Its so funny how willing to talk about moonlighting different fields are. In my experience Radiation Oncology is definitely a little hush hush about it, which is a tad odd.
Moonlighting will be of varying importance to different applicants, for me it was pretty important. Not one of my top criteria, but definitely something I actively considered and used a tie breaker a few times on my rank list. I have a family with children and so the first few years of residency will be very tight financially without a little bit of moonlighting.
Of the nearly 20 places I interviewed at maybe half allowed moonlighting, 5 strictly forbid it and the other 5 were on the fence, ie "We used to do it but that was so long ago I'm not sure if its still allowed."
First, as a Rad Onc resident if you apply for and obtain your own independent license you are absolutely legally allowed to moonlight. However, most hospitals require you to obtain permission from your PD before starting. So really, its the PD who will ultimately decide if you are allowed to moonlight in your program.
So, once you have your own license and your PD is on board with you moonlighting the next two things are where and for how many hours. Moonlighting hours count towards the 80 hour limit put in place by the ACGME. Which is one of the reasons why the rad onc work schedule allows for moonlighting.
As far as the types of moonlighting, you mentioned IM, but generally thats not where residents mooonlight. All the residents I know generally moonlight in one of three places: Emergency room, urgent care or radiology contrast center. Depending on your comfort level, you can choose which of those is the most appealing. Malpractice insurance is very important, but many steady moonlight gigs will provide it. If they don't, however, then you will be responsible for purchasing your own insurance.
One consideration to remember is that taxes generally aren't taken out when you are paid as a contractor for moonlighting. I've been told to set aside 40% of what you earn for taxes. So as you weigh whether its worth your time investment, take whatever hourly rate you think you'll earn (Varies VERY widely by where you are in the country, i've heard as low as $50 to as high as $150) and account for taxes. If you have a family with many mouths to feed, then it may be worth it. Most single rad onc residents can live comfortably on their stipends and value free time over more money and so choose not to moonlight, which is likely what I would do if I was single.
Lastly, if you want to find out who allows moonlighting, the only way to really find out is during your interview day. The best people to ask are the current residents. Either on the tour, dinner, lunch or visiting time just casually ask if any of the residents have done any moonlighting.
I wouldn't use moonlighting as a means of determining if Rad Onc is the right field for you, or even to limit which programs you apply to (apply to them all). However, if it is important to you, a good mix of programs you end up interviewing at will likely allow moonlighting and you can prioritize that however you'd like come rank list time. Good luck!
