Deformable Image Registration and Dose Accumulation for Locally Advanced Non-Small Cell Lung Cancer, Comparing Delivered and Planned Radiotherapy Doses

Abstract

Uncertainty in the radiotherapy doses actually received over the course of treatment for locally-advanced non-small cell lung cancer (LA-NSCLC) may explain, in part, low long term survival rates for these patients. This is because target and nodal dose coverage, up to this point, have been assumed constant; however disease volume and location are known to change during the course of radiation treatment. In this study, deformable registration (DIR) and dose accumulation (DA) were used to calculate the accumulated dose received over the course of treatment. These accumulated doses are then compared with the clinical treatment plan against acceptable tolerances. This single institution retrospective study randomly selected 26 patients diagnosed with LA-NSCLS receiving radical chemo-radiotherapy. 9 Patients received a dose of 60Gy/30fx and the other 17 patients received a dose of 66/33fx. The clinical delivered plan was exported into RayStation 4.5.2. Using this system's deformable image registration (DIR) tools, doses calculated on daily cone-beam CT images acquired for daily verification are deformed and mapped onto the planning CT images, thus accounting for daily treatment incorporating set-up shifts and changes in the patients anatomy. The accumulated dose delivered was then compared to the clinical treatment plan in terms of target coverage and avoidance of organs at risk. This study demonstrates successfully that, on average, the accumulated doses calculated were not statistically different from the clinical plan. Furthermore, the accumulated doses to the clinical target volumes (CTV's) for both targets and nodes are within acceptable range, illustrating that our current PTV margins are robust against anatomical changes observed during the course of radiation therapy treatment. Differences between CTV doses calculated for the clinical treatment plan compared to the accumulated plan was within 2%. The accumulated OAR doses are also maintained as compared to the clinical plan. We successfully demonstrated that DIR and DA is a useful and valued tool confirming doses received for patients receiving radiation for LA-NSCLC. We have confirmed that our PTV margins are adequate and robust from a dosimetric perspective. Given our relatively small sample size, our results may not be representative of the entire population. Further accrual would confirm our initial findings.