TOKYO, April 20 : The dollar headed for its highest level in a week at the start of Asian trading on Monday as renewed tensions in the Middle East sent investors scurrying for safe havens. The dollar index, which measures the greenback's strength against a basket of six currencies, climbed as much as 0.3 per cent to reach 98.485, its highest level since April 13. This reversed a selloff that saw the currency fall to its lowest levels since the start of the war on Friday as hopes for a peace