Lung dose calculations at kilovoltage x-ray energies using a model-based treatment planning system

The determination of the dose to organs from diagnostic x rays has become i mportant because of reports of radiation injury to patients from fluoroscop ically guided interventional procedures. We have modified a convolution/sup erposition-based treatment planning system to compute the dose distribution for kilovoltage beams. We computed lung doses using this system and compar ed them to those calculated using the CDI3 organ dose calculation program. We also computed average lung doses from a simulated radiofrequency ablatio n procedure and compared our results to published doses for a similar proce dure. Doses calculated using this system were an average of 20% lower for A P beams and 7% higher for PA beams than those obtained using CDI3. The rati o of the average dose to the lungs to the skin dose from the simulated abla tion procedure ranged from 25% higher to 15% lower than that determined by other authors. Our results show that a treatment planning system designed f or use in the megavoltage energy range can be used for calculating organ do ses in the diagnostic energy range. Our doses compare well with those previ ously reported. Differences are partly due to variations in experimental te chniques. Using a three-dimensional (3-D) treatment planning system to calc ulate dose also allows us to generate dose volume histograms (DVH) and comp ute normal tissue complication probabilities (NTCP) for diagnostic procedur es. (C) 2001 American Association of Physicists in Medicine.