Frameless radiosurgical third ventriculostomy: Technical report.

BACKGROUND: We describe the technical report and results of the first image-guided, linear accelerator, frameless radiosurgical third ventriculostomy. METHODS: We report a 20 years old man, with diplopia, balance disturbances, and limitation for gaze supraversion. Magnetic resonance imaging resonance imaging of the brain and cranial computed tomography showed showed a left thalamic-midbrain lesion that caused partial compression of the Silvio aqueduct and mild ventricular dilatation. The biopsy revealed the diagnosis of pleomorphic xanthoastrocytoma. Before radical treatment of the tumor with fractionated stereotactic radiotherapy, the patient underwent to frameless radiosurgical third ventriculostomy, on the TrueBeam STX® platform with the ExacTrac localization system. The target used was the one defined on the floor of the third ventricle, at the midpoint between the mammillary bodies and the infundibular recess. The prescription dose was 120 Gy, given using a monoisocentric technique of multiple noncoplanar circular arches. The geometric arrangement of the plan consisted of 15 arches, with a 4 mm cone, distributed over a 110° table. RESULTS: There was symptomatic and image improvement two days after radiosurgery. On CT, a reduction in ventricular dilation was observed with a reduction in the Evans index from 0.39 (initial CT) to 0.29 (CT at 15 days). In 3.0T magnetic resonance image at 3 months, we showed the third ventriculostomy. There have been no treatment failures or complications. CONCLUSION: It is possible to effectively perform the frameless radiosurgical third ventriculostomy without associated morbidity in the short term.

Radiotherapy for the treatment of pituitary adenomas: A dosimetric comparison of three planning techniques.

AIM: Our goal was to compare conformal 3D (C3D) radiotherapy (RT), modulated intensity RT (IMRT), and volumetric modulated arc therapy (VMAT) planning techniques in treating pituitary adenomas. BACKGROUND: RT is important for managing pituitary adenomas. Treatment planning advances allow for higher radiation dosing with less risk of affecting organs at risk (OAR). MATERIALS AND METHODS: We conducted a 5-year retrospective review of patients with pituitary adenoma treated with external beam radiation therapy (C3D with flattening filter, flattening filter-free [FFF], IMRT, and VMAT). We compared dose-volume histogram data. For OARs, we recorded D2%, maximum, and mean doses. For planning target volume (PTV), we registered V95%, V107%, D95%, D98%, D50%, D2%, minimum dose, conformity index (CI), and homogeneity index (HI). RESULTS: Fifty-eight patients with pituitary adenoma were included. Target-volume coverage was acceptable for all techniques. The HI values were 0.06, IMRT; 0.07, VMAT; 0.08, C3D; and 0.09, C3D FFF (p < 0.0001). VMAT and IMRT provided the best target volume conformity (CI, 0.64 and 0.74, respectively; p < 0.0001). VMAT yielded the lowest doses to the optic pathway, lens, and cochlea. The position of the neck in extreme flexion showed that it helps in planning mainly with VMAT by allowing only one arc to be used and achieving the desired conformity, decreasing the treatment time, while allowing greater protection to the organs of risk using C3D, C3DFFF. CONCLUSIONS: Our results confirmed that EBRT in pituitary adenomas using IMRT, VMAT, C3D, C3FFF provide adequate coverage to the target. VMAT with a single arc or incomplete arc had a better compliance with desired dosimetric goals, such as target coverage and normal structures dose constraints, as well as shorter treatment time. Neck extreme flexion may have benefits in treatment planning for better preservation of organs at risk. C3D with extreme neck flexion is an appropriate treatment option when other treatment techniques are not available.

Present status of Medical Physics practice in Mexico: An occupational analysis.

PURPOSE: To present an overview of the status of Medical Physics practice in Mexico, promote the legal recognition of Medical Physics high-end training, and provide information that will potentially improve the Mexican healthcare system. METHODS: For the purpose of this research, the concept of "Medical Physics Professional/s" (MPP) is introduced to refer to any person/s executing the role of a clinical medical physicist (cMP) in whole or in part independent of academic profile, training or experience. A database of MPP in Mexico was built from official sources and personal communication with peers. Database records included the following fields: employer/s, specialty, academic profile, and annual income (when available). RESULTS: 133 centers in Mexico employ MPP, 49% of which are public institutions. 360 positions involving cMP roles were identified at the National Healthcare System (occupied by 283 MPP), 77% of which corresponded to radiation therapy. Public healthcare services hold 65% of the reported positions. Only 40% of MPP hold a graduate degree in Medical Physics, 46% of whom were located in the most densely populated region of Mexico. Of all MPP, 32% were women. CONCLUSIONS: This work allowed to clearly identify the current challenges of Medical Physics practice in Mexico, such as: insufficiency and uneven geographical distribution of qualified manpower, gender imparity, multishifting and wage gap. The products derived from this work could be used to guide the efforts to improve the Mexican healthcare system.

Fractal anatomy of the hippocampal formation.

PURPOSE: We believed that the hippocampal complex is a fractal, and we try to demonstrate it. METHODS: We selected 12 magnetic resonance (MR) studies from healthy brains. Five women and 7 men without neurological or psychiatric disease were analyzed. The age range was 50-71 years old, with a mean 57.1 ± 7.6 years. Image series of MR were obtained through 3D SPGR in scanner GE Singa 3.0 T (general Electric, USA), matrix acquisition 512 Å-512 Å-120, field size 240 mm, voxel size 0.47 mm Å-0.47 mm Å-1.2 mm, repetition time of 13 ms and eco time of 5.6 ms. The MRI were imported in DICOM format in the OsiriXsoftware where they were contoured. Post processing was done with ImageJ software; Box Counting method for fractal analysis and we also used the Box Counting method of the BoneJ plugin. RESULTS: All of the hippocampus analyzed were a fractal. The fractal dimension analysis distribution of the measurements had a central tendency. The mean of hippocampal fractal dimension was 1.32635, the range was from 1.3373 to 1.5344. We found a short interval of variability in the hippocampal fractal number. CONCLUSIONS: The hippocampal complex is a fractal. The fractal analysis must be an objective measurement that can help us as a descriptive tool in hippocampal anatomy and maybe in a close future in the diagnosis of anatomical alterations.

Evaluation of a LED-based flatbed document scanner for radiochromic film dosimetry in transmission mode.

Flatbed scanners are the most frequently used reading instrument for radiochromic film dosimetry because its low cost, high spatial resolution, among other advantages. These scanners use a fluorescent lamp and a CCD array as light source and detector, respectively. Recently, manufacturers of flatbed scanners replaced the fluorescent lamp by light emission diodes (LED) as a light source. The goal of this work is to evaluate the performance of a commercial flatbed scanner with LED based source light for radiochromic film dosimetry. Film read out consistency, response uniformity, film-scanner sensitivity, long term stability and total dose uncertainty was evaluated. In overall, the performance of the LED flatbed scanner is comparable to that of a cold cathode fluorescent lamp (CCFL). There are important spectral differences between LED and CCFL lamps that results in a higher sensitivity of the LED scanner in the green channel. Total dose uncertainty, film response reproducibility and long-term stability of LED scanner are slightly better than those of the CCFL. However, the LED based scanner has a strong non-uniform response, up to 9%, that must be adequately corrected for radiotherapy dosimetry QA. The differences in light emission spectra between LED and CCFL lamps and its potential impact on film-scanner sensitivity suggest that the design of a dedicated flat-bed scanner with LEDs may improve sensitivity and dose uncertainty in radiochromic film dosimetry.