Edit in JSFiddle

var app = new Vue({
  el: "#app",
  data: {
    radius: 50
  }
});

              
<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset='utf-8'>
    <title>Vue App</title>
</head>
<body>
<div id="app">
  <svg xmlns="http://www.w3.org/2000/svg" version="1.1">
    <circle cx="100" cy="75" v-bind:r="radius" fill="lightpink" />
  </svg>
  <input type="range" min="0" max="100" v-model="radius">
</div>
<script src="https://cdn.jsdelivr.net/npm/vue@2.5.13/dist/vue.js"></script>
<script></script>
</body>
</html>