Block Modeling for Pediatric Patients Treated By Co-60 Radiotherapy in the National Wilms Tumor Study Cohort
J Jung1, M Nikakhtar2*, M Mille3, M Gopalakrishnan4, C Lee5, J Kalapurakal6, C Lee7, (1) East Carolina Univ, Greenville, NC, (2) East Carolina Univ, Greenville, NC, (3) National Cancer Institute, Bethesda, MD, (4) Northwestern Memorial Hospital, Chicago, IL, (5) University of Michigan, Ann Arbor, MI, (6) Northwestern Memorial Hospital, ,,(7) National Cancer Institute, Bethesda, MD
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PO-GePV-T-268 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To demonstrate an accurate organ dose reconstruction for Co-60 units using the Monte-Carlo based method and block models in the context of epidemiologic study of secondary cancer and other health risks.
Methods: Using the previously developed Theratron T-1000 Co-60 machine modeling, blocks were modeled. The size and shape of each field and abdomen field were individually designed by using block models and implemented into the TPS and MC simulations. A block modeling was performed by adjusting the phase space data in the MC code. The block shape (either aperture or mantle shape) was extracted from dicom files and the phase space data in the block at a central axial plane of the block was less weighted, i.e. 2.1% of the original. The treatments settings were acquired from the medical records of the ten Wilms tumor patients and simulated including the beam characteristics and the lead blocks.
Results: Near in-field and out-of-field absorbed dose calculations were conducted and compared for ten cases with the Monte Carlo code and TPS. No significant dose difference has been observed except out-of-fields where the relative difference can be up to 58 and 62% for ovary and testes, respectively, however the absolute dose difference was small (<0.6 Gy). The mean absolute dose difference between TPS and MC for various organs were as follows: left kidney 0.18 Gy (0.07–0.28 Gy); heart 0.39 Gy (0.15–0.59 Gy); testes 0.49 Gy (0.38–0.57 Gy) and ovaries 0.30 Gy (0.09–0.41 Gy).
Conclusion: This study shows an accurate method for dose estimation for patients treated with the Co-60 unit for Wilms tumor patients using Monte Carlo code, detailed block models, and hybrid pediatric phantoms.
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