Department of Computer Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Department of Biomedical Engineering, School of Engineering Sciences, University of Ghana, Legon, Accra, Ghana.
PLoS One. 2022 Aug 19;17(8):e0271000. doi: 10.1371/journal.pone.0271000. eCollection 2022.
In vivo dosimetry is a quality assurance tool that provides post-treatment measurement of the absorbed dose as delivered to the patient. This dosimetry compares the prescribed and measured dose delivered to the target volume. In this study, a tissue-equivalent water phantom provided the simulation of the human environment. The skin and entrance doses were measured using GafChromic EBT2 film for a Theratron® Equinox Cobalt-60 teletherapy machine.
We examined the behaviors of unencapsulated films and custom-made film encapsulation. Films were cut to 1 cm × 1 cm, calibrated, and used to assess skin dose depositions and entrance dose. We examined the response of the film for variations in field size, source to skin distance (SSD), gantry angle and wedge angle.
The estimated uncertainty in EBT2 film for absorbed dose measurement in phantom was ±1.72%. Comparison of the measurements of the two film configurations for the various irradiation parameters were field size (p = 0.0193, α = 0.05, n = 11), gantry angle (p = 0.0018, α = 0.05, n = 24), SSD (p = 0.1802, α = 0.05, n = 11) and wedge angle (p = 0.6834, α = 0.05, n = 4). For a prescribed dose of 200 cGy and at reference conditions (open field 10 cm x 10 cm, SSD = 100 cm, and gantry angle = 0º), the measured skin dose using the encapsulation material was 70% while that measured with the unencapsulated film was 24%. At reference irradiation conditions, the measured skin dose using the unencapsulated film was higher for open field configurations (24%) than wedged field configurations (19%). Estimation of the entrance dose using the unencapsulated film was within 3% of the prescribed dose.
GafChromic EBT2 film measurements were significantly affected at larger field sizes and gantry angles. Furthermore, we determined a high accuracy in entrance dose estimations using the film.
体内剂量学是一种质量保证工具，可提供治疗后对患者所接受的吸收剂量的测量。这种剂量学比较了目标体积的规定剂量和测量剂量。在这项研究中，组织等效水模体模拟了人体环境。使用 GafChromic EBT2 胶片测量 Theratron® Equinox 钴-60 远距离治疗机的皮肤和入射剂量。
我们研究了未封装胶片和定制胶片封装的行为。将胶片切割成 1cm×1cm 大小，进行校准，并用于评估皮肤剂量沉积和入射剂量。我们研究了胶片对射野大小、源皮距（SSD）、机架角度和楔形角度变化的响应。
EBT2 胶片在体模中吸收剂量测量的估计不确定度为±1.72%。比较两种胶片配置在各种照射参数下的测量结果，发现射野大小（p=0.0193，α=0.05，n=11）、机架角度（p=0.0018，α=0.05，n=24）、SSD（p=0.1802，α=0.05，n=11）和楔形角度（p=0.6834，α=0.05，n=4）有显著差异。在规定剂量为 200cGy 且参考条件（开放野 10cm×10cm，SSD=100cm，机架角度=0°）下，使用封装材料测量的皮肤剂量为 70%，而未封装胶片测量的皮肤剂量为 24%。在参考照射条件下，未封装胶片测量的开放野配置的皮肤剂量（24%）高于楔形野配置（19%）。使用未封装胶片估算入射剂量的误差在 3%以内。
GafChromic EBT2 胶片测量值在较大射野和机架角度下有显著影响。此外，我们还确定了使用该胶片进行入射剂量估算的高精度。
