Correlation between Edic vs. Components of the Immune System Using Whole Breast plus Lymph Nodes, Partial Breast, Hypo- and Conventionally Fractionated Prostate Radiation Therapy

Abstract

<h3>Purpose/Objective(s)</h3> To examine the relationship of Equivalent Dose in Circulating Blood (EDIC) (ref 1) to the changes of total lymphocyte counts (TLC), neutrophil counts (NC), IL7, and IL15 for 59 patients treated with 5 fraction partial breast, 25-30 fraction whole breast+lymph nodes, 5 fraction prostate SBRT, and 35-42 fraction prostate IMRT irradiation courses. To evaluate the use of EDIC to predict the immunological consequences of the radiation treatment for the above techniques. <h3>Materials/Methods</h3> The above parameters were measured before starting and after end of treatment (EOT) and after a 3-6 month follow up period (FU) for each patient. EDIC was calculated based on each patient's treatment planning DVHs using the formula and blood circulation data in Ref 1. EDIC and percentage values of immune parameters relative to baseline (TLC%, NC%, IL7% and IL15%) were compared with two-tailed t-tests between groups and time points, and a Spearman Rank test of EDIC vs. these values were calculated. <h3>Results</h3> There was a weakly significant difference between the baseline values of TLC in the short and the long breast courses (p=0.1), but not for the prostate courses. EDIC was correlated with TLC% for the study population as a whole, both at end of treatment (ρ= -0.84) and at follow up (ρ = -0.58). The TLC% at the end of treatment and follow-up was significantly larger for the conventionally-fractionated techniques than for the hypofractionated courses of the same site. EDIC showed strong correlation with %TLC at EOT for all breast and all prostate patients alone (ρ = -0.79, -0.74, respectively). EDIC only weakly correlated with TLC% changes within individual courses due to the limited range of EDIC values in each course. NC%, IL15%, and IL7% were not significant between groups at either time point and did not correlate with EDIC. At follow up, the long prostate course showed faster TLC recovery than the long breast course. Most likely, this is the consequence of the direct lymphocyte killing with the irradiation of the axillary, supraclavicular lymph nodes. Table 1 shows the average EDICs and TLC%s for all groups at the EOT and FU time points in order of increasing EDIC. <h3>Conclusion</h3> EDIC is a potentially useful tool in predicting TLC changes in patients undergoing radiotherapy for breast and prostate cancer, correlating well with TLC changes from baseline regardless of treatment. Our study shows that EDIC could be used to evaluate and compare immunological consequences of different fractionation and dose schemes.