Designed and Validation of In-House Head and Neck Phantom for Quality Assurance and Radiotherapy Dose Measurements

Introduction: In radiotherapy treatment of head and neck (H N) cancers, more complex quality assurance checks and patient-specific dosimetry are required to ensure accuracy in modern technology. In this paper, a new cost-effective human tissue equivalent H N phantom was designed to serve as an economical and adaptable tool for assessment and assurance of precise radiotherapy dose delivery. Material and Methods: The phantom was designed using locally available paraffin wax and tissue-equivalent materials. Computed tomography (CT) images of the phantom were acquired using a conventional CT simulator and were registered with the images of a real patient having approximately similar physical dimensions. The geometric and attenuation properties of the structures in the phantom were studied and compared to the structures of the real patient.  Results: Hounsfield unit (HU) values of different structures of the phantom were compared to the values obtained from the CT images of a real patient and were found to be in good agreement. HU values obtained for the right, and left eye, brain, larynx, and bone shell were 7(±10) HU, 6(±9), 30(±14) HU, -984(±6) HU and 873(±214) HU in phantom. Structures simulated in phantom agreed well on comparison regarding both their design and radiation properties with respect to real patient human tissues. Gamma analysis was performed for the axial dose plane at plan isocenter for both the calculated dose distribution in H N phantom and the patient agrees for 98.79% passing rate for 3% /3mm criteria. Conclusion: The designed phantom depicts human anatomy and meets the requirements of tissue equivalence. The result shows that phantom has proved to be a cost-effective and valuable tool for accurate verification of dose distributions in regions of clinical and dosimetric interests.