```python
from fastapi import FastAPI, Query
from fastapi.responses import JSONResponse

import helpers  # noqa: F401

app = FastAPI()


@app.get("/portfolio")
async def get_portfolio(symbols: str = Query(..., description="Comma-separated list of symbols")):
    symbol_list = [s.strip() for s in symbols.split(",") if s.strip()]
    # Dispatch all async price fetches concurrently
    prices_list = await asyncio.gather(*(helpers.afetch_price(symbol) for symbol in symbol_list))
    prices_dict = {symbol: price for symbol, price in zip(symbol_list, prices_list)}
    return JSONResponse(content={"prices": prices_dict}, status_code=200)
```