A Viking,
I think you're asking some very good questions. I think you have to approach this from a radiobiology perspective -- I assume you understand how radiation works, but it is also important to understand why radiation might ever NOT work. There are two main lessons we've learned about
radiation for prostate cancer over the last 20 years: (1) that an adequate dose must be given and (2) it is more effective to deliver the dose in some ways than in others.
We've learned that dose escalation was necessary to kill the cancer. More advanced cancers have a number of mechanisms that protect them from radiation (i.e., hypoxia, cell cycle, rapid growth, and repair if damage is minimal as with cancer stem cells), and it is now known that an IMRT dose of 80 Gy or more is necessary to kill them. LDR Brachy monotherapy delivers roughly an equivalent of only 74 Gy -- adequate for low volume, low grade tumors, but not really enough on its own for intermediate or high risk. The workaround is to supplement it with external beam radiation. Unfortunately, that also adds to the toxicity/side effects.
There are other solutions to this problem that have to do with how the radiation is delivered. It was discovered that prostate tumor cells are relatively unique among cancers in that the have what is called a low "alpha/beta ratio." This means they are killed more effectively by a few higher doses of radiation than by the prolonged low dose schedule that IMRT or LDR brachy delivers. The challenge was to deliver the higher doses safely.
The first solution was HDR brachy monotherapy. HDR brachy monotherapy delivers the equivalent of 102 Gy if it had been delivered in 2 Gy increments like IMRT. At UCLA, it is delivered in 6 fractions of 7 Gy each. It has enough cancer cell killing power that it can be used on its own in intermediate risk cases. However, the cure rates are lower for higher stages.For stage T2c, 77% of men had 5-yr biochemical recurrence-free survival, compared to 100% for stage T2b. As the stage goes up, so does the risk that it is no longer local. It is also extremely safe, with very few urinary symptoms. Potency retention was 83%. However, very few centers will treat intermediate risk men, especially those with multiple risk factors, with HDR monotherapy.
High dose brachytherapy as monotherapy for intermediate risk prostate cancer.The second solution was based on the success of HDR brachy, and is the external beam version - SBRT. The dose I received was biologically equivalent to 109 Gy if it had been delivered 2 Gy at a time like IMRT. I received 5 doses at 8 Gy each (=40 Gy). For intermediate risk men, Dr. Katz reports 92% freedom from biochemical failure after 6 years with extremely low rates of side effects (74% potency preservation).
Stereotactic Body Radiation Therapy for Low-, Intermediate-, and High-Risk Prostate Cancer: Disease Control and Quality of Life at 6 YearsThe nice thing about
both HDR monotherapy and SBRT is that while the
effective (i.e., cancer-killing) dose is much higher than LDR brachy or IMRT, the
nominal (i.e., healthy tissue damaging) dose is only half. This leaves
open the possibility of retreatment should there be a local failure. To date, very few of the failures have been local, however.
I think the key question you have to grapple with is how locally contained is it. Surgery is of course useless if it is not locally contained. Combo therapies (HDR brachy+IMRT or LDR brachy+IMRT) give an increased assurance of effectiveness, but at the cost of increased SEs. SBRT can be adjusted to penetrate to any distance in the prostate bed, and seems to give equivalent results with lower toxicity.