[en] Methylthioadenosine (MTA) phosphorylase purified 615-fold from human liver cleaved phosphorolytically nucleoside analogues at the decreasing specific activity: 5'-deoxyadenosine > 5'-iodo-5'-deoxyadenosine > MTA > adenosine > 2-chloroadenosine > 2-chloro-5'-O-methyl-2'-deoxyadenosine > 2-chloro-2'-deoxyadenosine >> 2'-deoxyadenosine. Adenosine and analogues of 5'-deoxyadenosine were strong competitive inhibitors of MTA phosphorolysis catalysed by the human liver enzyme. (author). 24 refs, 2 tabs

[en] Purpose: Evaluate and compare retrospective prostate treatment plan using Volumetric Modulated Arc Therapy (RapidArc™ - Varian) technique with single or double arcs at COI Group. Methods: Ten patients with present prostate and seminal vesicle neoplasia were replanned as a target treatment volume and a prescribed dose of 78 Gy. A baseline planning, using single arc, was developed for each case reaching for the best result on PTV, in order to minimize the dose on organs at risk (OAR). Maintaining the same optimization objectives used on baseline plan, two copies for optimizing single and double arcs, have been developed. The plans were performed with 10 MV photon beam energy on Eclipse software, version 11.0, making use of Trilogy linear accelerator with Millenium HD120 multileaf collimator. Comparisons on PTV have been performed, such as: maximum, minimum and mean dose, gradient dose, as well as the quantity of monitor units, treatment time and homogeneity and conformity index. OARs constrains dose have been evaluated, comparing both optimizations. Results: Regarding PTV coverage, the difference of the minimum, maximum and mean dose were 1.28%, 0.7% and 0.2% respectively higher for single arc. When analyzed the index of homogeneity found a difference of 0.99% higher when compared with double arcs. However homogeneity index was 0.97% lower on average by using single arc. The doses on the OARs, in both cases, were in compliance to the recommended limits RTOG 0415. With the use of single arc, the quantity of monitor units was 10,1% lower, as well as the Beam-On time, 41,78%, when comparing double arcs, respectively. Conclusion: Concerning the optimization of patients with present prostate and seminal vesicle neoplasia, the use of single arc reaches similar objectives, when compared to double arcs, in order to decrease the treatment time and the quantity of monitor units

No abstract available

[en] Radiation therapy is a complex treatment modality involving several technological and professional resources as well as a large number of attributions of these professionals with a high degree of interdependence. Thus there are many possibilities of failure in the treatment process that may lead to an accidental exposure. Regulatory agencies have established guidelines in order to prevent accidental exposures through security analysis planning and risk management. The System of EValuation of Risk in RAdiotherapy, also known as SEVRRA, is based on the risk matrix methodology and allows the risk assessment of radiation therapy facilities in a prescriptive way, highlighting events leading to high-risk levels. With SEVRRA it is also possible to establish an analysis of importance of the barriers proposed to avoid or mitigate such events. This work aimed to demonstrate the application of SEVRRA for the risk management of radiation therapy facilities. The risk profile was determined by identifying the highest risk level events, and the barriers of greater impact for the overall risk level. After implementing some missing barriers in the original facility profile, it was achieved a reduction from 31% to 8% in the number of events leading to high-risk level, showing the effectiveness of SEVRRA for the risk management in radiation therapy facilities. (author)

[en] Risk assessment deals with processes, barriers and risk levels to unveil the fragility and weakness and to point out mechanisms that should be implemented to strength an activity. The objective of this work is to investigate the most important aspects for radiological protection of patients, public in general and workers. These results were obtained from the application of the System of Evaluation of Risk in Radiation Therapy (SEVRRA), a software tool developed by the Ibero-American Forum of Radiological and Nuclear Regulatory Agencies - FORO with the purpose of facilitating the evaluation of the risk level on radiotherapy. Data has been collected from a group of twenty Brazilian radiation therapy facilities, which have performed the survey for weakness and strength in terms of initiating events and barriers preventing accidental sequences. It was observed that some of the initiating events occur with high-risk level for majority of facilities. It is related to the absence of some barriers proposed by SEVRRA. The attention is focused on these barriers once its presence would reduce the facilities global risk level. The present investigation reinforces the need to strength the mechanisms that guarantee the effectiveness of such barriers in radiotherapy procedures. The results also show that some radiation therapy accidents around the world could be prevented or mitigated if some kind of risk analysis would have been performed. SEVRRA works as a fundamental tool in the task of identifying national difficulties or weakness and to promote advances in the safety field for the regulation on radiotherapy. (author)

[en] Risk assessment deals with processes, accident-initiating events, barriers and risk ratings to unveil the fragility and weakness of some processes; within this study, specifically related to radiation therapy facilities. Barriers are technical or organizational safety measures put in place to avoid, prevent, detect, control, reduce or mitigate the consequences of an accident once an initiating event has occurred. In this work, radiological risk analysis was performed for a set of 20 Brazilian radiotherapy facilities making use of the freeware sevrra risk-management software. The objective of this study was to define parameters that could be useful in creating an overall risk profile. This profile would be helpful for establishing priorities for decision making and support a risk-informed regulatory process. The most relevant missing barriers in facilities were identified according to three parameters: the ‘importance index’, ‘impacted facilities index’ and the ‘barrier-effectiveness index’. Barriers such as ‘in vivo dosimetry in the first treatment session’, ‘weekly in vivo dosimetry to detect errors in the dose delivering process’, ‘annual external audit for the control of reference dose rate’ and ‘independent verification of calibration by various medical physicists with a different dosimetry equipment’ were found to be the most effective in reducing the risk level of the facilities. The present investigation reinforces the need to strengthen the mechanisms that guarantee the effectiveness of such barriers in radiation therapy procedures. (paper)