The objective of our study was to determine organ and effective doses to estimate the lifetime attributable risk (LAR) of cancer incidence related to chest tomography simulations for Radiotherapy Treatment Planning (RTTP) using patient-specific information. Patient data from 70 chest CT scans were used to compute effective dose. The effective dose was calculated by two methods: first using ImPACT patient dosimetry calculator software using International Comission on Radiological Protection (ICRP103) weighting factors for a 70 kg patient and then applying related correction factors according to the patient’s weight. Second using the scanner-derived dose-length product. LARs of cancer incidence was computed using the seven Biologic Effects of Ionizing Radiation (BEIR VII) report based on sex and age at each exposure. Mean±standard deviation values were 507.50±142.7 mGy.cm for DLP, 11.04±3.66mGy for CTDIvol, 46.88±6.65 cm for scan length. The mean±standard deviation value for the effective dose was 10.31±2.88mSv using ImPACT patient dosimetry calculator software and 8.62±2.42 mSv using the scanner-derived dose-length product. The mean ± SD of LAR of cancer incidence for all cancers, all solid cancers and leukemia were 65.49±28.54, 61.71±27.24, 6.62±2.46 cases per 100,000 individuals, respectively. Radiation exposure from the usage of CT for radiotherapy treatment planning (RTTP) causes non-negligible increases in lifetime attributable risk. The results of this study can be used as a guide by physicians to implement strategies based on the As Low As Reasonably Achievable (ALARA) princiciple that lead to a reduction dose without sacrificing diagnostic information.