COMPARISON BETWEEN MEASURED AND CALCULATED DOSE WITH IPLAN PENCIL BEAM ALGORITIMS AND ECPLIPSE AAA FOR SMALL FIELDS USED IN FRACTIONED STEREOTAXIA RADIOTHERAPY

Radiosurgery is indicated for the treatment of small intracranial lesions with small radiation fields. International Commission on Radiation Units and Measures (ICRU) No. 91 cites recent incidents that relate to small field dosimetry. The objective of this study is to experimentally compare dose delivery for small field planning calculated by TPS Eclipse and Iplan by using an anthropomorphic simulator, considering the tolerance of TRS 430. The entire procedure with all radiosurgery steps was performed, from tomography to delivery of the dose to the device. Two methodologies were used for small field dose measurement, one with an ionization chamber and another for the film. 3D, IMRT techniques were used for both softwares, but dynamic arc and cone arc only for the iPlan® RT software. Plans were made to cover 95% of PTV with 95% of the prescribed dose. Target volumes were plotted from the sensitive ionization chamber volume (Exradin A16 0.007 cc) to obtain equivalent fields ranging from 0.5 cm to 3.8 cm, and the PTV was formed by multi-leaf collimators ( MLC) with a planned dose of 300 cGy. For films, the appropriate dose for better sensitization in photographic dosimetry was 400 cGy and with a calibration curve raised from measurements taken at 1.5 cm depth in solid water. Error was considered to be the difference between the measured and the calculated dose, with tolerance of 3% (TRS 430). The planning results with equivalent fields smaller than 2 cm2 had differences greater than 3% and smaller than this value for larger fields when compared the measured dose with ionization chamber and the calculated dose. In photographic dosimetry, the differences between measured and calculated values were above 3% only for a field equivalent to 0.5 cm2. In this case, the measurements were around 60% of the calculated value for both TPS. The results of the measurements with films were better than those with ionization microchamber for fields smaller than 2 cm2 and larger than 0.5 cm2. The IPLAN was able to calculate the dose with error below 3% for the cone arch from 0.75 to 3 cm in diameter. For mlc plannings, 3% tolerance for error was achieved in the 0.85 cm and larger fields. For the 0.5 cm2 field the error was much larger than the tolerance. ECLIPSE obtained the same result.

Publication History

Article published online:
23 October 2019