Comparing Delivered and Planned Radiation Therapy Doses Using Deformable Image Registration and Dose Accumulation for Locally Advanced Non–small Cell Lung Cancer

Abstract

There are uncertainties in radiotherapy doses received over the course of treatment for locally-advanced non-small cell lung cancer (LA-NSCLC). This may explain poor long term survival rates for these patients as target and nodal dose coverage, have been assumed constant throughout treatment. However, disease volume and location are known to change. In this study, deformable registration (DIR) and dose accumulation (DA) were used to calculate the dose delivered over the course of treatment. These delivered doses were then compared with the clinical treatment plan. This single institution, retrospective study selected 26 sequential patients diagnosed with LA-NSCLC receiving radical chemo-radiotherapy. Using RayStation 4.5.2, doses were calculated on daily cone-beam CT images acquired for daily verification were then deformed and mapped back onto the planning CT images. DA results were compared to the clinical treatment plan for both target coverage and organs at risk. Findings are summarized in Table 1. On average, DA calculations were not statistically different from the clinical plan (p<0.05). The DA to the clinical target volumes for both targets (CTV-T) and nodes (CTV-N) demonstrated that coverage remained close to that planned. The DA for OARs was also maintained as compared to the clinical plan. While, on average, delivered doses remained within our routine clinical tolerances, outliers were observed. DA for each patient indicated a small decrease of the delivered dose with respect to their clinical plan, although large variations were observed for organs at risk. We successfully demonstrated that DIR and DA can assess delivered doses to patients receiving radiotherapy for LA-NSCLC. We have confirmed that, on average, our PTV margins are adequate and robust from a dosimetric perspective. Given our LA-NSCLC sample, our results may not be representative Non-Small Cell (NSCLC) population. Although no average differences seen, outliers persist and will be the focus of future research.Abstract 3659; Table 1Planned vs Accumulated DosesROIDelivered Dose(±SD)[Min – Max]Planned Dose(±SD)[Min – Max]% change from plan/patient (±SD)[Min – Max]ProtocolD99% CTV-T95.5 ± 3.9%[88 – 102%]97 ± 3.1%[91 – 102%]-1.3 ± 1.9[-6 – 2 %]92%D99% CTV-N94.7 ± 4.8%[79 – 100%]95.8 ± 3.2%[87 – 100%]-1.3 ± 2.2[-9 – 2 %]92%Spinal canal4450 ± 691 cGy[1317 – 5378 cGy]4438 ± 276 cGy[4008 – 5110 cGy]-2.0 ± 2.1[-5 – 5 %]4500 cGyMean lung dose1465 ± 412 cGy[657 – 1911 cGy]1401 ± 390 cGy[611 – 1876 cGy]-1.4 ± 3.5[-11 – 6 %]1800 cGyV20 lung25.9 ± 7.6%[9 – 34%]26.3 ± 8.9%[9 – 45%]-0.3 ± 4.4[-6 – 12%]30%V40 heart13.4 ±13.2%[0 – 50%]14.7 ± 13.1%[0 – 49%]-10.6 ± 24[-89 – 53%]60%V40 esophagus37 ± 17%[6 – 73%]36 ± 19%[0 – 74%]-0.8 ± 8%[-10 – 28%]60% Open table in a new tab