Part I - Nursing and Precision Proton Therapy
Part I - What is Proton Therapy? (An overview of basic principles)
In this two part article we’ll first take a look at the basic principles of proton therapy and later walk through a typical day as a nurse at the proton center. Working in Oncology for over a decade I’ve sometimes felt like we are at a stalemate in terms of progress. Don’t get me wrong, I’m certainly not trying to diminish the massive amount of work that continues to be done in my field. There’s billions of dollars in funding, piles of research and a notable amount of philanthropy - all lending a hand to the incredible advances in the Oncology world. During my few years on the job I’ve seen big changes in pediatric survival rates, antiemetic control, a rise in the use of integrative medicine and administration of new biologic therapies. I even had the opportunity to work on an exciting immune modulating phase I clinical trial as a research coordinator.
Despite seeing all of these advances first hand, my feelings somehow remained the same. Afterall, I still administer the same IV chemotherapies that my father received over thirty years ago. However, every so often something new comes along in your field that gets you excited for the future. Proton therapy? What’s that? Ooh, tell me more! I was bewildered and utterly fascinated.
I’m definitely no expert. In fact, the original purpose of this article is was to walk you through what it’s like to work as a nurse working in this type of facility. This can be difficult to explain without first discussing how this therapy actually works. Here’s a basic overview of what I do know about this modality:
Proton beam therapy is a type of radiation therapy. This treatment delivers a beam of positively supercharged particles (protons) directly to the cancer site (Mayo Foundation for Medical Education and Research, 2016). I’m not sure if every proton therapy center uses the exact same technology. Where I work they (not sure exactly who ‘they’ is - magical ion gnomes? More likely scientists in a nearby lab, I guess) actually separate hydrogen atoms to create the protons. Incredible! It involves the ionization process and the delivered energy release at the Bragg peak - see this website for a great explanation and even a comprehensive video on the principles of proton therapy:
In pediatrics I’ve mostly seen proton therapy used on brain and CNS tumors although I’ve heard they use it for other types of solid tumors in adults. This type of radiation allows for more precise delivery of treatment to the tumor - allowing higher doses to be given without intense effects to surrounding tissue (The University of Texas MD Anderson Cancer Center, 2016). The easiest way to think about the comparing the delivery of traditional radiation therapy to proton therapy is to imagine a spray bottle. When you have it on a wide spray - that’s traditional radiation therapy (covering a larger area). When you change it to a direct narrow stream - that’s proton therapy.
For an even more in depth look of the incredible science behind proton therapy read:
There are currently only 25 proton therapy centers in the United States (The National Association for Proton Therapy, 2016). I was lucky enough to fall into a per diem position at one. The center is calm, quiet, serene even. The overall feeling seems to promote an environment of healing. There’s no loud overhead paging system, only a handful of staff and usually no more than two patients at the same time.
Then there’s the gantry (the treatment room where proton beam is administered). Google image “proton therapy” to see more of what I’m trying to describe here. It will not disappoint). My mouth was probably wide open the whole time when I first laid eyes on it. The sheer mass of the gantry is intimidating. Truth be told, I’m mildly spastic so I’m still convinced I might one day fall into the huge gap in the floor between treatment table and the bottom of the gantry. There’s a lot of moving parts and as the only nurse in the room, I’m responsible for a few.
In part two of this article, I will go through a day at the proton center so I can better explain my role in such an amazing place.
Global Vision. (n.d.). PROTON THERAPY CENTER - Principles of Proton Therapy. Retrieved December 13, 2016, fromPrinciples of Proton Therapy - Proton Therapy Center, cancer treatment in Europe
Mayo Foundation for Medical Education and Research. (2016). Proton therapy. Retrieved December 08, 2016, from Overview - Proton therapy - Mayo Clinic
The National Association for Proton Therapy. (2016). Proton Therapy Centers Location Map and Listings. Retrieved December 08, 2016, from Proton Therapy Centers Location Map and Listings
The University of Texas MD Anderson Cancer Center. (2016). Benefits of Proton Therapy. Retrieved December 08, 2016, fromProton Therapy Benefits | MD Anderson Cancer CenterLast edit by Joe V on Oct 19, '17
About Ashley Hay, BSN, RN
Over 10 years of nursing experience in several areas of Pediatric & Adult Oncology including clinical research, chemotherapy, transplant, hematology, proton therapy, GI surgery, wound care, post anesthesia recovery, etc.
Ashley Hay, BSN, RN has '10' year(s) of experience and specializes in 'Oncology'. Joined Aug '16; Posts: 80; Likes: 277.Dec 23, '16First of all let me just say that as a physics nerd and the sister of a radiation oncologist and a radiation physicist, I appreciate your post and look forward to reading your second post describing a typical day at work.
This type of radiation allows for more precise delivery of treatment to the tumor - allowing higher doses to be given without intense effects to surrounding tissue (The University of Texas MD Anderson Cancer Center, 2016). The easiest way to think about the comparing the delivery of traditional radiation therapy to proton therapy is to imagine a spray bottle. When you have it on a wide spray - that’s traditional radiation therapy (covering a larger area). When you change it to a direct narrow stream - that’s proton therapy.
particle physics - Dose-depth curve of photons vs. protons - Physics Stack Exchange
. Comparison of depth dose curves for a 1 MV photon beam and a... - Figure 1 of 2
Eventhough there is scattering with both photons and protons, the width of the "spray" is mostly determined by field size. Sure, if you open up wide, something like 40 cm x 40 cm (like you would with a Total Body Irradiation) then you get (and want) a "wide spray", but not otherwise.
The difference between the photons and protons is how they deposit energy as they travel through the patient, so the difference is in the proximal --> distal direction of the radiation source. If protons do what the dosimetrist intended they will deliver a relatively low dose to the tissue that's before the target (tumor and margin), a high dose to the PTV (Planning Target Volume) itself and no exit dose (the tissue behind/after the target). Photons however will deliver some dose along their entire path but the treatment plans are meticulously made to maximize the dose in the PTV and minimize the dose to OARs (Organ At Risk = basically stuff we don't want to treat).
As far as I understand it protons aren't always better.
Some of the advantages are:
A high conformal/even dose in the target volume. Being able to deliver a high dose in the target volume. Steep dose gradients between PTV (Planning Target Volume) and PRV (Planning Organ at Risk Volume) (meaning high dose where we want to treat and low dose in the adjacent organs/tissue). Reduction of dose to normal tissue (compared to photons where entry and exit doses are delivered, often including tissue relatively far from the target volume).
Some of the disadvantages/challenges are:
Planning accurate treatments depends on knowing the density of all tissue that the radiation beam travels through. This is normally based on CT/Hounsfield Units (different densities are assigned different shades of gray so a proper calculation can be made of how the protons interact with the tissue). CT artifacts can have a large effect on the accuracy of proton planning.
Because protons have the characteristic Bragg's Peak and deposits a large part of its energy in a small volume it is vital to know that the peak actually hits the the PTV. If there are organs at risk in close vicinity to the area that is being targeted, a miscalculation of a centimeter or two might have serious effects. Underdosing to the PTV and a high dose to the OAR. In this situation the photon (traditional therapy) with its more "gently" shaped dose-depth curve is much more forgiving.
There will often be both intra- and interfractional variations ( a fraction = one treatment. Radiotherapy is seldom given as a single fraction, but the dose is for various reasons split up in many separate sessions). There are many reasons for intra/interfractional variations. Some examples are setup errors (positioning of the patient), target movement, organ movement/motion, anatomy changes (for example tumor shrinkage, newly developed effusions). Because of the shape of the proton's dose-depth curve these variations can likely have more significant consequences than with photons.
So, the good thing about protons is that they stop, the challenge is that we don't always know where.
Proton Beam Therapy for Non-Small Cell Lung Cancer: Current Clinical Evidence and Future Directions
Example Showing the Sensitivity of Proton Beam Therapy to Anatomic Changes. Patient being treated with pencil beam scanning for a cT3N0 NSCLC developed an effusion after two weeks of radiotherapy (panel A: dose colorwash at initial simulation; panel B: dose colorwash at verification scan 2 weeks into radiotherapy). Planning tumor volume outlined in light blue. Dose colorwash shown cutoff at 90% in both panels. In panel B, compared to panel A (dose distribution at initial CT simulation), the target volume is significantly undercovered.
Now, I started writing this because I ws worried that the way tradional radiation therapy was described might sound scary and I realize that perhaps instead I've managed to make proton therapy sound scary. That was not my intent. The challenges that protons present to radiation therapy professionals are known and they take these into account when planning the treatments. As described in the above article "adaptive re-planning" is commonly performed so that changes in anatomy during the course of treatment can be taken into account and adjusted for.
I personally think that both methods (proton and photon/traditional) have a place in modern oncology.
Working in Oncology for over a decade I’ve sometimes felt like we are at a stalemate in terms of progress. Don’t get me wrong, I’m certainly not trying to diminish the massive amount of work that continues to be done in my field.Dec 25, '16This is so interesting! Thanks OP and also Macawake for all the info. In fact I googled pictures of proton treatment centers to get a better idea of how it looks as opposed to the traditional radiation area.
I am really curious about your job and looking forward to learning more!!!Dec 26, '16Macawake thanks so much for your comment - you provided and explained so much additional information so well. I love learning about this stuff. Radiation is certainly not my specialty - proton was actually my first experience with any kind of RT hands on.
In terms of explaining the wide vs narrow spray I never thought of the fear factor it may instill in patients. It's a basic explanation that most families can understand and it seems to make the most sense to them. (While all of the information you provided is absolutely fascinating to me - it can be difficult to adjust to all educational levels in terms of explanation to patient/family in ways they can best understand.) It was one of those things that was passed down from preceptor to orientee multiple times and it seemed like a great explanation at the but I can see your point. Definitely room for improvement.
Planning accurate treatment is definitely a real challenge. Which is why the radiation therapists image, check, re-check, and re-image before providing each treatment; assuring the dose is being given to the correct site. "I personally think that both methods (proton and photon/traditional) have a place in modern oncology." Couldn't agree with you more and think you explained the benefits and disadvantages to both really well.
An finally yes, I agree - we certainly are making progress and that is important to remember in our ever changing field. Oh, and by the way... I really appreciate a fellow science nerdDec 26, '16Quote from Brenda F. JohnsonThanks Brenda!Very interesting! Waiting for the next one....Dec 26, '16Quote from nutellaThanks Nutella. I'm so glad you liked it. Looking forward to your thoughts on part II.This is so interesting! Thanks OP and also Macawake for all the info. In fact I googled pictures of proton treatment centers to get a better idea of how it looks as opposed to the traditional radiation area.
I am really curious about your job and looking forward to learning more!!!
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