Dosimetric impact of contrast medium on different photon energies using conformal & IMRT techniques in the treatment of carcinoma cervix and its validation with indigenous phantom

Introduction Considering the unwanted exposure to organs in path of the beam, 4-field (4F) and subsequently, Intensity-modulated-radiation-therapy (IMRT), is known as standard mode of treatment of carcinoma cervix. It is routine practice to inject intravenous contrast during simulation scan which elopes after that from patient body. Therefore, the impact of contrast media should be investigated for radiation dose calculations.Material & MethodsAn indigenously made phantom, named as ‘original contrast (OC)’, was used with dimensions 15 x 15 x 30 cm3. A sleeve was given to place the ionization chamber at the isocentre of the planning target volume (PTV) inside the cylindrical vial of iodinized contrast. Similarly, a virtual phantom was created with similar dimensions in presence and absence of contrast media, called as ‘virtual contrast (VC)’ and ‘virtual without contrast (VWC)’ phantom. Plans were generated with photon energies (6MV/10MV/15MV/6FFF/10FFF) using 4F and IMRT technique. Plans were evaluated for PTV (D99%, D10%, Dmean) and Bladder & Rectum (V30Gy, V10Gy). Normal-tissue-integral-dose (NTID) and total-monitor-units (TMU) were also evaluated.Results D99% of the PTV was comparable in VC and VWC phantoms but was decreased for OC phantom. Similarly, D10% was reportedly higher as 54.03 Gy (4F, 6 MV), 54.71 Gy (4F, 15 MV), 55.78 Gy (4F, 6 FFF) and 57.64 Gy (4F, 10 FFF) for OC phantom. D30% of the bladder and also the NTID was lesser for IMRT cases in all the selected phantoms. Additionally, 4F has shown lesser spillage with 6MV/15 MV photon beam energies in OC phantom. The ‘total monitor units (TMU)’ required for IMRT plans were significantly higher.ConclusionThe contrast material under-estimate the planned dose yet has insignificant influence on the dose calculation. Therefore, unnecessary exposure of dual scans should be avoided and use of 6MV and IMRT technique should be continued in the clinics.