For now xrt improvements are being made in dose conformity and treatment localization via imaging (ultrasound, xray,pet/ct). For example, in the 90s a prostate was treated with 4 radiation fields AP/PA and 2 laterals (for laymen one from the front,one from the back and two from the sides. Now there are up to 18 imrt fields (intensity modulated radiation therapy) moving leaves in the path of the beam turn a straight open beam into beamlets to deliver precise dose to a specific area. Because the radiation dose if more confined more radiation can be given and there a fewer side effects. Image guidance is also used daily to ensure the treatment volume is perfectly alligned.
Cyber knife/gamma knife offers non invasive options for tumors where surgery isn't an option.
Proton therapy although very expensive to provide uses proton particles rather than x-rays. The bragg peak of the protons eliminates exit dose, this makes it possible to treat tumors near vital organs with reduced side effects.
I doubt xrt will be obsolete within my life time. It seems many cancer treatments involve a three pronged approach of surgery, chemo, and xrt used in combination. Certain cancers are less sensitive to radiation than others, I believe it's the same with chemo. Radiation therapy is a localized treatment option rather than a systemic one like chemo. I can get into more specifics if necessary but I don't want to bore everyone. I'd be interested to learn if there are any cancers that were previously treated with xrt that now don't. The only one I'm aware of off the top of my head is leukemia, TBI (total body irradiation) used be an option followed by bone marrow transplant. I believe chemo is now the mainstay for leukemia.