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Year : 2014  |  Volume : 10  |  Issue : 1  |  Page : 21-25

Image guidance in prostate cancer - can offline corrections be an effective substitute for daily online imaging?

Department of Radiation Oncology, Tata Medical Center, Kolkata, West Bengal, India

Correspondence Address:
Indranil Mallick
Department of Radiation Oncology, Tata Medical Center, 14 MAR (EW), Newtown, Kolkata - 700 156, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-1482.131342

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Purpose: This aim of this study was to determine if a less resource-intensive and established offline correction protocol - the No Action Level (NAL) protocol was as effective as daily online corrections of setup deviations in curative high-dose radiotherapy of prostate cancer. Materials and Methods: A total of 683 daily megavoltage CT (MVCT) or kilovoltage CT (kvCBCT) images of 30 patients with localized prostate cancer treated with intensity modulated radiotherapy were evaluated. Daily image-guidance was performed and setup errors in three translational axes recorded. The NAL protocol was simulated by using the mean shift calculated from the first five fractions and implemented on all subsequent treatments. Using the imaging data from the remaining fractions, the daily residual error (RE) was determined. The proportion of fractions where the RE was greater than 3,5 and 7 mm was calculated, and also the actual PTV margin that would be required if the offline protocol was followed. Results: Using the NAL protocol reduced the systematic but not the random errors. Corrections made using the NAL protocol resulted in small and acceptable RE in the mediolateral (ML) and superoinferior (SI) directions with 46/533 (8.1%) and 48/533 (5%) residual shifts above 5 mm. However; residual errors greater than 5mm in the anteroposterior (AP) direction remained in 181/533 (34%) of fractions. The PTV margins calculated based on residual errors were 5mm, 5mm and 13 mm in the ML, SI and AP directions respectively. Conclusion: Offline correction using the NAL protocol resulted in unacceptably high residual errors in the AP direction, due to random uncertainties of rectal and bladder filling. Daily online imaging and corrections remain the standard image guidance policy for highly conformal radiotherapy of prostate cancer.

Abstract in Chinese

影像引导在前列腺癌的作用-离线校正可以替代每日在线成像么? 目的:本研究的目的是确定是否较少资源密集的和目前已建立的离线校正方案-不干预水平方案(NAL)和每日在线校正摆位误差在治疗前列腺癌的高剂量放疗中同样有效。 材料和方法:整合评估了30例调强放疗的局限性前列腺癌患者的共683份兆伏级CT或千伏级CT的每日影像。每日实施影像引导,3个轴的摆位误差均被记录。NAL方案通过前5次放疗的平均位移计算出以后放疗的实施方案。使用剩余放疗过程中的影像数据,确定了每日残留误差(RE)。并计算出RE大于3mm、5mm、7mm的放疗次数比例,如果随后实施离线方案,则必须同时确定真实的PTV范围。 结果:NAL方案减少了系统的而非随机误差。NAL方案中的修正导致了小而可接受的每日残留误差,在左右(ML)和头脚(SI)方向分别有46/533(8.1%)和48/533(5%)的残留位移超过5mm。然而,在腹背(AP)方向的残留误差超过5mm的仍然有181/533(34%)。PTV范围是基于左右、头脚、腹背方案的残留误差分别为5mm、5mm、13mm而得出的。 结论:离线校正的NAL方案导致了腹背方向的不可接受的高残留误差,原因是直肠膀胱充盈的随机不确定性。每日在线影像修正仍然是标准的前列腺癌高精度适形放疗的指导方案。 关键词:影像引导的放射治疗,前列腺癌,摆位误差

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