Dosimetric Effects on Small-field Beam-modeling for Stereotactic Body Radiation Therapy

다국어 초록 (Multilingual Abstract)

The treatment planning of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy(SBRT) requires high accuracy of dosimetric data for small radiation fields. The dosimetriceffects on the beam-modeling process of a treatment planning system (TPS) were investigated usingdifferent measured small-field data sets. We performed small-field dosimetry with three detectors:a CC13 ion chamber, a CC01 ion chamber, and an edge detector. Percentage depth doses (PDDs)and dose profiles for field sizes given by 3 × 3 cm2 , 2 × 2 cm2 , and 1 × 1 cm2 were obtainedfor 6 MV and 15 MV photon beams. Each measured data set was used as data input for a TPS,in which a beam-modeling process was implemented using the collapsed cone convolution (CCC)algorithm for dose calculation. The measured data were used to generate six beam-models basedon each combination of detector type and photon energy, which were then used to calculate the correspondingPDDs and dose profiles for various depths and field sizes. Root mean square differences(RMSDs) between the calculated and the measured doses were evaluated for the PDDs and the doseprofiles. The RMSDs of PDDs beyond the maximum dose depth were within an accuracy of 0.2 −0.6%, being clinically acceptable. The RMSDs of the dose profiles corresponding to the CC13, theCC01, and the edge detector were 2.80%, 1.49%, and 1.46% for a beam energy of 6 MV and 2.34%,1.15%, and 1.44% for a beam energy of 15 MV, respectively. The calculated results for the CC13ion chamber showed the most discrepancy compared to the measured data, due to the relativelylarge sensitive volume of this detector. However, the calculated dose profiles for the detectors werenot significantly different from another. The physical algorithm used in the beam-modeling processdid not seem to be sensitive to blurred data measured with detectors with large sensitive volumes.
Each beam-model was used to clinically evaluate lung and lymphatic node SBRT plans, yieldingalmost equal dose distributions for the treatment targets, while the mean doses related to the organsat risk (OARs) deviated by approximately 0.7 − 1.2%. The use of the measured data sets fromdifferent detectors for the beam-modeling process still provided acceptable dose distributions withaccuracies within 2%.

참고문헌 (Reference)

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