Document Type : Original Paper
Amity University, Gwalior, Madhya Pradesh
Department of Radiation Oncology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Vibhuti Khand Gomti Nagar, Lucknow -226010
Dept. of Physics, Tilak Dhari P. G. College, Jaunpur, (U.P.) - 222002, INDIA, V.B.S. Purvanchal University, Jaunpur, (U.P.) - 222003, INDIA and Dept. of Radiation Oncology, U.P.U.M.S., Saifai, Etawah (U.P.) - 206130, INDIA
Introduction: The objective of this work is to design the new kind of AHFP phantom to determine if this phantom is a realistic representation of actual cervical-cancer patients. This can be serve as a stand-in for the dosimetry quality assurance of a real patient.
Materials and method: An anthropomorphic heterogeneous female pelvic phantom was designed which was made of paraffin wax, a female pelvic bone, water, gauge, polyvinyl chloride (PVC) and polymerized siloxanes. The AHFP phantom was scanned using a CT scanner (Toshiba Alexion 16 multi Slice CT scanner) at 120kVp and 250mAs with a slice thickness of 2mm in order to assess how accurately the resulting phantom product simulates a real patient. The CT images were transferred to the Eclipse treatment planning system for dosimetry analysis.
Results: The AHFP phantom's CT numbers and relative electron densities of the uterus, bladder, rectum, muscles, fat, bones, and cavities were found close to real patients. The mean percentage variations between planned and measured doses of all RapidArc QA plans were as 2.14 % and standard deviation 0.633 (t=0.10422, p= .459072; p>0.05) for slab phantom¸ and 8.31% & standard deviation 2.77 (t=4.51488, p=0.000134; p< .05) for AHFP phantom.
Conclusion: It is concluded that the existing algorithms in TPS for dosimetry is working fine for homogeneous phantom, but it does not work good for heterogeneous (AHFP) phantom. Therefore, patient-specific absolute dosimetry should be performed using a heterogeneous phantom that closely resembles the actual human body in terms of both density and design.