Department of Radiation Oncology, Saarland University Medical Centre, Homburg/Saar, Germany.
PLoS One. 2013;8(1):e53799. doi: 10.1371/journal.pone.0053799. Epub 2013 Jan 10.
Respiratory motion during percutaneous radiotherapy can be considered based on respiration-correlated computed tomography (4DCT). However, most treatment planning systems perform the dose calculation based on a single primary CT data set, even though cine mode displays may allow for a visualisation of the complete breathing cycle. This might create the mistaken impression that the dose distribution were independent of tumour motion. We present a movie visualisation technique with the aim to direct attention to the fact that the dose distribution migrates to some degree with the tumour and discuss consequences for gated treatment, IMRT plans and flattening-filter-free beams. This is a feasibility test for a visualisation of tumour and isodose motion. Ten respiratory phases are distinguished on the CT, and the dose distribution from a stationary IMRT plan is calculated on each phase, to be integrated into a movie of tumour and dose motion during breathing. For one example patient out of the sample of five lesions, the plan is compared with a gated treatment plan with respect to tumour coverage and lung sparing. The interplay-effect for small segments in the IMRT plan is estimated. While the high dose rate, together with the cone-shaped beam profile, makes the use of flattening-filter-free beams more problematic for conformal and IMRT treatment, it can be the option of choice if gated treatment is preferred. The different effects of respiratory motion, dose build-up and beam properties (segments and flatness) for gated vs. un-gated treatment can best be considered if planning is performed on the full 4DCT data set, which may be an incentive for future developments of treatment planning systems.
在经皮放射治疗期间的呼吸运动可以根据呼吸相关的计算机断层扫描（4DCT）来考虑。然而，即使电影模式显示可以可视化完整的呼吸周期，大多数治疗计划系统仍基于单个原始 CT 数据集进行剂量计算。这可能会造成剂量分布与肿瘤运动无关的错误印象。我们提出了一种电影可视化技术，旨在引起人们注意剂量分布在一定程度上随肿瘤移动的事实，并讨论其对门控治疗、调强放疗计划和无均整滤过射束的影响。这是对肿瘤和等剂量移动的可视化的可行性测试。在 CT 上区分出十个呼吸相，在每个相上计算静止调强放疗计划的剂量分布，将其整合到呼吸过程中肿瘤和剂量移动的电影中。对于五个病变样本中的一个示例患者，将计划与门控治疗计划进行比较，以评估肿瘤覆盖范围和肺保护。估计了调强放疗计划中小段的相互作用效应。尽管高剂量率加上锥形束轮廓使得无均整滤过射束在适形和调强治疗中更具挑战性，但如果首选门控治疗，则可以选择这种射束。如果在完整的 4DCT 数据集上进行计划，则可以最好地考虑呼吸运动、剂量积累和射束特性（段和平坦度）对门控与非门控治疗的不同影响，这可能是未来治疗计划系统发展的动力。
