As with all emerging technologies, the publication of peer-reviewed research papers supporting the validity and effectiveness of proton therapy began modestly. An online search of the literature revealed 818 citations in 1990. However, this is changing: By 2000, the list had grown to 2,496 studies and by 2010, to 6,200 studies. Some proton therapy experts were asked to identify a recently published paper of noteworthy clinical significance. Here are summaries of three of the studies and brief commentaries from the experts.
Here is the paper selected by Jacob B. Flanz, Ph.D. of Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.
“A case study in proton pencil-beam scanning delivery”, by Kooy HM, Clasie BM, Hsiao-Ming L, Madden TM, Bentefour H, Depauw N, Adams JA, Trofimov AV, Demaret D, Delaney TF, Flanz JB. (Int J Radiation Oncology Biol Phys. 2009;76(2):624–30.)
Study summary: Scanned proton beams
The most conformal and efficient beam delivery is achieved with the beam scanning modality. Modulating the dose throughout the target volume creates an overall dose distribution that conforms to the target and minimizes the dose to tissues and organs outside the target. While a small pencil beam can exploit this potential for small tumors, the use of a larger scanned beam can also be extremely important for larger target volumes. It is, in fact, these larger volumes that, when treated with scattered proton beams, require highly complex treatment planning and costly patient-specific hardware — including brass apertures and range compensators — that cannot be reused. Treatment with scanned proton beams often eliminates that hardware, reduces the number of fields required and is much simpler to plan.
The case study of a 61-year-old man with a 21 x 12 cm retroperitoneal myxoid liposarcoma was presented. The patient was treated to 50.4 Gy relative biological effectiveness presurgery using a course of photons and protons to a clinical target volume, and a course of protons to the gross target volume. The use of beam scanning improved the dose distribution, reduced treatment time and lowered treatment costs.
“Much of the emphasis on the clinical use of beam scanning has been for small targets near critical structures; for example those in the head and neck area. This is due to the ability to use small (pencil sized) scanned beams to conform around concave shapes using multiple fields. The significant advantages of using scanned beams for larger targets seem to be less widely recognized. Large targets treated with scattered beams are difficult to plan, time consuming to treat, and require multiple fields with expensive patient-specific hardware. Using scanned beams (and they don’t even have to be so small) simplifies treatment planning and delivery and provides not only a better overall dose distribution, but also a more efficient and cost-effective treatment solution, even when compared with alternative modalities”, says Jacob B. Flanz, Ph.D. of Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.