The Usefulness of Apparent Diffusion Coefficient Maps in the Evaluation of Radiation Therapy for Primary Central Nerve System Lymphoma

Abstract

We retrospectively evaluated the usefulness of apparent diffusion coefficient (ADC) maps in the treatment of radiation therapy (RT) for primary central nerve system lymphoma (PCNSL) as an early response indicator. Between January 2012 and January 2015, eight consecutive patients with PCNSL who underwent radiation therapy were assessed. The median age was 73 years, ranging from 49 to 86, and five were males and three females. All patients were histologically confirmed as having diffuse large B-cell lymphoma. A median radiation dose of 45 Gy (45 - 50) in 25 sessions with a daily dose of 1.8 – 2.0 Gy was delivered using 3-D conformal radiation therapy. All patients underwent chemotherapy of a high dose methotrexate before performing RT. To evaluate treatment response, tumors were contoured on the MRI prior to biopsy by one radiologist and one radiation oncologist. ADC histogram parameters were given within the contour. The skewness and kurtosis of ADC in relation to overall survival and progression free survival were assessed among other possible predictive factors, including median values of minimum, maximum, and mode of ADC maps. Median observation time was 5 months (range 1-28 months), and 3 patients were observed over 19 months. One to three months after RT, 2 patients (25%) showed a complete response, 5 patients (63%) showed a partial response and 1 patient (13%) showed no change in tumor size when evaluated using the response evaluation criteria for solid tumors. The median values of minimum, maximum, median, mode, skewness and kurtosis of ADC were 536.5, 2500, 955.5, 1250, 1.03 and 0.75, respectively. The progression-free survival rate was statistically significantly higher in patients who had a higher minimum ADC value (P = 0.017), a lower maximum ADC value (P = 0.017), a lower kurtosis (P = 0.025) and a lower skewness (P = 0.025). No other significant relationship was found in any ADC histogram parameters or overall survival rates. ADC histogram parameters were useful as a biomarker for predicting the outcome of RT for PCNSL.