My experience is that differences in pressure can affect the swelling and that compression garments and massage can help to control it.
In my case the swelling appeared right after a flight two months after radiation. A change of pressure can provoke the onset of lymphedema as you can see in the following link:
http://www.lymphnet.org/pdfDocs/nlnairtravel.pdf
With the help of a compression garment and some physical therapy (lymphatic drainage masage) I was able to reduce it, but it is still there 5 months after the end of radiation.
I have flown a few times since this first flight and have worn the mask in all cases. After the flights there was no increased swelling.
I am a ski freak and as part of my revalidation, I went skiing for a few days. I wore the compression mask at all times in the slopes, but nevertheless the swelling increased very significantly. Probably this was due to the fast changes of pressure going up in the cable-car. After one week back home, the swelling went back to what it was before the vacation.
If you need further information or details do not hesitate to send me a message.
Cheers,
Jos