Real-time motion management in MRI-guided radiotherapy: Current status and AI-enabled prospects.

MRI-guided radiotherapy (MRIgRT) is a highly complex treatment modality, allowing adaptation to anatomical changes occurring from one treatment day to the other (inter-fractional), but also to motion occurring during a treatment fraction (intra-fractional). In this vision paper, we describe the different steps of intra-fractional motion management during MRIgRT, from imaging to beam adaptation, and the solutions currently available both clinically and at a research level. Furthermore, considering the latest developments in the literature, a workflow is foreseen in which motion-induced over- and/or under-dosage is compensated in 3D, with minimal impact to the radiotherapy treatment time. Considering the time constraints of real-time adaptation, a particular focus is put on artificial intelligence (AI) solutions as a fast and accurate alternative to conventional algorithms.

Peritoneal dialysis patients using sevelamer do not present the acidosis problems that hemodialysis patients do.

Acidosis is responsible for catabolic state in dialysis patients and should be avoided or corrected. The survival of patients on peritoneal dialysis (PD) is as good as that of patients on hemodialysis--if not better-mainly because PD patients are rarely in an acidotic-catabolic state as compared with hemodialysis patients. We investigated whether the use of sevelamer in PD patients contributes to significant acidosis as has been reported in the hemodialysis population. We compared serum bicarbonate in 12 PD patients on sevelamer and 77 PD patients not on that drug. Residual renal function, serum phosphate, and daily intake of calcium phosphate binder were also recorded. Patients on PD who take sevelamer maintain a serum bicarbonate level in the normal range as compared with hemodialysis patients, who frequently become acidotic. Serum bicarbonate is only slightly lower in PD patients taking sevelamer than in those not taking that drug.

Team approach in a peritoneal dialysis unit provides better control of hypertension than in a hemodialysis unit.

Hypertension is one of the main factors contributing to morbidity and mortality in dialysis patients. Peritoneal dialysis (PD) patients have been reported to have lower blood pressure (BP) in the first 6 months or so of treatment. After that, their BP can be the same or higher than that seen in hemodialysis (HD) patients. We compared BP control between our PD patients and our HD patients. Systolic BP and pulse pressure were better controlled in PD patients; those PD patients required many fewer drugs. The difference was statistically significant. Anuric PD patients had a BP as good as that of the non anuric PD patients. Because PD is a constant treatment, fluid removal is much easier than in HD. To achieve good BP control, nurses, dieticians, and physicians must all have the same approach: that is, always to be aggressive in volume control as a first measure for achieving an adequate BP The team approach results in better BP control than that seen in HD.

A partial explanation for the surprising ADEMEX result.

Among the many factors contributing to mortality and morbidity in dialysis patients, nutrition is one of the most important. The ADEMEX (Adequacy of Peritoneal Dialysis in Mexico) study suggests that increasing the amount of daily dialysis to compensate for loss of residual renal function (RRF) does not change mortality or morbidity in peritoneal dialysis (PD) patients. Our purpose in the present study was to determine whether a gradual increase in daily dialysis volume to compensate for loss of RRF interferes with the nutrition of patients. We studied the correlation between normalized protein catabolic rate (nPCR) and daily dialysis volume in 150 PD patients. The Student t-test was used to discover if the correlation was statistically significant. We found that, as the daily dialysis volume increases to replace lost RRF, nPCR declines significantly. This reverse relationship was statistically significant at a p value of 0.007. Replacement of lost RRF by an increase in daily dialysis volume in PD patients contributes significantly to their state of protein malnutrition. The large quantity of carbohydrate acquired through dialysis interferes with the patients' intake of protein. The resulting condition of malnutrition probably plays a significant role in mortality and morbidity in those patients.

The relationship between residual renal function, protein catabolic rate, and phosphate and magnesium levels in peritoneal dialysis patients.

Residual renal function (RRF) is an important factor in the well-being of peritoneal dialysis (PD) patients. Serum phosphate has been correlated with long-term morbidity and mortality. We wished to determine if RRF contributes to a lower level of serum phosphate and magnesium. We also investigated the relationship between protein catabolic rate (PCR) and phosphate and magnesium. We collected data related to serum phosphate, serum magnesium, PCR, and RRF in 100 PD patients. The Pearson correlation coefficient was used to study the correlation between RRF and magnesium, RRF and phosphate, PCR and magnesium, and PCR and phosphate. No relationship were seen between PCR and serum phosphate, and RRF and serum magnesium. Significant relationships were seen between PCR and serum magnesium and phosphate. The very good inverse correlation between RRF and serum phosphate highlights the importance of RRF in the control of serum phosphate. A very good relationship was also seen between PCR and serum magnesium.

Impact of Levovist ultrasonographic contrast agent on the diagnosis and management of hypertensive patients with suspected renal artery stenosis: a Canadian multicentre pilot study.

OBJECTIVES: To compare the diagnoses obtained with unenhanced ultrasonography (US), contrast-enhanced US and captopril-enhanced renal scintigraphy and to determine whether use of a contrast agent improves ability to assess the renal arteries with duplex Doppler US. SUBJECTS AND METHODS: The study was an open-label controlled trial involving 78 patients with hypertension suspected to have a renovascular cause. The patients underwent captopril-enhanced scintigraphy or routine unenhanced US (the usual diagnostic methods at the centres where the study was conducted) and contrast-enhanced US (with Levovist, Berlex Canada, Lachine, Que.). The patients were followed for 3 months after the diagnostic tests were performed. RESULTS: Enhanced US yielded a diagnosis for a significantly greater proportion of patients than did unenhanced US (77 [99%] v. 64 [82%] of 78 patients; p = 0.002) or captopril-enhanced scintigraphy (71 [99%] v. 58 [81%] of 72 patients; p = 0.002). Diagnosis was possible with both enhanced and unenhanced duplex Doppler US in only 64 (82%) of the 78 patients, and the diagnosis was the same with both methods for 63 (98%) of these 64 patients. In contrast, diagnosis was possible for only 58 (81%) of the 72 patients who underwent both enhanced US and captopril-enhanced scintigraphy; the same diagnosis was reported in 53 (91%) of these 58 cases. During follow-up, 11 patients (21 kidneys) underwent angiography. Significant stenosis was detected in 6 (55%) of the patients (8 [38%] of the kidneys). Both the enhanced and unenhanced US results agreed more often with angiography than did captopril-enhanced scintigraphy (9 [82%] v. 8 [73%] of the 11 patients). The proportion of patients in whom the left and right renal artery could be assessed by duplex Doppler US increased significantly (by 58% and 43%, respectively) with use of the contrast agent. CONCLUSION: Enhanced US had a higher rate of successful diagnosis than unenhanced US and captopril-enhanced renal scintigraphy. Enhanced US might therefore be suitable as a screening method for hypertensive patients with suspected renal artery stenosis.

Economic impact of an ultrasonographic contrast agent on the diagnosis and initial management of patients with suspected renal artery stenosis.

OBJECTIVES: To determine resource use in the diagnosis and management of Canadian hypertensive patients with suspected renal artery stenosis and to estimate the impact of diagnosis with contrast-enhanced duplex Doppler ultrasonography (US) on resource use. SUBJECTS AND METHODS: Seventy-eight patients with suspected renal artery stenosis underwent usual diagnostic tests (captopril-enhanced renal scintigraphy or duplex Doppler US) and contrast-enhanced US. A management pathway ("planned") describing the medical resources required for further patient care was outlined on the basis of results from each test (separately), and a modified management pathway ("recommended"), which considered data from both diagnostic methods, was also outlined. Medical resources and productivity losses were assessed prospectively for a 3-month period after patients underwent both tests ("actual" management pathway). RESULTS: With usual diagnostic methods, 14 (18%) of the tests were inconclusive, whereas only 1 (1%) of the enhanced US examinations was inconclusive; the cost-efficacy ratio was $422 and $343 per successful diagnosis, respectively. Further management costs for patients with an inconclusive diagnosis were estimated at $6370 after the usual diagnostic tests, but only $1278 with enhanced US. Although the costs of the planned and recommended management pathways were similar ($227 and $294 per patient respectively), the proportion of patients requiring further resources was lower with enhanced US (56% v. 46%). Three-month actual management costs ranged from $121 to $1605 per patient (mean $360). Diagnostic tests and surgical procedures were the major cost drivers in all pathways, and costs were highest for patients in whom stenosis was diagnosed. CONCLUSIONS: For patients with suspected renal artery stenosis, contrast-enhanced US had a higher diagnostic success rate than usual diagnostic methods and afforded savings through lower administrative costs and lower medical resource consumption for patients whose diagnosis was unclear after usual diagnostic tests.