SBRT dose escalation

This was a series of dose escalation studies in Canada where they raised the SBRT dose from 35 Gy to 40 Gy. Their 40 Gy cure rates were very good, but toxicities were very high. This again shows the importance of adhering to tight dose constraints and using excellent image guidance when using anything as powerful as SBRT.

/pcnrv.blogspot.com/2017/05/sbrt-dose-escalation.html

Interesting, My treatment was 36.25gy with a SIB of 40gy. It is a clinical trial at UAB to be finished in 2018. So far I am having no problems I can attribute to the SBRT. I think that with the advancements in targeting and delivery this form or PC treatment looks to be one of if not the best for curative and low SE'S for low to intermediate risk PCa in the near future. My RO (without giving specifics) said that most of the men in this trial have tolerated the treatment extremely well with minimal side effects to date. Only time will tell what the long term toxicities will be but I am hopeful that they too will be minimal.
Perry

I didn't go into a lot of detail about it in that write up, but there was some very serious (grade 3 and 4) rectal toxicity in their high-dose study. They learned that no more than 2.0 cm3 of rectal tissue may receive more than 38 Gy, and they have adjusted their treatment plans accordingly. That's why those dose-volume histograms are so important. A SIB near the rectum may easily cause a violation of rectal dose constraints like that, and given the lack of evidence for SIB efficacy, that ought to be considered optional. My RO uses no treatment margin whatever on the rectal side of the prostate, and treats only the proximal part of the seminal vesicles (also with no margin).

But the plan is only part of the story. My RO once showed me a fluoroscopic video of gas moving through the rectum during a patient's treatment. The prostate was totally pushed out of field by it. This brought home to me the importance of intrafractional motion tracking throughout the SBRT treatment, and also why a treatment should be cancelled if there is bowel distension. A rectal balloon pushes most of the rectum away from the treatment field, but pushes some of the rectum farther into it (so they have to look carefully at point doses received). Spacers may distort the shape of the prostate and don't seem to reduce toxicity very much.

The one benefit to IMRT (1.8-2.0 Gy/fx) is that it is more forgiving than SBRT. If it's off a little on one day or another, it won't matter very much. The margins can be much wider (up to 1 cm), and dose constraints need not be as tight. Also, I think that the skill of the RO and physicist are less important.

Here, for example, is the set of dose constraints used for SBRT at Georgetown:

/www.ncbi.nlm.nih.gov/pmc/articles/PMC4870496/table/T1/