A Dosimetric Study of Volumetric Arc Modulation with RapidArc Versus Intensity-modulated Radiotherapy inCervical Cancer Patients

Introduction: The method of radiotherapy has moved away from two-dimensional and three-dimensional conformal radiotherapy towards Volumetric-Modulated Arc Therapy (VMAT) for advanced carcinomas. VMAT treatments often result in significant clinical advantage, particularly when concave dose distributions are required as is often the situation since these tumours are in close proximity to several critical structures. Aim:To investigate the potential clinical role of volumetric arc therapy on cervical cancer patients and its comparison with fixed-field Intensity-Modulated Radiotherapy (IMRT) was used as a benchmark. Materials and Methods: Retrospectively, radiotherapy treatment plans of fifteen cervical cancer patients were selected for this study. These patients were previously treated with sliding window IMRT techniques during January 2020 to November 2020. For dosimetric comparison of sliding window IMRT techniques with RapidArc, a new set of plans were created using VMAT/RapidArc technique. For each patient two plans were generated and in this way total 30 plans were analysed. The prescription dose to Planning Target Volume (PTV) was 50.4 Gy in 28 fractions (1.8Gy/fraction) for the 6 MV photon beam. Comparison of each plan done on the basis of Organs At Risk (OARs) sparing, coverage index (C), Conformity Index (CI), Homogeneity Index (HI), dose Gradient Index (GI), and Unified Dosimetry Index (UDI). This study utilised UDI scoring for evaluation and comparison of RapidArc and IMRT plans. Treatment Time (TT) for patient comfort and the number of Monitor Units (MUs) for long-term side-effects was also taken into consideration. A paired two-tailed t-test was executed for the dosimetric study of volumetric arc modulation with RapidArc and its comparison with the IMRT technique in the radiotherapy treatment of cervical cancer patients. All the collected data was analysed using Statistical Package for Social Sciences (SPSS) version 20.0. The (p-value<0.05) was contemplated for the level of statistical significance. Results: Comparable target coverage and better sparing of OARs were achieved with the RapidArc technique in comparison to IMRT. As was evident with results of present study, the values of CI (1.55±0.07), HI (1.07±0.07), GI (0.98±0.01) and UDI (1.25±0.11) of RapidArc technique showed significant difference from respective values of IMRT Technique (1.67±0.06, 1.10±0.06, 0.96±0.01 and 1.38±0.13). Values of MUs (1560.47±52.16) and treatment time (3.71±0.73 mins) were significantlly high in IMRT technique as compared to RapidArc technique (542.33±51.09 and 2.39±0.35 mins respectively). Conclusion: From this study, it is clear that a similar planning goal can be achieved by RapidArc in comparison to fixed-field IMRT with less normal organ toxicity. RapidArc is a faster and precise treatment technique. The most significant change comes to see in the number of MUs and TT, which is much lesser in RapidArc.