Seminal vesicle intrafraction motion during the delivery of radiotherapy sessions on a 1.5 T MR-Linac.

PURPOSE: To evaluate seminal vesicle (SV) intrafraction motion using cinematic magnetic resonance imaging (cine-MR) during the delivery of online adaptive MR-Linac radiotherapy fractions, in preparation of MR-guided extremely hypofractionated radiotherapy for intermediate to high-risk prostate cancer patients. MATERIAL AND METHODS: Fifty prostate cancer patients were treated with 5 × 7.25 Gy on a 1.5 Tesla MR-Linac. 3D Cine-MR imaging was started simultaneously and acquired over the full beam-on period. Intrafraction motion in this cine-MR was determined for each SV separately with a previously validated soft-tissue contrast-based tracking algorithm. Motion statistics and coverage probability for the SVs and prostate were determined based on the obtained results. RESULTS: SV motion was automatically determined during the beam-on period (approx. 10 min) for 247 fractions. SV intrafraction motion shows larger spread than prostate intrafraction motion and increases over time. This difference is especially evident in the anterior and cranial translation directions. Significant difference in rotation about the left-right axis was found, with larger rotation for the SVs than the prostate. Intra-fraction coverage probability of 99% can be achieved when using 5 mm isometric expansion for the left and right SV and 3 mm for the prostate. CONCLUSION: This is the first study to investigate SV intrafraction motion during MR-guided RT sessions on an MR-Linac. We have shown that high quality 3D cine-MR imaging and SV tracking during RT is feasible with beam-on. The tracking method as described may be used as input for a fast replanning algorithm, which allows for intrafraction plan adaptation.

Anatomically-adaptive multi-modal image registration for image-guided external-beam radiotherapy.

Image-guided radiotherapy (IGRT) allows observation of the location and shape of the tumor and organs-at-risk (OAR) over the course of a radiation cancer treatment. Such information may in turn be used for reducing geometric uncertainties during therapeutic planning, dose delivery and response assessment. However, given the multiple imaging modalities and/or contrasts potentially included within the imaging protocol over the course of the treatment, the current manual approach to determining tissue displacement may become time-consuming and error prone. In this context, variational multi-modal deformable image registration (DIR) algorithms allow automatic estimation of tumor and OAR deformations across the acquired images. In addition, they require short computational times and a low number of input parameters, which is particularly beneficial for online adaptive applications, which require on-the-fly adaptions with the patient on the treatment table. However, the majority of such DIR algorithms assume that all structures across the entire field-of-view (FOV) undergo a similar deformation pattern. Given that various anatomical structures may behave considerably different, this may lead to the estimation of anatomically implausible deformations at some locations, thus limiting their validity. Therefore, in this paper we propose an anatomically-adaptive variational multi-modal DIR algorithm, which employs a regionalized registration model in accordance with the local underlying anatomy. The algorithm was compared against two existing methods which employ global assumptions on the estimated deformations patterns. Compared to the existing approaches, the proposed method has demonstrated an improved anatomical plausibility of the estimated deformations over the entire FOV as well as displaying overall higher accuracy. Moreover, despite the more complex registration model, the proposed approach is very fast and thus suitable for online scenarios. Therefore, future adaptive IGRT workflows may benefit from an anatomically-adaptive registration model for precise contour propagation and dose accumulation, in areas showcasing considerable variations in anatomical properties.

Prostate intrafraction motion during the preparation and delivery of MR-guided radiotherapy sessions on a 1.5T MR-Linac.

PURPOSE: To evaluate prostate intrafraction motion using MRI during the full course of online adaptive MR-Linac radiotherapy (RT) fractions, in preparation of MR-guided extremely hypofractionated RT. MATERIAL AND METHODS: Five low and intermediate risk prostate cancer patients were treated with 20 × 3.1 Gy fractions on a 1.5T MR-Linac. Each fraction, initial MRI (Pre) scans were obtained at the start of every treatment session. Pre-treatment planning MRI contours were propagated and adapted to this Pre scan after which plan re-optimization was started in the treatment planning system followed by dose delivery. 3D Cine-MR imaging was started simultaneously with beam-on and acquired over the full beam-on period. Prostate intrafraction motion in this cine-MR was determined with a previously validated soft-tissue contrast based tracking algorithm. In addition, absolute accuracy of the method was determined using a 4D phantom. RESULTS: Prostate motion was completely automatically determined over the full on-couch period (approx. 45 min) with no identified mis-registrations. The translation 95% confidence intervals are within clinically applied margins of 5 mm, and plan adaption for intrafraction motion was required in only 4 out of 100 fractions. CONCLUSION: This is the first study to investigate prostate intrafraction motions during entire MR-guided RT sessions on an MR-Linac. We have shown that high quality 3D cine-MR imaging and prostate tracking during RT is feasible with beam-on. The clinically applied margins of 5 mm have proven to be sufficient for these treatments and may potentially be further reduced using intrafraction plan adaptation guided by cine-MR imaging.

An internalist view on the value of life and some tricky cases relevant to it.

If we understand death as the irreversible loss of the good life, we can give meaning to the idea that for suffering patients in the end stage of their illness, life may become an evil and death no longer a threat. Life may lose its good already in the living person. But what does the good of life consist in, then? I defend an internalist view according to which the goodness of life is intrinsically related to the attitudes, concerns, interests and experiences of the person who is leading the life. This results in the contention that the core of what we understand as the value of the person's life is to be identified with what makes life go well for the person living the particular life. This internalist view does not presuppose (or imply) hedonism or mentalism, nor does it pose an experience requirement. Something may be good for you, because it is valuable as seen from your authentic viewpoint, even if you do not actually experience this goodness, or think otherwise because you are mistaken about your own well-being. To test this position, and the authenticity-requirement it includes, I discuss three cases of patients who are persistent in denying that in their life any value is left and who contend that death is not worse than further living. Internalism acknowledges that in the life of these patients there may be 'functionings' and 'beings' that are worthwhile, where the test of value is at least partially independent of subjective assessment. Still, internalism claims that something truly valuable can only contribute to the good of one's life of it has positive meaning as seen from the attitudinal viewpoint that identifies oneself.

Communitarian illusions: or why the Dutch proposal for setting priorities in health care must fail.

This article accounts for the failure of the Dutch Government Committee on Choices in Health Care to develop useful criteria of necessary care by which to set health care priorities and ration resources. The Government Committee has been inspired by philosophers who think that allocation problems cannot be solved without placing broad moral questions about the good life, and about the place of health and illness in our lives on the public agenda. The fruitless attempts of the Committee to formulate an effective notion of essential care, based upon a community-oriented perspective of health, shows why the communitarian approach is bound to fail. Questions about essential health care cannot be answered on a macro-level. The only way to get some reasonable control over day-to-day health care allocation decisions in hospitals and institutions is by trying to understand the history, laws, habits and contingencies of what is going on between doctors and patients. Such an understanding can be gained by developing a relational and biographical view on the doctor-patient relationship.