Ocular Melanoma treatment options for the 21st
Century
Working as a technician for a retina specialist for the last
18 months I have seen many different diseases of the retina. None is more fascinating or scary than ocular
melanoma. While some patients with
ocular melanoma have had other cancers, many have never been diagnosed with any
form of cancer and the diagnosis is quite a surprise. Typically a patient reports a fuzzy spot in
their vision, or flashes and floaters.
In some cases patients may not notice anything at all and the melanoma
is caught by a routine eye exam.
Currently there are two common treatments for ocular
melanoma which mirror treatments for other forms of cancer; plaque radiation (Brachytherapy)
and enucleation. Plaque radiation involves surgically placing
a radioactive piece of metal on the back of the eye where it can selectively
treat the tumor with radiation. It is
removed after 3-7 days. Alternatively,
enucleation is the surgical removal of the eye containing the tumor, taking
care to make sure that the margins of the tumor do not extend beyond the
eye. The advantages of plaque radiation are
twofold; first, the tumor is not excised, reducing possible risk of metastasis,
and secondly, the patient retains their eye and possibly some vision. After extensive study it was found that there
is no difference between metastasis and recurrence between plaque radiation and
enucleation, leading to widespread acceptance of plaque radiation as the preferred
therapy. (Diener-West 2001)
There is however, a third option that isn’t always discussed
due to limited availability, and that is proton beam therapy. There are currently only 11 US medical
centers that offer proton beam therapy. ( NAPTC 2013) Proton beam therapy is
different than external beam radiotherapy in that instead of photons (x-rays) emitted
from a radioactive source, it uses a beam of protons generated by a particle accelerator. The nature of protons means that the depth of
penetration can be controlled. In external
beam radiotherapy the x-rays travel through all the overlying tissues, through
the tumor and continue through whatever tissues lie behind the tumor. This can cause radiation sickness and lead to
secondary tumors years down the road.
Conversely, proton beam therapy enters the overlying tissue at minimum
energy, peaks at maximum energy at the tumor, and does not radiate tissues
behind the tumor. The physics of this
mechanism are beyond the scope of this discussion, however the significance is
the tumor can be selectively treated with minimum collateral damage. (Gaudio 1997)
The next reasonable question is why isn’t proton beam
therapy more widespread? The answer is
that in order to effectively direct the beam to the tumor, advanced imaging and
modeling is necessary. The information from
the scans is crunched by sophisticated programs which calculate the power and
duration of the beam. Finally the
greatest hurdle in widespread acceptance of proton beam therapy is the cost
which can be over $200 million. (Lavelle
2012)
Proton beam therapy can be used in treating many types of
cancer, not just ocular cancers, and judging by the number of facilities currently
under construction in the US (8) that you will see it offered more frequently
in the future.
References:
Diener-West M, Earle JD, Fine SL, Hawkins BS, Moy CS,
Reynolds SM, Schachat a P, Straatsma BR. 2001. The COMS randomized trial of
iodine 125 brachytherapy for choroidal melanoma, III: initial mortality
findings. COMS Report No. 18. Archives of ophthalmology [Internet] 119:969–82.
Available from: http://www.ncbi.nlm.nih.gov/pubmed/11448319
Gaudio P, Tolentino M, Gragoudas ES. 1997. Proton Beam
Irradiation for the Treatment of Uveal Melanoma. Digital Journal of
Ophthalmology [Internet] 3. Available from: http://www.djo.harvard.edu/site.php?url=/physicians/oa/389
Lavelle J. 2012. UCSD downsizes plans for proton center. UT
San Diego [Internet]. Available from: http://www.utsandiego.com/news/2012/Jan/12/ucsd-switches-plans-proton-center/
The National Association of Proton Therapy Centers (NAPTC).
2013. Proton Therapy Centers. Available from: http://www.proton-therapy.org/map.htm
Brad,
ReplyDeleteThose are some complicated and intense medical treatments right there. I feel like vision is a sense that many people often take for granted. Not only are the physics behind vision astounding, but also the physiological mechanisms that allow us to process and interpret light are incredible. As such, the treatment and detection of any sort of cancer or disease in the eye is extremely important. After reading your post, I was really curious about Proton Beam Therapy, not only because of its immense cost, but also because of its specific and unique mechanism. In an article published in Radiation Research in January 2013 discusses the relative effectiveness of the radiation on specific cells. As it turns out, it may even more effective than what previous professionals had thought. The range of intensity of the beam showed improved killing of the cancer cells, but could potentially cause more damage to those cells that are distal to the beam (Britten et al.). Overall, pretty interesting article and begs the question of how advancements in medicine, technology, and science are coming together in an effort to combat biology.
References:
Britten RA, Nazaryan V, Davis LK, Klein SB, Nichiporov D, Medonca MS, Wolanski M, Nie X, George J, Keppel C. (2013). Variations in the RBE for cell killing along the depth-dose profile of a modulated proton therapy beam. Department of Radiation Oncology. 179(1): 21-28. Available from: http://ebscohost.com/
Brad,
ReplyDeleteThose are some complicated and intense medical treatments right there. I feel like vision is a sense that many people often take for granted. Not only are the physics behind vision astounding, but also the physiological mechanisms that allow us to process and interpret light are incredible. As such, the treatment and detection of any sort of cancer or disease in the eye is extremely important. After reading your post, I was really curious about Proton Beam Therapy, not only because of its immense cost, but also because of its specific and unique mechanism. In an article published in Radiation Research in January 2013 discusses the relative effectiveness of the radiation on specific cells. As it turns out, it may even more effective than what previous professionals had thought. The range of intensity of the beam showed improved killing of the cancer cells, but could potentially cause more damage to those cells that are distal to the beam (Britten et al.). Overall, pretty interesting article and begs the question of how advancements in medicine, technology, and science are coming together in an effort to combat biology.
References:
Britten RA, Nazaryan V, Davis LK, Klein SB, Nichiporov D, Medonca MS, Wolanski M, Nie X, George J, Keppel C. (2013). Variations in the RBE for cell killing along the depth-dose profile of a modulated proton therapy beam. Department of Radiation Oncology. 179(1): 21-28. Available from: http://ebscohost.com/
Garrett,
DeleteGlad to hear that other studies are showing that is proton beam therapy is very effective. With all the new treatment centers slated to be built in the next few years it can be another tool in the oncologists belt and ultimately help us defeat cancer.
Brad,
ReplyDeleteThat was a very interesting article! I have heard of therapy such as that for the treatment of cancer, particularly the gamma knife treatment at Swedish in Seattle. I was wondering about the symptomology that you had mentioned such as floaters. I have had floaters for quite a long time, so my question is at what point should someone be concerned about experiencing these fairly typical ocular disturbances? I know it is recommended to contact an ophthalmologist if there is an increase in the number of floaters, but are there any other indicators/symptoms to be aware of?
Kelsey,
ReplyDeleteGamma knife is another useful radiotherapy treatment and is probably more well known than proton beam therapy. I wasn't able to find any studies comparing the effectiveness of the two therapies, maybe that will come in the near future.
As for floaters, here is some information from the American Academy of Ophthalmology (AAO) website
http://www.aao.org/theeyeshaveit/disturbances/floaters.cfm
The only way to know for sure if your floaters are anything serious is to have a dilated eye exam by an ophthalmologist or optometrist.*
*The opinions expressed in this blog are not intended to be medical advice and should not be used as such.