Follow-up Scans After Lutetium-177 (Lu-177) Treatment
After Lu-177 therapy, follow-up imaging should be performed at 1,3,6, and 12 months post-treatment, then yearly thereafter if findings remain stable. 1
Imaging Schedule Based on Treatment Type
For Neuroendocrine Tumors (NETs)
- First year follow-up:
- 1 month after treatment
- 3 months after treatment
- 6 months after treatment
- 12 months after treatment
- Subsequent years: Yearly imaging if findings remain stable 1
For Lu-177 PSMA Therapy (Prostate Cancer)
- Complete blood count every 2-4 weeks after treatment
- Renal and liver function tests before subsequent treatment cycles
- Whole-body imaging following each cycle to document radiopharmaceutical distribution 1
- PSA monitoring at 6 weeks after each cycle 2
Types of Follow-up Scans
Functional Imaging:
Anatomical Imaging:
- CT or MRI to evaluate anatomical response
- Particularly important for measuring tumor size changes according to RECIST criteria 3
Post-therapy Scans:
- Whole-body imaging immediately following each treatment cycle to document radiopharmaceutical distribution 1
Special Considerations
Long-term Follow-up
- After the first year, if no abnormalities are detected, imaging can be performed yearly until the fifth post-treatment year 1
- If imaging remains stable for 2 years, intervals between scans may be extended to every 2-3 years in low-risk patients 4
Monitoring for Toxicity
- Regular blood tests (complete blood count, renal and liver function) every 8-12 weeks for the first 12 months 1
- Special attention to renal function as Lu-177 is primarily eliminated through the kidneys 1, 5
Response Assessment
- Evaluate both biochemical markers (e.g., chromogranin A for NETs, PSA for prostate cancer) and imaging findings 2
- PSA response after the first cycle has prognostic significance for overall survival in prostate cancer patients 2
Retreatment Considerations
If disease progression occurs after initial Lu-177 therapy:
- Retreatment can be considered after a minimum interval of 6 months following completion of initial treatment 1, 3
- Retreatment typically consists of 1-2 additional cycles 1
- Before retreatment, a new baseline functional imaging scan (Ga-68 PET/CT) should be performed to confirm receptor expression 3
Pitfalls and Caveats
- Radiation Exposure: Consider using MRI instead of CT after the first year to reduce cumulative radiation exposure when frequent controls are required 4
- Pseudoprogression: Transient increase in tumor size or appearance of new lesions may occur due to inflammatory response rather than true progression
- Variable Response Patterns: Some patients who don't respond after the first cycle may become responders after completing all planned cycles (approximately 20% of cases) 2
- Kidney Monitoring: Special attention to renal function is needed as kidneys are dose-limiting organs, though cross-dose radiation to kidneys is generally low (<2% in most cases) 5
Following this systematic approach to post-Lu-177 treatment imaging ensures optimal monitoring of treatment response, early detection of disease progression, and timely identification of potential treatment-related toxicities.