A Dense Plasma Focus (DPF) is a pulsed device able to produce a hot and dense short-lived plasma that could become a fast radiation source for diagnostic applications, external radiotherapy, or intra-operative radiation therapy. The plasma confinement phase, identified as “pinch”, lasts few tens of nanoseconds, during which thermonuclear temperatures and densities could be reached. When the DPF vacuum chamber is filled with gases such as nitrogen, the only significant output are self-collimated charged particle beams (electrons and ions in opposite direction). Using that electron beam, it is possible to devise an ultra-high dose-rate source, with applications for direct irradiation of a tumor bed or for photon conversion after the interaction with a suitable target. The ultra-high dose rate could have potential benefits in mitigating the intrinsic or acquired malignant cell radio-resistance, which can be considered the main obstacle to the long-term survival of a patient, also sparing healthy tissues. This is due as the faster the dose deposition, the more relevant is the radiobiological efficacy (as the tumor cells do not have the time to activate the sub-lethal damage repair mechanisms responsible of the radio-resistance). Due to the novelty of the fast source, the usual models cannot easily describe the biological outcomes, therefore new numerical approaches are needed for predicting the RBE outlined in these regimens.

A parametric investigation through the Monte Carlo Damage Simulation Software (MCDS), coupled with the Monte Carlo N-Particle (MCNP) code, has been performed for supporting the experimental results previously obtained by irradiating melanoma cell lines with the Plasma Focus Device for Medical Applications #3 (PFMA-3) as UHDR source and a conventional XRT as standard of comparison.

The experimental data were benchmarked with MCNP-MCDS, properly fitting the XRT curves. The validation of the MCDS-MCNP coupling was performed by comparing literature data for conventional XRT, with less than 4% of differences. Next, the experimentally evaluated RBE highlighted that for high doses the RBE calculated on the basis of the surviving fraction (RBE(SF)), is the same of the one from double strand break damages (RBE(DSB)), making coherent the application of the Repair Misrepair Fixation theory (RMF) and providing a basis for a reliable comparison between the two devices. The DPF irradiation outcome has been numerically investigated correlating the experimental experiences with a wide range of code parameter variations to find numerical conditions able to reproduce the data. A recipe based on a combination of more than one SF curves to fit the clonogenic assay in UHDR regimen has also been proposed.

The results suggested that the UHDR regimen obtained from the DPF source could change the environmental conditions (e.g., oxygen concentration) while cumulating the dose. This implies that a combination of data and MCDS-MCNP analysis could be applied as a strategy for quantifying biological effects.

密集等离子焦点 (DPF) 是一种脉冲设备，能够产生热而密集的短寿命等离子体，可以成为诊断应用、外部放射治疗或术中放射治疗的快速辐射源。等离子体限制阶段，被称为“收缩”，持续几十纳秒，在此期间可以达到热核温度和密度。当 DPF 真空室充满氮气等气体时，唯一重要的输出是自准直的带电粒子束（电子和离子方向相反）。使用该电子束，可以设计一种超高剂量率源，用于直接照射肿瘤床或在与合适的靶标相互作用后进行光子转换。超高剂量率可能在减轻固有或获得性恶性细胞放射抗性方面具有潜在益处，这可被认为是患者长期生存的主要障碍，同时也保护了健康组织。这是因为剂量沉积越快，放射生物学功效就越相关（因为肿瘤细胞没有时间激活负责放射抗性的亚致死损伤修复机制）。由于快速源的新颖性，通常的模型不能轻易地描述生物学结果，因此需要新的数值方法来预测这些方案中概述的 RBE。这是因为剂量沉积越快，放射生物学功效就越相关（因为肿瘤细胞没有时间激活负责放射抗性的亚致死损伤修复机制）。由于快速源的新颖性，通常的模型不能轻易地描述生物学结果，因此需要新的数值方法来预测这些方案中概述的 RBE。这是因为剂量沉积越快，放射生物学功效就越相关（因为肿瘤细胞没有时间激活负责放射抗性的亚致死损伤修复机制）。由于快速源的新颖性，通常的模型不能轻易地描述生物学结果，因此需要新的数值方法来预测这些方案中概述的 RBE。

通过 Monte Carlo 损伤模拟软件 (MCDS) 和 Monte Carlo N-Particle (MCNP) 代码进行了参数研究，以支持先前通过医疗应用等离子聚焦装置照射黑色素瘤细胞系获得的实验结果#3 (PFMA-3) 作为 UHDR 源和常规 XRT 作为比较标准。

实验数据以 MCNP-MCDS 为基准，正确拟合 XRT 曲线。通过比较传统 XRT 的文献数据来验证 MCDS-MCNP 耦合，差异小于 4%。接下来，实验评估的 RBE 强调，对于高剂量，基于存活分数 (RBE(SF)) 计算的 RBE 与双链断裂损伤 (RBE(DSB)) 的 RBE 相同，从而使应用程序连贯修复误修固定理论 (RMF) 的基础，并为两种设备之间的可靠比较提供了基础。已经对 DPF 辐照结果进行了数值研究，将实验经验与各种代码参数变化相关联，以找到能够重现数据的数值条件。

结果表明，从 DPF 源获得的 UHDR 方案可以在累积剂量的同时改变环境条件（例如，氧气浓度）。这意味着数据和 MCDS-MCNP 分析的组合可以用作量化生物效应的策略。