Endocrine Abstracts

Background: A small portion (11%) of radioactive decay of 177Lu involves the emission of gamma photons, allowing for post-treatment imaging. Despite this capability, most centers do not routinely conduct post-treatment imaging. It is not well recognized that qualitative findings from post-PRRT imaging can influence clinical management. The aim of this study was to evaluate the rate of change in management from post treatment imaging.

Methods: 100 patients who received 177Lu-DOTATATE for metastatic well-differentiated NETs at our institution between 2016 and 2021 retrospectively analyzed. Included patients received minimum two cycles & underwent 24-hour post-therapy SPECT/CT imaging after each cycle. Scans were compared to baseline post-cycle 1 images to assess response, divided into four groups: 1: Marked reduction in tumor volume; 2: Reduction but with residual disease; 3: Stable disease; 4: Development of new SSTR positive lesions. Changes in management, were grouped into major and minor. Major: PRRT stopped due to progressION, stopped due to marked response, delayed for targeted treatment of new/growing lesion, and stopped due to lab values. Minor: PRRT continued despite of borderline low/low lab value, characterization of pseudoprogression, and hydronephrosis noted leading to stent placement.

Results: 100 patients were analyzed. 84% had GEP NET (bronchial 6%, others 10%). 36% were Grade 1, 58% were Grade 2 & 6% were Grade 3. 64% received four cycles, 21% received three cycles and 15% received two cycles. Most patients (78% in post-cycle 2, 78.8% in post-cycle 3, and 73.4% in post-cycle 4 images) exhibited qualitatively stable disease on SPECT/CT over the course of PRRT. Post-therapy SPECT/CT resulted in a change in management in 27%. In 77% of those cases, post-therapy imaging led to major changes. Patients with a higher tumor grade had a higher proportion of change in management. However, no significant relationship was noted between the tumor grade and the impact on management.Table 1: Break down of change in management by Grade in patients with NETs that underwent post therapy SPECT imaging.

Conclusion: In a considerable proportion of patients (27%), post-treatment SPECT/CT imaging resulted in a change in management. The rate of change was higher in patients with higher-grade tumors. Although post-treatment imaging is typically discussed in the setting of dosimetry, qualitative impact of post-treatment imaging is common.

Abstract ID 23467