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: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=664781
• 关键词: Advanced; Accurate; Dosimetry; Techniques; Radiation

Introduction**In 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.**Objectives*1. 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.**Impact*Modern 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.

简介**在放射治疗 (RT) 中，治疗过程中的剂量测定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% 的剂量测定精度。传递到目标和关键结构的吸收剂量是多个步骤的结果，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。该研究计划解决了确定肿瘤剂量链中的第一步，即参考剂量测定。**对于传统 RT 束，校准链从充气电离室开始，根据水吸收剂量进行校准在 10 x 10 cm^2 的高能光子束（通常是 Co-60）的标准参考场中。虽然这些校准条件适合三维适形放射治疗中使用的射野类型和深度，但在现代放射治疗中，立体定向身体放射治疗 (SBRT) 或调强放射治疗 (IMRT) 中使用小射野或动态组合小射野。 ）。为了解决这些束流的精确参考剂量测定问题，国际原子能机构的一个工作组提出了一种新的剂量测定形式，其中该提案的 PI 发挥了关键作用。为了将这种新的剂量测定形式付诸实践，需要有关用于校准这些光束的探测器的校正因子的数据。剂量测定不确定性的第二个领域是使用探测器表征的术中 kV 辐射源，探测器通过不确定的剂量转换过程根据空气比释动能进行校准，而感兴趣的量是水的吸收剂量。对于放射治疗来说，第三个日益重要的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。该研究计划的总体目标是使用量热技术和蒙特卡罗模拟解决这些具有挑战性的条件下参考剂量测定的不确定性。这项工作的长期目标是通过改进这些非标准区域的剂量测定来提高放射治疗的成功率。**目标*1。解决小场和复合场中的剂量测定不确定性：(i) 研究确定小场条件下加速器输出的源参数（光斑尺寸、射束调节器等）。 (ii) 使用适用于小场协议的可用小场探测器来测量和计算输出测量的校正因子，(iii) 测试选择合适的计划级特定参考场的标准。*2。解决术中 kV 源的剂量测定不确定性：(i) 开发并调试灵敏度更高的探针量热计； (ii) 将 kV 源的校准与其他探测器测量和蒙特卡罗模拟进行比较。*3。解决碳束和质子束的剂量测定不确定性：(i) 开发用于测量碳束和质子小束的水热量计； (ii) 将水量热计与石墨量热法和电离室检测器进行比较。**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分数，以改善局部控制。辐射传输非常复杂，需要通过大量小射野，其剂量测定提出了重大挑战。该计划的影响是在非标准光束的剂量测定中带来整体更好的一致性、概念清晰度和更高的准确性。从长远来看，提高准确性将带来更好的治疗结果。