Planning Aspects of Volumetric Modulated Arc Therapy and Intensity Modulated Radio therapy in Carcinoma Left Breast - A Comparative Study


Background: The advantages of Rapid Arc plans versus Intensity modulated radiotherapy plans forCarcinoma left breast were analyzed. Materials and
Methods: In this study 20 Post mastectomy carcinoma leftbreast patients were analyzed. Both Intensity modulated Radiotherapy and Rapid Arc plans were generated forthese patients. IMRT plans with 7 beams in an arc fashion and VMAT plans with two semi arcs were made toachieve 95% dose coverage to 100% volume. The plans were evaluated using Dose volume Histograms.
Results:The mean Conformity and Homogeneity index in VMAT is found to be 1.05 and 0.065 respectively whereas inIMRT it was 1.07 and 0.069. The 20% volume of Heart received a mean dose of 960cGy in VMAT and 1300cGyin IMRT. The mean dose was 1236cGy in VMAT and 1870cGy in IMRT. The ipsilateral Lung received 3395cGyto 5% volume and 1840cGy to 20% volume on an average and the mean dose was 1205cGy in VMAT, while thesame were found to be 3525cGy, 2012cGy and 1435cGy respectively in IMRT. The Contralateral Lung receiveda mean dose of 505cGy in VMAT and 553cGy in IMRT. The mean Monitor units in VMAT were 512MU and1170MU in IMRT. The NTID in VMAT is 108.8 x 105 Gycm3 and 110.1 x 105 Gycm3 in IMRT.
Conclusions: Thetarget coverage, homogeneity and Conformity index were better in VMAT plans. The Ipsilateral Lung and heartdose were very less in VMAT plans. The Contralateral Lung dose and the Normal Tissue Integral Dose werealso lesser in VMAT plans however the difference is not very appreciable. The MU in VMAT plans is almost50% that of the IMRT plans which results in the reduction of treatment time. On the whole VMAT proves tobe a better modality for treating Ca. Left Breast Patients.