Adaptive proton therapy

Abstract

Radiation therapy treatments are typically planned based on a single image set, assuming that the patient’s anatomy and its position relative to the delivery system remains constant during the course of treatment. Similarly, the prescription dose assumes constant biological dose-response over the treatment course. However, variations can and do occur on multiple time scales. For treatment sites with significant intra-fractional motion, geometric changes happen over seconds or minutes, while biological considerations change over days or weeks. At an intermediate timescale, geometric changes occur between daily treatment fractions. Adaptive radiation therapy is applied to consider changes in patient anatomy during the course of fractionated treatment delivery. While traditionally adaptation has been done off-line with replanning based on new CT images, online treatment adaptation based on on-board imaging has gained momentum in recent years due to advanced imaging techniques combined with treatment delivery systems. Adaptation is particularly important in proton therapy where small changes in patient anatomy can lead to significant dose perturbations due to the dose conformality and finite range of proton beams. This review summarizes the current state-of-the-art of on-line adaptive proton therapy and identifies areas requiring further research.

Considerations for Upright Particle Therapy Patient Positioning and Associated Image Guidance

“…Now, with commercial options for vertical CT systems (8,9), and the drive for reducing the upfront investment for opening new particle therapy centers (3,10), upright treatment positioning systems have gained renewed interest (11,12). Moreover, advanced techniques for intra-treatment verification and adaptation (13)(14)(15) are currently reaching clinical maturity. These techniques could, not only overcome the previous issues associated with anatomical motion for upright treatment positions, but together with upright treatment postures, further open possibilities for advanced beam delivery schemes, e.g., particle arc therapy (16) with continuous patient rotation.…”

Management of Motion and Anatomical Variations in Charged Particle Therapy: Past, Present, and Into the Future

“…In addition, because carbon ions exhibit a distal tail of dose beyond the Bragg peak due to nuclear fragmentation, the potential for dose uncertainties distal to the target volume are of greater concern ( 24 ). Additionally, for carbon and heavier ions, RBE is nonlinear with respect to the absorbed dose level, particle energy, and atomic number ( 25 ), thus while it is typical to consider a constant RBE for proton radiotherapy ( 26 ), when considering the carbon ion interplay effects, the changing RBE along the beam path should be taken into consideration.…”

Evaluating Proton Dose and Associated Range Uncertainty Using Daily Cone-Beam CT

“…The use of daily cone-beam CT (CBCT) guidance has improved patient setup accuracy and precision in various radiotherapy delivery modalities, including proton therapy ( 1 , 2 ). Since the proton range, and hence the proton dose distribution, is sensitive toward any density change along the beam path, CBCT can provide an additional benefit of verifying proton range and dose distribution, complementing the geometrical verification of the patient anatomy daily ( 3 – 5 ). However, the Hounsfield unit (HU) accuracy and image quality of the CBCT images are inferior to those of regular CT and often considered inadequate for proton dose calculation without correction.…”