Suitability Assessment of an Indigenous Heterogeneous Thoracic Phantom for Patient-Specific Quality Assurance in Radiotherapy.

Abstract

Objective: Patient-specific quality assurance (PSQA) assumes a vital role in precise and accurate radiation delivery to cancer patients. Since the patient body comprises heterogeneous media, the present study aimed to fabricate a heterogeneous thoracic phantom for PSQA. Materials and Methods: Heterogeneous thoracic (HT) phantom was fabricated using rib cage made up of bone equivalent material, kail-wood to mimic lungs and wax to mimic the various body parts. The physical density of all these materials used in phantom fabrication was measured and compared with that of the corresponding part of the actual human thorax. One beam was planned on the computed tomography (CT) images of the phantom and actual patient thorax region. Dose distribution in both the plans was measured and analyzed. Results: The estimated densities of heart, lung, ribs, scapula, spine, and chest wall tissues were 0.804 ± 0.007, 0.186 ± 0.010, 1.796 ± 0.061, 2.017 ± 0.026, 2.106 ± 0.029 and 0.739 ± 0.028 respectively in case of HT phantom while 1.038 ± 0.010, 0.199 ± 0.031, 1.715 ± 0.040, 2.006 ± 0.019, 1.929 ± 0.065 and 0.816 ± 0.028 g/cc, respectively in case of actual human thorax region.The depths of isodose curves in HT phantom were also comparable to the isodose curve’s depths in real patient. The PSQA results were within ± 3% for flat beam (FB) and flattening filtered free beam (FFFB) of 6 megavolts (MV) energy.Conclusion: The density and the dose distribution pattern in the HT phantom were similar to that in the actual human thorax region. Thus, fabricated HT phantom can be utilized for radiation dosimetry in thoracic cancer patients. The materials used to develop HT phantom are easily available in the market at an affordable price and easy to craft.