Volumetric and Dosimetric Assessment by Cone-Beam Computed Tomography Scans in Head and Neck Radiation Therapy: A Monitoring in Four Phases of Treatment

Due to the anatomical changes frequently occurring during the course of head and neck (H&N) cancer radiotherapy, the dose distribution, which was actually delivered to the patient, might significantly differ from that planned. The aim of this paper is to investigate these volumetric changes and the resulting dosimetric implications on organs at risk (OARs) and clinical target volumes (CTVs) by cone beam computed tomography (CBCT) scans throughout the treatment. Ten H&N patients, treated by Intensity Modulated Radiotherapy, were analyzed. CTVs and OARs were delineated on four CBCT, acquired at the 10th, 15th, 20th and 25th treatment session, and then compared with the ones at planning CT. The planned beams were applied to each CBCT to recalculate the dose distribution and the corresponding dose volume histograms were compared with those generated on planning CT. To evaluate the HU discrepancies between the conventional CT and CBCT images we used a Catphan® 504, observing a maximum discrepancy of about 30 HU. We evaluated the impact of this HU difference in dose calculation and a not clinically relevant error, within 2.8%, was estimated. No inhomogeneity correction was used. The results showed an increased CTV mean dose (Dmean) of about 3% was found, without significant reduction in volume. Due to the parotids' shrinkage (up to 42%), significant dosimetric increases were observed: ipsilateral gland at 15th CBCT (Dmean by 18%; V30 by 31%); controlateral gland at the 10th CBCT (Dmean by 12.2%; V30 by 18.7%). For the larynx, a significant increase of volume was found at the 20th (15.7%) and 25th CBCT (13.3%) but it complied with dose constraint. The differences observed for the spinal cord and mandible maximum doses were not clinically relevant. In conclusion, the dosimetric analysis on CBCT can help clinicians to monitor treatment progress and to evaluate whether and when a new plan is necessary. The main benefit of replanning could be to preserve the parotids and our data support the hypothesis that the 3rd week of radiotherapy should be a check point for parotids

A straightforward multiparametric quality control protocol for proton magnetic resonance spectroscopy: Validation and comparison of various 1.5 T and 3 T clinical scanner systems

Purpose: The aim of this study was to propose and validate across various clinical scanner systems a straightforward multiparametric quality assurance procedure for proton magnetic resonance spectroscopy (MRS). Methods: Eighteen clinical 1.5 T and 3 T scanner systems for MRS, from 16 centres and 3 different manufacturers, were enrolled in the study. A standard spherical water phantom was employed by all centres. The acquisition protocol included 3 sets of single (isotropic) voxel (size 20 mm) PRESS acquisitions with unsuppressed water signal and acquisition voxel position at isocenter as well as off-center, repeated 4/5 times within approximately 2 months. Water peak linewidth (LW) and area under the water peak (AP) were estimated. Results: LW values [mean (standard deviation)] were 1.4 (1.0) Hz and 0.8 (0.3) Hz for 3 T and 1.5 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficient of variation of LW and AP for different spatial positions of acquisition voxel were 43% (20%) and 11% (11%), respectively. The mean (standard deviation) phantom T2 values were 1145 (50) ms and 1010 (95) ms for 1.5 T and 3 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficients of variation for repeated measurements of LW, AP and T2 were 25% (20%), 10% (14%) and 5% (2%), respectively. Conclusions: We proposed a straightforward multiparametric and not time consuming quality control protocol for MRS, which can be included in routine and periodic quality assurance procedures. The protocol has been validated and proven to be feasible in a multicentre comparison study of a fairly large number of clinical 1.5 T and 3 T scanner systems

The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs

We report the temperature dependent x-ray powder diffraction of the quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 K and 95 K. We have detected the structural phase transition from the tetragonal phase, with P4/nmm space group, to the orthorhombic or monoclinic phase, with Cmma or P112/a1 (or P2/c) space group, over a broad temperature range from 150 K to 120 K, centered at T0 ~137 K. Therefore the temperature of this structural phase transition is strongly reduced, by about ~30K, by increasing the internal chemical pressure going from LaOFeAs to NdOFeAs. In contrast the superconducting critical temperature increases from 27 K to 51 K going from LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped orthorhombic Cmma phase competes with the superconducting tetragonal phase. Therefore by controlling the internal chemical pressure in new materials it should be possible to push toward zero the critical temperature T0 of the structural phase transition, giving the striped phase, in order to get superconductors with higher Tc.Comment: 9 pages, 3 figure

Feshbach resonances and mesoscopic phase separation near a quantum critical point in multiband FeAs-based superconductors

High Tc superconductivity in FeAs-based multilayers (pnictides), evading temperature decoherence effects in a quantum condensate, is assigned to a Feshbach resonance (called also shape resonance) in the exchange-like interband pairing. The resonance is switched on by tuning the chemical potential at an electronic topological transition (ETT) near a band edge, where the Fermi surface topology of one of the subbands changes from 1D to 2D topology. We show that the tuning is realized by changing i) the misfit strain between the superconducting planes and the spacers ii) the charge density and iii) the disorder. The system is at the verge of a catastrophe i.e. near a structural and magnetic phase transition associated with the stripes (analogous to the 1/8 stripe phase in cuprates) order to disorder phase transition. Fine tuning of both the chemical potential and the disorder pushes the critical temperature Ts of this phase transition to zero giving a quantum critical point. Here the quantum lattice and magnetic fluctuations promote the Feshbach resonance of the exchange-like anisotropic pairing. This superconducting phase that resists to the attacks of temperature is shown to be controlled by the interplay of the hopping energy between stripes and the quantum fluctuations. The superconducting gaps in the multiple Fermi surface spots reported by the recent ARPES experiment of D. V. Evtushinsky et al. arXiv:0809.4455 are shown to support the Feshbach scenario.Comment: 31 pages, 7 figure

The Role of Adjuvant Radiotherapy for a Case of Primary Breast Sarcoma: A Plan Comparison between Three Modern Techniques and a Review of the Literature

A 65-year-old woman, affected by a malignant fibrous histiocytoma (undifferentiated pleomorphic sarcoma) of the left breast, presented to our department to receive the postoperative radiotherapy. In the absence of prospective and randomized trials and investigations on breast sarcoma irradiation in literature, due to the rarity of this pathology, the role of adjuvant radiotherapy remains unclear. To identify the best radiotherapy technique for this patient, three methods were compared: 3D conformal radiotherapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and volumetric arc therapy (VMAT) or RapidArc® (RA). 50 Gy was prescribed to the chest wall and 66 Gy to the tumor bed. Three plans were designed, and target coverage, organs-at-risk sparing, and treatment efficiency were compared. IMRT and RA improved both target coverage and dose uniformity/homogeneity. Planning objective for the lung is always satisfied comparing the different techniques, but the volume receiving 20 Gy drops to 17% by RA compared to 3D-CRT. The heart volume receiving 30 Gy was 10% by IMRT, against 13% and 16% by RA and 3D-CRT. The monitor unit (MU) required by 3D-CRT was 527 MU, followed by RA and IMRT. Treatment time was similar with 3D-CRT and RA but doubled using IMRT. Although all three radiotherapy techniques offered a satisfactory solution, RA and IMRT offer some improvement on target coverage, dose homogeneity, and conformity for this particular case of breast sarcoma

Is ExacTrac x-ray system an alternative to CBCT for positioning patients with head and neck cancers?

Purpose: To evaluate the usefulness of a six-degrees-of freedom (6D) correction using ExacTrac robotics system in patients with head-and-neck (HN) cancer receiving radiation therapy.Methods: Local setup accuracy was analyzed for 12 patients undergoing intensity-modulated radiation therapy (IMRT). Patient position was imaged daily upon two different protocols, cone-beam computed tomography (CBCT), and ExacTrac (ET) images correction. Setup data from either approach were compared in terms of both residual errors after correction and punctual displacement of selected regions of interest (Mandible, C2, and C6 vertebral bodies).Results: On average, both protocols achieved reasonably low residual errors after initial correction. The observed differences in shift vectors between the two protocols showed that CBCT tends to weight more C2 and C6 at the expense of the mandible, while ET tends to average more differences among the different ROIs.Conclusions: CBCT, even without 6D correction capabilities, seems preferable to ET for better consistent alignment and the capability to see soft tissues. Therefore, in our experience, CBCT represents a benchmark for positioning head and neck cancer patients. (C) 2013 American Association of Physicists in Medicine

Volumetric and Dosimetric Assessment by Cone-Beam Computed Tomography Scans in Head and Neck Radiation Therapy: A Monitoring in Four Phases of Treatment

Due to the anatomical changes frequently occurring during the course of head and neck (H&N) cancer radiotherapy, the dose distribution, which was actually delivered to the patient, might significantly differ from that planned. The aim of this paper is to investigate these volumetric changes and the resulting dosimetric implications on organs at risk (OARs) and clinical target volumes (CTVs) by cone beam computed tomography (CBCT) scans throughout the treatment. Ten H&N patients, treated by Intensity Modulated Radiotherapy, were analyzed. CTVs and OARs were delineated on four CBCT, acquired at the 10th, 15th, 20th and 25th treatment session, and then compared with the ones at planning CT. The planned beams were applied to each CBCT to recalculate the dose distribution and the corresponding dose volume histograms were compared with those generated on planning CT. To evaluate the HU discrepancies between the conventional CT and CBCT images we used a Catphan® 504, observing a maximum discrepancy of about 30 HU. We evaluated the impact of this HU difference in dose calculation and a not clinically relevant error, within 2.8%, was estimated. No inhomogeneity correction was used. The results showed an increased CTV mean dose (Dmean) of about 3% was found, without significant reduction in volume. Due to the parotids' shrinkage (up to 42%), significant dosimetric increases were observed: ipsilateral gland at 15th CBCT (Dmean by 18%; V30 by 31%); controlateral gland at the 10th CBCT (Dmean by 12.2%; V30 by 18.7%). For the larynx, a significant increase of volume was found at the 20th (15.7%) and 25th CBCT (13.3%) but it complied with dose constraint. The differences observed for the spinal cord and mandible maximum doses were not clinically relevant. In conclusion, the dosimetric analysis on CBCT can help clinicians to monitor treatment progress and to evaluate whether and when a new plan is necessary. The main benefit of replanning could be to preserve the parotids and our data support the hypothesis that the 3rd week of radiotherapy should be a check point for parotids

Role of radiotherapy in the treatment of renal cell cancer: updated and critical review

The growing incidence of renal cell carcinoma (RCC) raises many questions about the management of these patients. The late clinical presentation, the presence of locally advanced or metastatic disease at diagnosis, the difficulty of radical surgical excision, and radioresistance make it one of the more challenging tumors to treat. The primary objective of this article is to propose an updated and critical review of the role of radiotherapy (RT) in the treatment of RCC