Imaging Guidelines - Salvage IMRT Planning

[Rams91]

I'm planning to start my post-op salvage treatment after my PSA breached 0.1 few weeks ago. I'm OK with the extent of the treatment proposed, which is 5 weeks of IMRT (VMAT) to the prostatic fossa and pelvic LNs. However, I'm not confident with the accuracy of radiation delivery to the target area. Knowing well this could be my last chance at a cure, I have spent a lot of time researching articles on the internet on how this 'invisible target' (prostatic bed after removal of the prostate and anatomic changes caused by surgery) should be contoured. In the era of dynamic MRI imaging, I'm worried that using CT guided imaging alone -as is used in my treatment center- to delineate pelvic area will not create as 'complete' a target area as when used in conjunction with MRIs (pre and post-operative) in the planning and treatment sessions. Obviously, I do not want to have another recurrence few years down the road because of missed pelvic target, so my question is how important is the imaging technique in order to map the right target volume when it comes to salvage IMRT? For those who went through salvage radiation using conventional fractionation, what kind of imaging was used in your planning and/or treatment sessions? My RO is very experienced, but he doesn't think MRI will add any value when I asked to have one post-surgery. Do they just go with established guidelines using defined landmarks when coming up with target volume OR do they map individual cases based on one's anatomy (post-surgery) and take into account individual's grade, stage and pathological findings? Thanks.

[Tall_Allen]

"how important is the imaging technique in order to map the right target volume when it comes to salvage IMRT?"

It is much less important than you imagine. For the treatment area, they contour the X-rays on anatomical landmarks, and the planning CT is quite good. They also use bony landmarks at the start of each session for imaging accuracy to minimize toxicity. Toxicity is the only advantage of MRI gating (not treatment area definition). MRI-targeters claim they can reduce toxicity by reducing the treatment margins, but they have not yet proved that reducing the margins is as effective in killing all the cancer.

[Rams91 in reply to Tall_Allen]

Thank you Allen. From what I read, there are roughly four consensus guidelines published for post-op external beam radiation focusing on Clinical Target Volume (CTV) and they were all based on CT imaging. At least in one study, by fusing the preoperative mpMRI to the CT, it showed that CTVs from guidelines did not cover the MRI-defined prostate generating an average prostate volume geographic miss of 18%-35%. What I can't gather is whether these guidelines have been revised to include MRI findings and if not, do they encourage clinicians to include pre/post operative MRIs in their CTV calculations?

[Tall_Allen in reply to Rams91]

Often, the planning imaging fuses MRI and CT. But MRI misses 80% of tumor volume.

ncbi.nlm.nih.gov/pmc/articl...

This is why the planning target volume and not the clinical target volume is what is really important.

You are obsessing over details that do not matter.

[Rams91 in reply to Tall_Allen]

I agree. I'm obsessed and worried too. That's why I'm reading everything and ask questions from experts like you, which by the way, I truly appreciate your time. Here is what I'm referring to as my last defense

For postoperative RT, gross tumor volume (GTV) does not exist clearly in adjuvant setting and it can be hardly estimated, clinically or radiologically, for salvage purpose in condition of a rising PSA because it remains microscopic most of the time. CTV definition is based from pathological study of the prostate: size of the gland, seminal vesicle (SV) invasion, and location of positive margins (5).

The potential reasons for local failure include an inadequate radiation dose and inadequate definition of the clinical target volume (CTV). Successful RT in the era of three-dimensional conformal RT (3D-CRT) and intensity-modulated RT (IMRT) requires physicians to accurately delineate treatment targets while simultaneously avoiding normal tissue to limit organ at risk (OAR) toxicity.

ncbi.nlm.nih.gov/pmc/articl...

[Tall_Allen in reply to Rams91]

I have no idea what your point is. As I said, you are obsessing over unimportant (to the patient) things. The only things a patient should legitimately be concerned with is effectiveness and toxicity, and all widely used technologies in the US can maximize effectiveness and minimize toxicity. The skill and experience of the RO is much more important. Your dive into Dr Google will never be able to supplant their training and expertise. Find one who has excellent experience and track record, and you can feel comfortable he knows what he's doing.

[Justfor_]

Two RO I had consult with, one uses CT, for planning needs, the other MRI. Both said that recent (to irradiation) imaging is essential. Still no sRT for me.

[Lizzo30]

HI Rams91 I hope you dont mind me asking but apart from your PSA rising have they found more cancer in scans I am presuming you have had ?

I ask bc my husbands psa has risen and they want him to have radiation bc of that

[Rams91 in reply to Lizzo30]

Not according to the PSMA/Pet scan I did a few months ago. I'm just being proactive since I know post-op rising PSA in the range of 0.1 to 0.2 has the best chance of cure with radiation.

[Lizzo30 in reply to Rams91]

How do you know that Rams91 can you share the source ?

[Justfor_ in reply to Lizzo30]

There has been a paper claiming that at PSA 0.1 the success rate is somewhere around 70%, declining by 2-3% for every 0.1 increase in PSA. Numbers are off my head but not far away from the published ones.