Dosimetric Application of Phosphorus Doped Fibre for X-ray and Proton Therapy.

Phosphorous-doped silica optical fibres with a core diameter of 4 µm were tested in X-ray and proton fields for application in cancer therapy dosimetry. Specifically, the radiation-induced attenuation was investigated in terms of linearity in deposited dose in 15 MV and 6 MV photons and 74 MeV protons, as well as Bragg-peak detection along the proton track. Fibres were found to demonstrate linear relative dose response in both radiation modalities, but possible saturation did occur at the high linear energy transfer of the Bragg peak. This demonstrates the possibility to use these fibres as a relative dosimeter for radiation therapy applications.

Atrial fibrillation ablation in patients with transthyretin cardiac amyloidosis.

AIMS: Atrial fibrillation (AF) occurs in as many as 70% of patients with transthyretin cardiac amyloidosis (ATTR CA). The aim of our study was to investigate the impact of AF ablation on freedom from recurrent arrhythmia, hospitalization for AF or heart failure (HF), and mortality. METHODS AND RESULTS: This was a retrospective observational cohort study of 72 patients with ATTR CA and AF, of whom 24 underwent AF ablation and were matched in a 2:1 manner based on age, gender, ATTR CA stage, New York Heart Association functional class, ejection fraction, and date of AF diagnosis with 48 patients with ATTR CA and AF undergoing medical management. During a mean follow-up of 39 ± 26 months, 10 (42%) patients remained free of recurrent arrhythmia following ablation. Ablation was significantly more effective in those with Stage I or II ATTR CA, with 9/14 (64%) patients with Stage I or II ATTR CA remaining free of recurrent arrhythmia compared to only 1/10 (10%) patients with Stage III disease (P = 0.005). Death occurred in 7 (29%) patients in the ablation group compared to 36 (75%) in the non-ablation arm (P = 0.01). Rates of ischaemic stroke were similar in both groups. Ablation was associated with a significant reduction in the frequency of hospitalization for HF/arrhythmia (1.7 ± 2.4 hospitalizations vs. 4 ± 3.5, P = 0.005). On Cox proportional hazards analyses, ablation was associated with improved survival (hazard ratio 0.38, 95% confidence intervals 0.17-0.86; P = 0.02). CONCLUSION: Atrial fibrillation ablation is associated with reduced mortality in ATTR CA and is most effective when performed earlier during the disease process.

Cardiac devices in patients with transthyretin amyloidosis: Impact on functional class, left ventricular function, mitral regurgitation, and mortality.

BACKGROUND: The aim of our study was to investigate outcomes of patients with ATTR (amyloidosis and transthyretin) CA (cardiac amyloidosis) and implantable devices with respect to left ventricular ejection fraction (LVEF), mitral regurgitation (MR), New York Heart Association (NYHA) functional class, and mortality. METHODS: This was a retrospective observational cohort study of 78 patients with ATTR CA and implantable devices. During a mean follow-up of 42 months we investigated the impact of right ventricular (RV) pacing burden and biventricular (BiV) pacing on LVEF, MR severity, NYHA functional class, and mortality. RESULTS: Worsening MR occurred in 11% of patients with a RV pacing % <40% compared to 62% of those with a RV pacing burden >40% (P = .002). Similarly, worsening LVEF occurred in 26% of patients who were RV paced <40% and 89% of those who were RV paced >40% of the time (P < .0001) and worsening in NYHA functional class occurred in 22% and 89%, respectively (P < .0001). Improvement in LVEF, NYHA functional class, and MR severity occurred in 78%, 67%, and 67%, respectively, in those with BiV devices. Death occurred in 67% of patients in the cardiac resynchronization therapy group compared to 68% of those with a RV pacing burden <40% and 92% of those with a RV pacing burden >40%. CONCLUSION: A higher RV pacing burden is associated with deleterious remodeling and congestive heart failure in patients with ATTR CA, whereas BiV pacing is associated with improvements in LVEF, NYHA class, and degree of MR. BiV pacing should be considered in patients with ATTR CA and an indication for pacing. However, further larger prospective studies will need to be performed.

Mass-manufacturable scintillation-based optical fiber dosimeters for brachytherapy.

Scintillation-based fiber dosimeters are a powerful tool for minimally invasive localized real-time monitoring of the dose rate during Low Dose Rate (LDR) and High Dose Rate (HDR) brachytherapy (BT). This paper presents the design, fabrication, and characterization of such dosimeters, consisting of scintillating sensor tips attached to polymer optical fiber (POF). The sensor tips consist of inorganic scintillators, i.e. Gd2O2S:Tb for LDR-BT, and Y2O3:Eu+4YVO4:Eu for HDR-BT, dispersed in a polymer host. The shape and size of the tips are optimized using non-sequential ray tracing simulations towards maximizing the collection and coupling of the scintillation signal into the POF. They are then manufactured by means of a custom moulding process implemented on a commercial hot embossing machine, paving the way towards series production. Dosimetry experiments in water phantoms show that both the HDR-BT and LDR-BT sensors feature good consistency in the magnitude of the average photon count rate and that the photon count rate signal is not significantly affected by variations in sensor tip composition and geometry. Whilst individual calibration remains necessary, the proposed dosimeters show great potential for in-vivo dosimetry for brachytherapy.

Benchmarking a novel inorganic scintillation detector for applications in radiation therapy.

PURPOSE: The aim of this study was to investigate the contribution of Cerenkov radiation to the overall signal measured with a novel inorganic scintillating detector (ISD). METHODS: An ISD based on terbium doped gadolinium oxysulphide (Gd2O2S:Tb) was used. A hyperspectral technique separated the Cerenkov signal from the radioluminescence (RL) signal of the ISD. The relative contribution of Cerenkov radiation was evaluated under different conditions. The efficiency of using simple spectral correction to reduce the Cerenkov contribution was quantified. Other experiments investigated were the dose-per-pulse dependence observed in our previous study and the absorbed-dose energy dependence when acquiring percentage depth dose curves using Monte Carlo (MC) simulations. RESULTS: The maximum relative contribution of Cerenkov radiation was 2.10% for a 10 × 10 cm2 field at 10 cm depth. However, this percentage increased to 24% when the ISD was 7 cm out of field and exposed to a 10 × 10 cm2 field. Using 15 nm and 5 nm band-pass filters reduced the Cerenkov contribution across all experimental conditions by a maximum of 75% and 82%, respectively. The MC simulation results show discrepancies between the measured and simulated PDD profiles using the Gd2O2S:Tb scintillator at depth. CONCLUSION: This study showed that while Gd2O2S:Tb ISD provides high-signal intensity, the contribution of Cerenkov radiation under specific conditions can be significant. However, narrow band-pass filters can reduce the Cerenkov signal to a negligible level. The MC simulations suggest mechanisms other than the stem effect and the absorbed-dose energy dependence influence the response of the Gd2O2S:Tb scintillator measurements at depth.

A Monte Carlo study of the effect of an ultrasound transducer on surface dose during intrafraction motion imaging for external beam radiation therapy.

PURPOSE: The aim of this study was to estimate changes in surface dose due to the presence of the Clarity Autoscan™ ultrasound (US) probe during prostate radiotherapy using Monte Carlo (MC) methods. METHODS: MC models of the Autoscan US probe were developed using the BEAMnrc/DOSXYZnrc code based on kV and MV CT images. CT datasets were converted to voxelized mass density phantoms using a CT number-to-mass density calibration. The dosimetric effect of the probe, in the contact region (an 8 mm × 12 mm single layer of voxels), was investigated using a phantom set-up mimicking two scenarios (a) a transperineal imaging configuration (radiation beam perpendicular to the central US axial direction), and (b) a transabdominal imaging configuration (radiation beam parallel to the central US axial direction). For scenario (a), the dosimetric effect was evaluated as a function of the probe to inferior radiation field edge distance. Clinically applicable distances from 5 mm separation to 2 mm overlap were determined from the radiotherapy plans of 27 patients receiving Clarity imaging. Overlaps of 3 to 14 (1 to 3 SD) mm were also considered to include the effect of interfraction motion correction. The influence of voxel size on surface dose estimation was investigated. Approved clinical plans from two prostate patients were used to simulate worst-case dosimetric impact of the probe when large couch translations were applied to correct for interfraction prostate motion. RESULTS: The dosimetric impact of both the MV and kV probe models agreed within ±2% for both beam configurations. For scenario (a) and 1 mm voxel model, the probe gave mean dose increases of 1.2% to 4.6% (of the dose at isocenter) for 5 mm separation to 0 mm overlap in the probe-phantom contact region, respectively. This increased to 27.5% for the largest interfraction motion correction considered (14 mm overlap). For separations of ≥ 2 mm dose differences were < 2%. Simulated dose perturbations were found to be superficial; for the 14 mm overlap the dose increase reduced to < 3% at 5.0 mm within the phantom. For scenario (b), dose increases due to the probe were < 5% in all cases. The dose increase was underestimated by up to ~13% when the voxel size was increased from 1 mm to 3 mm. MC simulated dose to the PTV and OARs for the two clinical plans considered showed good agreement with commercial treatment planning system results (within 2%). Mean dose increases due to the presence of the probe, after the maximum interfraction motion correction, were ~16.3% and ~8.0%, in the contact region, for plan 1 and plan 2, respectively. CONCLUSIONS: The presence of the probe results in superficial dose perturbations for patients with an overlap between the probe and the radiation field present in either the original treatment plan or due to translation of the radiation field to simulate correction of interfraction internal prostate motion.