Lung dose calculations at fluoroscopic X-ray energies using a model-based treatment planning system

Accurate determination of the dose to various organs from diagnostic X-rays has become increasingly important in recent years because of incidents of radiation injury to patients undergoing certain interventional fluoroscopically-guided procedures. We have modified a convolution/superposition-based treatment planning system (ADAC Pinnacle) and used it to determine the dose distribution within the body from kilovoltage X-rays and computed the lung dose from them. We compared the average lung doses calculated by the planning system to those of a widely used organ dose calculation program (CDI3) for 32 different field sizes and orientations using a standard man phantom. We then used the system to compute average lung doses from a simulated ablation procedure and compared our results to published doses for similar procedures. Doses calculated using Pinnacle were an average of 20% lower for AP beams and 10% higher for PA beams than those obtained using CDI3. The ratio of the average dose to the lungs to the skin dose from the simulated ablation procedure ranged from 15% higher to 30% lower than that estimated by other authors. In conclusion, our results show that a treatment planning system can be a viable tool to calculate organ doses in the diagnostic energy range. There are differences between our results and those obtained by other methods which can be partly explained by the variations among the different methods