Mathematical estimation and in vivo dose measurement for cone-beam computed tomography on prostate cancer patients

Background and purpose: Cone-beam computed tomography (CBCT) increases the doses on normal tissues. Our study sought to develop a mathematical model that would provide an estimate of and verify in vivo rectal dose from CBCT in prostate cancer patients. Materials and methods: Thermoluminescent dosimeters (TLDs) and Rando phantoms were used to measure doses to the pelvic region. We used an endorectal balloon to measure rectal doses for 10 prostate cancer patients who underwent radiotherapy and for whom we were able to acquire CBCT images. A solid water phantom and TLDs were used to correlate the rectal doses with body thickness/widths. A mathematical method was established to simulate the dose to which the patient is exposed during CBCT for the determined body parameters. The estimated doses were compared with the measured doses to determine the effectiveness of the model. Results: The average measured rectal dose from CBCT was 2.8 ± 0.3 cGy. The mathematical method was able to predict the rectal dose, with the limits of agreement of -0.03 ± 0.18 cGy. The average difference between predictions and measurements was -1.1 ± 3.6%. Conclusion: Our mathematical model was effective in estimating the exposed dose from CBCT.