```python
from fastapi import FastAPI
import asyncio
import helpers

app = FastAPI()


@app.get("/portfolio")
async def portfolio(symbols: str = ""):
    symbol_list = [s.strip() for s in symbols.split(",") if s.strip()]

    if not symbol_list:
        return {"prices": {}}

    async def fetch_all():
        tasks = [helpers.afetch_price(symbol) for symbol in symbol_list]
        results = await asyncio.gather(*tasks)
        return {symbol: result for symbol, result in zip(symbol_list, results)}

    prices = await fetch_all()
    return {"prices": prices}
```