Advanced Accurate Dosimetry Techniques in Radiation Therapy using Calorimetric Techniques and Monte Carlo Simulations

使用量热技术和蒙特卡罗模拟的放射治疗中先进的精确剂量测定技术

• 批准号: RGPIN-2014-06475
• 负责人: Seuntjens, Jan
• 金额: $ 3.79万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=632936
• 关键词: Advanced; Accurate; Dosimetry; Techniques; Radiation

IntroductionIn radiation therapy (RT), dosimetric uncertainties in treatment delivery are directly associated with variations in tumor control and complication rate and a dosimetric accuracy of 3.5% is traditionally considered required. The absorbed-dose delivered to the target and critical structures is the result of a number of steps involving machine calibration, localization of target volume and critical structures, treatment planning dose calculation and radiation delivery. This research program addresses the first step in the chain leading to the determination of dose to the tumour, i.e., reference dosimetry.For conventional RT beams, the calibration chain starts with air-filled ionization chambers calibrated in terms of absorbed dose to water in a standard reference field of 10 x 10 cm^2 of a high-energy photon beam (usually Co-60). While these calibration conditions are appropriate for the field types and depths used in three-dimensional conformal radiation therapy, in modern radiation therapy, small fields or dynamically combined small fields are used in stereotactic body radiation therapy (SBRT) or intensity modulated radiation therapy (IMRT). To address accurate reference dosimetry of these beams, a new dosimetry formalism was proposed by a working group of the International Atomic Energy Agency in which the PI of this proposal played a key role. To put this new dosimetry formalism in practice, data is required on correction factors for detectors used in the calibration of these beams. A second area of dosimetric uncertainty is that of intraoperative kV radiation sources that are characterized using detectors, which are calibrated in terms of air kerma with an uncertain dose conversion process, while the quantity of interest is absorbed dose to water. A third area of emerging importance for radiation treatment, are heavy charged particle beams (proton, carbon) where also considerable uncertainties are involved. The overall objective of this research program is to address uncertainty in reference dosimetry in these challenging conditions using calorimetric techniques and Monte Carlo simulations. The long-term goal of this work is to improve success of radiation treatments through improved dosimetry in these nonstandard fields.Objectives1. Address dosimetric uncertainties in small and composite fields: (i) Study the source parameters (spot size, beam modifiers, etc) that determine the accelerator output in small field conditions. (ii) Measure and calculate correction factors for output measurements using available small field detectors for application in the small field protocol, (iii) test the criteria for selection of suitable plan-class specific reference fields.2. Address dosimetric uncertainties for the intraoperative kV source: (i) develop and commission a probe calorimeter with improved sensitivity; (ii) compare the calibration of the kV source with other detector measurements and Monte Carlo simulation.3. Address dosimetric uncertainties in carbon and proton beams: (i) develop the water calorimeter for measurements in carbon and proton small beams; (ii) compare the water calorimeter with graphite calorimetry and ionization chamber detectors.ImpactModern radiation therapy techniques increasingly use very high doses in reduced fractions for improved local control. Radiation delivery is highly complex, through a large number of small fields the dosimetry of which presents significant challenges. The impact of this program is to bring overall better consistency, conceptual clarity and improved accuracy in the dosimetry of nonstandard beams. Improved accuracy in the long term will lead to better treatment outcomes.

在放射治疗（RT）中，剂量学的不确定性与肿瘤控制和并发症发生率的变化直接相关，传统上认为需要3.5%的剂量学准确度。传递到目标和关键结构的吸收剂量是一系列步骤的结果，包括机器校准、目标体积和关键结构的定位、治疗计划、剂量计算和辐射传递。本研究计划解决了导致肿瘤剂量测定的第一步，即参考剂量测定。对于传统的RT光束，校准链从充满空气的电离室开始，根据在10 x 10 cm^2的高能光子束（通常为Co-60）的标准参考场中对水的吸收剂量进行校准。虽然这些校准条件适用于三维适形放射治疗中使用的场类型和深度，但在现代放射治疗中，小场或动态组合小场用于立体定向放射治疗（SBRT）或调强放射治疗（IMRT）。为了解决这些光束的精确参考剂量学问题，国际原子能机构的一个工作组提出了一种新的剂量学形式，其中该提议的PI发挥了关键作用。为了将这种新的剂量学形式应用于实践，需要在这些光束的校准中使用的探测器的校正因子的数据。剂量学不确定的第二个领域是术中千伏辐射源，这些辐射源使用检测器进行表征，这些辐射源是根据具有不确定剂量转换过程的空气克氏度校准的，而感兴趣的量是对水的吸收剂量。放射治疗的第三个新兴重要领域是重带电粒子束（质子、碳），其中也涉及相当大的不确定性。本研究计划的总体目标是在这些具有挑战性的条件下，利用量热技术和蒙特卡罗模拟来解决参考剂量学的不确定性。本研究的长期目标是通过改进剂量学在这些非标准领域的应用，提高放射治疗的成功率。解决小场和复合场的剂量学不确定性问题：(i)研究在小场条件下决定加速器输出的源参数（光斑大小、光束修正器等）。使用现有的小型现场探测器测量和计算输出测量的校正系数，以便应用于小型现场协议；测试选择合适的计划级特定参考场的标准。解决术中kV源剂量学的不确定性：(i)开发和使用灵敏度更高的探针量热计；(2)将千伏源的校准与其他探测器的测量和蒙特卡罗模拟进行比较。解决碳和质子束剂量学的不确定性问题：(i)开发用于碳和质子小束测量的水量热计；将水量热计与石墨量热计和电离室探测器进行比较。影响现代放射治疗技术越来越多地使用非常高的剂量，以减少部分，以改善局部控制。辐射传递是高度复杂的，通过大量的小领域，其剂量测量提出了重大挑战。该计划的影响是在非标准光束的剂量学中带来更好的一致性，概念清晰度和更高的准确性。从长远来看，准确性的提高将带来更好的治疗结果。