Real-time in vivo proton range verification in proton therapy with thallium bromide detectors

Summary
Radiotherapy using protons is an attractive option as it has the potential to better preserve healthy tissue
compared to radiation with photons or electrons, and because trial outcomes indicate it can replace surgery for
radical cancer treatments as well. Proton therapy makes use of the finite range of heavy charged particles with
an intensity maximum at the end of their path (Bragg peak) followed by a sharp fall-off of the dose. However,
predicting the proton range based on computed tomography (CT) scans carries an estimation uncertainty. For
treatments with proximal critical organs and limited accessibility (head and neck), high heterogeneities (lung),
or significant breath motion (liver) such uncertainty is too high and the therapy is in the best case challenging, if
not impossible. New instrumentation is needed to monitor the location of the Bragg peak to 1-2 mm accuracy
within several seconds in these challenging scenarios.
We propose to use the novel Cerenkov Charge Induction (CCI) thallium bromide (TlBr) detectors for proton
range verification (PRV) in proton therapy. CCI TlBr detectors combine the detection of Cerenkov light, which
provides sub-nanosecond timing resolution with the conventional readout of semiconductor detectors, which
provides excellent energy resolution and 3-D segmentation. Moreover, TlBr has a shorter attenuation length
than most commonly used scintillation materials for prompt-gammas up to 6.1 MeV. CCI TlBr detectors provide
a unique performance, as they offer simultaneous excellent performance in energy, time, and spatial
resolution, that fits the needs of PRV in proton therapy.
In this project, we will test the feasibility of using a non-collimated prompt gamma timing – Compton camera
(PGT-CC) camera based on pixel CCI TlBr detectors for PRV in proton therapy. We will 1) manufacture pixel
CCI TlBr detectors with optimized surface treatment to couple the photodetector and with highly-stable long-
lasting electrodes; 2) characterize the detector features of pixel CCI TlBr devices in a benchtop setting using
sealed sources, including energy, spatial, and timing resolution; 3) evaluate the performance of a PGT-CC
camera for PRV made with pixel CCI TlBr detectors in a beamline with protons accelerated to 67.5 MeV; and
4) compare the performance of our PGT-CC camera prototype with gold standard techniques following realistic
treatment protocols at a clinical beamline with protons accelerated to >200 MeV.
The accomplishment of the aims of this project will determine the potential of CCI TlBr detectors to become the
most competitive devices for PRV in proton therapy. A successful performance of the proposed detection
system would allow to exploit the benefits of proton therapy in treatment regions that are currently very
challenging, leading to increased treatment efficacy and lower toxicity in the healthy organs of the patients.

Grant Number: 5R01EB029533-04
NIH Institute/Center: NIH
Principal Investigator: Gerard Arino Estrada