Optimizing the effective spot size and the dosimetric leaf gap of the AcurosXB algorithm for VMAT treatment planning

PURPOSE

The aim of this study is to provide and test a new methodology to adjust the AcurosXB beam model for VMAT treatment plans.

METHOD

The effective target spot size of the AcurosXB v15 algorithm was adjusted in order to minimize the difference between calculated and measured penumbras. The dosimetric leaf gap (DLG) was adjusted using the asynchronous oscillating sweeping gap tests defined in the literature and the MLC transmission was measured. The impact of the four parameters on the small field output factors was assessed using a design of experiment methodology. Patient quality controls were performed for the three beam models investigated including two energies and two MLC models.

RESULTS

Effective target spot sizes differed from the manufacturer recommendations and strongly depended on the MLC model considered. DLG values ranged from 0.7 to 2.3 mm and were found to be larger than the ones based on the sweeping gap tests. All parameters were found to significantly influence the calculated output factors, especially for the 0.5 cm × 0.5 cm field size. Interactions were also identified for fields smaller than 2 cm × 2 cm, suggesting that adjusting the parameters on the small field output factors should be done with caution. All patient quality controls passed the universal action limit of 90%.

CONCLUSION

The methodology provided is simple to implement in clinical practice. It was validated for three beam models covering a large variety of treatment types and localizations.

Evaluation and application of a new scintillator-based heat-resistant back-scattered electron detector during heat treatment in the scanning electron microscope

A new high-temperature detector dedicated to the collection of backscattered electrons is used in combination with heating stages up to 1050°C, in high-vacuum and low-vacuum modes in order to evaluate its possibilities through signal-to-noise ration measurements and different applications. Four examples of material transformations occurring at high temperature are herein reported: grain growth during annealing of a rolled platinum foil, recrystallisation of a multiphased alloy, oxidation of a Ni-based alloy and complex phase transformations occurring during the annealing of an Al-Si coated boron steel. The detector could be potentially adapted to any type of SEM and it offers good opportunities to perform high-temperature experiments in various atmospheres.

Comparison of five dose calculation algorithms in a heterogeneous media using design of experiment

PURPOSE

Design of experiments (DoE) provides a methodology to reveal the influence of input values on the measured output with a limited number of trials. The purpose of this study was to describe how DoE can be used to evaluate the performances of several dose calculation systems in heterogeneous media, including algorithms like Pencil Beam (PB), Anisotropic Analytical Algorithm (AAA), Acuros XB (AXB), Monte Carlo (MC) and Collapsed Cone Volume (CCV).

METHOD

This study was carried out using a CIRS Model 002LFC IMRT Thorax Phantom customized with a water-equivalent heterogeneity inside the lung. The calculated dose distributions were compared to Gafchromic® EBT3 film measurements. The beam configurations were selected using DoE to study the influence of five parameters simultaneously (energy, collimator angulation, gantry angulation, X and Y jaws) and to optimize the number of experiments. An analysis of variance was performed over the entire irradiation field and over various regions of interest (tumour, shadow of tumour and lungs).

RESULTS

DoE enabled to quantify and determine the statistically significant factors, leading to an evaluation of the dose calculation systems in the lung case. The resulting scoring could be as follow (from best to worst): AXB_D_m, CCV, AXB_D_w, XVMC_D_m, XVMC_D_w, AAA and last PB. Differences between the algorithms were specially observed in the tumour and the shadow regions.

CONCLUSION

DoE is a robust statistical method to compare several dose calculation systems. The various analyses lead to the conclusion that AXB handled more accurately most of the situations investigated in heterogeneous media.

Study of the remarkable reactivity of HNCO/urea with NO2 in the NOx SCR by urea process over an oxide-based catalyst

An exceptional reactivity between NO₂ and the reductant species was demonstrated during NO₂-SCR experiments with urea, when only NO₂ was used as NO_x.

Chronic active Epstein-Barr virus infection with cutaneous and sinus lymphoproliferation in a white female patient with 25 years' follow-up: an original case report

Chronic active Epstein-Barr virus infection (CAEBV) is characterized by chronic infectious mononucleosis-like symptoms associated with very high viral load, as assessed by quantitative polymerase chain reaction. We present an unusual case in a French woman who was followed up over 25 years with cutaneous and sinus lymphoproliferation. This white woman presented with a long history of recurrent cutaneous necrotic papules of the skin, which started during childhood and healed spontaneously with depressed scars. The lesions spread to the left maxillary sinus and were associated with hepatomegaly and splenomegaly with no other visceral locations. Pathological examination of the skin and sinus revealed a dermal monoclonal T-cell lymphoproliferative disorder, CD7(+) and CD20(-) , with no epidermotropism. T-cell receptor rearrangement was positive, showing the monoclonality from the first biopsy. This T-cell proliferation was positive for EBV-encoded small RNA and was associated with a high EBV viral load. Since then, the patient has been in good health, despite a permanently high EBV viral load. Hydroa vacciniforme (HV)-like lymphoma and natural killer/T-cell lymphoma were discussed, but none really fit our case. Natural killer cell lymphoma was ruled out because of the indolent course, but sinus lesions do not exist in HV-like lymphoma. A therapeutic approach is difficult because of the coexistence of viral infection and monoclonal T-cell proliferation. Chemotherapy is not efficient and induces immunosuppression, which may worsen the prognosis. Although rituximab may have an immunomodulatory function, it was not effective in our case.

Synthesis and biological evaluation of O-alkylated tropolones and related alpha-ketohydroxy derivatives as ribonucleotide reductase inhibitors

A series of O-alkylated tropolones and related alpha-ketohydroxy compounds were evaluated for their biological activities and were shown to present an expected ribonucleotide reductase inhibition and cytotoxicity against some cancer cell lines but no antitubulin activity. Pharmacomodulation studies were realised to understand and enhance the observed activities. These original benzylic, heterocyclic and allylic compounds have been synthesised by a phase-transfer catalysed O-alkylation developed in our laboratories.

Riluzole series. Synthesis and in vivo "antiglutamate" activity of 6-substituted-2-benzothiazolamines and 3-substituted-2-imino-benzothiazolines

Two series of analogues of riluzole, a blocker of excitatory amino acid mediated neurotransmission, have been synthesized: monosubstituted 2-benzothiazolamines and 3-substituted derivatives. Of all the compounds prepared in the first series, only 2-benzothiazolamines bearing alkyl, polyfluoroalkyl, or polyfluoroalkoxy substituents in the 6-position showed potent anticonvulsant activity against administration of glutamic acid in rats. The most active compounds displaying in vivo "antiglutamate" activity were the 6-OCF(3) (riluzole), 6-OCF(2)CF(3), 6-CF(3), and 6-CF(2)CF(3) substituted derivatives with ED(50) values between 2.5 and 3.2 mg/kg i.p. Among the second series of variously substituted benzothiazolines, compounds as active as riluzole or up to 3 times more potent were identified in two series: benzothiazolines bearing a beta-dialkylaminoethyl moiety and compounds with an alkylthioalkyl chain and their corresponding sulfoxides and sulfones. The most potent derivatives were 2-imino-3-(2-methylthio)- and 2-imino-3-(2-methylsulfinyl)-ethyl-6-trifluoromethoxybenzothiazolines (61 and 64, ED(50) = 1.0 and 1.1 mg/kg i.p., respectively). In addition, intraperitoneal administration of some of the best benzothiazolines protected mice from mortality produced by hypobaric hypoxia.

Asymmetrically substituted ethylenediamine platinum(II) complexes as antitumor agents: synthesis and structure-activity relationships

A series of platinum dichloroethylenediamine complexes [PtCl2(R-en)] bearing a side chain on one carbon atom of the ethylenediamine ligand, with or without a functional group on the side chain, have been prepared and investigated for antitumor activity against L1210 leukemia. They were tested both in vitro, with cisplatin-sensitive and resistant cell lines, and in vivo, with cisplatin-sensitive and resistant tumors grafted i.p. in B6D2F1 mice. The rationale for this study was to test how charge, polarity and shape of the R side chain influence antitumor activity. Complexes carrying one or more ammonium groups on the side chain were all inactive. Derivatives with a carbamate function attached by the nitrogen atom, via a methylene group, to the ethylenediamine moiety ('N-bound' carbamate) were highly active in vitro and in vivo. The best results were obtained with these carbamates bearing hydrophobic substituents of intermediate size. Replacement of N-bound by O-bound carbamate or by urea groups led to decreased in vivo activity. Sulfonamide derivatives were all inactive. Good to excellent activities were also recorded for complexes bearing bulky bicycloalkyl substituents, without any functional group, attached to one ethylenediamine carbon atom. Thus, it is the steric features of the side chain rather than its polarity that appear to favor the antitumor activity of the complex. Compared to cisplatin and oxaliplatin, the present complexes do not exhibit advantages in terms of experimental antitumor activities in solid tumor models.