There is unfortunately very little published evidence to help guide the answer to this very important question. It's potentially a big topic, so I am going to attempt an answer from a spine reirradiation perspective (Reirradiation of other sites such as weight-bearing long bones may have different c...

The large RCTs used 4-6 weeks to retreat; the main data on the retreat is the NCIC SC20 study (Chow et al).

I agree with the above comments and would add the following: Single-fraction palliation may have ongoing symptom relief for up to a few weeks after delivery, so I would wait at least 3-4 weeks to assess. If RT did not provide more durable relief (i.e., > 3 months), then the same treatment is un...

I will answer the question assuming it was a non-spine bone metastasis. I have often started with 800 cGy single fraction and then reassessed benefit at 4-6 weeks later. If that single fraction didn't give pain relief, I have given fractionated treatment such as 20 Gy in 5 or 30 Gy in 10. My impress...

In my experience in the VA for the past decade, single-fraction radiotherapy for uncomplicated bone metastases is becoming more institutionalized in its use.1. Dawson GA, Moghanaki D, Gutt-Garg R, et al. Consensus Statement Supporting the Recommendation for Single-Fraction Palliative Radiotherapy fo...

As far as timing is concerned, I agree with @Drew Moghanaki's rules of thumb above (2 weeks to see benefit and 2 months before retreatment). However, unless the patient's life expectancy and/or performance status are limited, I would hesitate to retreat with the same 8 Gy x 1 regimen as before...

Patients ask this question all the time. I provide a simple response to help them remember: "2 weeks to see a benefit and 2 months to consider more treatment". It is a recommendation informed by RCT data. 

I would give 6 weeks for the partial relief of pain. I would re-irradiate at that point if there is no relief or would consider alternative methods.

I find Dr. @George Dawson's point about selecting prostate cancer patients for single-fraction treatment very thought-provoking. I have often heard the opposite argument for protracted/multi-fraction regimens, predominately because of the slightly higher but most often not statistically significant ...