基于 TLD 的图像引导方法，用于前列腺癌质子治疗中使用直肠内气囊的体内直肠剂量验证。

Image-guided method for TLD-based in vivo rectal dose verification with endorectal balloon in proton therapy for prostate cancer.

机构信息

ProCure Proton Therapy Center, Oklahoma City, Oklahoma 73142, USA.

出版信息

Med Phys. 2013 May;40(5):051715. doi: 10.1118/1.4801901.

DOI:10.1118/1.4801901

PMID:23635263

Abstract

PURPOSE

To present a practical image-guided method to position an endorectal balloon that improves in vivo thermoluminiscent dosimeter (TLD) measurements of rectal doses in proton therapy for prostate cancer.

METHODS

TLDs were combined with endorectal balloons to measure dose at the anterior rectal wall during daily proton treatment delivery. Radiopaque metallic markers were employed as surrogates for balloon position reproducibility in rotation and translation. The markers were utilized to guide the balloon orientation during daily treatment employing orthogonal x-ray image-guided patient positioning. TLDs were placed at the 12 o'clock position on the anterior balloon surface at the midprostatic plane. Markers were placed at the 3 and 9 o'clock positions on the balloon to align it with respect to the planned orientation. The balloon rotation along its stem axis, referred to as roll, causes TLD displacement along the anterior-posterior direction. The magnitude of TLD displacement is revealed by the separation distance between markers at opposite sides of the balloon on sagittal x-ray images.

RESULTS

A total of 81 in vivo TLD measurements were performed on six patients. Eighty-three percent of all measurements (65 TLD readings) were within +5% and -10% of the planning dose with a mean of -2.1% and a standard deviation of 3.5%. Examination of marker positions with in-room x-ray images of measured doses between -10% and -20% of the planned dose revealed a strong correlation between balloon roll and TLD displacement posteriorly from the planned position. The magnitude of the roll was confirmed by separations of 10-20 mm between the markers which could be corrected by manually adjusting the balloon position and verified by a repeat x-ray image prior to proton delivery. This approach could properly correct the balloon roll, resulting in TLD positioning within 2 mm along the anterior-posterior direction.

CONCLUSIONS

Our results show that image-guided TLD-based in vivo dosimetry for rectal dose verification can be perfomed reliably and reproducibly for proton therapy in prostate cancer.

摘要

目的

提出一种实用的图像引导方法来定位直肠内球囊，以改善前列腺癌质子治疗中直肠剂量的体内热释光剂量计（TLD）测量。

方法

将 TLD 与直肠内球囊结合，以在质子治疗过程中测量前直肠壁的剂量。使用不透射线的金属标记物作为球囊旋转和平移再现性的替代物。使用这些标记物在每日治疗过程中引导球囊方向，采用正交 X 射线图像引导患者定位。TLD 放置在前球囊表面的 12 点钟位置，在前列腺中部平面。将标记物放置在球囊的 3 点钟和 9 点钟位置，以使其与计划方向对齐。球囊沿其茎轴的旋转，称为滚动，导致 TLD 在前后方向上的位移。球囊两侧标记物之间的分离距离揭示了 TLD 位移的幅度，通过矢状 X 射线图像可以看到。

结果

在 6 名患者中进行了总共 81 次体内 TLD 测量。所有测量结果的 83%（65 个 TLD 读数）在计划剂量的+5%和-10%范围内，平均值为-2.1%，标准差为 3.5%。在计划剂量的-10%和-20%之间的测量剂量的室内 X 射线图像上检查标记物位置，发现球囊滚动与 TLD 从计划位置向后的位移之间存在很强的相关性。通过标记物之间 10-20mm 的分离可以确认滚动的幅度，通过手动调整球囊位置并在质子输送前通过重复 X 射线图像进行验证，可以纠正这种分离。这种方法可以正确纠正球囊滚动，使 TLD 在前后方向上的定位在 2mm 以内。