Baba Misba H, Mohib-Ul-Haq M, Khan Aijaz A
Int J Health Sci (Qassim). 2013 Jan;7(1):15-21. doi: 10.12816/0006016.
The goal of the Radiation standards and Dosimetry is to ensure that the output of the Teletherapy Unit is within ±2% of the stated one and the output of the treatment dose calculation methods are within ±5%. In the present paper, we studied the dosimetry of Cobalt-60 (Co-60) Teletherapy unit at Sher-I-Kashmir Institute of Medical Sciences (SKIMS) for last 10 years. Radioactivity is the phenomenon of disintegration of unstable nuclides called radionuclides. Among these radionuclides, Cobalt-60, incorporated in Telecobalt Unit, is commonly used in therapeutic treatment of cancer. Cobalt-60 being unstable decays continuously into Ni-60 with half life of 5.27 years thereby resulting in the decrease in its activity, hence dose rate (output). It is, therefore, mandatory to measure the dose rate of the Cobalt-60 source regularly so that the patient receives the same dose every time as prescribed by the radiation oncologist. The under dosage may lead to unsatisfactory treatment of cancer and over dosage may cause radiation hazards. Our study emphasizes the consistency between actual output and output obtained using decay method.
The methodology involved in the present study is the calculations of actual dose rate of Co-60 Teletherapy Unit by two techniques i.e. Source to Surface Distance (SSD) and Source to Axis Distance (SAD), used for the External Beam Radiotherapy, of various cancers, using the standard methods. Thereby, a year wise comparison has been made between average actual dosimetric output (dose rate) and the average expected output values (obtained by using decay method for Co-60.).
The present study shows that there is a consistency in the average output (dose rate) obtained by the actual dosimetry values and the expected output values obtained using decay method. The values obtained by actual dosimetry are within ±2% of the expected values.
The results thus obtained in a year wise comparison of average output by actual dosimetry done regularly as a part of Quality Assurance of the Telecobalt Radiotherapy Unit and its deviation from the expected output data is within the permissible limits. Thus our study shows a trend towards uniformity and a better dose delivery.
放射标准与剂量测定的目标是确保远距离治疗设备的输出在规定输出的±2%以内，且治疗剂量计算方法的输出在±5%以内。在本文中，我们研究了过去10年克什米尔医学科学研究所（SKIMS）钴-60（Co-60）远距离治疗设备的剂量测定情况。放射性是不稳定核素（称为放射性核素）衰变的现象。在这些放射性核素中，用于远距离钴治疗设备的钴-60常用于癌症的治疗。钴-60不稳定，以5.27年的半衰期持续衰变为镍-60，从而导致其活度降低，进而剂量率（输出）降低。因此，必须定期测量钴-60源的剂量率，以便患者每次都能接受放射肿瘤学家规定的相同剂量。剂量不足可能导致癌症治疗效果不理想，而剂量过量可能会造成辐射危害。我们的研究强调了实际输出与使用衰变方法获得的输出之间的一致性。
本研究涉及的方法是通过两种技术，即源皮距（SSD）和源轴距（SAD），使用标准方法计算Co-60远距离治疗设备的实际剂量率，这两种技术用于各种癌症的外照射放疗。由此，对平均实际剂量测定输出（剂量率）与平均预期输出值（通过使用Co-60的衰变方法获得）进行了逐年比较。
本研究表明，实际剂量测定值获得的平均输出（剂量率）与使用衰变方法获得的预期输出值之间存在一致性。实际剂量测定获得的值在预期值的±2%以内。
作为远距离钴放射治疗设备质量保证的一部分，定期进行实际剂量测定得到的平均输出逐年比较结果以及其与预期输出数据的偏差在允许范围内。因此，我们的研究显示出趋于均匀和更好剂量传递的趋势。
