```python
from fastapi import FastAPI, Query
from typing import Dict
import asyncio

import helpers  # noqa: F401  (the provided API)

app = FastAPI()


@app.get("/portfolio")
async def get_portfolio(symbols: str = Query(...)):
    # Split comma-separated symbols, strip spaces, filter out blanks
    symbol_list = [s.strip() for s in symbols.split(",") if s.strip()]
    # Fire async calls concurrently
    prices = await asyncio.gather(*(helpers.afetch_price(s) for s in symbol_list))
    return {"prices": dict(zip(symbol_list, prices))}
```