## **Core Concept**
Wilms tumor, also known as nephroblastoma, is a type of kidney cancer that primarily affects children. The treatment of Wilms tumor is multimodal, involving surgery, chemotherapy, and sometimes radiotherapy. Radiotherapy is considered for tumors that are of a higher stage or have a high risk of recurrence.

## **Why the Correct Answer is Right**
The correct timing of radiotherapy for Wilms tumor after surgery is generally within 10 days. Early initiation of radiotherapy is crucial because it helps in reducing the risk of local recurrence, especially in cases with positive margins, high-stage disease, or certain histological features that indicate a higher risk of recurrence. Delaying radiotherapy could potentially allow microscopic disease to progress, making it more challenging to control.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a delay that might be too long for the optimal effect of radiotherapy in preventing recurrence in Wilms tumor.
- **Option B:** Similarly, this option also suggests a delay that could be detrimental in the context of managing Wilms tumor, especially in high-risk cases.
- **Option D:** Suggesting radiotherapy before surgery might not always be feasible or necessary, as the initial approach often involves surgical intervention to debulk the tumor.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the management of Wilms tumor is highly stage-dependent and involves a multidisciplinary approach. For most cases, especially those with a higher stage or certain adverse features, radiotherapy is recommended to start within 10 days post-operatively to minimize the risk of local recurrence.

## **Correct Answer:** . Within 10 days