Adaptive radiotherapy in lung cancer: dosimetric benefits and clinical outcome.

OBJECTIVE: Anatomical changes during radiotherapy (RT) might introduce discrepancies between planned and delivered doses. This study evaluates the need for adaptive treatment in lung cancer RT. METHODS: 15 patients with non-small-cell lung cancer, undergoing radical RT with or without concurrent chemotherapy, consecutively underwent planning CT scans at baseline and after 44-46 Gy. Target volumes were delineated on both scans. Phase I delivered 44-46 Gy to the initial planning target volume (PTV). Two Phase II plans for 16-20 Gy were developed on initial and mid-treatment scans, the treatment being delivered with the mid-treatment plan. The second CT structure set was fused with the initial scan data set using dose wash. Volumetric and dosimetric changes in target volumes and critical structures were assessed. RESULTS: There was significant reduction in primary gross tumour volume (34.00%; p = 0.02) and PTV (34.70%; p < 0.01) in the second scan. In Plan 2, delivering the same dose to the initial PTV would have resulted in a significantly higher dose to the lung PTV (V20, 52.18%; V5, 21.76%; mean, 23.93%), contralateral lung (mean, 29.43%), heart (V10, 81.47%; V5, 56.62%; mean, 35.21%) and spinal cord (maximum dose, 37.53%). CONCLUSION: Treatment replanning can account for anatomical changes during RT and thereby enable better normal tissue sparing, while allowing radical target doses with the possibility of maximizing local control. ADVANCES IN KNOWLEDGE: This study supports the sparse dosimetric data regarding the quantitative tumour volume reduction, re-emphasizing the need for adaptive replanning for minimizing normal tissue toxicity without compromising local control, and adds to the existing body of literature.

Dosimetric comparison between Volumetric Modulated Arc Therapy (VMAT) vs Intensity Modulated Radiation Therapy (IMRT) for radiotherapy of mid esophageal carcinoma.

AIMS: Dosimetric comparison of VMAT with IMRT in middle third esophageal cancer for planning target volume (PTV) and organs at risk (OAR). MATERIALS AND METHODS: Ten patients in various stages from I‒III were inducted in the neo-adjuvant chemoradiation protocol for this study. The prescribed dose was 4500 cGy in 25 fractions. Both VMAT and IMRT plan were generated in all cases and Dose Volume Histogram (DVH) comparative analysis was performed for PTV and OAR. Paired t-test was used for statistical analysis. RESULTS: The PTV Dmean and D95 in IMRT and VMAT plan were 4566.6±50.6 cGy vs 4462.8±81.8 cGy (P=0.1) and 4379.8±50.6 cGy Vs 4424.3±109.8 cGy (P=0.1), respectively. The CI and HI for PTV in IMRT vs VMAT plans were 0.96±0.02 vs 0.97±0.01 (P=0.4) and 10.58±3.07 vs 9.45±2.42 (P=0.2), respectively. Lung doses for VMAT vs IMRT were 4.19 vs 2.59% (P=0.03) for V35-7.63 vs 4.76% (P=0.01) for V30-13.6 vs 9.98% (P=0.01) for V25-24.77 vs 18.57% (P=0.04) for V20-46.5 vs 34.73% (P=0.002) for V15. The Mean Lung Dose (MLD) was reduced by VMAT technique compared to IMRT; 1524.6±308.37 cGy and 1353±186.32 cGy (P=0.012). There was no change in Dmax to spinal cord in both the techniques. There was a dose reduction by VMAT compared to IMRT to the heart but it was statistically insignificant; V35-6.75% vs 5.55% (P=0.223); V30-12.3% vs 10.91% (P=0.352); V25-21.81% vs 20.16% (P=0.459); V20-38.11% vs 32.88% (P=0.070); V15-61.05% vs 54.2% (P=0.10). CONCLUSION: VMAT can be a better option in treating mid esophageal carcinoma as compared to IMRT. The VMAT plans resulted in equivalent or superior dose distribution with a reduction in the dose to lung and heart.