Linac Based Volumetric Modulated Arc Therapy (VMAT) Total Body Irradiation (TBI)

05:10pm - 05:15pm ET

Room 162

Presenter(s)

Fauzia Shaikh, MD - NYU Langone Health- Radiation Oncology, New York, NY

F. Shaikh¹, J. R. Teruel², B. Levinson³, J. Xiao¹, J. A. Goldberg³, M. Abdul-Hay⁴, P. Galavis², B. T. Cooper¹, and N. K. Gerber¹; ¹Department of Radiation Oncology, NYU Grossman School of Medicine, New York, NY, ²Department of Radiation Oncology, NYU Langone Health, New York, NY, ³Department of Population Health, NYU Grossman School of Medicine, New York, NY, ⁴NYU Grossman School of Medicine, New York, NY

Purpose/Objective(s):

To report dosimetric and clinical outcomes and toxicity of myeloablative Volumetric Modulated Arc Therapy (VMAT) Total Body Irradiation (TBI) as a conditioning regimen prior to allogeneic stem cell transplant.

Materials/Methods:

This is an open label phase II trial in which eligible patients were treated with linac based VMAT TBI as part of their conditioning regimen for transplantation. Eligible patients included bone marrow transplant candidates at least 10 years old, receiving a myeloablative radiation conditioning regimen with a TBI dose of 12Gy or higher, and with no prior history of thoracic radiation. VMAT TBI was planned using an automated approach for a multiple isocenter plan using Eclipse scripting. The primary endpoint was meeting specified dosimetric endpoints for coverage and lung sparing, the secondary endpoints were overall survival, event free survival and cumulative incidence rate of radiation pneumonitis. Planned sample size for this study was initially 25 patients and was expanded to 35 patients in a protocol amendment. With 35 patients, if the true success rate is = 85%, the lower edge of the exact Clopper Pearson one-sided 95% confidence interval will be = 68.9%.

Results:

The present study enrolled 35 patients, of whom 33 patients were treated with TBI according to protocol. Two patients did not undergo TBI treatment as the plan for transplant was cancelled. The median follow-up was 37.4 months, with 95% confidence interval (CI) of 29.9 – 47.0. Median age was 37 years old (range 14-60). All patients had acute lymphoblastic leukemia (ALL), 79% with B-cell ALL, 21% with T-cell ALL. The mean percent of the planning target volume (PTV) getting 100% of the prescribed dose was 92.6%, (95% CI 92.1-93.2) with all patients achieving the goal coverage of 90%. The mean lung dose (MLD) was 743.2 cGy (95% CI 734.8-751.6), with all patients achieving the goal MLD < 900 cGy.

The overall survival (OS) rate at 1 year was 93.9% (95% CI 86.1 - 100) and the event free survival (EFS) rate at 1 year was 90.9% (95% CI 81.6 - 100). Median OS and EFS were not reached. The cumulative incidence rate of radiation pneumonitis of any grade at 1 year was 18.2% (95% CI 8.7 - 38.0). Three patients (9.1%) experienced grade 3 or higher pneumonitis. There were two cases (6.1%) of treatment related mortality attributed to sepsis in which radiation pneumonitis may have played a role.

Conclusion:

VMAT TBI conditioning prior to allogeneic stem cell transplant was well tolerated and achieved dosimetric endpoints, with excellent disease control and acceptable toxicity profile.