Correction of megavoltage cone-beam CT images of the pelvic region based on phantom measurements for dose calculation purposes.

Megavoltage cone-beam CT (MVCBCT) is an imaging technology that provides a 3D representation of the patient in treatment position. Because it is a form of x-ray tomography, MVCBCT images give information about the attenuation coefficients of the imaged tissues, and thus could be used for dose calculation. However, the cupping and missing data artifacts seen on MVCBCT images can cause inaccuracies in dose calculations. To eliminate these inaccuracies, a correction method specific to pelvis imaging and based on phantom measurements has been devised. Pelvis-shaped water phantoms of three different sizes were designed and imaged with MVCBCT. Three sets of correction factors were created from the artifacts observed in these MVCBCT images by dividing the measured CT number by the predefined CT number for water. Linear interpolation is performed between the sets of correction factors to take into account the varying size of different patients. To compensate for the missing anatomy due to the limited field of view of the MVCBCT system, the MVCBCT image is complemented with the kilovoltage CT (kVCT) image acquired for treatment planning.When the correction method is applied to an anthropomorphic pelvis phantom, the standard deviation between dose calculations performed with kVCT and MVCBCT images is 0.6%, with 98% of the dose points agreeing within +/- 3%.With uncorrected MVCBCT images this percentage falls to 75%. An example of dose calculation performed with a corrected clinicalMVCBCT image of a prostate cancer patient shows that changes in anatomy of normal tissues result in variation of the dose distribution received by these tissues.This correction method enablesMVCBCT images to be used for the verification of the daily dose distribution for patients treated in the pelvis region

Feasibility of MV CBCT-based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT-based dose calculations.

Unlike scheduled radiotherapy treatments, treatment planning time and resources are limited for emergency treatments. Consequently, plans are often simple 2D image-based treatments that lag behind technical capabilities available for nonurgent radiotherapy. We have developed a novel integrated urgent workflow that uses onboard MV CBCT imaging for patient simulation to improve planning accuracy and reduce the total time for urgent treatments. This study evaluates both MV CBCT dose planning accuracy and novel urgent workflow feasibility for a variety of anatomic sites. We sought to limit local mean dose differences to less than 5% compared to conventional CT simulation. To improve dose calculation accuracy, we created separate Hounsfield unit-to-density calibration curves for regular and extended field-of-view (FOV) MV CBCTs. We evaluated dose calculation accuracy on phantoms and four clinical anatomical sites (brain, thorax/spine, pelvis, and extremities). Plans were created for each case and dose was calculated on both the CT and MV CBCT. All steps (simulation, planning, setup verification, QA, and dose delivery) were performed in one 30 min session using phantoms. The monitor units (MU) for each plan were compared and dose distribution agreement was evaluated using mean dose difference over the entire volume and gamma index on the central 2D axial plane. All whole-brain dose distributions gave gamma passing rates higher than 95% for 2%/2 mm criteria, and pelvic sites ranged between 90% and 98% for 3%/3 mm criteria. However, thoracic spine treatments produced gamma passing rates as low as 47% for 3%/3 mm criteria. Our novel MV CBCT-based dose planning and delivery approach was feasible and time-efficient for the majority of cases. Limited MV CBCT FOV precluded workflow use for pelvic sites of larger patients and resulted in image clearance issues when tumor position was far off midline. The agreement of calculated MU on CT and MV CBCT was acceptable for all treatment sites

Premières mentions et répartition de la Salamandre sombre du Nord, Desmognathus fuscus, sur la rive nord du fleuve Saint-Laurent, au Québec

La Salamandre sombre du Nord (Desmognathus fuscus) est une espèce qui a fait l’objet de plusieurs inventaires au Québec étant donné qu’elle y est à la limite nord de sa répartition. Nous rapportons les premières observations de cette espèce au nord du fleuve Saint-Laurent, depuis Trois-Rivières, à l’ouest, jusqu’à Cap-Tourmente, vers l’est. Ces mentions ont été faites de 1987 à 2003, dans 20 sites. La majorité des sites où fut découverte la Salamandre sombre du Nord sont des ruisseaux et des résurgences d’eau

Découverte de la Salamandre à quatre orteils, Hemidactylium scutatum, à Québec, Québec : limite nord-est de l'espèce sur la rive nord du fleuve Saint-Laurent

En 1999 trois spécimens de Salamandre à quatre orteils ont été observés à Québec, sur la rive nord du fleuve Saint-Laurent. Des recherches effectuées au même site en 2001 ont permis de découvrir d’autres spécimens de même que des pontes. Ces mentions élargissent la distribution connue de l’espèce de 90 km vers le nord-est-est et 80 km vers le nord-nord-ouest. Il s’agit vraisemblablement de la limite nord-est de cette salamandre, sur la rive nord du Saint-Laurent.In 1999, three Four-toed Salamanders were observed at Québec, north shore of the St. Lawrence River. Field searches in 2001 allowed the discovery of another specimen as well as egg clutches. These records extend the known range of the species 90 km north-east-east and 80 km north-north-west. This is probably the northeastern limit of this salamander’s range on the north shore of St. Lawrence River

Development and Growth of Northern Leopard Frog, Lithobates pipiens, Tadpoles in North American Waterfowl Management Plan Permanent Basins and in Natural Wetlands

We monitored the development and growth of a cohort of Northern Leopard Frog (Lithobates pipiens) tadpoles, in one North American Waterfowl Management Plan (NAWMP) permanent basin and in one natural environment, a bay of the St. Lawrence River. We wanted to know if this kind of artificial wetland could be considered as suitable habitat for this declining species and compare the environment that was provided to the tadpoles to those found in natural conditions. We also measured metamorphs' snout-vent length at three different permanent basins and natural bays to verify if the results from the detailed monitoring could be generalized. Our results have showed that the tadpoles were able to complete their development in the permanent basin and that their growth was superior to those from the natural site. The metamorphs from the permanent basins were also, on average, longer than those from the natural sites. The NAWMP permanent basins are suitable for the Northern Leopard Frog and could be a useful tool in the conservation of this species.Nous avons suivi le développement et la croissance d'une cohorte de têtards de Grenouille Léopard du Nord (Lithobates pipiens) dans un bassin permanent du Plan Nord Américain de Gestion de la Sauvagine (PNAGS) et dans un site naturel, une baie du fleuve Saint-Laurent. Nous voulions vérifier si ce type d'aménagement pouvait être considéré comme un habitat potentiel pour cette espèce en déclin et comparer les conditions environnementales disponibles pour les têtards. Nous avons aussi mesuré la longueur museau-cloaque des métamorphes provenant de trois bassins permanents et de trois baies du Saint-Laurent pour vérifier si les résultats obtenus par le suivi détaillé pouvaient être généralisés. Nos résultats ont montré que les têtards pouvaient compléter leur développement dans le bassin permanent et que leur croissance était aussi supérieure que dans le site naturel. Les métamorphes des trois bassins permanents étaient aussi, en moyenne, de taille supérieure à que ceux des sites naturels. Les bassins permanents du PNAGS peuvent être considérés comme des habitats potentiels pour la Grenouille Léopard du Nord. Ils pourraient représenter des outils utiles pour la conservation de cette espèce

Clinical applications of custom-made vaginal cylinders constructed using three-dimensional printing technology.

PurposeThree-dimensional (3D) printing technology allows physicians to rapidly create customized devices for patients. We report our initial clinical experience using this technology to create custom applicators for vaginal brachytherapy.Material and methodsThree brachytherapy patients with unique clinical needs were identified as likely to benefit from a customized vaginal applicator. Patient 1 underwent intracavitary vaginal cuff brachytherapy after hysterectomy and chemotherapy for stage IA papillary serous endometrial cancer using a custom printed 2.75 cm diameter segmented vaginal cylinder with a central channel. Patient 2 underwent interstitial brachytherapy for a vaginal cuff recurrence of endometrial cancer after prior hysterectomy, whole pelvis radiotherapy, and brachytherapy boost. We printed a 2 cm diameter vaginal cylinder with one central and six peripheral catheter channels to fit a narrow vaginal canal. Patient 3 underwent interstitial brachytherapy boost for stage IIIA vulvar cancer with vaginal extension. For more secure applicator fit within a wide vaginal canal, we printed a 3.5 cm diameter solid cylinder with one central tandem channel and ten peripheral catheter channels. The applicators were printed in a biocompatible, sterilizable thermoplastic.ResultsPatient 1 received 31.5 Gy to the surface in three fractions over two weeks. Patient 2 received 36 Gy to the CTV in six fractions over two implants one week apart, with interstitial hyperthermia once per implant. Patient 3 received 18 Gy in three fractions over one implant after 45 Gy external beam radiotherapy. Brachytherapy was tolerated well with no grade 3 or higher toxicity and no local recurrences.ConclusionsWe established a workflow to rapidly manufacture and implement customized vaginal applicators that can be sterilized and are made of biocompatible material, resulting in high-quality brachytherapy for patients whose anatomy is not ideally suited for standard, commercially available applicators

Investigating the clinical advantages of a robotic linac equipped with a multileaf collimator in the treatment of brain and prostate cancer patients.

The purpose of this study was to evaluate the performance of a commercially available CyberKnife system with a multileaf collimator (CK-MLC) for stereotactic body radiotherapy (SBRT) and standard fractionated intensity-modulated radiotherapy (IMRT) applications. Ten prostate and ten intracranial cases were planned for the CK-MLC. Half of these cases were compared with clinically approved SBRT plans generated for the CyberKnife with circular collimators, and the other half were compared with clinically approved standard fractionated IMRT plans generated for conventional linacs. The plans were compared on target coverage, conformity, homogeneity, dose to organs at risk (OAR), low dose to the surrounding tissue, total monitor units (MU), and treatment time. CK-MLC plans generated for the SBRT cases achieved more homogeneous dose to the target than the CK plans with the circular collimators, for equivalent coverage, conformity, and dose to OARs. Total monitor units were reduced by 40% to 70% and treatment time was reduced by half. The CK-MLC plans generated for the standard fractionated cases achieved prescription isodose lines between 86% and 93%, which was 2%-3% below the plans generated for conventional linacs. Compared to standard IMRT plans, the total MU were up to three times greater for the prostate (whole pelvis) plans and up to 1.4 times greater for the intracranial plans. Average treatment time was 25 min for the whole pelvis plans and 19 min for the intracranial cases. The CK-MLC system provides significant improvements in treatment time and target homogeneity compared to the CK system with circular collimators, while maintaining high conformity and dose sparing to critical organs. Standard fractionated plans for large target volumes (>100 cm3) were generated that achieved high prescription isodose levels. The CK-MLC system provides more efficient SRS and SBRT treatments and, in select clinical cases, might be a potential alternative for standard fractionated treatments. PACS numbers: 87.56.nk, 87.56.bd