Real-time image-guided treatment of mobile tumors in proton therapy by a library of treatment plans: a simulation study

PURPOSE

To improve target coverage and reduce the dose in the surrounding organs-at-risks (OARs), we developed an image-guided treatment method based on a precomputed library of treatment plans controlled and delivered in real-time.

METHODS

A library of treatment plans is constructed by optimizing a plan for each breathing phase of a four dimensional computed tomography (4DCT). Treatments are delivered by simulation on a continuous sequence of synthetic computed tomographies (CTs) generated from real magnetic resonance imaging (MRI) sequences. During treatment, the plans for which the tumor are at a close distance to the current tumor position are selected to deliver their spots. The study is conducted on five liver cases.

RESULTS

We tested our approach under imperfect knowledge of the tumor positions with a 2 mm distance error. On average, compared to a 4D robustly optimized treatment plan, our approach led to a dose homogeneity increase of 5% (defined as 1 - D 5 - D 95 prescription $1-\frac{D_5-D_{95}}{\text{prescription}}$ ) in the target and a mean liver dose decrease of 23%. The treatment time was roughly increased by a factor of 2 but remained below 4 min on average.

CONCLUSIONS

Our image-guided treatment framework outperforms state-of-the-art 4D-robust plans for all patients in this study on both target coverage and OARs sparing, with an acceptable increase in treatment time under the current accuracy of the tumor tracking technology.

Mitigating inherent noise in Monte Carlo dose distributions using dilated U-Net

PURPOSE

Monte Carlo (MC) algorithms offer accurate modeling of dose calculation by simulating the transport and interactions of many particles through the patient geometry. However, given their random nature, the resulting dose distributions have statistical uncertainty (noise), which prevents making reliable clinical decisions. This issue is partly addressable using a huge number of simulated particles but is computationally expensive as it results in significantly greater computation times. Therefore, there is a trade-off between the computation time and the noise level in MC dose maps. In this work, we address the mitigation of noise inherent to MC dose distributions using dilated U-Net - an encoder-decoder-styled fully convolutional neural network, which allows fast and fully automated denoising of whole-volume dose maps.

METHODS

We use mean squared error (MSE) as loss function to train the model, where training is done in 2D and 2.5D settings by considering a number of adjacent slices. Our model is trained on proton therapy MC dose distributions of different tumor sites (brain, head and neck, liver, lungs, and prostate) acquired from 35 patients. We provide the network with input MC dose distributions simulated using 1 × 10 6 particles while keeping 1 × 10 9 particles as reference.

RESULTS

After training, our model successfully denoises new MC dose maps. On average (averaged over five patients with different tumor sites), our model recovers D 95 of 55.99 Gy from the noisy MC input of 49.51 Gy, whereas the low noise MC (reference) offers 56.03 Gy. We observed a significant reduction in average RMSE (thresholded >10% max ref) for reference vs denoised (1.25 Gy) than reference vs input (16.96 Gy) leading to an improvement in signal-to-noise ratio (ISNR) by 18.06 dB. Moreover, the inference time of our model for a dose distribution is less than 10 s vs 100 min (MC simulation using 1 × 10 9 particles).

CONCLUSIONS

We propose an end-to-end fully convolutional network that can denoise Monte Carlo dose distributions. The networks provide comparable qualitative and quantitative results as the MC dose distribution simulated with 1 × 10 9 particles, offering a significant reduction in computation time.

Kyste mucoïde adventitiel de l'artère radiale associé à un kyste arthrosynovial radiocarpien de la gouttière du pouls. À propos d'un cas

The authors report a rare case of a 51-years old woman presenting with cystic mucoid adventitial disease of the radial artery associated with a volar wrist ganglion. Imaging namely doppler sonography, magnetic resonance scanning and angio-MR was performed preoperatively because of a history of radial artery aneurysm in the opposite wrist. The radial artery was resected and the defect bridged by a venous autograft; the volar wrist ganglia was removed. Postoperative histological analysis confirmed mucoid adventitial cyst without communication with the volar wrist ganglion. Surgeons ought to be aware of this rare differential diagnosis (less than ten cases in the literature) in cases of preoperative or peroperative diagnostic doubt.

Dysregulated apoptosis in primary varicose veins

OBJECTIVE

Programmed cell death plays a critical role in various physiological processes. To investigate its possible pathogenic role in primary varicose veins we studied histological changes in surgical specimens from human varicose veins. In varicose and healthy veins, we also determined the number of cells in apoptosis, and investigated mediators regulating the intrinsic apoptotic mitochondrial pathway (Bax and caspase 9).

METHODS

A total 23 varicose veins were obtained from 18 patients undergoing lower-extremity varicose vein surgery for primary varicose disorders. We used nine healthy veins obtained from nine patients undergoing distal arterial bypass grafting surgery as controls. The venous segment analysed was the distal part of the greater saphenous vein. Specimens for histological examination were stained with hematoxylin and eosin, trichromic and Victoria blue. Cell apoptoses and mediators of the mitochondrial pathway were detected in the media by immunohistochemistry using antibodies to peroxidase in situ apoptosis, Bax and caspase 9. Results were expressed as indexes for the three antibodies tested. The Mann-Whitney test was used to compare the results obtained in the two groups.

RESULTS

Varicose vein specimens exhibited a more disorganised architecture than healthy veins and showed an increased number of collagen fibres and a decrease in the density and size of elastic fibres. All anti-apoptotic antibodies tested detected significantly fewer immunoreactive cells in tissue sections from the media of varicose veins than of healthy veins (peroxidase in situ, varicose veins (VV) median 2.4% (inter-quartile range 1.6-3.9) versus control (C) 14% (IQR 8.8-19); Bax, VV 1.4% (IQR 0.36-2.4) versus C 11% (IQR 7.6-15); and caspase 9, VV 1.7% (IQR 0.06-3.4) versus C 10% (IQR 9.1-12), P=0.0001 (Mann-Whitney test).

CONCLUSION

Apoptosis is down regulated in the medial layer of varicose veins. This dysregulation of the cellular mechanism that maintains normal tissue integrity is mediated through the intrinsic apoptotic pathway and may be among the causes of primary varicose veins.

Heparin-induced thrombocytopenia with acute aortic and renal thrombosis in a patient treated with low-molecular-weight heparin

Heparin-induced thrombocytopenia is a rare but serious complication of heparin therapy. Most of cases are related to unfractionated heparin, but a few are due to low molecular weight heparin sometimes associated with unfractionated heparin. A patient with pulmonary contusions after chest injury developed a catheter related subclavian vein thrombosis on day 16. He was treated by increasing doses of low molecular weight heparin. Aortic and renal thromboses occurred on day 21. Surgical thrombectomy, performed after starting alternative anticoagulation treatment led to complete arterial recovery. In case of suspicion of heparin-induced thrombocytopenia, with unfractionated or low-molecular-weight heparin, heparin treatment must be discontinued before the results of biological tests become available. Arterial and/or venous thrombosis is a serious complication of heparin-induced thrombocytopenia. The treatment has two aims: first, to restore arterial patency by clot removal by thrombectomy, bypass or thrombolysis, and second, to avoid new thrombosis formation by substitutive anticoagulation treatment: danaparoid may have cross-reaction with heparin, or lepirudin has anaphylactic risks and needs biological follow-up. Heparin-induced thrombocytopenia and thrombosis can be complicated by death or disabilities such as amputations, stroke, renal or bowel infarction. Once HIT has been diagnosed heparin should never be given again, but if cardiopulmonary bypass is required, it might be reintroduced during operation only if serum antibodies have disappeared.

Connection Between a Long-standing Traumatic Arteriovenous Fistula and Development of Aneurysmal Disease

Long-standing peripheral arteriovenous fistulas (AVFs) are always accompanied by ectasia of the proximal arteries. In the literature, traumatic fistulas of the lower limbs are frequently reported to be associated with iliac and even infrarenal aortic aneurysms; however, no study dealing with associated visceral aneurysms has been published. We report a case in which a traumatic AVF was accompanied by the late development of not only an infrarenal aortic aneurysm but also both superior mesenteric and right renal artery aneurysm. No causal relationship may be inferred between the tibial fistula and the other aneurysms, but this previously unreported finding does raise the question of a possible connection.

[Superficial femoral artery autotransplantation for popliteal artery damage: a good solution?]

We chose not to use a vein to bypass a popliteal artery lesion in four preferring to perform an autotransplantation of a proximal segment of the homolateral superficial femoral artery. The proximal arterial segment translated downstream being replaced by a synthetic graft. This approach was used to treat a popliteal aneurysm in two patients and cystic adventitiel disease in two others. The great saphenous was unfit for bypass in two patients. One patient died with a patent transplant nine Months after surgery due to an unrelated urological problem. The other three patients were alive and symptom free, at least forty-two Months after surgery. All three had a patent transplant despite obstruction of the proximal synthetic bypass in one patient. Provided that the outcome in a larger number of cases confirms these favourable results, we think that this technique offers an attractive alternative to venous bypass, at least whenever a venous graft cannot be used.

[Primary infected aneurysm of the infra-renal aorta:in situ or extra-anatomic bypass?]

There is no agreement in the literature as regards the best treatment for primary infected aneurysms. There is agreement concerning in situ treatment, inlay graft for supra-renal aneurysms. For infra-renal localizations no consensus has been reached. Most Authors prefer biological grafts over prosthetic materials for infected grafts or primary infected aneurysms. We report here a case of primary infected aneurysm treated in two stages. An initial axillo-bifemoral bypass was followed one Month later by aneurysmectomy and wide debridement of infected tIssue. Results were good at two years.

Popliteal Artery Entrapment Associated with Cannabis Arteritis

OBJECTIVE

To report popliteal artery entrapment in a patient with distal necrosis and cannabis-related arteritis, two rare or exceptional disorders never described in association. To conduct a targeted review and especially to seek information on the clinical presentation with characteristics specific to each disorder so as to hasten the diagnosis and choose appropriate management.

MATERIAL AND METHODS

A 19-year-old man who presented with plantar claudication associated with necrosis in a toe underwent diagnostic arteriography and surgery for popliteal artery entrapment type III.

RESULTS

Surgical clearance resolved the popliteal artery entrapment but left the clinical symptoms unchanged. Closer questioning disclosed a history of cannabis consumption and intravenous vasodilatory therapy was started. After the 21-day course of vasodilator agents the pain disappeared and the toe necrosis regressed. The patient stopped taking cannabis and had no signs of recurrence.

CONCLUSION

Whereas a popliteal artery entrapment, albeit a rare event, is well described and responds to standardized treatment, popliteal artery entrapment associated with cannabis-induced arteritis is an exceptional event that could confuse management. Because young people-the age group mainly at risk for popliteal artery entrapment-increasingly use cannabis, cannabis arteritis could become a more frequent event associated with other arterial disorders that may confuse the diagnosis and complicate management. Our experience in a young patient suggests that coexisting popliteal artery entrapment and distal necrosis in a young patient should raise a strong suspicion of an associated vascular disorder possibly related to cannabis consumption. Intravenous vasodilatation treatment is successful provided that cannabis use is discontinued.

Tumor-related osteomalacia followed after treatment by hyperparathyroidism

Tumor-induced osteomalacia is due to renal phosphate wasting in response to a humoral factor produced by a tumor, usually a benign mesenchymal tumor. Removal of the tumor is followed by resolution of the metabolic disorder. Physicians should be aware that sporadic renal phosphate wasting in an adult should prompt a search for a tumor. A case of tumor-induced osteomalacia due to a nonossifying fibroma of the radius is reported. After removal of the tumor, renal phosphate excretion returned to normal, but the patient developed tertiary hyperparathyroidism. Eight years elapsed between symptom onset and the diagnosis of the tumor. The pathogenesis of tumor-induced osteomalacia and the role of treatment for renal phosphate wasting on the subsequent development of hyperthyroidism are discussed.