Room: Stars at Night Ballroom 1
Purpose: While patients with locally advanced pancreatic cancer that develop severe treatment related lymphopenia have been shown to have a significantly decreased overall survival, there is no computational model to predict the lymph kill due to radiation therapy treatment. We evaluated lymphocyte reduction from pancreatic cancer radiation treatment as a function of dosimetric data of critical and target organs, time dependence after treatment, and treatment fractionation.
Methods: We analyzed 92 patients who received RT to the pancreas . Blood data for these patients were accessed. The following structures were contoured: superior mesenteric artery, celiac artery, portal vein, inferior vena cava, aorta, liver, stomach, bowel, kidney, spleen, and duodenum. For each patient the maximum, mean, and integral dose to above organs and PTV volume; dose fractionation and treatment technique were recorded . Using the analytical software suite provided by IBM SPSS Statistics, we have analyzed 70 of the above patients to evaluate the order of importance of each parameter to lymphopenia when designing a simulation model.
Results: Lymphocyte drop is maximum at day 35 following initiation of RT, which is about a 79% reduction from Pre-Tx LYA value. Even at day 185, the reduction is 65%. However, if the total dose is less than or equal to 45Gy, lymphocyte drop is less than 0.75x109 cells per L. Lymphocyte drop increases with the number of fractions. There was no significant correlation observed as a factor of PTV volume . The highest Spearman rank correlations were observed for stomach, bowel, and kidney, suggesting the importance of these organs for dose sparing in pancreas radiation.
Conclusion: Lymphocyte changes correlated most strongly with dose to stomach, bowel, and kidney and number of fractions of treatment. Differences in lymphocyte flux in fast moving great vessels compared to relatively stationary gut anatomy might account for these findings.