Clinical Technology

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.

Long-term results: prostate cancer

Early-stage prostate cancer patients (n=393) were treated with conformal photon therapy to a fixed dose of 50.4 Gy followed by a proton- beam boost dose of either 19.8 Gy (conventional dose) or 28.8 Gy (high dose). The median follow-up of patients was 8.9 years.

In this randomized trial, high-dose external proton beam radiation therapy provided better long-term cancer control than did conventional- dose proton beam radiation therapy in men with localized prostate cancer. Dose escalation to 79.2 Gy was safely achieved without an increase in late urinary or rectal morbidity. These findings show that patients receiving a high-dose boost following conformal photon therapy will more likely be free from an increasing PSA 10 years later and less likely to require additional cancer therapy.

“The PROG 95-09 data certainly support the use of Proton Therapy for the treatment of prostate cancer. Of the six-dose escalation studies that have been published, it remains the only one that used a Proton Therapy component. Its inclusion allowed for safe dose escalation without an increase in rectal toxicity. It speaks volumes about the value of Proton Therapy.”
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 pre-surgery 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.”
Long-Term Results: Prostate Cancer

Proton Therapy used to treat seven children with pediatric bladder/prostate rhabdomyosarcoma provided significant dose savings to normal structures, such as the bladder, femoral heads, growth plates and pelvic bones, compared to intensity-modulated radiation therapy.

Proton Therapy was well tolerated in these patients. Five of the seven children had intact bladders and were without evidence of disease at study completion. Although identifying the long-term impact of these reduced doses was beyond the scope of this retrospective study, the hope is that the decreased treatment toxicity associated with Proton Therapy will lead to fewer acute and late complications related to treatment.

“With a median follow-up of 27 months, the late-effect profile of this patient population looks promising to date. Further studies with extended follow-up and quality-of-life analyses are needed to confirm these early findings.”


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