Charged-particle beams consisting of protons or helium ions are a type of particulate radiation therapy that contrast with conventional electromagnetic (i.e., photon) radiation therapy due to the unique properties of minimal scatter as the particulate beams pass through the tissue, and deposition of the ionizing energy at a precise depth (i.e., the Bragg Peak). Thus radiation exposure to surrounding normal tissues is minimized. The theoretical advantages of protons and other charged-particle beams may improve outcomes but this has not been proven. Studies for brain tumors are primarily in the form of case series and retrospective reviews. Overall survival, local control, progression, and recurrence rates varied based on the type and location of tumors. Studies comparing PBT to conventional external beam radiation therapy and other types of stereotactic radiosurgery are lacking. At the same time proton beam radiotherapy is significantly more expensive than other modalities.
Proton beam therapy systems are approved by the FDA 510(k) process as a “medical device designed to produce and deliver a proton beam for the treatment of patients with localized tumors and other conditions susceptible to treatment by radiation” (FDA, 2006). Examples of such systems are the Optivus Proton Beam Therapy System (Optivus Technology Inc., Loma Linda, CA) and the IBA Proton Therapy System-Proteus 235 (Ion Beam Applications S.A., Philadelphia, PA).
The Agency for Healthcare Research and Quality published a 2009 technology report on particle beam radiation therapies for the treatment of cancers including skull base and brain tumors. They noted that there is a proposed advantage of using particle beam therapy, including PBT, where precise radiation targeting is critical in tumors of the skull base and tumors adjacent to the brain and brain stem. The report concluded that studies on charged particle therapy “do not document the circumstances in contemporary treatment strategies in which radiotherapy with charged particles is superior to other modalities. Comparative studies in general, and randomized trials in particular (when feasible) are needed to document the theoretical advantages of charged particle radiotherapy to specific clinical situations”.
In a technology assessment on the use of PBT for the treatment of cancer, the Australia and New Zealand Horizon Scanning Network (2006) stated that PBT “may be of particular benefit” in the treatment of patients with intermediate depth tumors such as those in the head, cancers that are located in difficult or dangerous-to-treat areas, and tumors in locations where “conventional radiotherapy would damage surrounding tissue to an unacceptable level” (e.g., central nervous system and head). PBT “may be ideal for use in the treatment of pediatric patients where the need to avoid secondary tumors is important due to the potentially long life span after radiation treatment when they may develop radiation induced malignancies.
Y. Lievens, W. den BogaertProton beam therapy: Too expensive to become true?. Radiotherapy and Oncology, Volume 75, Issue 2, Pages 131-133 2005
Yock TI, Tarbell NJ.Technology insight: Proton beam radiotherapy for treatment in pediatric brain tumors. Nat Clin Pract Oncol. 2004 Dec;1(2):97-103;
Semenova J.Proton beam radiation therapy in the treatment of pediatric central nervous system malignancies: a review of the literature. J Pediatr Oncol Nurs. 2009 May-Jun;26(3):142-9. Epub 2009 May 21.
Tian X, Liu K, Hou Y, Cheng J, Zhang J. The evolution of proton beam therapy:Current and future status. Mol Clin Oncol. 2018 Jan;8(1):15-21.
Doyen J, Bondiau PY, Bénézéry K, et al. Current situation and perspectives of proton
therapy. Cancer Radiother. 2015 May;19(3):211-9; quiz 231-2, 235.
Mishra MV, Aggarwal S, Bentzen SM, et. al Establishing Evidence-Based Indications for Proton Therapy: An Overview of Current Clinical Trials. Int J Radiat Oncol Biol Phys. 2017 Feb 1;97(2):228-235.