Single-center, retrospective study on changes in pain-relieving therapy after bone metastasis detection by bone scintigraphy in prostate cancer patients

Abstract Whole-body bone scintigraphy (WB-BS) is used for detecting and monitoring metastatic spread of prostate cancer (PCa) and to investigate bone pain episodes. To investigate the impact of a positive WB-BS on pain-relieving medicine prescription in PCa patients, a single-center, retrospective cohort study with PCa patients classified as positive for bone metastases (BM) by WB-BS was conducted. Demographic, clinical, and ambulatory pain-relieving medicine prescription data were evaluated. Pain-relieving medicines were categorized according to the WHO 'Analgesic Ladder'. Regimens adopted before and after WB-BS were compared. Differences were considered significant at p<0.05. A total of 180 PCa patients were diagnosed with BM, 64.4% of whom were ≥65 years of age. Thirty-three patients were prescribed analgesics only after WB-BS, mostly including NSAIDs and weak opioids. Pain-relieving prescription changed after WB-BS in patients with prescriptions before and after WB-BS, with a reduction in NSAIDs and adjuvants and an increase in weak and strong opioids. In addition, 40% of patients with WHO analgesic step 1 drugs and 21.7% of patients with WHO step 2 drugs before WB-BS changed to other WHO steps after WB-BS. Pain-relieving prescriptions changed after a positive WB-BS, providing evidence that it could contribute to clinical management of painful metastatic PCa patients.

Ultrahigh-speed point scanning two-photon microscopy using high dynamic range silicon photomultipliers.

Conventional two-photon microscopes use photomultiplier tubes, which enable high sensitivity but can detect relatively few photons per second, forcing longer pixel integration times and limiting maximum imaging rates. We introduce novel detection electronics using silicon photomultipliers that greatly extend dynamic range, enabling more than an order of magnitude increased photon detection rate as compared to state-of-the-art photomultiplier tubes. We demonstrate that this capability can dramatically improve both imaging rates and signal-to-noise ratio (SNR) in two-photon microscopy using human surgical specimens. Finally, to enable wider use of more advanced detection technology, we have formed the OpenSiPM project, which aims to provide open source detector designs for high-speed two-photon and confocal microscopy.

SiPM-based gamma detector with a central GRIN lens for a visible/NIRF/gamma multi-modal laparoscope.

Intraoperative imaging has been studied using conventional devices such as near infrared (NIR) optical probes and gamma probes. However, these devices have limited depth penetration and spatial resolution. In a previous study, we realized a multi-modal endoscopic system. However, charge-coupled device (CCD)-based gamma imaging required long acquisition times and lacked gamma energy information. A silicon photomultiplier (SiPM)-based gamma detector is implemented in a multi-modal laparoscope herein. A gradient index (GRIN) lens and CCD are used to transfer and readout visible and NIR photons. The feasibility of in-vivo sentinel lymph node (SLN) mapping was successfully performed with the proposed system.

Stereoscopic portable hybrid gamma imaging for source depth estimation.

Advances in gamma imaging technology mean that is now technologically feasible to conduct stereoscopic gamma imaging in a hand-held unit. This paper derives an analytical model for stereoscopic pinhole imaging which can be used to predict performance for a wide range of camera configurations. Investigation of this concept through Monte Carlo and benchtop studies, for an example configuration, shows camera-source distance measurements with a mean deviation between calculated and actual distances of <5 mm for imaging distances of 50-250 mm. By combining this technique with stereoscopic optical imaging, we are then able to calculate the depth of a radioisotope source beneath a surface without any external positional tracking. This new hybrid technique has the potential to improve surgical localisation in procedures such as sentinel lymph node biopsy.

Energy and electron drift time measurements in a pixel CCI TlBr detector with 1.3 MeV prompt-gammas.

Assessing the position of the Bragg peak (BP) in hadron radiotherapy utilizing prompt-gamma imaging (PGI) presents many challenges in terms of detector physics. Gamma detectors with the capability of extracting the best energy, timing, and spatial information from each gamma interaction, as well as with high detection efficiency and count rate performance, are needed for this application. In this work we present the characterization of a pixel Cerenkov charge induction (CCI) thallium bromide (TlBr) detector in terms of energy and and electron drift time for its potential use in PGI. The CCI TlBr detector had dimensions of 4 × 4 × 5 mm3 and one of its electrodes was segmented in pixels with 1.7 mm pitch. A silicon photomultiplier (SiPM) was optically coupled to one of the faces of the TlBr slab to read out the Cerenkov light promptly emitted after the interaction of a gamma ray. The detector was operated stand-alone and the 1.275 prompt gammas from a 22Na radioactive source were used for the study. The electron drift time was obtained by combining the Cerenkov and charge induction signals and then used as a measure of the depth of interaction. The electron mobility in TlBr was estimated as ∼27 cm2 V-1 s-1. Energy resolutions between 3.4% and 4.0% at 1.275 MeV were obtained after depth-correction. These values improved to 3.0%-3.3% when events with drift times of 3-6 µs were selected. These results show the potential of pixel CCI TlBr detectors to resolve gamma interactions in the detector with mm-like accuracy in 3D and with excellent energy resolution. Previous studies with CCI TlBr devices have shown a timing resolution of <400 ps full width at half maximum when detecting 511 keV gamma rays, therefore, the timing accuracy is expected to improve with the increased energy of the gamma rays in PGI. While other important detector characteristics such as count rate capability remain to be studied, results from this work combined with other preliminary data show pixel CCI detectors can simultaneously provide excellent energy, timing, and spatial resolution performance and are a very promising option for PGI in hadron therapy.

MTF of columnar phosphors with a homogenous part: an analytical approach.

A method for the theoretical estimation of the MTF of columnar phosphors with a homogeneous part at the end used in X-ray imaging has been developed. This method considers the light transport inside the scintillator through an analytical modelling, the optical photon beams distribution on the scintillator-optical sensor interface, and uses the definition of the PSF and a Gauss fitted LSF to estimate the MTF of an indirect detector. This method was applied to a columnar CsI:Tl scintillator and validated against experimental results found in literature, and a good agreement was observed. It was found that, by increasing the pixel size of the optical detector and the thickness of the scintillator, the MTF decreased as expected. This method may be used in evaluating the performance of the columnar phosphors used in medical imaging, given their physical and geometrical characteristics.Graphical abstract (a) Side view of a part of the scintillator where five crystal columns with homogeneous ends attached to an optical sensor is shown. (b) Propagation of two random optical photon beams emitted from point K with different angles of emission is shown. All the symbols are explained analytically in the text.

Selective Neck Dissection Guided by a Radioactive I125 Seed for Papillary Thyroid Carcinoma Recurrence. / Disección cervical radioguiada con semillas de I125 como tratamiento de la recurrencia de cáncer papilar de tiroides.

Lymph nodes are the most common place of recurrence of papillary thyroid cancer, and surgery can be considered a therapeutic option. The risks of surgery increase with every intervention. We present 3 cases of cervical non palpable thyroid cancer recurrence managed with I125 seed radioguided cervical dissection from 2017 to 2019. Two of the cases had already a thyroidectomy and central compartment lymphadenectomy performed. The seed was placed guided by US on the lesion and its position was confirmed afterwards. The target was successfully localized in 100% of cases. There was no post surgery complications. There was no evidence of recurrence with a mean follow up of 15 months. Radioguided surgery using I125 seed it is a save technique and it offers a precise localization of the non palpable thyroid cancer recurrence.

Computational model for detector timing effects in Compton-camera based prompt-gamma imaging for proton radiotherapy.

This paper describes a realistic simulation of a Compton-camera (CC) based prompt-gamma (PG) imaging system for proton range verification for a range of clinical dose rates, and its comparison to PG measured data with a pre-clinical CC. We used a Monte Carlo plus Detector Effects (MCDE) model to simulate the production of prompt gamma-rays (PG) and their energy depositions in the CC. With Monte Carlo, we simulated PG emission resulting from irradiation of a high density polyethylene phantom with a 150 MeV proton pencil beam at dose rates of 5.0 × 108, 2.6 × 109, and 4.6 × 109 p+ s-1. Realistic detector timing effects (e.g. delayed triggering time, event-coincidence, dead time, etc,) were added in post-processing to allow for flexible count rate variations. We acquired PG emission measurements with our pre-clinical CC during irradiation with a clinical 150 MeV proton pencil beam at the same dose rates. For simulations and measurements, three primary changes could be seen in the PG emission data as the dose rate increased: (1) reduction in the total number of detected events due to increased dead-time percentage; (2) increase in false-coincidence events (i.e. multiple PGs interacting, rather than a single PG scatter); and (3) loss of distinct PG emission peaks in the energy spectrum. We used the MCDE model to estimate the quality of our measured PG data, primarily with regards to true and false double-scatters and triple-scatters recorded by the CC. The simulation results showed that of the recorded double-scatter PG interactions 22%, 57%, and 70% were false double-scatters and for triple-scatter interactions 3%, 21%, and 35% were false events at 5.0 × 108, 2.6 × 109, and 4.6 × 109 p+ s-1, respectively. These false scatter events represent noise in the data, and the high percentage of these events in the data represents a major limitation in our ability to produce usable PG images with our prototype CC.

Assessment of an in-house phantom for the quality control of a clinical gamma camera.

OBJECTIVE: Since in-house phantoms may provide effective quality control for gamma cameras in clinical settings, this study aims to assess an in-house phantom designed to perform quality control tests of a gamma camera using locally available, affordable materials. This is of particular importance in developing countries where scientific support may not be readily available. MATERIALS AND METHODS: The phantom was made from cylindrical plexiglass with a diameter of 230 mm and thickness of 60 mm. The phantom design was based on NEMA recommendations and only used materials that are locally available and generally accessible to most nuclear medicine departments and require minimal engineering instruction. RESULTS: The phantom demonstrated high levels of reliability and accuracy. The integral uniformity range was between 1.93% and 2.40%. The differential uniformity ranged between 1.48% and 1.70%. CONCLUSION: This work demonstrates that in-house phantoms are capable of monitoring gamma camera performance. This approach is particularly useful when scientific support is not easily accessible and when commercial phantoms are not readily available.

Comparison of Radio-guided Occult Lesion Localization (ROLL) and Magnetic Occult Lesion Localization (MOLL) for Non-palpable Lesions: A Phantom Model Study.

BACKGROUND: Localization of nonpalpable breast cancers can be achieved with several techniques. We sought to compare radio-guided localization (ROLL) and magnetic tracer localization (MOLL) techniques by using a phantom model we previously developed, which can provide an accurate simulation for excision of nonpalpable breast lesions. MATERIALS AND METHODS: We designed 20 phantom models (10 MOLL, 10 ROLL group) for localization. A handheld gamma probe for the ROLL group and a manual magnetometer (SentiMag) for the MOLL group were used to test the ability of the modality to detect olives in turkey breasts. The excision time for each procedure, specimen size, and weight of the specimens removed from the turkey breasts were recorded. RESULTS: Both techniques resulted in 100% retrieval of the lesions. There was no difference between the groups in the duration of operative excision, specimen weight, or specimen volume. CONCLUSION: This experimental trial found similar success rates for ROLL and MOLL in localization of occult lesions using the turkey breast phantom model. MOLL can be performed in clinics without the need for a nuclear medicine team and radiation safety procedures.

Portable gamma-camera for the diagnosis of brain death diagnosis. / Minigammacámara portátil para el diagnóstico de muerte encefálica.

OBJECTIVE: To evaluate the feasibility of using the Sentinella® portable gamma-camera for the diagnosis of brain death (BD). DESIGN: A prospective, observational feasibility study was carried out. SETTING: Intensive Care Unit of a third level hospital. PATIENTS: Consecutive recording was made of the adults diagnosed with brain death based on clinical criteria following admission to the Intensive Care Unit in the period from January to December 2017. INTERVENTIONS: The procedure was performed at the patient bedside with the intravenous administration of technetium 99 metastable hexamethylpropylene amine oxime. The absence of perfusion in the cerebral hemispheres and brainstem was described as a pattern consistent with BD. The diagnosis was correlated to the transcranial Doppler and / or electroencephalographic findings. RESULTS: A total of 66.1% of the patients were men with an average age of 60 years [IQR: 51-72]. The most frequent causes resulting in BD were hemorrhagic stroke (48.2%, n=27), followed by traumatic brain injury (30.4%, n=17), ischemic stroke (10.7%, n=6) and post-cardiac arrest anoxic encephalopathy (7.1%, n=4). A clinical diagnosis of BD was made in all cases, and the portable gamma-camera confirmed the diagnosis in 100% of the patients with a pattern characterized by the absence of brain perfusion. In addition, the results were compared with the transcranial Doppler findings in 46 patients, confirming the presence of diastolic reverberation and / or systolic peaks. The electroencephalographic tracing was obtained in 10 cases, with the appearance of electrical silence, due to the absence of an acoustic window in the transcranial Doppler study. CONCLUSIONS: A portable gamma-camera could be a useful and feasible tool for the diagnosis of BD.

Utilização de radiofármacos marcados com tecnécio 99m como potenciais marcadores na obtenção de imagens de perfusão miocárdica / Using technetium-99m-marked radiopharmaceuticals as potential markers in obtaining myocardial perfusion images

A Organização Mundial de Saúde (OMS) aponta as doenças cardiovasculares como a principal causa de morte no mundo, caracterizando um grave problema na saúde pública. Os três tipos de doenças que mais acarretam em óbito são: acidente vascular cerebral, seguido de infarto agudo do miocárdio e outras doenças isquêmicas do coração.Apesar dos avanços terapêuticos das últimas décadas, o infarto ainda apresenta altas taxas de mortalidade. Para as pessoas com doenças cardiovasculares ou com alto risco cardiovascular é fundamental o diagnóstico precoce da doença. A cintilografia de perfusão miocárdica é um método de investigação diagnóstica e prognóstico não invasivo de várias doenças cardiovasculares. Esse exame consiste na administração de um radiofármaco para obtenção de imagens de perfusão cardíaca. Dois traçadores marcados com Tecnécio-99m são amplamente utilizados na clínica, porém, esses dois radiofármacos não atendem aos requisitos de um agente de perfusão ideal, por sofrerem significativa excreção biliar, produzindo artefatos na imagem, o que pode inteferir um diagnóstico preciso, já que a qualidade é comprometida, e prolongando o tempo de obtenção da imagem após a administração do radiotraçador. Para superar essa lacuna, pesquisadores vêm estudando novos complexos catiônicos marcados com o Tecnécio. O objetivo desse artigo é fazer uma revisão, abordando a literatura sobre os radiofármacos que estão sendo estudados, suas vantagens e desvantagens sobre os traçadores já utilizados, e sobre sua potencial utilização na obtenção de imagem de perfusão cardíaca.

The World Health Organization (WHO) acknowledges cardiovascular diseases as the leading cause of death in the world, being regarded as a serious public health issue. The three types of diseases with the greatest mortality are: stroke, followed by acute myocardial infarction (AMI) and other ischemic heart diseases. Despite the therapeutic advances of the last decades, AMI still presents high mortality rates. Early diagnosis is essential for people with cardiovascular diseases or with a high cardiovascular risk. Myocardial perfusion scintigraphy is a method of diagnostic investigation and noninvasive prognosis of various cardiovascular diseases. This examination consists in the administration of a radiopharmaceutical drug to obtain images of cardiac perfusion. Two tracers labeled with Technetium-99m are widely used, however, these two radiopharmaceuticals do not meet the requirements of an ideal perfusion agent, because they have a high liver absorption, producing artifacts in the image, which can disrupt a precise diagnosis, since the quality is compromised, and prolonging the imaging time after administration of the radioisotope. To overcome this gap, researchers have been studying new cationic complexes marked with technetium. The objective of this article is to review the literature on the radiopharmaceuticals being studied, their advantages and disadvantages on the tracers already used, and their potential use in obtaining a cardiac perfusion image.

Effect of iterative reconstruction techniques on image quality in low radiation dose chest CT: a phantom study.

PURPOSE: We aimed to evaluate the quality of chest computed tomography (CT) images obtained with low-dose CT using three iterative reconstruction (IR) algorithms. METHODS: Two 64-detector spiral CT scanners (HDCT and iCT) were used to scan a chest phantom containing 6 ground-glass nodules (GGNs) at 11 radiation dose levels. CT images were reconstructed by filtered back projection or three IR algorithms. Reconstructed images were analyzed for CT values, average noise, contrast-to-noise ratio (CNR) values, subjective image noise, and diagnostic acceptability of the GGNs. Repeated-measures analysis of variance was used for statistical analyses. RESULTS: Average noise decreased and CNR increased with increasing radiation dose when the same reconstruction algorithm was applied. Average image noise was significantly lower when reconstructed with MBIR than with iDOSE4 at the same low radiation doses. The two radiologists showed good interobserver consistency in image quality with kappa 0.83. A significant relationship was found between image noise and diagnostic acceptability of the GGNs. CONCLUSION: Three IR algorithms are able to reduce the image noise and improve the image quality of low-dose CT. In the same radiation dose, the low-dose CT image quality reconstructed with MBIR algorithms is better than that of other IR algorithms.

Clinical evaluation of General Electric new Swiftscan solution in bone scintigraphy on NaI-camera: A head to head comparison with Siemens Symbia.

PURPOSE: The General Electric (GE) Swiftscan solution combines a new Low Energy High Resolution and Sensitivity collimator (LEHRS) with image processing (Clarity 2D) and tomographic step and shoot continuous mode. The aim of this study was to compare clinical and physical performances of this new technology in bone scintigraphy. METHODS: Physical phantom measurements were performed using GE LEHRS, GE Low Energy High Resolution (LEHR) and Siemens LEHR collimators. These measurements were associated with a prospective clinical study. Sixty-seven patients referred for bone scintigraphy were enrolled from February to July 2018. Each patient underwent two acquisitions consecutively on GE and Siemens gamma camera, using respectively Swiftscan solution and LEHR collimator. RESULTS: On planar acquisitions, maximum sensitivity was 100 cts/MBq for Siemens LEHR. GE SwiftScan LEHRS and GE LEHR maximum sensitivity were respectively 9% and 22% lower. Using Clarity 2D, GE Swiftscan LEHRS spatial resolution was the best with 9.2 mm versus 10.1 mm and 10.6 mm for GE LEHR and Siemens LEHR collimators. In tomographic mode, the sensitivity of GE Swiftscan solution was superior to both LEHR systems (16% and 25% respectively for Siemens and GE). There was no significant difference in spatial resolution. In clinical use, signal was higher on Siemens system and noise was lower on GE Swiftscan solution. Contrast-to-noise ratios were not significantly different between the two systems. There was a significant image quality improvement with GE SwiftScan in planar images and in whole body scan. No significant difference in image quality was observed on SPECT images. CONCLUSION: New GE SwiftScan collimator design improved sensitivity compared to "classical" GE LEHR collimator without compromising resolution. GE SwiftScan solution enhances planar image quality with a better Clarity 2D resolution recovery and noise treatment. In SPECT mode, GE SwiftScan solution improves volumetric sensitivity without significant impact on image quality, and could lead to time or dose reduction.

Sentinel lymph node fingerprinting.

BACKGROUND: When locating the sentinel lymph node (SLN), surgeons use state-of-the-art imaging devices, such as a 1D gamma probe or less widely spread a 2D gamma camera. These devices project the 3D subspace onto a 1D respectively 2D space, hence loosing accuracy and the depth of the SLN which is very important, especially in the head and neck area with many critical structures in close vicinity. Recent methods which use a multi-pinhole collimator and a single gamma detector image try to gain a depth estimation of the SLN. The low intensity of the sources together with the computational cost of the optimization process make the reconstruction in real-time, however, very challenging. RESULTS: In this paper, we use an optimal design approach to improve the classical pinhole design, resulting in a non-symmetric distribution of the pinholes of the collimator. This new design shows a great improvement of the accuracy when reconstructing the position and depth of the radioactive tracer. Then, we introduce our Sentinel lymph node fingerprinting (SLNF) algorithm, inspired by MR-fingerprinting, for fast and accurate reconstruction of the tracer distribution in 3D space using a single gamma detector image. As a further advantage, the method requires no pre-processing, i.e. filtering of the detector image. The method is very stable in its performance even for low exposure times. In our ex vivo experiments, we successfully located multiple Technetium 99m (Tc-99m) sources with an exposure time of only one second and still, with a very small L 2-error. CONCLUSION: These promising results under short exposure time are very encouraging for SLN biopsy. Although, this device has not been tested on patients yet, we believe: that this approach will give the surgeon accurate 3D positions of the SLN and hence, can potentially reduce the trauma for the patient.

Impact of short-term low-dose tamoxifen on molecular breast imaging background parenchymal uptake: a pilot study.

BACKGROUND: High background parenchymal uptake (BPU) on molecular breast imaging (MBI) has been identified as a breast cancer risk factor. We explored the feasibility of offering a short-term intervention of low-dose oral tamoxifen to women with high BPU and examined whether this intervention would reduce BPU. METHODS: Women with a history of high BPU and no breast cancer history were invited to the study. Participants had an MBI exam, followed by 30 days of low-dose oral tamoxifen at either 5 mg or 10 mg/day, and a post-tamoxifen MBI exam. BPU on pre- and post-tamoxifen MBI exams was quantitatively assessed as the ratio of average counts in breast fibroglandular tissue vs. average counts in subcutaneous fat. Pre-tamoxifen and post-tamoxifen BPU were compared with paired t tests. RESULTS: Of 47 women invited, 22 enrolled and 21 completed the study (10 taking 5 mg tamoxifen, 11 taking 10 mg tamoxifen). Mean age was 47.7 years (range 41-56 years). After 30 days low-dose tamoxifen, 8 of 21 women (38%) showed a decline in BPU, defined as a decrease from the pre-tamoxifen MBI of at least 15%; 11 of 21 (52%) had no change in BPU (within ± 15%); 2 of 21 (10%) had an increase in BPU of greater than 15%. Overall, the average post-tamoxifen BPU was not significantly different from pre-tamoxifen BPU (1.34 post vs. 1.43 pre, p = 0.11). However, among women taking 10 mg tamoxifen, 5 of 11 (45%) showed a decline in BPU; average BPU was 1.19 post-tamoxifen vs. 1.34 pre-tamoxifen (p = 0.005). In women taking 5 mg tamoxifen, 2 of 10 (20%) showed a decline in BPU; average BPU was 1.51 post-tamoxifen vs.1.53 pre-tamoxifen (p = 0.99). CONCLUSIONS: Short-term intervention with low-dose tamoxifen may reduce high BPU on MBI for some patients. Our preliminary findings suggest that 10 mg tamoxifen per day may be more effective than 5 mg for inducing declines in BPU within 30 days. Given the variability in BPU response to tamoxifen observed among study participants, future study is warranted to determine if BPU response could predict the effectiveness of tamoxifen for breast cancer risk reduction within an individual. TRIAL REGISTRATION: ClinicalTrials.gov NCT02979301 . Registered 01 December 2016.

PICS: a platform for planar imaging of curved surfaces of brain and other tissue.

Optical imaging of wholemount tissue samples provides greater understanding of structure-function relationships as the architecture of these specimens is generally well preserved. However, difficulties arise when attempting to stitch together images of multiple regions of larger, oddly shaped specimens. These difficulties include (1) maintaining consistent signal-to-noise ratios when the overlying sample surface is uneven, (2) ensuring sample viability when live samples are required, and (3) stabilizing the specimen in a fixed position in a flowing medium without distorting the tissue sample. To address these problems, we designed a simple and cost-efficient device that can be 3D-printed and machined. The design for the device, named the Platform for Planar Imaging of Curved Surfaces (PICS), consists of a sample holder, or "cap" with gaps for fluid flow and a depression for securing the sample in a fixed position without glue or pins, a basket with two arms that move along an external radius to rotate the sample around a central axis, and a customizable platform designed to fit on a commercially available temperature control system for slice electrophysiology. We tested the system using wholemounts of the murine subventricular zone (SVZ), which has a high degree of curvature, to assess sample viability and image quality through cell movement for over an hour for each sample. Using the PICS system, tissues remained viable throughout the imaging sessions, there were no noticeable decreases in the image SNR across an imaging plane, and there was no noticeable displacement of the specimen due to fluid flow.

Annihilation gamma imaging for carbon ion beam range monitoring using Si/CdTe Compton camera.

In this study, we performed on-beam monitoring of 511 keV annihilation gamma emissions using a Compton camera. Beam monitoring experiments were conducted using carbon ion beams of 290 MeV/u irradiated on a polymethyl methacrylate (PMMA) phantom. The intensity of the beams was 3 × 109 particles per pulse, with 20 pulses per minute. A Compton camera based on a silicon/cadmium telluride (Si/CdTe) detector was used to monitor the annihilation gamma rays emitted from the phantom. We successfully reconstructed the energy events of 511 keV annihilation gamma rays and developed Compton images using a simple back-projection method. The distribution of the annihilation gamma ray generation traced the beam trajectory and the peak intensity position was a few millimeters shorter than the Bragg peak position. Moreover, the effect of the beam range shifter with 30, 60, and 90 mm water equivalent thickness (WET) was clearly visualized in the reconstructed Compton images. The experimentally measured values of the corresponding range shifts in the PMMA phantom (28.70 mm, 52.49 mm, and 76.77 mm, respectively) were consistent with the shifts of the Bragg peak position (25.50 mm, 51.30 mm and 76.70 mm, respectively) evaluated by Monte Carlo simulation. The results show that the Si/CdTe Compton camera has strong potential for on-beam monitoring of annihilation gamma rays in particle therapy in clinical situations.