Simultaneous Multiple Liver Metastasis Treated with Pencil Beam Proton Stereotactic Body Radiotherapy (SBRT)

Abstract

Compared with photon stereotactic body radiotherapy (SBRT) plans that may have to use many more penetrating x-ray beams for each isocenter, proton SBRT with ultrahypofractionated doses use fewer beam angles and offer significantly reduced low-dose radiation bath to normal liver tissue. We demonstrate techniques to deliver safe and effective proton SBRT, where planning and organ motion complexity further increased with multiple liver lesions. For treatment planning, we recommend robust and logical beam angles, avoiding devices and encouraging entry perpendicular to the dominant motion, as well as volumetric repainting to mitigate the interplay effect to clinically acceptable levels. This report highlights the significant technical challenges with ultrahypofractionated proton pencil beam scanning liver therapy, how they are managed, and the effectiveness of this treatment.

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

“…For charged particle therapy, thin belts made of homogenous materials are preferred to ensure that the belt has a minimal and reproducible impact on the charged particle range ( 37 ). For PBS proton therapy, the use of AC has been shown to be valuable for reducing moderate to large motion during treatment of liver tumors ( 37 , 38 ). Additionally, AC in combination with layered rescanning and respiratory gating has been clinically adopted for motion mitigation in carbon ion therapy ( 39 ).…”

“…The compression belt typically has fiducial markers and pressure meter to ensure consistent positioning of the belt during treatment. Nonetheless, it is recommended to avoid having particle beam passing through the device to avoid potential water equivalent thickness (WET) variations in the setup ( 38 ).…”

Special stereotactic radiotherapy techniques: procedures and equipment for treatment simulation and dose delivery

“…Protons have been tested; their use has been advocated as preferred treatment for larger and more complex lesions in order to reduce the risk of toxicity [55]. As very few studies have been published [56][57][58][59], research is needed before their seletive avantages can be defined. Another innovative method for SRT is the PET-guided radiotherapy, or biology-guided radiotherapy, performed by the RefleXion TM X1, a system that obtained the marketing authorization from the FDA in 2020.…”

The role of proton therapy in gynecological radiation oncology

“…When delivering proton therapy, factors such as bowel gas, body habitus changes, internal organ motion, and implanted hardware (eg, hip replacements) increase the uncertainty of delivering treatment accurately to the abdomino-pelvic organs. 19 In addition to these significant issues with organ motion and range of uncertainties, lack of high-quality on-treatment imaging such as cone beam CT (until recently), has limited confidence in the wide use of proton therapy. As an example, when the proton beam must traverse an area of bowel gas to reach a target, uncertainty that the treatment will be delivered as planned is increased, particularly when the volume of bowel gas changes daily.…”