The Impact of Surveillance Imaging After Curative Intent Radiotherapy for Limited Stage Follicular Lymphoma

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Approximately 50% of patients treated with curative intent radiotherapy for limited stage follicular lymphoma (FL) will have a lymphoma relapse. The ideal follow-up strategy for detecting relapse is uncertain. The purpose of this study was to evaluate the impact of surveillance imaging (SI) in patients treated with radiotherapy for limited stage follicular lymphoma (FL).Patients with limited stage IA-IIA, grade 1-3A, FL treated with curative intent radiotherapy alone between 2000-2015 were retrospectively reviewed. Relapse detection was categorized into clinical detection (investigations based on signs/symptoms or laboratory abnormalities) or SI detection (radiologic investigations in asymptomatic patients). Survival outcomes were stratified based on method of relapse detection.A total of 330 patients were included with a median follow-up of 8.1 (0.5-20.0) years. All patients received ≥20Gy of involved site radiotherapy (ISRT). 222 (67.3%) patients had SI investigations with a mean of 0.4 (0.1-1.7) per year of follow-up. The most common SI modality used was computed tomography (48.6%). Of all SI investigations (n = 830), 761 (91.7%) showed no evidence of relapse, 49 (5.9%) showed findings of suspected relapse that were that were subsequently found to be false positive, and 20 (2.4%) led to confirmed relapse. The resulting positive predictive value and specificity of SI was 29.0% and 94.0%, respectively. In the follow-up period, 146 (44.2%) patients had a relapse; 126 (86.3%) were detected clinically and 20 (13.7%) were detected with SI. In relapses that were clinically detected (n = 126), 11 (8.7%) were associated with clinically significant patient morbidity, manifesting as deep vein thrombosis (n = 2), pleural effusion (n = 1), biliary duct obstruction (n = 1), renal failure (n = 2), spinal cord or nerve root involvement (n = 4), or symptomatic hypercalcemia (n = 1). The 5- and 10-year overall survival (OS) from the date of diagnosis were 85.6% and 65.2% for clinically detected versus 84.7% and 74.1% for SI detected relapses (P = 0.71). The 5- and 10-year OS from the date of relapse were 70.1% and 50.6% for clinically detected versus 80.2% and 59.4% for SI detected relapses (P = 0.54).This retrospective cohort revealed no significant OS differences between relapse detection by SI versus clinical assessment. The incidence of morbidity was low in relapses that were detected clinically. Only 2.4% of SI investigations led to a confirmed relapse suggesting they may have limited utility in the follow-up of limited stage FL patients treated with curative intent radiotherapy. A prospective analysis of cost-effectiveness and impact of SI on psychological and physical morbidity may help guide clinicians when considering a SI follow-up strategy.