# Coded-aperture Compton scatter imaging for real-time tumor motion tracking during ablative radiotherapy

> **NIH NIH R21** · UNIVERSITY OF COLORADO DENVER · 2021 · $172,460

## Abstract

Project Summary/Abstract
 Stereotactic Body Radiation Therapy (SBRT) is an aggressive, ablative local therapy that can be an
effective treatment for many hard-to-treat tumors, such as pancreatic adenocarcinoma, non-small cell lung
cancer, melanoma, and renal cell carcinoma. By delivering large, ablative doses of radiation in a small number
of treatments, SBRT leads to significantly improved local control. However, there is a trade-off between
delivering aggressive doses of radiation in the abdomen with SBRT and dose-limiting side-effects. A major
problem is that the breathing-induced motion of the abdomen is erratic and unstable, rendering traditional
methods of motion management ineffective.
 To enable safe and effective dose escalation for these tumors, we are proposing a novel imaging system
that measures the position of fiducial markers implanted inside the patient. This system, called Coded Aperture
Scatter Imaging (CASI), passively measures the position of tumors during treatment with no additional
radiation dose. During radiotherapy, a beam of megavoltage x-rays is directed towards the tumor, and some of
those photons undergo scattering interactions within the patient. These photons are more likely to interact in
the dense, high-atomic-number fiducial markers, providing a differential signal that can be measured by an
imager placed orthogonal to the beam. We propose to use coded aperture imaging to decode the location of
these fiducial markers in real time. The coded aperture technique, utilized in fields such as astronomy and
nuclear medicine, can help identify faint point sources within a broad background.
 CASI is clinically attractive for several reasons. This passive technique provides real-time motion
information with no additional imaging dose, since it forms an image using scattered photons from the
treatment beam. CASI is easily implementable on any existing clinical linear accelerator, since all modern
linacs are equipped with a kV imaging panel placed orthogonal to the treatment beam. Fiducial markers are
commonly implanted in these tumors, and the only additional hardware needed is the coded aperture itself,
which can simply be placed between the patient and the detector. Finally, by measuring the motion of tumors
during treatment one could increase the accuracy of treatment delivery, which could enable more effective,
dose-escalated treatments that avoid toxicity to normal tissues. The goal of this work is to design, fabricate,
and test an optimized aperture for CASI-guided radiotherapy.

## Key facts

- **NIH application ID:** 10127825
- **Project number:** 1R21CA249647-01A1
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** Bernard L Jones
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $172,460
- **Award type:** 1
- **Project period:** 2020-12-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10127825

## Citation

> US National Institutes of Health, RePORTER application 10127825, Coded-aperture Compton scatter imaging for real-time tumor motion tracking during ablative radiotherapy (1R21CA249647-01A1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10127825. Licensed CC0.

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