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(Jagadheeskumar, N, Vellore Institute of Technology, India)
The aim of this research work is to dosimetrically compare the different radiotherapy delivery techniques available at present to treat thoracic tumours. In this study, we have included the carcinoma of lung, breast, bilateral breast and oesophagus. The delivery techniques such as intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), stereotactic body radiotherapy (SBRT), deep inspirated breath hold (DIBH) technique, phantom study on gated delivery and synthetic CT dose calculation accuracy were evaluated. The feasibility of synchronous bilateral breast carcinoma (SBBC) treatment using VMAT technique with flattening filter free (FFF) beam was analysed and compared to flattened beam (FF) using physical parameters (CI, HI, PTV and OAR dose coverages) as well as biological parameters (EUD, TCP, NTCP, UTCP) as the modern linear accelerator uses mostly FFF beams alone even for large fields. We found the dose coverage achieved using FFF beams were as good as FF beams. High dose delivery in shorter number of fraction (5-6) is considerably increasing after covid pandemic for breast radiotherapy. We have studied the dosimetric advantages of using DIBH gated radiotherapy delivery for FAST Forward trial (26Gy in 5 fractions) compared to free breathing. For this study, we employed VMAT, field in field techniques using FFF and FF beams and results were compared using physical parameters as per FAST Forward trial. SBRT based VMAT treatments for carcinoma of lung poses lot delivery challenges as the tumour and surrounding OARs were moving continuously due to respiration. For DIBH gated radiotherapy verification of lung tumour, a phantom was self-crafted and used to find the optimal breath hold window level to use for SBRT using FFF-VMAT. Adaptive radiotherapy uses the synthetic CT (SCT) images for replanning. We have evaluated the dose calculation accuracy of SCT images using AAA and Acuros-XB algorithms in the treatment of Ca. Oesophagus as it involves more heterogeneities.
Keywords: SBBC, FFF, VMAT, FAST Forward, DIBH, Breath Hold Window level, synthetic CT,AAA, Acuros XB, SBRT, Ca. Lung, Ca. Breast, Ca. Oesophagus