Response Assessment by PET CT as compared to CECT in childhood Hodgkin Lymphoma can reduce the need for radiotherapy in low and middle income countries

Introduction: The InPOG-HL-15-01, a multi-centric prospective study used a risk-stratified and response-based approach with a doxorubicin, bleomycin, vinblastine and dacarbazine (ABVD) backbone to treat children with newly diagnosed Hodgkin Lymphoma (HL) and reduce the use of radiation therapy (RT). Children/adolescents with bulky disease or inadequate response at early response assessment (ERA) after 2 cycles of chemotherapy were assigned to receive RT. For ERA, positron emission tomography computed tomography (PET-CT) was recommended but not mandatory in view of limited access. This study aimed to compare the impact of using contrast enhanced computed tomography (CECT) vs PET-CT on treatment decisions and outcomes. Methodology: 396 patients were enrolled and 382 had an ERA at the assigned time point. Results: At ERA, satisfactory response was documented in 277/382 (72.5%) participants and this was significantly higher in PET-CT (151/186, 81.2%) as compared to CECT (126/196, 64.3%) respectively (p value<0.001). Amongst the 203 patients with non-bulky disease (wherein the indication for RT was entirely dependent on ERA), 96/114 (84.2%) and 61/89 (68.5%) patients achieved a satisfactory response according to the PET-CT and CECT (p value=0.008) respectively and hence a lesser proportion of patients in the PET-CT arm received RT. Despite a lower usage of RT the 5 year overall survival (OS) of both groups- ERA based on CECT (91.8%) vs PET-CT (94.1%) was comparable (p value=0.391) and so was the 5 year event free survival (EFS) (86.7 vs 85.5%, p value=0.724). Conclusion: Use of PET-CT as the modality for ERA is more likely to indicate a satisfactory response as compared to CECT and thereby decreases the need for RT in response-based treatment algorithm for HL afflicted children. The reduction in the application of RT did not impact the overall outcome and plausibly would lower the risk of delayed toxic effects.