3384 - Lost in Lunglation: Unraveling the Mystery of Idiopathic Pulmonary Syndrome Post-Total Body Irradiation for Bone Marrow Transplant

R. Jin¹, I. Baharmand¹, M. Chan^2,3, J. Chan^2,4, A. C. Lo^2,4, Y. Abou Mourad^5,6, C. R. Duzenli^4,7, and J. Oh^3,4; ¹MD Undergraduate Program, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, ²Department of Radiation Oncology, British Columbia Cancer, Vancouver, BC, Canada, ³Department of Radiation Oncology, BC Cancer, Vancouver, BC, Canada, ⁴Division of Radiation Oncology, Department of Surgery, University of British Columbia, Vancouver, BC, Canada, ⁵British Columbia Cancer Agency, Vancouver, BC, Canada, ⁶Division of Hematology, Department of Medicine, University of British Columbia, Vancouver, BC, Canada, ⁷Department of Medical Physics, British Columbia Cancer Agency, Vancouver, BC, Canada

Purpose/Objective(s): Total body irradiation (TBI) is often used as part of myeloablative conditioning prior to allogeneic hematopoietic stem cell transplantation (HPSCT) for high risk, relapsed, or refractory hematologic malignancies. Recent trials have demonstrated improved relapse free survival and potential overall survival (OS) with TBI conditioning. However, TBI is associated with significant treatment-related morbidity and a 25-50% non-relapse mortality risk. Pulmonary toxicity (PT) is a common, debilitating complication of TBI and includes infectious pneumonia, diffuse alveolar hemorrhage, and interstitial pneumonitis. Distinguishing direct radiation-related PT from infection-related cases poses a challenge due to PT’s multifactorial nature. Recently, the term idiopathic pulmonary syndrome (IPS) - widespread alveolar injury without cardiogenic or infectious causes - has emerged as a term for treatment-related PT. Our study aimed to determine clinical factors and radiation metrics contributing to PT versus IPS in adult patients post-TBI for HPSCT. Materials/

Methods: Retrospective analysis of adult patients treated at our facility with TBI prior to allogeneic HPSCT from 2015 to 2022 was performed. Patient demographics, disease information and treatment related factors (including TBI and lung dose) were collected. Outcomes reported included OS and pre-/post-transplant pulmonary function testing. Clinical notes and chest imaging were also reviewed for PT and IPS within and post-100 days of HPSCT. Univariate and multivariate analysis with Cox regression was performed to assess factors associated with PT and IPS. Actuarial survival and incidence of PT and IPS was calculated using the Kaplan-Meier method and compared via log-rank test.
Results: 124 adult patients (=18 years old) were identified (median age: 36.5 years). Preliminary analyses on 63 patients (51% of total) have been performed. Radiation was delivered uniformly at 75-100 cGy/field with parallel opposed pairs using Cobalt-60, with resulting dose ranging 4.9-14.1 cGy per minute. Acute Lymphoid Leukemia was the most common diagnosis (29/63, 46%), and OS was 55.4 months (SD: 5.7 months). Incidence of post-transplant infections was high (54/63, 85.7%) with 29 of these being bloodstream infections (29/54, 53.7%). Importantly, the incidence of PT within 100 days was in keeping with previous studies (25/63, 39.7%), of which 2 were IPS. After the 100-day mark, cumulative incidence of PT was higher (28/49, 57.1%), with 5 cases of IPS.
Conclusion: Our preliminary results (63 out of 124 adult patients) demonstrated PT rates in keeping with previous studies. The incidence of IPS observed has been low thus far, limiting our current assessment of clinical/functional significance on the included patients. However, final results including clinical and treatment factors associated with IPS will be reported at ASTRO ASM 2024 pending abstract acceptance.