Repeat Imaging Timing for Metastatic Wilms Tumor on SIOP Preoperative Chemotherapy
Repeat imaging should be performed after every 2 cycles of preoperative chemotherapy to assess tumor response and determine surgical candidacy. 1
Imaging Schedule and Modalities
Standard Response Assessment Protocol
Clinical and radiological response evaluation is mandatory after every 2 cycles of chemotherapy to avoid delaying surgery in non-responding disease and to assess for maximal tumor response, which typically occurs after 6-12 months of preoperative treatment. 1
Chest CT with thin cuts (approximately 1 cm slice thickness) is required to evaluate pulmonary metastases, with complete or near-complete resolution needed before proceeding to surgery. 1
MRI is the preferred imaging modality for evaluating the primary renal tumor response, particularly when considering nephron-sparing surgery, as it provides superior soft tissue characterization and assessment of bilateral disease. 1
Critical Timing Considerations
The mean duration of preoperative chemotherapy in SIOP protocols is approximately 80 days (range 47-89 days), with 77% of patients operated before the third month of preoperative chemotherapy when using a tailored approach based on tumor response. 2
Early tumor response assessment is mandatory to prevent unnecessary delays in surgery for patients with non-responding disease. 1
Response Assessment Criteria
Imaging-Based Evaluation
Radiographic response does not equal pathologic response: 25-40% of patients with complete radiological response harbor viable tumor at resection, and 10-75% of partial responders have no tumor at final pathology. 1
Current imaging modalities have limited sensitivity and may misclassify patients, underscoring the need for surgical resection even with apparent complete radiographic response. 1
Surgical Candidacy Criteria After Imaging
The following must be documented on repeat imaging before proceeding to surgery:
Tumor must be resectable with clear surgical margins achievable, with adequate vascular assessment showing no prohibitive vascular encasement. 1
Patient must have good performance status to tolerate surgery, with no evidence of progressive disease elsewhere during chemotherapy. 1
Limited, resectable metastatic burden must remain after chemotherapy. 1
Common Pitfalls to Avoid
Do not rely solely on radiographic complete response to defer surgery, as a significant proportion of these patients have viable tumor requiring resection. 1
Do not delay imaging assessments beyond every 2 cycles, as this may result in prolonged chemotherapy for non-responding tumors that should proceed directly to surgery. 1
Ensure chest CT has adequate thin cuts (approximately 1 cm slice thickness) rather than standard chest imaging, as small pulmonary nodules may be missed with thicker slices. 1
Additional Surveillance Considerations
For patients with genetic predisposition syndromes (WT1, Beckwith-Wiedemann, DICER1), renal ultrasound surveillance every 3 months until age 7-8 years is required for the contralateral kidney and family members. 3, 4
Abdominal ultrasound at 3 months after therapy completion should be considered if there is clinical concern for residual disease. 5