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.

引言**在放射疗法（RT）中，治疗分娩中的剂量学不确定性直接与肿瘤控制和并发症发生率的变化有关，传统上则认为需要3.5％的剂量准确性。传递到目标和关键结构的吸收剂量是涉及机器校准，目标体积和关键结构的定位，治疗计划剂量计算和辐射输送的许多步骤的结果。该研究计划解决了链条中的第一步，导致对肿瘤的剂量确定，即参考剂量法。虽然这些校准条件适用于三维形成性辐射疗法中使用的田间类型和深度，但在现代放射疗法中，小场或动态组合的小田地用于立体定向的身体放射疗法（SBRT）或强度模型辐射疗法（IMRT）。为了解决这些光束的准确参考剂量法，由国际原子能局的一个工作组提出了一种新的剂量形式，该提案的PI发挥了关键作用。为了将这种新的剂型形式主义放在实践中，需要对这些梁校准的检测器进行校正因子的数据。剂量计不确定性的第二个区域是使用检测器表征的术中KV辐射源的区域，该源是根据空气kerma进行校准的，并具有不确定的剂量转换过程，而感兴趣的量被吸收到水中。辐射处理重要性的第三个区域是重电的颗粒梁（质子，碳），其中还涉及大量不确定性。该研究计划的总体目的是使用量热法和蒙特卡洛模拟来解决这些挑战性剂量测定中参考剂量法的不确定性。这项工作的长期目标是通过在这些非标准领域改善剂量测定法改善辐射处理的成功。**目标*1。地址在小型和复合场中的剂量学不确定性：（i）研究在小田间条件下确定加速器输出的源参数（点尺寸，束修饰符等）。 （ii）使用可用的小场探测器在小场协议中应用，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字段的标准。*2。地址术中KV来源的剂量学不确定性：（i）开发和委托具有提高敏感性的探针量热计； （ii）将KV源的校准与其他检测器测量和蒙特卡洛模拟进行比较。*3。解决碳和质子梁中的剂量不确定性：（i）开发水热量表，以测量碳和质子小型梁； （ii）将水热量表与石墨量热法和电离室探测器进行比较。通过大量小田地，辐射输送非常复杂，剂量法提出了重大挑战。该程序的影响是带来总体上更好的一致性，概念清晰度和提高非标准光束剂量测定的准确性。从长远来看，提高准确性将带来更好的治疗结果。