Comparison of proton beam therapy and plate brachytherapy in ocular melanoma
Alexei Trofimov, PhD, a medical physicist in the Department of Radiation Oncology at Massachusetts General Hospital and assistant professor of radiation oncology at Harvard Medical School, is lead author of a new study in the International Journal of Radiation Oncology Biology Physics , A systematic comparison of dose distributions administered in 125 I plaque brachytherapy and proton radiotherapy for ocular melanoma.
What was the question you wanted to answer with this study?
Proton beam radiation therapy and plaque brachytherapy using radioactive iodine seeds are both established treatments for ocular melanoma (a rare form of cancer that affects the eye), and both options are available to patients. as part of our joint MGH-MEE program on ocular melanoma.
Our group was interested in characterizing how the dose distribution delivered with these two modalities of therapeutic radiation varies according to the size of the tumor and its location in relation to the critical structures of the eye, such as the optic disc, the retina, the lens.
We were particularly interested in identifying specific tumor presentations for which protons or plaques provided better sparing of critical structures.
What are the top two or three takeaways?
We have identified more than 100 cases of interest: tumors of different size and location in the eye.
Then, radiotherapy plans were created for these cases with the software used for clinical treatments.
Although the tools we used were not exactly new or unique, we are one of very few hospital systems with expertise in both radiation modalities.
What were your conclusions?
The interesting physical property of proton beams is that they can be stopped at the desired depth and can completely spare healthy tissue posterior and lateral to the irradiated tumor.
An interesting finding from our study was that although protons in a typical treatment can completely spare the center of the lens, the dose delivered to the periphery of the lens was more effectively reduced with plates in most cases.
Similarly, protons were able to completely spare large sections of the retina, but areas irradiated at 50% of the prescribed dose and above were more closely on target in plaque treatments.
Plaque treatments have also shown a dosimetric benefit by sparing the optic nerve and fovea in nasal targets, especially those of larger circumference and height. The protons performed better in the temporal, upper and lower locations.
Free access to the article (no registration, registration or fee is required) is provided until November 13, 2022 at the following link https://authors.elsevier.com/a/1fowu1Hx52CHPc.
What are the clinical implications?
Our team identified several important distinctions between proton and plaque dose distributions. However, dosimetry is only one of the factors influencing care decisions. We anticipate that our results will be useful to providers and patients in making decisions about individualized treatments.
One aspect that has not been taken into account in our comparison is the difference in the biological effect of the doses delivered by the proton beams and the gamma radiation from the iodine plates.
Not only are different species of radiation particles used in these therapies, but also the length of treatment and the rate at which the dose is delivered vary widely.
Future research will improve our understanding of the biological effects of different types of radiation on the critical tissues and structures of the eye.
Trofimov, AV, Aronow, ME, Gragoudas, ES, Keane, FK, Kim, IK, Shih, HA and Bhagwat, MS (2022). A systematic comparison of the distributions of doses delivered in 125I Plaque brachytherapy and proton radiotherapy for ocular melanoma. International Journal of Radiation Oncology, Biology, Physics, S0360-3016(22)00739-8. Early online publication. https://doi.org/10.1016/j.ijrobp.2022.07.017
About Massachusetts General Hospital
Massachusetts General Hospital, founded in 1811, is Harvard Medical School’s first and largest teaching hospital. The Mass General Research Institute conducts the largest hospital-based research program in the nation, with annual research operations of more than $1 billion and includes more than 9,500 researchers working in more than 30 institutes, centers and departments. In July 2022, Mass General was named #8 in U.S. News & World Report’s list of “America’s Best Hospitals.” MGH is a founding member of the Mass General Brigham Health System.