Experimental validation of Monte Carlo dosimetry for therapeutic beta emitters with radiochromic film in a 3D-printed phantom.
Experimental validation of Monte Carlo dosimetry for therapeutic beta emitters with radiochromic film in a 3D-printed phantom.
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DOI：
10.1002/mp.15926
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发表时间：
2023-01
期刊：
影响因子：
3.8
通讯作者：
Wilderman, Scott J.
中科院分区：
文献类型：
--
作者：
Van, Benjamin;Dewaraja, Yuni K.;Niedbala, Jeremy T.;Rosebush, Gerrid;Kazmierski, Matthew;Hubers, David;Mikell, Justin K.;Wilderman, Scott J.
剂量测定软件的验证，如用于患者特异性吸收剂量估计的蒙特卡罗（MC）辐射传输代码，在临床决策中使用之前至关重要。然而，由于测量短程粒子沉积能量的挑战，临床中通常不会对用于放射性药物治疗（RPT）的低/中能量β发射器进行直接实验验证。我们的目标是为基于放射致色膜（RF）的β -放射核素吸收剂量测量设计一个实用的模体几何，并进行实验来直接验证我们内部开发的剂量计划方法（DPM） MC代码，该代码专门用于内部剂量测定。该实验装置设计用于测量β辐射体的吸收剂量，该辐射体在水中的穿透范围足以达到~ 200 μm，并捕获任何光子对吸收剂量的贡献。测试的177Lu和90Y液体源（13-450 MBq，估计可向RF的敏感层提供0.5-10 Gy）被注入两个3D打印的半圆柱体的腔中，这些半圆柱体已被12.7 μm或25.4 μm厚的Kapton Tape密封。一条3.8 × 6厘米的GafChromic EBT3 RF条夹在两个带胶带的半圆柱体之间。曝光2-48小时后，取出薄膜并擦拭检测污染。采用商用三通道剂量学优化方法和6 MV光子束校准法测量射频吸收剂量。在RF的中心1 cm2区域分析剖面以进行验证。用177Lu和90Y分别在生理盐水和骨当量溶液中完成了11次和9次实验。在单填充的半圆柱体和丙烯酸衬底之间叠加多个RF条，得到177Lu和90Y的深度剂量曲线。所有实验都在DPM中建模，以产生体素化的MC吸收剂量估计。我们将研究扩展到通用MC代码MCNP6和EGSnrc，并根据实验结果进行基准测试。总共20个实验表明，3D打印的幻影和最终吸收剂量值都是可重复的。从射频测量得出的吸收剂量估计值与DPM之间的一致性在所有单膜177Lu实验中平均为- 4.0%（范围为- 10.9%至3.2%），在所有单膜90Y实验中平均为- 1.0%（范围为- 2.7%至0.7%）。在177Lu的所有深度中，DPM估计的吸收深度剂量与RF一致，平均为1.2%（范围为- 8.0%至15.2%），在90Y的所有深度中，平均为4.0%（范围为- 5.0%至9.3%）。DPM吸收剂量估计值与EGSnrc和MCNP的估计值完全一致，在所有几何形状和所有深度下，177Lu和90Y的吸收剂量估计值分别在4.7%和3.4%以内。MC显示，177Lu中β对射频的吸收剂量大于总剂量（β +其他辐射）的92%，表明我们的设计测量了主要的β贡献。在为液体源设计的简单模体中使用射频插入的可重复结果表明，这是一种可靠的装置，可用于实验验证β -发射非密封源治疗中使用的剂量学算法。用DPM MC代码估计的吸收剂量与射频测量和两个通用MC代码的结果非常吻合，从而验证了该算法用于临床RPT剂量测定的有效性。
Validation of dosimetry software, such as Monte Carlo (MC) radiation transport codes used for patient‐specific absorbed dose estimation, is critical prior to their use in clinical decision making. However, direct experimental validation in the clinic is generally not performed for low/medium‐energy beta emitters used in radiopharmaceutical therapy (RPT) due to the challenges of measuring energy deposited by short‐range particles. Our objective was to design a practical phantom geometry for radiochromic film (RF)‐based absorbed dose measurements of beta‐emitting radionuclides and perform experiments to directly validate our in‐house developed Dose Planning Method (DPM) MC code dedicated to internal dosimetry. The experimental setup was designed for measuring absorbed dose from beta emitters that have a range sufficiently penetrating to ∼200 μm in water as well as to capture any photon contributions to absorbed dose. Assayed 177Lu and 90Y liquid sources, 13–450 MBq estimated to deliver 0.5–10 Gy to the sensitive layer of the RF, were injected into the cavity of two 3D‐printed half‐cylinders that had been sealed with 12.7 μm or 25.4 μm thick Kapton Tape. A 3.8 × 6 cm strip of GafChromic EBT3 RF was sandwiched between the two taped half‐cylinders. After 2–48 h exposures, films were retrieved and wipe tested for contamination. Absorbed dose to the RF was measured using a commercial triple‐channel dosimetry optimization method and a calibration generated via 6 MV photon beam. Profiles were analyzed across the central 1 cm2 area of the RF for validation. Eleven experiments were completed with 177Lu and nine with 90Y both in saline and a bone equivalent solution. Depth dose curves were generated for 177Lu and 90Y stacking multiple RF strips between a single filled half‐cylinder and an acrylic backing. All experiments were modeled in DPM to generate voxelized MC absorbed dose estimates. We extended our study to benchmark general purpose MC codes MCNP6 and EGSnrc against the experimental results as well. A total of 20 experiments showed that both the 3D‐printed phantoms and the final absorbed dose values were reproducible. The agreement between the absorbed dose estimates from the RF measurements and DPM was on average −4.0% (range −10.9% to 3.2%) for all single film 177Lu experiments and was on average −1.0% (range −2.7% to 0.7%) for all single film 90Y experiments. Absorbed depth dose estimates by DPM agreed with RF on average 1.2% (range −8.0% to 15.2%) across all depths for 177Lu and on average 4.0% (range −5.0% to 9.3%) across all depths for 90Y. DPM absorbed dose estimates agreed with estimates from EGSnrc and MCNP across the board, within 4.7% and within 3.4% for 177Lu and 90Y respectively, for all geometries and across all depths. MC showed that absorbed dose to RF from betas was greater than 92% of the total (betas + other radiations) for 177Lu, indicating measurement of dominant beta contribution with our design. The reproducible results with a RF insert in a simple phantom designed for liquid sources demonstrate that this is a reliable setup for experimentally validating dosimetry algorithms used in therapies with beta‐emitting unsealed sources. Absorbed doses estimated with the DPM MC code showed close agreement with RF measurement and with results from two general purpose MC codes, thereby validating the use of this algorithms for clinical RPT dosimetry.
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4.9
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