RT Journal Article SR Electronic T1 Tumor-Absorbed Dose Predicts Progression-Free Survival Following 131I-Tositumomab Radioimmunotherapy JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1047 OP 1053 DO 10.2967/jnumed.113.136044 VO 55 IS 7 A1 Yuni K. Dewaraja A1 Matthew J. Schipper A1 Jincheng Shen A1 Lauren B. Smith A1 Jure Murgic A1 Hatice Savas A1 Ehab Youssef A1 Denise Regan A1 Scott J. Wilderman A1 Peter L. Roberson A1 Mark S. Kaminski A1 Anca M. Avram YR 2014 UL http://jnm.snmjournals.org/content/55/7/1047.abstract AB The study aimed at identifying patient-specific dosimetric and nondosimetric factors predicting outcome of non-Hodgkin lymphoma patients after 131I-tositumomab radioimmunotherapy for potential use in treatment planning. Methods: Tumor-absorbed dose measures were estimated for 130 tumors in 39 relapsed or refractory non-Hodgkin lymphoma patients by coupling SPECT/CT imaging with the Dose Planning Method (DPM) Monte Carlo code. Equivalent biologic effect was calculated to assess the biologic effects of nonuniform absorbed dose including the effects of the unlabeled antibody. Evaluated nondosimetric covariates included histology, presence of bulky disease, and prior treatment history. Tumor level outcome was based on volume shrinkage assessed on follow-up CT. Patient level outcome measures were overall response (OR), complete response (CR), and progression-free survival (PFS), determined from clinical assessments that included PET/CT. Results: The estimated mean tumor-absorbed dose had a median value of 275 cGy (range, 94–711 cGy). A high correlation was observed between tracer-predicted and therapy-delivered mean tumor-absorbed doses (P < 0.001; r = 0.85). In univariate tumor-level analysis, tumor shrinkage correlated significantly with almost all of the evaluated dosimetric factors, including equivalent biologic effect. Regression analysis showed that OR, CR, and PFS were associated with the dosimetric factors and equivalent biologic effect. Both mean tumor-absorbed dose (P = 0.025) and equivalent biologic effect (P = 0.035) were significant predictors of PFS whereas none of the nondosimetric covariates were found to be statistically significant factors affecting PFS. The most important finding of the study was that in Kaplan–Meier curves stratified by mean dose, longer PFS was observed in patients receiving mean tumor-absorbed doses greater than 200 cGy than in those receiving 200 cGy or less (median PFS, 13.6 vs. 1.9 mo for the 2 dose groups; log-rank P < 0.0001). Conclusion: A higher mean tumor-absorbed dose was significantly predictive of improved PFS after 131I-tositumomab radioimmunotherapy. Hence tumor-absorbed dose, which can be estimated before therapy, can potentially be used to design radioimmunotherapy protocols to improve efficacy.