I've been through Pluvicto and am in the process of repeating the treatments. The guidelines say stay 3 feet or more away for the first 3 days, for extended periods of time. My recommendation is to have him sit in the back on the passenger side, opposite the driver . Moisture, when exhaled will be radioactive (as is urine, sweat, etc). Keep the heater/air conditioning FAN on medium or higher. This will bring in the most outside air, maintaing positive pressure inside the car, which forces the air out through the louvers in the back (trunk). DO NOT use the recirculation setting. You want all fresh outside air. Depending on the weather, a partially open window would be helpful to get rid of the contaminated air.
While in the hospital, watch the medical staff. It's not as scary as you might think, but definitely follow the guidelines.