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Dosimetric impact of Lipiodol in stereotactic body radiation therapy on liver after trans‐arterial chemoembolization
Author(s) -
Kawahara Daisuke,
Ozawa Shuichi,
Saito Akito,
Nishio Teiji,
Kimura Tomoki,
Suzuki Tatsuhiko,
Hioki Kazunari,
Nakashima Takeo,
Ohno Yoshimi,
Murakami Yuji,
Nagata Yasushi
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12028
Subject(s) - lipiodol , imaging phantom , nuclear medicine , radiation treatment planning , dosimetry , radiosurgery , medicine , radiation therapy , radiology , embolization
Purpose Stereotactic body radiation therapy ( SBRT ) combining trans‐arterial chemoembolization ( TACE ) with Lipiodol is expected to improve local control. This study is aimed to estimate the dose enhancement in Lipiodol's proximity and to evaluate the dose calculation accuracy of the Acuros XB ( AXB ) algorithm and anisotropic analytical algorithm ( AAA ) in the Eclipse treatment planning system ( TPS ) (ver. 11, Varian Medical Systems, Palo Alto, USA ), compared with that of the Monte Carlo ( MC ) calculation (using BEAM nrc/ DOSXYZ nrc code) for a virtual phantom and a treatment plan for liver SBRT after TACE . Methods The MC calculation accuracy was validated by comparing its results with the percent depth dose ( PDD ) and the off‐axis ratio ( OAR ) measured using a water‐equivalent phantom containing Lipiodol. The dose difference in Lipiodol's proximity and the inhomogeneity correction accuracies of the AAA , AXB algorithm, and MC calculation were evaluated by calculating the PDD s and OAR s for the virtual phantom with Lipiodol and the lateral profile for the clinical plan data. Results The measured data and the MC results agreed within 3%. The average dose in the Lipiodol uptake region was higher by 8.1% for the virtual phantom and 6.0% for the clinical case compared to that in regions without Lipiodol uptake. For the virtual phantom, compared with the MC calculation, the AAA and the AXB algorithm underestimated the doses immediately upstream of the Lipiodol region by 5.0% and 4.2%, in the Lipiodol region by 7.4% and 9.8%, and downstream of the Lipiodol region by 5.5% and 3.9% respectively. These discrepancy between the AXB and MC calculations were due to the incorrect assignment of Lipiodol material properties. Namely, the bone material was assigned automatically by the AXB algorithm as the materials for the AXB algorithm do not contain iodine, which is the main constituent of Lipiodol. Conclusions The MC calculation indicated a larger and more accurate dose increase in Lipiodol compared with the TPS algorithms. The observed dose enhancement in the tumor area could be clinically significant.