Purpose: Intensity modulated radiotherapy (IMRT) in the recent past has established itself as a gold standard for organs at risk (OAR) sparing, target coverage and dose conformity. With the advent of a rotational treatment technology such as volumetric modulated arc therapy (VMAT), an inter-comparison is warranted to address the advantages and disadvantages of each technique. Methods: Twenty patients were selected retrospectively from our patient database. Sites included were brain, head and neck, chest wall, and prostate, with five patients for each site. For all the selected patients, both the IMRT and VMAT treatment plans were generated. Plan comparison was done in terms of OAR dose, dose homogeneity index (HI), dose conformity index (CI), target coverage, low isodose volumes, monitor units (MUs), and treatment time. Results: The VMAT showed better sparing of "parotids minus planning target volume (PTV)", spinal cord and head of femur as compared to the IMRT. The lung V40 for VMAT was lower, whereas the lung V10, contralateral lung mean dose, contralateral breast mean dose and mean body dose were lower with IMRT for chest wall cases. Both the VMAT and IMRT achieved comparable HI except for the brain site, where IMRT scored over VMAT. The CI achieved by the IMRT and VMAT were similar except for chest wall cases, whereas the VMAT achieved better dose conformity. The target coverage was comparable with both the plans. The VMAT clearly scored over IMRT in terms of average MUs (486 versus 812 respectively) and average treatment time (2.54 minutes versus 5.54 minutes) per treatment session. Conclusion: The VMAT (RapidArc) has a potential to generate treatment plans for various anatomical sites which are comparable with the corresponding IMRT plans in terms of OAR sparing and plan quality parameters. The VMAT significantly reduces treatment time as compared to the IMRT, thus VMAT can increase the throughput of a busy radiotherapy department.
Purpose: To verify the volumetric modulated arc therapy (Rapidarc) plans using a independent three dimensional dose computation algorithm using COMPASS system. Methods: Rapidarc is a treatment technique which produces conformal dose distribution by delivering the dose in a rotational fashion while simultaneously changing MLC position, dose rate as well as gantry speed. COMPASS dosimetry system uses the Collapsed Cone Convolution(CCC) algorithm as a dose calculation engine which requires machine model information and beam modeling to display the 3D dose distribution on a patient CT data. Treatment plans (10 patients) generated for Rapidarc on Eclipse (version 8.9) Treatment Planning System (TPS) using Analytical Anisotropic Algorithm (AAA) were exported as DICOM file to COMPASS for recalculation using CCC algorithm. Pilot studies were performed for 2DRT, 3DCRT and IMRT plans prior to VMAT plan verification. The doses and dose‐volume histograms computed using CCC were compared with TPS calculated plans. Plans were analyzed in terms of Conformity Index (CI) for PTV, maximum and mean doses for OARs and difference in three dimensional gamma. Results: The average 3D mean gamma for 1mm(DTA) and 1%(DD) criteria for 2DRT and 3DCRT was 0.11 ±0.002 . Maximum and minimum deviation of PTV Volume receiving 95% of the prescribed dose(V95%) for IMRT and Rapidarc were found to be 1.01%, 0.79% and 1.24%, 0.86% respectively. Average deviation of maximum and mean doses of OARˈs for IMRT and Rapidarc were 0.91±0.002 %, 0.55±0.008 % and 0.25±0.005 %, 1.05±0.009 % respectively. Conclusions: This study illustrates that the compass three dimensional dosimetry system can be used as an accurate and effective tool to clinically validate the Rapidarc plans independently.
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