Dosimetric comparison of 2D, 2D (MLC), 3DCRT and IMRT in Carcinoma of Cervix
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Abstract
Aim: To investigate the dosimetric eccentricities of 2D, 2D (MLC), 3DCRT and IMRT radiotherapy treatment techniques in carcinoma of cervix.
Materials and methods: We retrospectively included ten previously treated carcinoma of cervix in this study. All the ten patients under went CT simulation along with immobilization and positional devices. Targets and organ at risk (OAR) were delineated slice by slice for all the patients. Treatment plans were created with 15MV for 2D plans using AP/PA beams based on anatomical landmarks using the secondary jaws, whereas 2D (MLC) plans were created as same as the 2D plans, but fit the multi leaf collimator (MLC) to the planning target volume (PTV). 3D plans were created with 15MV photons using 4 field’s box techniques and MLC fitted to the PTV. Intensity Modulated Radiation Therapy (IMRT) plans were created with 6MV beams with equally distributed 7 gantry angels. We intend to deliver 50 Gy in 25 fractions for all the patients. Doses to the critical structures and targets were recorded from the dose volume histogram for evaluation.
Results: Target homogeneity for all the 2D, 2D (MLC), 3DCRT and IMRT plans were comparable. Conformity index shows that 2D plans over treat by 660% more than PTV volume, 2D (MLC) plans by 363%, 3DCRT by 152% and IMRT by 22%. Low dose volumes (V5, V10 & V15) were high in IMRT, but high dose regions were comparatively less in IMRT. In IMRT plans, the rectal mean dose were reduced by 28% compared to 3DCRT, 2D (MLC) and 2D plans, which may result less toxicity in rectum, whereas 3DCRT reduced by 4% compare to 2D (MLC) and 2D plans. In IMRT plans bladder mean dose were reduced by 26% compared to 3DCRT, 2D (MLC) and 2D plans.
Conclusion: IMRT shows superior OAR sparing compared to 3DCRT, 2D (MLC) and 2D plans. Centers don’t have IMRT / VMAT provision can use 4 field box technique using 15MV beams to reduce the high dose irradiation volume, which may results in low toxicity profile.