Physics in medicine and biology
-
Respiratory induced resonance offset (RIRO) is a periodic disturbance of a magnetic field due to breathing. Such disturbance handicaps the accuracy of the proton resonance frequency shift (PRFS) method of MRI temperature mapping in anatomies situated nearby the lungs and chest wall. In this work, we propose a method capable of minimizing errors caused by RIRO in PRFS temperature maps. ⋯ Then, the calculated temperature changes are corrected for the additional contribution caused by RIRO using the pre-treatment baseline images acquired at the identical instances of the respiratory cycle. Our method is shown to improve the accuracy and stability of PRFS temperature maps in the presence of RIRO and inter-scan motion in phantom and volunteers' breathing experiments. Our method is also shown to be applicable to anatomies moving during breathing if a proper registration procedure is applied.
-
Comparative Study
Deformable registration of the planning image (kVCT) and the daily images (MVCT) for adaptive radiation therapy.
The incorporation of daily images into the radiotherapy process leads to adaptive radiation therapy (ART), in which the treatment is evaluated periodically and the plan is adaptively modified for the remaining course of radiotherapy. Deformable registration between the planning image and the daily images is a key component of ART. In this paper, we report our researches on deformable registration between the planning kVCT and the daily MVCT image sets. ⋯ We registered the MVCT images with their corresponding kVCT image. The similarity measures and visual inspections of contour matches by physicians validated this technique. The applications of deformable registration in ART, including 'deformable dose accumulation', 'automatic re-contouring' and 'tumour growth/regression evaluation' throughout the course of radiotherapy are also studied.
-
The purpose of this study is to extend an algorithm proposed for beam orientation optimization in classical conformal radiotherapy to intensity-modulated radiation therapy (IMRT) and to evaluate the algorithm's performance in IMRT scenarios. In addition, the effect of the candidate pool of beam orientations, in terms of beam orientation resolution and starting orientation, on the optimized beam configuration, plan quality and optimization time is also explored. The algorithm is based on the technique of mixed integer linear programming in which binary and positive float variables are employed to represent candidates for beam orientation and beamlet weights in beam intensity maps. ⋯ It is also found that decreasing beam orientation resolution to 10 degrees greatly reduced the size of the candidate pool of beam orientations without significant influence on the optimized beam configuration and plan quality, while selecting different starting orientations had large influence. Our study demonstrates that the algorithm can be applied to IMRT scenarios, and better beam orientation configurations can be obtained using this algorithm. Furthermore, the optimization efficiency can be greatly increased through proper selection of beam orientation resolution and starting beam orientation while guaranteeing the optimized beam configurations and plan quality.
-
The initial area under the gadolinium curve (IAUGC) is often used in addition to or as an alternative to parameters derived from pharmacokinetic modelling of T1-weighted dynamic contrast-enhanced (DCE) MRI data in the assessment of response to treatment of cancer. However, the physiological meaning of the IAUGC has not been rigorously defined with respect to model-based parameters. ⋯ It is shown that IAUGC is a mixed parameter that can display correlation with K(trans), v(e) and v(p) and ultimately has an intractable relationship with all three. Furthermore, it is demonstrated that the range over which IAUGC is taken and the nature of the vascular input function do not significantly affect this relationship.
-
High linear energy transfer (LET) radiation for internal targeted therapy has been a long time coming on to the medical therapy scene. While fundamental principles were established many decades ago, the clinical implementation has been slow. Localized neutron capture therapy, and more recently systemic targeted alpha therapy, are at the clinical trial stage. ⋯ This has been the task of chemotherapy, but palliation is the major application. Finally, there is the inability to inhibit the development of lethal metastatic cancer after successful treatment of the primary cancer. This review charts, from an Australian perspective, the developing role of local and systemic high LET, internal radiation therapy.