SU-E-T-331: Dose Comparison of IVD2 Measurement and Eclipse Treatment Planning Calculation for Whole Brain Irradiation

Abstract

Purpose: To compare the dmax doses measured by Sun Nuclear IVD2 system with the doses calculated by Varian Eclipse treatment planning system (TPS) in the whole brain irradiation (WBI) of a humanoid unsliced phantom using standard lateral fields. Methods: The IVD2 system was carefully calibrated for measuring the dmax dose (at 1.5cm) of Varian Trilogy 6 MV photon beams. This system was also experimentally validated for the dependencies of field size, SSD, dose rate, and beam incident angle. The head and neck part of the phantom was scanned by a Phillips CT at the slice thickness of 2mm. A WBI plan was created using 6MV photon beams and parallel opposed lateral fields with the multiple leave collimator to spare the orbital structures. The plan was normalized to the weight point and with >=98% of brain volume covered by >=98% of prescription dose (300cGy/fraction). The phantom setup and target location were verified by the kV imaging and CBCT; the diodes were carefully placed at various locations. The comparison was made between the measured dose and the planned dose for all interested anatomical sites. Results: Our results indicated that the measured doses agree with the planned dose within 7.9% for the sites in the treatment fields such as mid right/left parietal bones. For the sites outside or partially outside the fields, such as the low chin and right/left orbits, the difference between the measurement and the TPS prediction was varied between 8.3% and 33.8%. Conclusion: Though the human head is relatively small in size, the dose at dmax of WBI can be accurately predicted by TPS and measured by IVD2 system if the points of the interest are inside of the fields. A difference up to 33.8% could be expected if the points are located on the boarder of the fields.