Therapeutic proton and heavier ion beams generate prompt gamma photons that may escape from the patient. In principle, this allows for real-time, in situ monitoring of the treatment delivery, in particular, the hadron range within the patient, by imaging the emitted prompt gamma rays. Unfortunately, the neutrons simultaneously created with the prompt photons create a background that may obscure the prompt gamma signal. To enhance the accuracy of proton dose verification by prompt gamma imaging, we therefore propose a time-of-flight (TOF) technique to reject this neutron background, involving a shifting time window to account for the propagation of the protons through the patient. Time-resolved Monte Carlo simulations of the generation and transport of prompt gamma photons and neutrons upon irradiation of a PMMA phantom with 100, 150 and 200 MeV protons were performed using Geant4 (version 9.2.p02) and MCNPX (version 2.7.D). The influence of angular collimation and TOF selection on the prompt gamma and neutron longitudinal profiles is studied. Furthermore, the implications of the proton beam microstructure (characterized by the proton bunch width and repetition period) are investigated. The application of a shifting TOF window having a width of ΔTOF(z) = 1.0 ns appears to reduce the neutron background by more than 99%. Subsequent application of an energy threshold does not appear to sharpen the distal falloff of the prompt gamma profile but reduces the tail that is observed beyond the proton range. Investigations of the influence of the beam time structure show that TOF rejection of the neutron background is expected to be effective for typical therapeutic proton cyclotrons.

In-vivo imaging is a strategy to monitor the range of protons inside the patient during radiation treatment. A possible method of in-vivo imaging is detection of secondary 'prompt' gamma (PG) photons outside the body, which are produced by inelastic proton-nuclear interactions inside the patient. In this paper, important parameters influencing the relationship between the PG profile and percentage depth dose (PDD) in a uniform cylindrical phantom are explored. Monte Carlo simulations are performed with the new Geant4 based code TOPAS for mono-energetic proton pencil beams (range: 100-250 MeV) and an idealized PG detector. PG depth profiles are evaluated using the inflection point on a sigmoid fit in the fall-off region of the profile. A strong correlation between the inflection point and the proton range determined from the PDD is found for all conditions. Variations between 1.5 mm and 2.7 mm in the distance between the proton range and the inflection point are found when either the mass density, phantom diameter, or detector acceptance angle is changed. A change in cut-off energy of the detector could induce a range difference of maximum 4 mm. Applying time-of-flight discrimination during detection, changing the primary energy of the beam or changing the elemental composition of the tissue affects the accuracy of the range prediction by less than 1 mm. The results indicate that the PG signal is rather robust to many parameter variations, but millimetre accurate range monitoring requires all medium and detector properties to be carefully taken into account.

Positron emission tomography (PET) is the imaging modality most extensively tested for treatment monitoring in particle therapy. Optimal use of PET in proton therapy requires in situ acquisition of the relatively strong (15)O signal due to its relatively short half-life (~2 min) and high oxygen content in biological tissues, enabling shorter scans that are less sensitive to biological washout. This paper presents the first performance tests of a scaled-down in situ time-of-flight (TOF) PET system based on digital photon counters (DPCs) coupled to Cerium-doped Lutetium Yttrium Silicate (LYSO:Ce) crystals, providing quantitative results representative of a dual-head tomograph that complies with spatial constraints typically encountered in clinical practice (2  ×  50°, of 360°, transaxial angular acceptance). The proton-induced activity inside polymethylmethacrylate (PMMA) and polyethylene (PE) phantoms was acquired within beam pauses (in-beam) and immediately after irradiation by an actively-delivered synchrotron pencil-beam, with clinically relevant 125.67 MeV/u, 4.6  ×  10(8) protons s(-1), and 10(10) total protons. 3D activity maps reconstructed with and without TOF information are compared to FLUKA simulations, demonstrating the benefit of TOF-PET to reduce limited-angle artefacts using a 382 ps full width at half maximum coincidence resolving time. The time-dependent contributions from different radionuclides to the total count-rate are investigated. We furthermore study the impact of the acquisition time window on the laterally integrated activity depth-profiles, with emphasis on 2 min acquisitions starting at different time points. The results depend on phantom composition and reflect the differences in relative contributions from the radionuclides originating from carbon and oxygen. We observe very good agreement between the shapes of the simulated and measured activity depth-profiles for post-beam protocols. However, our results also suggest that available experimental cross sections underestimate the production of (10)C for in-beam acquisitions, which in PE results in an overestimation of the predicted activity range by 1.4 mm. The uncertainty in the activity range measured in PMMA using the DPC-based TOF-PET prototype setup equals 0.2 mm-0.3 mm.

Proton range monitoring may facilitate online adaptive proton therapy and improve treatment outcomes. Imaging of proton-induced prompt gamma (PG) rays using a knife-edge slit collimator is currently under investigation as a potential tool for real-time proton range monitoring. A major challenge in collimated PG imaging is the suppression of neutron-induced background counts. In this work, we present an initial performance test of two knife-edge slit camera prototypes based on arrays of digital photon counters (DPCs). PG profiles emitted from a PMMA target upon irradiation with a 160 MeV proton pencil beams (about 6.5 × 10(9) protons delivered in total) were measured using detector modules equipped with four DPC arrays coupled to BGO or LYSO : Ce crystal matrices. The knife-edge slit collimator and detector module were placed at 15 cm and 30 cm from the beam axis, respectively, in all cases. The use of LYSO : Ce enabled time-of-flight (TOF) rejection of background events, by synchronizing the DPC readout electronics with the 106 MHz radiofrequency signal of the cyclotron. The signal-to-background (S/B) ratio of 1.6 obtained with a 1.5 ns TOF window and a 3 MeV-7 MeV energy window was about 3 times higher than that obtained with the same detector module without TOF discrimination and 2 times higher than the S/B ratio obtained with the BGO module. Even 1 mm shifts of the Bragg peak position translated into clear and consistent shifts of the PG profile if TOF discrimination was applied, for a total number of protons as low as about 6.5 × 10(8) and a detector surface of 6.6 cm × 6.6 cm.

Prompt-gamma (PG) imaging has the potential for monitoring proton therapy in real time. Different approaches are investigated. We focus on developing multi-slat collimators to image PG quanta, aiming at optimizing collimator performance to detect deviations in treatment delivery. We investigated six different multi-slat configurations, which have either optimal (analytical) intrinsic spatial resolution at fixed efficiency, or otherwise; at different distances from the proton pencil-beam axis (15 cm-35 cm). We used Geant4 to simulate irradiations of the head (energy: 130 MeV) and pelvis (200 MeV) of an anthropomorphic phantom, with and without physiologic/morphologic or setup changes of clinical dosimetric relevance. The particles escaping the phantom were transported through each of these multi-slat configurations and the gamma counts profiles were recorded at the collimator exit. Median filtering was applied to the registered PG-profiles to mitigate the effects of septa shadowing and statistical fluctuations. Time-of-flight discrimination was used to enhance the signal-to-background ratio, which appeared crucial for 200 MeV irradiations. Visual detection of the artificially introduced changes was possible by comparing the PG to the depth-dose profiles. Moreover, 2 mm range shifts could be detected in the head irradiation case using a simple linear regression fit to the falloff of the PG-profile. The influence of changes in complex, patient-like dose distributions on the PG-profiles obtained with multi-slat collimation is first studied in this work, which further gives insight on collimator design optimization and highlights its potential and simplicity for detecting proton treatment deviations over a wide range of Bragg peak positions.

Precise monitoring of the particle range inside the body, preferably in real-time, is a primary interest in quality assurance of particle therapy. Prompt-gamma (PG) detection aims at this task, but such a system is technically challenging to implement. For mechanically collimated PG detection, neutron-induced background radiation originating in the collimator material is a major issue. We study by Monte-Carlo simulations (Geant4), the influence of different collimator designs and their geometric parameters -such as distance to source, size and septa thickness -on the correlation between transmitted PG profiles and the longitudinal depth-dose profile. The impact of background rejection by time-of-flight (TOF) is also addressed. A single-parallel-slit collimator scanned along the beam axis was primarily studied and results show that the background can be efficiently reduced by TOF discrimination. Due to reduced statistics, signal integration from neighbouring pencil-beams was further considered, accounting for typical clinical proton fluences. Furthermore, first direct-comparison results between multi-slat collimation and a knife-edge-slit collimator are presented, obtained both by simulation and analytical calculations of their geometric performances. Advantages and disadvantages of both approaches are highlighted and some design improvements are proposed. Energy thresholding was also addressed, showing that a low-energy threshold of 4 MeV increases the signal-to-background ratio in all simulation results, a factor mostly important if TOF rejection cannot be applied.

Background and PurposeLiterature is non-conclusive regarding selection of beam configurations in radiotherapy for mediastinal lymphoma (ML) radiotherapy, and published studies are based on manual planning with its inherent limitations. In this study, coplanar and non-coplanar beam configurations were systematically compared, using a large number of automatically generated plans.Material and MethodsAn autoplanning workflow, including beam configuration optimization, was configured for young female ML patients. For each of 25 patients, 24 plans with different beam configurations were generated with autoplanning: 11 coplanar CP_x plans and 11 non-coplanar NCP_x plans with x = 5 to 15 IMRT beams with computer-optimized, patient-specific configurations, and the coplanar VMAT and non-coplanar Butterfly VMAT (B-VMAT) beam angle class solutions (600 plans in total).ResultsAutoplans compared favorably with manually generated, clinically delivered plans, ensuring that beam configuration comparisons were performed with high quality plans. There was no beam configuration approach that was best for all patients and all plan parameters. Overall there was a clear tendency towards higher plan quality with non-coplanar configurations (NCP_x≥12 and B-VMAT). NCP_x≥12 produced highly conformal plans with on average reduced high doses in lungs and patient and also a reduced heart Dmean, while B-VMAT resulted in reduced low-dose spread in lungs and left breast.ConclusionsNon-coplanar beam configurations were favorable for young female mediastinal lymphoma patients, with patient-specific and plan-parameter-dependent dosimetric advantages of NCP_x≥12 and B-VMAT. Individualization of beam configuration approach, considering also the faster delivery of B-VMAT vs. NCP_x≥12, can importantly improve the treatments.

In this work, we considered the feasibility of Raman spectroscopy for discriminating between adenocarcinomatous and normal mucosal formalin-fixed colonic tissues. Unlike earlier studies in colorectal cancer, a spectral deconvolution model was implemented to derive spectral information. Eleven samples of human colon were used, and 55 spectra were analyzed. Each spectrum was resolved into 25 bands from 975 to 1720 cm(-1), where modes of proteins, lipids, and nucleic acids are observed. From a comparative study of band intensities, those presenting higher differences between tissue types were correlated to biochemical assignments. Results from fitting procedure were further used as inputs for linear discriminant analysis, where combinations of band intensities and intensity ratios were tested, yielding accuracies up to 81%. This analysis yields objective discriminating parameters after fitting optimization. The bands with higher diagnosis relevance detected by spectra deconvolution enable to confine the study to some spectral regions instead of broader ranges. A critical view upon limitations of this approach is presented, along with a comparison of our results to earlier ones obtained in fresh colonic tissues. This enabled to assess the effect of formalin fixation in colonic tissues, and determine its relevance in the present analysis.