ESTRO 2025 - Abstract Book

S34

Invited Speaker

ESTRO 2025

Abstract: Reduction of range uncertainties through methods that allow to visualize in-vivo the stopping position of protons and light ions has been the subject of intensive research since the very early days of particle therapy. Investigated methods have traditionally relied on the detection of penetrating radiation (typically photons) produced in nuclear interactions between the impinging particles and the irradiated tissue. Here, positron emission tomography and prompt gamma imaging are among the most extensively studied approaches that already reached the stage of clinical evaluation since many years, although their adoption is still limited to certain institutions. Additional techniques such as protoacoustics/ionoacoustics are also gaining interest owing to their small footprint, cost-effectiveness and the wider spread of new particle therapy technologies that favour the generation of thermoacoustic emissions. However, none of the proposed approaches is able to provide a direct visualization of the Bragg peak in-vivo, but different methods have been proposed to infer the beam range and even the underlying dose from the measured irradiation-induced signals. This talk will present an overview of these solutions, highlighting ongoing research which aims to leverage advancements in instrumentation and computational methods, along with the challenges but also new opportunities from emerging irradiation techniques, toward new approaches of in-vivo treatment verification, ideally real-time during treatment delivery.

4701

Speaker Abstracts Is there a killer application for in vivo treatment verification? Thomas Bortfeld Radiation Oncology, Massachusetts General Hospital, Boston, USA

Abstract:

In a slight variation of the usual meaning of “killer application”, we will interpret the term here as a clinical application of in-vivo treatment verification with enormous benefit for the patients. We will discuss four killer applications of in-vivo verification:

1. Shaping dose distributions with the distal edge of the Bragg peak

Physically, in proton therapy the distal edge of the Bragg peak is twice as sharp as the lateral edge. However, the distal edge is rarely used to shape dose distributions or to protect distal organs-at-risk (OAR). Using the distal edge to shape dose distributions will unleash the full power of proton (and heavier ion) therapy. Examples of clinical treatments that benefit from distal dose shaping include the treatment of breast cancer with anterior beams while protecting the heart, treatment of prostate cancer with anterior beams (instead of lateral beams) protecting the rectum, and the treatment of para-spinal tumors with posterior beams, stopping in front of the spinal cord.

2. Creating more flexibility in beam angle placement

To avoid overdosing OARs, proton beams are typically placed such that they avoid OARs tangentially, instead of distally. This strategy ensures OAR protection even when the beam overshoots beyond the nominal range. However, the price to be paid for this includes large restrictions on beam angle placement, which compromises the plan quality. Controlling the beam range with in-vivo verification leads to much greater flexibility in beam placement. With that said, it has recently been shown that spreading the beams out with arc therapy may have an even greater benefit than controlling the range of individual beams.

3. Revival of distal edge tracking