Flejmer Anna Maria, Dohlmar Frida, Nilsson Mats, Stenmarker Margaretha, Dasu Alexandru
Department of Oncology and Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
Anticancer Res. 2015 May;35(5):2841-8.
The present study aimed to investigate the implications of using the analytical anisotropic algorithm (AAA) for calculation of target coverage and radiation burden of normal tissues. Most model parameters, recommendations and planning guidelines associated with a certain outcome are from the era of pencil beam convolution (PBC) calculations on relatively simple assumptions of energy transport in media. Their relevance for AAA calculations that predict more realistic dose distributions needs to be evaluated.
Forty patients with left-sided breast cancer receiving 3D conformal radiation therapy were planned using PBC with a standard protocol with 50 Gy in 25 fractions according to existing re-commendations. The plans were subsequently recalculated with the AAA and relevant dose parameters were determined and compared to their PBC equivalents.
The majority of the AAA-based plans had a significantly worse coverage of the planning target volume and also a higher maximum dose in hotspots near sensitive structures, suggesting that these criteria could be relaxed for AAA-calculated plans. Furthermore, the AAA predicts higher volumes of the ipsilateral lung will receive doses below 25 Gy and smaller volume doses above 25 Gy. These results indicate that lung tolerance criteria might also have to be relaxed for AAA planning in order to maintain the level of normal tissue toxicity. The AAA also predicts lower doses to the heart, thus indicating that this organ might be more sensitive to radiation than thought from PBC-based calculations.
The AAA should be preferred over the PBC algorithm for breast cancer radiotherapy as it gives more realistic dose distributions. Guidelines for plan acceptance might have to be re-evaluated to account for differences in dose predictions in order to maintain the current levels of control and complication rates. The results also suggest an increased radiosensitivity of the heart, thus indicating that a revision of the current models for cardiovascular complications may be needed.
本研究旨在探讨使用分析各向异性算法（AAA）计算靶区覆盖范围和正常组织辐射负担的意义。大多数与特定结果相关的模型参数、建议和计划指南都来自铅笔束卷积（PBC）计算时代，当时对介质中能量传输的假设相对简单。它们与预测更真实剂量分布的AAA计算的相关性需要评估。
40例左侧乳腺癌患者接受三维适形放射治疗，根据现有建议，采用PBC和标准方案进行计划，分25次给予50 Gy。随后用AAA重新计算计划，并确定相关剂量参数，与PBC等效参数进行比较。
大多数基于AAA的计划对计划靶区的覆盖明显较差，并且在敏感结构附近的热点区域最大剂量也更高，这表明对于AAA计算的计划，这些标准可以放宽。此外，AAA预测同侧肺接受低于25 Gy剂量的体积更大，接受高于25 Gy剂量的体积更小。这些结果表明，为了维持正常组织毒性水平，在AAA计划中也可能需要放宽肺耐受标准。AAA还预测心脏接受的剂量更低，因此表明该器官可能比基于PBC计算所认为的对辐射更敏感。
在乳腺癌放射治疗中，AAA应优于PBC算法，因为它能给出更真实的剂量分布。可能需要重新评估计划验收指南，以考虑剂量预测的差异，从而维持当前的控制水平和并发症发生率。结果还表明心脏的放射敏感性增加，因此表明可能需要修订当前的心血管并发症模型。
