Purpose: Some clinics are exploring the use diagnostic CTs in radiation treatment planning to improve efficiency. The CT-to-density table for these diagnostic CTs may not be available in treatment planning system. Therefore, understanding the impact of CT-to-density table on plan quality is crucial in ensuring the quality of patient care. This study aims at evaluating the impact of CT-to-density table on plan qualities.
Methods: Ten VMATapp lung patients’ plans in our clinics were chosen and the original treatment plans were recomputed based on two CT-to-density tables created from original CT-to-density table Tapp. One table was created by raising the density for each point by 10% and denoted by Thigh, and another table was created by lowering density for each point by 10% and denoted by Tlow. The original plans were re-calculated with the same MUs but with the two tables and the plans are denoted as VMAThigh and VMATlow. The scorecards used to evaluate the plan qualities in our clinics were compared between the three plans.
Results: PTV coverage for all VMATlow plans are better or the same as the VMATapp, while VMAThigh deteriorate significantly. For six out of 10 plans, VMATlow normal structures still met all the primary dose constraints for normal structures, while other 4 plans failed on one criteria. All the VMAThigh plans met the normal structure criteria.
Conclusion: VMAThigh quality deteriorate much worse than VMATlow and this implies that underestimate of CT-to-density table have more negative impact on the plan qualities than overestimate.