CT based prostate cancer patient-specific transperineal ultrasound probe setups for image guided radiotherapy

\u3cp\u3eRadiotherapy aims at irradiating tumor tissue, while sparing normal tissue as much as possible and it is a suitable treatment option for prostate cancer. A crucial aspect of the radiotherapy workflow is patient positioning. It has been shown that frequent imaging during the course of the treatment (image guided radiotherapy) can improve this positioning accuracy. Despite the many advantages of ultrasound imaging (high soft tissue contrast, 4D imaging, etc.) its use in image guided radiotherapy workflows is not widespread. This can be primarily attributed to the need for a trained operator during image acquisition. In this study, patient-specific transperineal ultrasound probe setups were automatically calculated based on CT scans of prostate cancer patients. These setups seem to meet clinical requirements and their use can potentially minimize operator dependence and improve usability for relatively untrained operators. In the end, this could allow patients to fully benefit from the unique characteristics of this imaging modality.\u3c/p\u3

Various approaches for pseudo-CT scan creation based on ultrasound to ultrasound deformable image registration between different treatment time points for radiotherapy treatment plan adaptation in prostate cancer patients

The purpose of this study was to evaluate eight possible approaches to create pseudo-CT images for radiotherapy (RT) treatment re-planning. These re-planning CT scans would normally require a separate CT scan session. If important changes occur in patient's anatomy between simulation (SIM) and treatment (TX) stages, 3D ultrasound (US) images acquired at the two stages, available in US guided RT workflows, can be used to produce a deformation field. Proof of concept research showed that the application of this deformation field to the SIM CT image yields a pseudo-CT which can be more representative of the patient at TX than SIM CT. Co-registered CT and US volumes acquired at five different time points during the RT course of a prostate cancer patient were combined into data pairs, providing ground truth CT images (CTtx). Eight different methods were explored to create the deformation field that was used to produce the pseudo-CT scan. Anatomical structure comparison and γ index calculations were used to compare the similarity of the pseudo-CT volumes and the reference TX CT volumes. In five out of ten data pairs, all the eight approaches resulted in the creation of a pseudo-CT equally or more similar to the TX CT than the SIM CT within the region of interest, with an average improvement of 54.1% (range: 5.1%–126.5%) in dice similarity coefficient (DSC) and 32.3% (range: 0.3%–52.6%) in γ index. For the remaining data pairs, four up to seven approaches resulted in an improvement in both DSC (range: 4.3%–54%) and γ index (range: 0.8%–41.3%). In conclusion, at least four out of eight explored approaches resulted in more representative pseudo-CT images in all the data pairs. In particular, the approaches in which an initial rigid alignment was combined with deformable registration performed best

CT scan based prostate cancer patient-specific transperineal ultrasound probe setups for image guided radiotherapy

Radiotherapy (RT) is a possible treatment modality for prostate cancer patients. The aim of RT is to irradiate tumor tissue, while sparing normal tissue as much as possible. Prior to treatment delivery, a CT scan is usually acquired, on which a treatment plan is prepared. Subsequently, the radiation dose is delivered to the patient in multiple fractions. The patients' setup prior to each of these fractions should replicate the setup during the CT scan, in order to deliver the dose to the correct location. This makes patient setup a crucial aspect of the RT workflow. It has been shown that frequent imaging during the course of the treatment (image guided RT, IGRT) can allow a more accurate patient positioning. The use of 4D ultrasound (US) imaging in these IGRT workflows is not widespread, despite the many advantages (e.g. superior soft-tissue contrast, real-time volumetric organ tracking and no extra radiation). This can be mainly attributed to the high operator dependence of this image modality. In this study, the planning CT scans of prostate cancer patients were used to calculate patient-specific transperineal US (TPUS) probe setups. The use of these setups can potentially minimize operator dependence and possibly even remove the need for a trained operator

The use of ultrasound imaging in the external beam radiotherapy workflow of prostate cancer patients

\u3cp\u3eExternal beam radiotherapy (EBRT) is one of the curative treatment options for prostate cancer patients. The aim of this treatment option is to irradiate tumor tissue, while sparing normal tissue as much as possible. Frequent imaging during the course of the treatment (image guided radiotherapy) allows for determination of the location and shape of the prostate (target) and of the organs at risk. This information is used to increase accuracy in radiation dose delivery resulting in better tumor control and lower toxicity. Ultrasound imaging is harmless for the patient, it is cost-effective, and it allows for real-time volumetric organ tracking. For these reasons, it is an ideal technique for image guidance during EBRT workflows. Review papers have been published in which the use of ultrasound imaging in EBRT workflows for different cancer sites (prostate, breast, etc.) was extensively covered. This new review paper aims at providing the readers with an update on the current status for prostate cancer ultrasound guided EBRT treatments.\u3c/p\u3

Automated patient-specific transperineal ultrasound probe setups for prostate cancer patients undergoing radiotherapy

\u3cp\u3ePurpose: The use of ultrasound imaging is not widespread in prostate cancer radiotherapy workflows, despite several advantages (eg, allowing real-time volumetric organ tracking). This can be partially attributed to the need for a trained operator during acquisition and interpretation of the images. We introduce and evaluate an algorithm that can propose a patient-specific transperineal ultrasound probe setup, based on a CT scan and anatomical structure delineations. The use of this setup during the simulation and treatment stage could improve usability of ultrasound imaging for relatively untrained operators (radiotherapists with less than 1 yr experience with ultrasound). Methods: The internal perineum boundaries of three prostate cancer patients were identified based on bone masks extracted from their CT scans. After projection of these boundaries to the skin and exclusion of specific areas, this resulted in a skin area accessible for transperineal ultrasound probe placement in clinical practice. Several possible probe setups on this area were proposed by the algorithm and the optimal setup was automatically selected. In the end, this optimal setup was evaluated based on a comparison with a corresponding transperineal ultrasound volume acquired by a radiation oncologist. Results: The algorithm-proposed setups allowed visualization of 100% of the clinically required anatomical structures, including the whole prostate and seminal vesicles, as well as the adjacent edges of the bladder and rectum. In addition, these setups allowed visualization of 94% of the anatomical structures, which were also visualized by the physician during the acquisition of an actual ultrasound volume. Conclusion: Provided that the ultrasound probe setup proposed by the algorithm, is properly reproduced on the patient, it allows visualization of all clinically required structures for image guided radiotherapy purposes. Future work should validate these results on a patient population and optimize the workflow to enable a relatively untrained operator to perform the procedure.\u3c/p\u3