Bawazeer Omemh, Herath Sisira, Sarasanandarajah Siva, Kron Tomas, Deb Pradip
Discipline of Medical Radiations, School of Medical Science, RMIT University, Melbourne, Victoria, Australia.
Discipline of Sciences, School of Medical Physics, Umm Al-Qura University, Mecca, Saudi Arabia.
J Med Phys. 2017 Apr-Jun;42(2):90-95. doi: 10.4103/jmp.JMP_98_16.
This study investigates the impact of cine acquisition mode on the dosimetric characteristics of a Varian aS500 amorphous silicon electronic portal imaging device (a-Si EPID).
The performance of an a-Si EPID operated in cine mode was assessed and compared to its performance when operated in an integrated mode and dose measurements using an ionization chamber. This study was conducted at different photon energies and the EPID performance was assessed as function of the delivered dose, dose rate, multileaf collimator speed, field size, phantom thickness, and intensity-modulated radiation therapy fields.
The worst nonlinearity was observed at low monitor unit (MU) settings < 100 MU with the highest dose per frame. The nonlinearity of response at a low MU setting was attributed due to the loss of four cine images during each delivery. The EPID response with changing dose rate for 10 MU delivered had similar results to its performance in an integrated mode and ionization chamber. Despite the nonlinearity of response with low MU delivered, EPID performance operated in cine and integrated acquisition modes had comparable responses within 2%.
For EPID dosimetry application using cine mode, this study recommends the calibration of the EPID images to be undertaken at a large MU. There were no additional corrections that were required when the EPID operated in cine acquisition mode as compared to calibration in integrated mode.
本研究调查电影采集模式对瓦里安aS500非晶硅电子射野影像装置（a-Si EPID）剂量学特性的影响。
评估了a-Si EPID在电影模式下的性能，并将其与在集成模式下的性能以及使用电离室进行的剂量测量结果进行比较。本研究在不同光子能量下进行，EPID性能根据输送剂量、剂量率、多叶准直器速度、射野大小、模体厚度和调强放射治疗射野进行评估。
在监测单位（MU）设置<100 MU且每帧剂量最高的低MU设置下观察到最严重的非线性。低MU设置下响应的非线性归因于每次输送过程中丢失四张电影图像。对于输送10 MU时剂量率变化的EPID响应，其结果与其在集成模式和电离室中的性能相似。尽管低MU输送时响应存在非线性，但电影和集成采集模式下运行的EPID性能在2%范围内具有可比的响应。
对于使用电影模式的EPID剂量学应用，本研究建议在大MU下对EPID图像进行校准。与集成模式下的校准相比，EPID在电影采集模式下运行时无需额外校正。
