Results of Proton Therapy - 023

Good news and questionable bad news

I underwent proton therapy from January 10, 2023, through February 24, 2023. Some days included days when the machine was down, which wasn't very often, and others were for planning scans.

The first part was for applying proton beams to the lymphatic chains on both sides of my aorta from the top of my pelvis to the bottom of my diaphragm. The second part was for "boosting" the six areas of visible metastases that lit up on the prostate-specific membrane antigen (PSMA) positron emission tomography (PET) computerized tomography (CT) scan.

The PSMA PET scan

On May 30, 2023, I returned for another PSMA PET CT scan and my prostate-specific antigen (PSA) tumor marker results that had been drawn the week before. I wasn't nervous because I had just undergone an intensive round of proton therapy, and I trusted the technology to be effective.

Undergoing the PET scan was becoming old hat. The technician injected the radioisotope, and then I sat in the reclining chair for an hour. I moved into the CT scanning room and lay in the machine with my arms above my head. Soon it was over, and I grabbed Mike out of the waiting room on our way to the exam room.

The results

My favorite nurse practitioner, Katrina, came into the room with a big smile, and we said our hellos. She mentioned that she had just taken a quick look at the scan, and nothing jumped out at her. That made me feel good, but then she said, "Your PSA went up a bit." That made me feel really disappointed, and my mind started racing. How could my PSA go up when we had just done proton therapy, and nothing jumped out at her on the scan?

Katrina asked how I had been doing, and I explained that I felt good except for some ongoing fatigue. She explained that I could still be having fatigue related to the proton therapy and reminded me it didn't help that I'd had a bout of COVID the week before starting it.

At about this time, Dr. Ackerman walked into the room as his usual cheerful self. Dr. Stroud was on vacation so Dr. Ackerman would give me the results. He smiled and shook both of our hands. We chatted a bit, and then he pulled up the PET scan on his computer, making sure Mike and I could see the screen.

My heart starts beating faster when the computer screen displays my PET scan. Dr. Ackerman zooms in and out using the mouse and moves up and down the screen, viewing the entire scan. Then he pulls up my previous PET scan and places them side by side. It is obvious to both of us that the areas that lit up previously are no longer there, and he points that out.

I take a deep breath and feel relieved. But why did my PSA go up? I never asked Dr. Ackerman that question. Trying to put a positive spin on things, he points out that my PSA doubling time has significantly slowed. He knows I'm a physician, and I'll come up with potential reasons why the PSA bumped up.

PSA doubling time

The PSA doubling time (PSADT) reflects the rate of tumor growth. A PSDT of fewer than ten months generally indicates aggressive cancer, while a PSADT of more than twenty-four months may suggest slow-growing and less aggressive cancer.

Using PSA levels since 2022, my PSADT before proton therapy was 19.4 months, and now it's 25.3 months. That is the slowest my PSADT has ever been since I started this journey. The proton therapy tipped the scales in my favor!

Reasons for the rise in PSA

Remember that my PSA level should be zero since I no longer have a prostate. So what are some potential reasons for the rising PSA?

Unfortunately, one potential reason is that my body's remaining prostate cancer cells don't have the prostate-specific membrane antigen (PSMA) protein on their cell surfaces. For a detailed discussion of the PSMA protein, read newsletter 012.

We know that my previous PSMA PET CT showed six areas of tumor in my para-aortic lymph nodes, which meant those tumor cells were expressing PSMA. I had just assumed those six areas created all the PSA in my body. Maybe I was wrong. The current PSMA PET CT shows that those areas are gone, so one would think the PSA would at least have gone down.

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Remember the incredible heterogeneity of prostate cancer cells. There can be multiple types of prostate cancer cells in one's body.

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So why are we using the PMSA PET CT if it won't pick up all potential tumor cell types? Because the PSMA PET CT is considered the "gold standard" PET scan in men who have undergone definitive therapy and have a rising PSA. Definitive therapy is a treatment intended to cure prostate cancer, including prostatectomy and radiation therapy.

Clinical trials show that the PSMA PET CT scan is superior to regular CT scans and bone scans in detecting metastases. In addition, other clinical trials show that, in some cases, it is superior to other PET CT scans. In the future, I'll write an entire newsletter on the different types of PET scans for prostate cancer.

PSA bounce

Another possible reason for the rise in my PSA level despite an improved PET scan is a "PSA bounce." According to the National Cancer Institute, PSA bounce is a brief rise and then fall in the blood level of PSA that occurs in some patients one to three years after receiving radiation treatment for prostate cancer.

This definition is strange because the PSA bounce can occur three years after radiation. There are so many variables that can occur within three years after radiation. It would be strange for patients and physicians to watch the PSA rise three years after radiation and think it was due to the radiation.

One meta-analysis showed that a PSA bounce occurs more frequently and with greater amplitude in brachytherapy (radiation implants in the prostate gland) than in external beam radiation, and younger age is associated with a higher incidence and greater amplitude of the bounce.

Another study involving 691 prostate cancer patients showed that the range for a PSA bounce is 0.4–17.0, with a median magnitude of the bounce being on the lower end at 1.0 ng/mL.

So it is established that in some men who receive radiation therapy, the PSA level rises before it falls. But another complicating issue of this definition is that this phenomenon has only been studied in men who received radiation to their prostate and still have an intact prostate gland. My prostate gland is gone.

So this wouldn't apply to me? Not necessarily. I found a published case study showing that a PSA bounce can also occur in a patient who's undergone a previous radical prostatectomy like me.

I will keep an open mind and consider that my mild rise in PSA after proton therapy could be due to a PSA bounce. After all, the CT portion of the latest scan didn't show any lymph node enlargement, soft tissue masses, or bone lesions. I know most prostate cancer specialists would consider this idea unlikely, but I don't care.

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Anything is possible, and miracles occur every day.

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Next steps

Dr. Ackerman recommended we repeat my PSA level in three months and then make further decisions based on that. Of course, if I develop symptoms in the interim, I could undergo imaging. Whether we use a PSMA PET CT or another type of PET scan in the future remains to be seen.

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This is another lesson for me about maintaining a positive mindset.

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If anyone has a prostate cancer topic you'd like me to write about, please put it in the comments section.

Happy 4th of July!

Keith

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