Particle therapy treatment planning requires accurate volumetric maps of the relative stopping power, which can directly be acquired using proton computed tomography (pCT). With fluence-modulated pCT (FMpCT) imaging fluence is concentrated in a region-of-interest (ROI), which can be the vicinity of the treatment beam path, and imaging dose is reduced elsewhere. In this work we present a novel optimization algorithm for FMpCT which, for the first time, calculates modulated imaging fluences for joint imaging dose and image variance objectives. Thereby, image quality is maintained in the ROI to ensure accurate calculations of the treatment dose, and imaging dose is minimized outside the ROI with stronger minimization penalties given to imaging organs-at-risk. The optimization requires an initial scan at uniform fluence or a previous x-ray CT scan. We simulated and optimized FMpCT images for three pediatric patients with tumors in the head region. We verified that the target image variance inside the ROI was achieved and demonstrated imaging dose reductions outside of the ROI of 74% on average, reducing the imaging dose from 1.2 to 0.3 mGy. Such dose savings are expected to be relevant compared to the therapeutic dose outside of the treatment field. Treatment doses were re-calculated on the FMpCT images and compared to treatment doses re-recalculated on uniform fluence pCT scans using a 1% criterion. Passing rates were above 98.3% for all patients. Passing rates comparing FMpCT treatment doses to the ground truth treatment dose were above 88.5% for all patients. Evaluation of the proton range with a 1 mm criterion resulted in passing rates above 97.5% (FMpCT/pCT) and 95.3% (FMpCT/ground truth). Jointly optimized fluence-modulated pCT images can be used for proton dose calculation maintaining the full dosimetric accuracy of pCT but reducing the required imaging dose considerably by three quarters. This may allow for daily imaging during particle therapy ensuring a safe and accurate delivery of the therapeutic dose and avoiding excess dose from imaging.

粒子疗法治疗计划需要准确的相对停止能力的体积图，可以使用质子计算机断层扫描 (pCT) 直接获取。使用注量调制 pCT (FMpCT) 成像注量集中在感兴趣区域 (ROI) 中，该区域可以是治疗光束路径的附近，并且在其他地方减少了成像剂量。在这项工作中，我们提出了一种新的 FMpCT 优化算法，该算法首次计算联合成像剂量和图像方差目标的调制成像注量。因此，在 ROI 中保持图像质量以确保治疗剂量的准确计算，并且在 ROI 之外最小化成像剂量，同时对处于危险中的成像器官给予更强的最小化惩罚。优化需要以均匀能量密度进行初始扫描或之前的 X 射线 CT 扫描。我们为三名头部有肿瘤的儿科患者模拟和优化了 FMpCT 图像。我们验证了 ROI 内的目标图像差异已实现，并证明 ROI 外的成像剂量平均减少了 74%，将成像剂量从 1.2 减少到 0.3 mGy。与治疗场外的治疗剂量相比，预计这种剂量节省是相关的。在 FMpCT 图像上重新计算治疗剂量，并与使用 1% 标准在均匀能量 pCT 扫描上重新计算的治疗剂量进行比较。所有患者的通过率均在98.3%以上。所有患者的 FMpCT 治疗剂量与真实治疗剂量的通过率均高于 88.5%。使用 1 mm 标准评估质子范围导致通过率高于 97.5% (FMpCT/pCT) 和 95。3%（FMpCT/地面实况）。联合优化的通量调制 pCT 图像可用于质子剂量计算，保持 pCT 的完整剂量测量精度，但所需的成像剂量显着减少四分之三。这可以允许在粒子治疗期间进行日常成像，以确保安全和准确地输送治疗剂量并避免成像中的过量剂量。