AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams
AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams
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DOI：
10.1118/1.598691
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发表时间：
1999-09-01
期刊：
影响因子：
3.8
通讯作者：
Rogers, DWO
中科院分区：
文献类型：
--
作者：
Almond, PR;Biggs, PJ;Rogers, DWO
为使用标称能量在Co-60和50 MV之间的光子束和标称能量在4和50 MeV之间的电子束进行外部束放射治疗的临床参考剂量测定规定了一种方案。该方案由美国医学物理学家协会（AAPM）放射治疗委员会第51工作组（TG-51）编写，并已被AAPM正式批准临床使用。该方案使用的离子室具有可追溯至国家一级标准的吸收剂量-水校准因子N-D，w(60Co)，方程D-w(Q) = Mk(Q)N(D,w)(60Co)，其中Q为临床光束的光束质量，DP为放置在参考条件下的离子室在测量点对水的吸收剂量，M为完全校正后的离子室读数。kg是质量转换因子，它将Co-60光束的校准因子转换为质量为Q的光束的校准因子。对于许多离子室，ka的值是Q的函数。M的值由M = PionPTPPelecPpolMraw给出，其中M-raw是未经校正的离子室读数和离子重组时的p离子校正值，P-TP表示温度和压力变化，P-elec表示静电计单独校准时的不准确性，P-pol表示室极性效应。光束质量,Q,指定(我)光子束,由% dd (10) (x)的光子组件百分深度剂量在10厘米深度字段大小为10 * 10厘米(2)表面上的幻影100厘米的SSD和电子束(ii),由R-50的深度吸收剂量降至50%的最大剂量在梁场大小大于或等于10 x 10厘米(2)表面的幽灵(大于或等于20 x 20厘米(2)R-50 > 8.5厘米)的SSD 100厘米。R-50直接由I-50的测量值确定，即电离深度下降到其最大值的50%。所有临床参考剂量测定均在水模中进行。用于校准目的的参考深度为光子束为10厘米，电子束为0.6R(50)-0.1厘米。对于光子光束，临床参考剂量测定在SSD或SAD装置中进行，SSD装置的幻像表面上定义了10 x 10 cm(2)的场大小，SAD装置的探测器深度处定义了10 x 10 cm(2)的场大小。对于电子束临床参考剂量测定，在90和110厘米之间的SSD上，视场尺寸大于或等于10 × 10厘米(2)（R-50 bb0 8.5厘米大于或等于20 × 20厘米(2)）。与AAPM的TG-21方案相比，该方案大大简化了，因为不需要大的停止功率比和质能吸收系数表，用户也不需要计算任何理论剂量学因子。各种情况下的工作表连同所需设备的清单一起呈现。(C) 1999年美国医学物理学家协会。[s0094 - 2405(99) 00209 - 6]。
A protocol is prescribed for clinical reference dosimetry of external beam radiation therapy using photon beams with nominal energies between Co-60 and 50 MV and electron beams with nominal energies between 4 and 50 MeV. The protocol was written by Task Group 51 (TG-51) of the Radiation Therapy Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol uses ion chambers with absorbed-dose-to-water calibration factors, N-D,w(60Co), which are traceable to national primary standards, and the equation D-w(Q) = Mk(Q)N(D,w)(60Co), where Q is the beam quality of the clinical beam, DP is the absorbed dose to water at the point of measurement of the ion chamber placed under reference conditions, M is the fully corrected ion chamber reading, and kg is the quality conversion factor which converts the calibration factor for a Co-60 beam to that for a beam of quality Q. Values of ka are presented as a function of Q for many ion chambers. The value of M is given by M = PionPTPPelecPpolMraw, where M-raw is the raw, uncorrected ion chamber reading and P-ion corrects for ion recombination, P-TP for temperature and pressure variations, P-elec for inaccuracy of the electrometer if calibrated separately, and P-pol for chamber polarity effects. Beam quality, Q, is specified (i) for photon beams, by %dd(10)(x), the photon component of the percentage depth dose at 10 cm depth for a field size of 10 x 10 cm(2) on the surface of a phantom at an SSD of 100 cm and (ii) for electron beams, by R-50, the depth at which the absorbed-dose falls to 50% of the maximum dose in a beam with field size greater than or equal to 10 x 10 cm(2) on the surface of the phantom (greater than or equal to 20 x 20 cm(2) for R-50> 8.5 cm) at an SSD of 100 cm. R-50 is determined directly from the measured value of I-50, the depth at which the ionization falls to 50% of its maximum value. All clinical reference dosimetry is performed in a water phantom. The reference depth for calibration purposes is 10 cm for photon beams and 0.6R(50)-0.1 cm for electron beams. For photon beams clinical reference dosimetry is performed in either an SSD or SAD setup with a 10 x 10 cm(2) field size defined on the phantom surface for an SSD setup or at the depth of the detector for an SAD setup. For electron beams clinical reference dosimetry is performed with a field size of greater than or equal to 10 x 10 cm(2) (greater than or equal to 20 x 20 cm(2) for R-50> 8.5 cm) at an SSD between 90 and 110 cm. This protocol represents a major simplification compared to the AAPM's TG-21 protocol in the sense that large tables of stopping-power ratios and mass-energy absorption coefficients are not needed and the user does not need to calculate any theoretical dosimetry factors. Worksheets for various situations are presented along with a list of equipment required. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)00209-6].