Stereotactic Radiosurgery (SRS) is a procedure that uses ionizing radiation in a single fraction or few fractions to treat intracranial lesions. Usually, for these treatments, small photon fields, formed by circular collimators or micro multileaf collimators are used. The objective of the present work is to compare the measurements of the dose in depth (PDD), the off-axis ratio (OAR), and the output factor (OF) using Edge diode and radiochromic films and analyzing the agreement between the two detectors during these measures. In the gamma index analysis of the profiles, the minimum percentage reached was 98.3% of the points in the criterion 1% and 0.5 mm. The maximum percentage difference in the output factor was 2.79% for a cone 4 mm and 10FFF. In the gamma index analysis of the PDDs, the minimum percentage reached was 97% of the points in the criterion 1% and 1mm. The results show a good agreement between the edge detector and the film in small field measurements for radiosurgery.

The stereotactic radiosurgery (SRS) is a technique that uses multiple beams extremely collimated of ionizingradiation to treat intracranial lesions and functional abnormalities, with high geometric precision and dosimetricaccuracy. The use of small fields is already a reality in modern radiotherapy techniques. However, the accuracyin small-field dosimetry is challenging because of several process physics and aspects related to the detector. Theaim of this paper is to evaluate the response of a dosimetric system developed by Nuclear Energy Department ofFederal University of Pernambuco (DEN/UFPE) for small field dosimetry. Measurements of, output factor (OF),off-axis ratio (OAR) and percentage depth dose (PDP) were performed with this dosimetric system andcompared with the results obtained with a commercial diode and treatment planning system data. The resultsshowed that the Diode-DEN presents a reliable and economical alternative for small fields dosimetry used intreatments of SRS. This detector can be used for validation of dates obtained in commissioning of linearaccelerator and inserted in Treatment Planning Systems (TPS).

The aim of this work is to evaluate the planning parameters obtain by the HyperArc (HA) planning in comparison with obtained with VMAT planning for stereotactic radiosurgery treatment. Materials/Methods: VMAT and HA planning were performed for 20 patients, that presented between 1 to 6 brain tumors. The dosimetric parameters for PTV (homogeneity index, HI; homogeneity index ICRU83, HI ICRU83; conformity index, CI; conformity index Paddick, CI Paddick; gradient index, GI; gradient Measure, GM) and brain tissue (V10Gy) were calculated for both planning systems. These parameters were compared besides the physical characteristics (Monitor unit, MU) of both treatments in order to evaluate the difference between both methods. Results: The results of GM obtained with VMAT (0.49 AE 0.09) and HA (0.46 AE 0.11) planning systems, did not present significant difference (p Z 0.05), and the same behavior was observed for the values GI for HA (3.53 AE 0.81) and VMAT (3.96 AE 1.45). Although the difference was not significant it was observed that the dose fall-off with HA is higher than VMAT, indicated that normal Brain tissue more preserved. The following parameters, obtained respectively with VMAT and HA, also don't present significant differences (p Z 0.05) as shown by the results: CI (1.10 AE 0.12 vs. 1.08 AE 0.06), CI Paddick (0.90 AE 0.07 vs. 0.88 AE 0.05). The ICRU 83 parameter obtained with VMAT was 0.36 AE 0.10 and for HA was 0.27 AE 0.06. The t-student test showed significant difference between them with 95% confidentiality. This difference can be explained because in HA planning the maximum dose was not fixed and in this case the algorithm in general try to adjust the same homogeneity index. The VMAT planning the definition of homogeneity index is depending of the person that is planning the treatment. No significant differences in the volume of healthy brain (V10Gy) and Monitor Unit MU were observed. It's important to emphasis that the time spend to planning SRS VMAT was around four times that necessary to obtain the same planning with HA system. Conclusion: It is possible to conclude that the planning quality with VMAT and HA are similar, but the time for optimization of the procedure with HA is faster than with VMAT, resulting in better resulting in faster patient treatment.