Stephan Walrand1, Michel Hesse2, Francois Jamar2, Renaud Lhommel2. 1. Nuclear Medicine, Molecular Imaging, Radiotherapy, and Oncology Unit (MIRO), IECR, Université Catholique de Louvain, Brussels, Belgium stephan.walrand@uclouvain.be. 2. Nuclear Medicine, Molecular Imaging, Radiotherapy, and Oncology Unit (MIRO), IECR, Université Catholique de Louvain, Brussels, Belgium.
Abstract
UNLABELLED: The 50% normal-tissue complication probability (NTCP) after lobar irradiation of the liver results in highly variable biologic effective doses depending on the modality used: a biologic effective dose for 50% (BED50) of 115, 93, and 250 Gy for external-beam radiotherapy, resin microsphere radioembolization, and glass microsphere radioembolization, respectively. This misunderstood property has made it difficult to predict the maximal tolerable dose as a function of microsphere activity and targeted liver volume. The evolution toward more selective catheterization techniques, resulting in more variable targeted volumes, makes it urgent to solve this issue. METHODS: We computed by Monte Carlo simulations the microsphere distribution in the portal triads based on microsphere transport dynamics through a synthetically grown hepatic arterial tree. Afterward, the microscale dose distribution was computed using a dose deposition kernel. We showed that the equivalent uniform dose cannot handle microscale dosimetry and fails to solve the discordance between the BED50 values. Consequently, we developed a new radiobiologic model to compute the liver NTCP from the microscale dose distribution. RESULTS: The new model explains all the observed BED50 values and provides a way to compute the hepatic dose-toxicity relationship as a function of microsphere activity and targeted liver volume. The NTCP obtained is in agreement with the data reported from clinical radioembolization studies. CONCLUSION: The results should encourage interventional radiologists to fine-tune the delivered dose to the liver as a function of the targeted volume. The present model could be used as the backbone of the treatment planning, allowing optimization of the absorbed dose to the tumors.
UNLABELLED: The 50% normal-tissue complication probability (NTCP) after lobar irradiation of the liver results in highly variable biologic effective doses depending on the modality used: a biologic effective dose for 50% (BED50) of 115, 93, and 250 Gy for external-beam radiotherapy, resin microsphere radioembolization, and glass microsphere radioembolization, respectively. This misunderstood property has made it difficult to predict the maximal tolerable dose as a function of microsphere activity and targeted liver volume. The evolution toward more selective catheterization techniques, resulting in more variable targeted volumes, makes it urgent to solve this issue. METHODS: We computed by Monte Carlo simulations the microsphere distribution in the portal triads based on microsphere transport dynamics through a synthetically grown hepatic arterial tree. Afterward, the microscale dose distribution was computed using a dose deposition kernel. We showed that the equivalent uniform dose cannot handle microscale dosimetry and fails to solve the discordance between the BED50 values. Consequently, we developed a new radiobiologic model to compute the liver NTCP from the microscale dose distribution. RESULTS: The new model explains all the observed BED50 values and provides a way to compute the hepatic dose-toxicity relationship as a function of microsphere activity and targeted liver volume. The NTCP obtained is in agreement with the data reported from clinical radioembolization studies. CONCLUSION: The results should encourage interventional radiologists to fine-tune the delivered dose to the liver as a function of the targeted volume. The present model could be used as the backbone of the treatment planning, allowing optimization of the absorbed dose to the tumors.
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