Protons 101: Proton Therapy and SpaceOAR at The Oklahoma Proton Center

Less radiation dose to normal structures is a key component of cancer treatment.

Today, we’ll review very briefly 1) what SpaceOAR is, 2) why at the Oklahoma Proton Center we use it for most patients, and 3) why we think it is a great match for proton therapy and prostate cancer treatment.

What is SpaceOAR?

As you see in the image below, it is a temporary gel placed between the prostate and rectum that creates space between the prostate and rectum. This “little space” of about 13mm can make a “big difference” in reducing the amount of radiation to the rectum when prostate cancer is treated with radiation.

MRI Implant
MRI showing normal prostate and rectum anatomy on the left. In the middle, SpaceOAR gel has been placed creating “space” between the prostate and rectum. On the right, is an MRI showing 12 months post implant where the SpaceOAR has been absorbed.

We use it because it reduces dose to the rectum and improves patient outcomes.

Below there are 3 charts. The first shows that when using SpaceOAR, less radiation hits the rectum and penile bulb. These are normal structures that aren’t at risk and therefore, less radiation dose is better.

Dosimetry Less Dose Rectum Penile Bulb
This second chart, shows that with less dose, patients had less side effects – mainly a lower risk of rectal bleeding.

Rectal Toxicity Space OAR

This third chart is interesting because it shows a broader look at side effects. This chart shows patients had less declines in their Quality of Life related to treatment when SpaceOAR was used.

QOLImprovement_SpaceOAR

Why the Oklahoma Proton Center thinks it is a great match for proton therapy.

IMRT can treat about 56 degrees of the 360 degrees and fully utilize SpaceOAR. Below I’ve drawn a few lines. “Above” or Anterior to the lines are the prostate and below these lines are a reasonable portion of the rectum. As the lines get steeper, the sparing of the rectum decreases or goes to zero for those field angles. I did a study of 6 consecutive patients and just put some reasonable angles on that show that traditional radiation can utilize about 1/6th of available angles and still effectively “use” the full advantage of the SpaceOAR. Proton Therapy on the other hand uses lateral fields for prostate cancer treatment. Lateral fields will utilize the space advantage 100% of time.

I think the data for SpaceOAR is great and the procedure is pretty simple and straightforward with low risks. I think it is even a stronger compliment to proton therapy than with traditional radiation and that is why we using it here at the Oklahoma Proton Center.

Lines showing approximate potential angles that utilize the entire advantage of SpaceOAR. The “best” angles fall in the lateral direction and typically represent about 60 degrees that are available for the most effective beam angles. Proton therapy will deliver 100% of dose through these effective angels. IMRT or traditional radiation will not.
Lines showing approximate potential angles that utilize the entire advantage of SpaceOAR. The “best” angles fall in the lateral direction and typically represent about 60 degrees that are available for the most effective beam angles. Proton therapy will deliver 100% of dose through these effective angels. IMRT or traditional radiation will not.

Space OAR Effective Angles OKC Proton
Lines showing approximate potential angles that utilize the entire advantage of SpaceOAR. The “best” angles fall in the lateral direction and typically represent about 60 degrees that are available for the most effective beam angles. Proton therapy will deliver 100% of dose through these effective angels. IMRT or traditional radiation will not.

CREDIT: The SpaceOAR image and the three bar graphs are taken directly from the SpaceOAR site. The final study and the language explaining our rational here at the Oklahoma Proton Center are mine. If you have further questions please head to the SpaceOAR site or our main OKCProton site.

Dr. Mark Storey MD
Medical Director, Oklahoma Proton Center

OKCProton.com