Presenter(s)
I. Akhionbare1,2, F. Gholami3,4, G. Whitten4, G. M. Walls1,3, C. McGarry3,4, and J. McAleese1,3; 1Department of Clinical Oncology, Cancer Centre Belfast City Hospital, Belfast Health & Social Care Trust, Belfast, United Kingdom, 2Centre for Medical Education, Queen’s University Belfast, Belfast, United Kingdom, 3Johnston Cancer Research Centre, Queen’s University Belfast, Belfast, United Kingdom, 4Radiotherapy Physics, Cancer Centre Belfast City Hospital, Belfast Health & Social Care Trust, Belfast, United Kingdom
Purpose/Objective(s):
Asymptomatic and symptomatic radiation-induced rib fractures (RIRF) are observed in select patients following treatment with stereotactic body radiation therapy (SBRT) for peripheral lung cancer. While patients are counselled regarding the possibility of this side effect, the clinical risk factors associated with a higher risk are not well characterized. This study investigated the relationship between baseline factors and RIRF after lung cancer SBRT at a regional cancer center.
Materials/Methods:
The prospective clinical database of a regional radiotherapy center was interrogated for patients that completed SBRT and at least one follow-up CT thorax. Clinical variables recorded for each patient included gender, age, and dose-fractionation. Rib fractures were manually detected from the reports of response assessment CT thorax studies, which were routinely performed at 6-month intervals for 3 years and annually thereafter, unless symptoms prompted an additional scan. Symptom status was recorded from the documentation of the corresponding outpatient clinical assessments. Asymptomatic RIRF were classified as grade 1, and symptomatic as grade 2. Fine-Gray multivariable analysis was conducted to assess associations between clinical variables and RIRF with adjustment for the competing risk of death.
Results:
Data were available for 600 patients and the median follow-up was 27.5 months. The median age at treatment was 74 years, and 344 patients were female (57.3%). The most common dose fractionations were 54Gy in 3# (103, 17.3%), 55Gy in 5# (397, 66.2%) and 60Gy in 8# (95, 15.8%). RIRF was detected in 51 patients (8.5%), of which 28 were grade 1 and 23 were grade 2. The incidence of RIRF was higher in females (11.6% vs 4.3%). The 4-year cumulative incidence was 9.3% for all fractures (grade =1), and 4.0% for symptomatic fractures (grade =2). On Fine-Gray multivariable analysis, female sex was the only clinical factor associated with RIRF across the whole population (HR 2.83, 95% CI 1.47–5.43, p=0.002). In grade 2 fractures, female sex (HR 3.45, 95% CI 1.19–10.05, p=0.023) and younger age (HR 1.05 95% CI 1.01–1.10, p=0.028) were both associated with RIRF. Fractionation was not significantly associated with symptomatic fractures.
Conclusion:
Female gender was associated with increased risk of RIRF in one of the largest lung SBRT RIRF datasets reported. Potential explanations may include sex-based differential age-related bone mineralisation reductions. That higher age was protective for symptomatic fractures is a hypothesis-generating finding. Consideration of sex may be warranted during the consent process for thoracic SBRT.