Is three-Dimensional CT based Conformal Radiotherapy Superior to Two-dimensional X ray-based Radiotherapy for Neoadjuvant Radiotherapy in Locally advanced Carcinoma Rectum?

4.7-Abstract Aim: Estimate deficiency in target volume coverage when using conventional X ray-based planning using bony landmarks in carcinoma rectum. Methods and Material: The study consists of 86 biopsy proven patients of carcinoma rectum. The planned area of treatment was demarcated as per 2D bony landmarks in AP and lateral portals were used following which a 3-field plan was created. This plan was projected on a CT scan in which gross tumour volume, clinical target volume and planning target volume were delineated as per RTOG guidelines, thus comparing 2 dimensional vs. 3 dimensional techniques of treatment. Geographic miss of the nodal target when using conventional technique was estimated in comparison to 3D volume planning on the CT scan. Statistical analysis used: Data were statistically described in terms of mean ± standard deviation, median, and range. Comparison between the study plans was done using Chi square test. P < 0.05 was considered statistically significant. All statistical calculations were done using computer programs SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) version 15 for Microsoft Windows. Results: When the PTV was superimposed on digital reconstructed radiograph (DRR), 32 out of 86 patients had geographical miss at the superior border, hence missing to cover the internal iliac group of lymph nodes when conventional 2-dimensional techniques were used to delineate target volume. When 2D plan coverage was superimposed on 3D volume DRR, volume receiving 95% of dose was 93% in the 2D plan whereas the coverage of V95 was 98 % (p value 0.01) in 3DCRT plan. The geographic miss of nodal target volume was 1.4cm superiorly. When this missed volume was included into the target and planned, PTV coverage was achieved and small bowel dose was within the planned constraint of V40<30%. Conclusion: CT based planning should be encouraged and in radiation departments where 2-dimensional treatment is practiced, a diagnostic CT scan should be recommended, and the radiation portals should be revised as per the findings of the scan.