This study demonstrated the feasibility of engineering a multimodal contrast agent with prolonged contrast enhancement in vivo for use in CT and MR. This contrast agent may serve as a valuable tool for cardiovascular imaging as well as image registration and guidance applications in radiation therapy.
Purpose: To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons.Methods: Dosimetric and toxicity information was analyzed for 12 patients with cervical (8), endometrial (2) or vaginal (2) cancer previously treated with external beam pelvic radiotherapy and a CRT boost. Optimized IMRT boost treatment plans were then developed for each of the 12 patients and compared to CRT and 4FB plans. The plans were compared in terms of dose conformality and critical normal tissue avoidance.
Results:The median planning target volume (PTV) was 151 cm 3 (range 58-512 cm 3 ). The median overlap of the contoured rectum with the PTV was 15 (1-56) %, and 11 (4-35) % for the bladder. Two of the 12 patients, both with large PTVs and large overlap of the contoured rectum and PTV, developed grade 3 rectal bleeding. The dose conformity was significantly improved with IMRT over CRT and 4FB (p ≤ 0.001 for both). IMRT also yielded an overall improvement in the rectal and bladder dose-volume distributions relative to CRT and 4FB. The volume of rectum that received the highest doses (>66% of the prescription) was reduced by 22% (p < 0.001) with IMRT relative to 4FB, and the bladder volume was reduced by 19% (p < 0.001). This was at the expense of an increase in the volume of these organs receiving doses in the lowest range (<33%).
Conclusion:These results indicate that IMRT can improve target coverage and reduce dose to critical structures in gynecologic patients receiving an external beam radiotherapy boost. This dosimetric advantage will be integrated with other patient and treatment-specific factors, particularly internal tumor movement during fractionated radiotherapy, in the context of a future image-guided radiation therapy study.
Monte Carlo-based simulation of positron emission tomography (PET) data plays a key role in the design and optimization of data correction and processing methods. Our first aim was to adapt and configure the PET-SORTEO Monte Carlo simulation program for the geometry of the widely distributed Inveon PET preclinical scanner manufactured by Siemens Preclinical Solutions. The validation was carried out against actual measurements performed on the Inveon PET scanner at the Australian Nuclear Science and Technology Organisation in Australia and at the Brain & Mind Research Institute and by strictly following the NEMA NU 4-2008 standard. The comparison of simulated and experimental performance measurements included spatial resolution, sensitivity, scatter fraction and count rates, image quality and Derenzo phantom studies. Results showed that PET-SORTEO reliably reproduces the performances of this Inveon preclinical system. In addition, imaging studies showed that the PET-SORTEO simulation program provides raw data for the Inveon scanner that can be fully corrected and reconstructed using the same programs as for the actual data. All correction techniques (attenuation, scatter, randoms, dead-time, and normalization) can be applied on the simulated data leading to fully quantitative reconstructed images. In the second part of the study, we demonstrated its ability to generate fast and realistic biological studies. PET-SORTEO is a workable and reliable tool that can be used, in a classical way, to validate and/or optimize a single PET data processing step such as a reconstruction method. However, we demonstrated that by combining a realistic simulated biological study ([(11)C]Raclopride here) involving different condition groups, simulation allows one also to assess and optimize the data correction, reconstruction and data processing line flow as a whole, specifically for each biological study, which is our ultimate intent.
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