A prospective study to evaluate the role of PET-CT in response evaluation of patients of primary CNS lymphoma

Primary CNS lymphoma comprises 2-3 % of all Non Hodgkin’s Lymphoma [1,2].With standard High dose Methotrexate based regimens the complete response rate is 66% .Primary CNS lymphomas have poor overall outcomes specifically those who failed to attains complete remission with Hd Mtx based regimens. Contrast enhanced Magnetic resonance imaging (MRI) is the standard technique used in the initial evaluation and assessment of the response of the primary central nervous system lymphoma (PCNSL). However it has its own limitations 1. Limitations in interpreting tumour activity after chemotherapy & radiation therapy. 2. Limitations of interpreting the non-enhancing lesion of PCNSL & specifically the Lymphomatosis cerebri. **3.**Contrast enhancement in MRI is due to the altered blood brain barrier which can be due to either tumour or chemo/radiotherapy or surgical procedures which cannot be differentiated.

PET-CT is routinely used in staging and response assessment of systemic lymphoma & it predicts long term outcome of the disease . Interim(midcycle) PET CT have role in modification of therapies in systemic lymphoma. Several studies have analysed the role of PET CT in the initial assessment of PCNSL & their good correlation with MRI [3,4,5] .However, only few studies have analysed the role of PET CT in the response assessment.

This is a study to determine the utility of PET-CT for response evaluation in patients of PCNSL at interim & post treatment completion & its prognostic significance.

In this study patients with diagnosis of PCNSL and receiving standard induction chemotherapy will be included in the analysis. Patients will undergo response assessment with MRI brain (P+ Contract) as per standard practice after 2 cycle & after 4 cycles of induction chemo . For the study purpose, patients will undergo PET-CT after 2 cycles and 4 cycles of induction.

The sensitivity and specificity of PET-CT based response will be calculated with MRI response assessment used as reference standard. Patients will be followed as per routine clinical practice after this and outcomes will be recorded for disease free and overall survival.