Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital (MGH), Boston, USA.
Department of Medical Physics & Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland.
Radiother Oncol. 2020 Mar;144:79-85. doi: 10.1016/j.radonc.2019.10.010. Epub 2019 Nov 14.
Treatment planning for proton therapy requires the relative proton stopping power ratio (RSP) information of the patient for accurate dose calculations. RSP are conventionally obtained after mapping of the Hounsfield units (HU) from a calibrated patient computed tomography (CT). One or multiple CT are needed for a given treatment which represents additional, undesired dose to the patient. For prostate cancer, magnetic resonance imaging (MRI) scans are the gold standard for segmentation while offering dose-less imaging. We here quantify the clinical applicability of converted MR images as a substitute for intensity modulated proton therapy (IMPT) treatment of the prostate.
MRCAT (Magnetic Resonance for Calculating ATtenuation) is a Philips-developed technology which produces a synthetic CT image consisting of five HU from a specific set of MRI acquisitions. MRCAT and original planning CT data sets were obtained for ten patients. An IMPT plan was generated on the MRCAT for each patient. Plans were produced such that they fulfill the prostate protocol in use at Massachusetts General Hospital (MGH). The plans were then recomputed onto the nominal planning CT for each patient. Robustness analyses (±5 mm setup shifts and ±3.5 % range uncertainties) were also performed.
Comparison of MRCAT plans and their recomputation onto the planning CT plan showed excellent agreement. Likewise, dose perturbations due to setup shifts and range uncertainties were well within clinical acceptance demonstrating the clinical viability of the approach.
This work demonstrate the clinical acceptability of substituting MR converted RSP images instead of CT for IMPT planning of prostate cancer. This further translates into higher contouring accuracy along with lesser imaging dose.
质子治疗计划需要患者的相对质子阻止比（RSP）信息，以进行准确的剂量计算。RSP 通常是通过对校准后的患者计算机断层扫描（CT）进行 Hounsfield 单位（HU）映射获得的。对于给定的治疗，需要进行一次或多次 CT 扫描，这会给患者带来额外的、不期望的剂量。对于前列腺癌，磁共振成像（MRI）扫描是分割的金标准，同时提供无剂量成像。我们在这里量化了转换后的 MR 图像作为替代强度调制质子治疗（IMPT）治疗前列腺的临床适用性。
MRCAT（用于计算衰减的磁共振）是飞利浦开发的一种技术，它可以从一组特定的 MRI 采集数据中生成一个包含五个 HU 的合成 CT 图像。为十位患者获得了 MRCAT 和原始计划 CT 数据集。为每位患者在 MRCAT 上生成了一个 IMPT 计划。这些计划是根据马萨诸塞州综合医院（MGH）正在使用的前列腺协议生成的。然后，将计划重新计算到每位患者的名义计划 CT 上。还进行了稳健性分析（±5mm 的设置偏移和±3.5%的范围不确定性）。
MRCAT 计划与重新计算到计划 CT 计划上的计划之间的比较显示出极好的一致性。同样，由于设置偏移和范围不确定性引起的剂量扰动也在临床可接受范围内，证明了该方法的临床可行性。
这项工作证明了用 MR 转换的 RSP 图像代替 CT 进行前列腺癌的 IMPT 计划的临床可接受性。这进一步转化为更高的轮廓准确性和更少的成像剂量。
