三维适形放射治疗剂量计算模型研究
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摘要
放射治疗是治疗肿瘤的主要方法之一，计算机三维放射治疗计划系统是当今放射治疗的灵魂。本文针对放射治疗计划系统中的关键问题之一：剂最计算模型进行了系统而深入的研究。
剂量计算的精度和速度是评价一个放射治疗计划系统实用与否的标准之一。文中根据照射野形状，将高能X射线分成规则野和不规则野两种类型，通过建立相应的剂量计算模型以取得折衷的计算精度和速度。
文中建立的规则野剂量计算模型是基于测量剂量数据的校正模型，这一模型可以迅述给出临床上常用的矩形野、楔形野和非对称野及其组合野的三维剂量分布。我们在对原有规则野剂量计算模型和算法中存在的各种缺陷进行改进和有机合成的基础上，提出了一整套规则野剂量计算的更优解决方案。具体内容包括：建立了对称矩形野、楔形野和非对称矩形野的剂量计算模型；研究了射野深度剂量和离轴比计算的插值和拟合方法。由于该模型算法简单，数据源充分，所以在计算规则野的三维剂量分布时具有较高的计算精度和几乎是实时的计算速度，是一种实用的规则野剂量计算方法。
文中建立的不规则野剂最计算模型是基于二维卷积原理的模型，这一模型可用于计算适形放疗中各类不规则野的剂量分布。这部分的主要研究成果有：建立了用解卷积方法提取笔射束核的笔射束模型；系统研究了不规则野的半影计算模型和快述算法：描述了基于二维卷积原理的吸收剂量计算方法：介绍了不规则野的确定方法。针对这一模型，我们进行了大量的实验测量和计算，取得了一致的实验结果。实验表明，我们建立的笔射束模型能够取得满意的精度并具有很强的通用性，尤其在文中快速算法的支持下，其计算速度完全能为临床应用所接受，是用于三维放射治疗计划系统的可行的解决方案。
文中最后对工作中的遗留问题作了说明，并对今后的工作进行了展望。
Radiotherapy is one of the most important methods for tumor treatment and engages computer radiotherapy treatment planning system as its key tool. In this thesis, we focused on one of the key problems: dose calculation, which is crucial to develop a three-dimensional radiotherapy treatment planning system.
The precision attained and the time spent in computing dose is crucial to the practicability of a radiotherapy treatment planning system. According to the shape of irradiation field, we advance two kinds of dose calculation models separately for high-energy X-ray regular and irregular field, thus achieving the compromise precision and speed.
The dose calculation model used for regular irradiation field is a corrected model using measured dose data. Using this model, dose computing result of regular field can be obtained immediately. Through reforming original dose calculation models established for regular irradiation field, we present a set of more efficient and systematical solution to calculate dose distribution of regular irradiation field. The detailed topics include: dose calculation models on opening symmetric rectangle field, wedge field and asymmetric rectangle field; revised numerical processing methods for depth dose and off axis ratio. Because of easy method and ample data sources, this dose calculation model is feasible for its more accurate precision and almost real-time speed when used for computing three-dimensional dose distribution with the regular irradiation fields.
The dose calculation model advanced for irregular irradiation field bases on two-dimensional convolution principle. This model can be applied to calculate three-dimensional dose distribution for irregular irradiation field configured for conformal radiation therapy. In this part, our research results are as follows: a pencil
beam model established on the basis of extraction pencil beam kernel by the deconvolution method; a penumbra calculating model and its fast algorithm; convolution kernels reconstruction methods based on pencil beam; the irregular field forming method. We have done a lot of experiments, and the results have shown that this dose calculation model can achieve satisfactory precision and fast speed. As a result, it is a general method to dose calculation.
At the end of this thesis, we also discuss some problems which haven't been completed. In addition, we prospect some work which we'll do in the future.
剂量计算的精度和速度是评价一个放射治疗计划系统实用与否的标准之一。文中根据照射野形状，将高能X射线分成规则野和不规则野两种类型，通过建立相应的剂量计算模型以取得折衷的计算精度和速度。
文中建立的规则野剂量计算模型是基于测量剂量数据的校正模型，这一模型可以迅述给出临床上常用的矩形野、楔形野和非对称野及其组合野的三维剂量分布。我们在对原有规则野剂量计算模型和算法中存在的各种缺陷进行改进和有机合成的基础上，提出了一整套规则野剂量计算的更优解决方案。具体内容包括：建立了对称矩形野、楔形野和非对称矩形野的剂量计算模型；研究了射野深度剂量和离轴比计算的插值和拟合方法。由于该模型算法简单，数据源充分，所以在计算规则野的三维剂量分布时具有较高的计算精度和几乎是实时的计算速度，是一种实用的规则野剂量计算方法。
文中建立的不规则野剂最计算模型是基于二维卷积原理的模型，这一模型可用于计算适形放疗中各类不规则野的剂量分布。这部分的主要研究成果有：建立了用解卷积方法提取笔射束核的笔射束模型；系统研究了不规则野的半影计算模型和快述算法：描述了基于二维卷积原理的吸收剂量计算方法：介绍了不规则野的确定方法。针对这一模型，我们进行了大量的实验测量和计算，取得了一致的实验结果。实验表明，我们建立的笔射束模型能够取得满意的精度并具有很强的通用性，尤其在文中快速算法的支持下，其计算速度完全能为临床应用所接受，是用于三维放射治疗计划系统的可行的解决方案。
文中最后对工作中的遗留问题作了说明，并对今后的工作进行了展望。
Radiotherapy is one of the most important methods for tumor treatment and engages computer radiotherapy treatment planning system as its key tool. In this thesis, we focused on one of the key problems: dose calculation, which is crucial to develop a three-dimensional radiotherapy treatment planning system.
The precision attained and the time spent in computing dose is crucial to the practicability of a radiotherapy treatment planning system. According to the shape of irradiation field, we advance two kinds of dose calculation models separately for high-energy X-ray regular and irregular field, thus achieving the compromise precision and speed.
The dose calculation model used for regular irradiation field is a corrected model using measured dose data. Using this model, dose computing result of regular field can be obtained immediately. Through reforming original dose calculation models established for regular irradiation field, we present a set of more efficient and systematical solution to calculate dose distribution of regular irradiation field. The detailed topics include: dose calculation models on opening symmetric rectangle field, wedge field and asymmetric rectangle field; revised numerical processing methods for depth dose and off axis ratio. Because of easy method and ample data sources, this dose calculation model is feasible for its more accurate precision and almost real-time speed when used for computing three-dimensional dose distribution with the regular irradiation fields.
The dose calculation model advanced for irregular irradiation field bases on two-dimensional convolution principle. This model can be applied to calculate three-dimensional dose distribution for irregular irradiation field configured for conformal radiation therapy. In this part, our research results are as follows: a pencil
beam model established on the basis of extraction pencil beam kernel by the deconvolution method; a penumbra calculating model and its fast algorithm; convolution kernels reconstruction methods based on pencil beam; the irregular field forming method. We have done a lot of experiments, and the results have shown that this dose calculation model can achieve satisfactory precision and fast speed. As a result, it is a general method to dose calculation.
At the end of this thesis, we also discuss some problems which haven't been completed. In addition, we prospect some work which we'll do in the future.
引文
1 ICRU 1987. Use of computers in external beam radiotherapy procedures with high energy photons and electrons. ICRU report 42.
2 Bently RE, Milan J. An interactive digital computer system for radiotherapy treatment planning. Br. J. Radiol., 1971, 44: 307-317.
3 Weinkam J., Sterling T. A Versatile system for three dimensional radiation dose computation and display. RTP. Comput. Prog. Biomed., 1972, 2: 178-191.
4 Ira J. Kalet. Multiview three-dimensional treatment planning. Front. Radiat. Ther. Oncol., 1987, 21: 33-43.
5 ICRU. Report 24. Determination of absorbed dose in a patient irradiated by beams of X or Gamma rays in radiotherapy procedures. 1976.
6 BJR. Central axis depth dose data for use in radiotherapy. Br. J. Radiol. Suppl. No. 17; 1983
7 Milan J., Bentley R. E. The storage and manipulation of radiation-dose data in a small digital computer. Br. J. Radiol., 1974, 47: 115-121.
8 Meredith W. J., Neary G. J. The production of isodose curves and calculation of energy absorption from standard depth dose data. Br. J. Radiol., 1944, 17: 75-126.
9 Cunningham J. R. Scatter-air ratios. Phys. Med. Biol., 1972, 17: 42-51.
10 Johns H. E., Cunningham J. R. The physics of radiology, 4th Edition. Springfield, 1983.
11 Paul J. M., Koch R. F. Characteristics of mevatron 77 15-MV photon beam. Med. Phys., 1983, 10: 237.
12 Clarson J. R. A note on depth doses in fields of irregular shape. Br. J. Radiol., 1941, 14: 265.
13 Day M. J. A note on the calculation of dose in fields of irregular shape. Br. J. Radiol., 1941, 14: 265.
14 Haywood J. K., Bomford C. K. A less empirical method of representing megavoltage beams for use in rapid radiotherapy dose calculations. Br. J. Radiol., 1979, 52: 709.
15 Ulam S. M., Von Neumann J. On combination of stochastic and deterministic processes. Bull. Amer. Math. Soc., 1947, 53: 1120.
16 Goldberger M. L. The interaction of high energy neutrons and heavy nuclei. Phys. Rev., 1948, 72: 1269-1277.
17 Webb S. The absorbed dose in the vicinity of an interface between two media irradiated by a Co-60 source. Br. J. Radiol., 1979, 52, 962.
18 Mohan R., Chui C. S. Use of fast Fourier transforms in calculating dose distributions for irregular shaped fields for three dimensional treatment planning. Med. Phys., 1987, 14(1): 70-77.
19 Worthy B. Equivalent square of rectangular fields. Br. J. Radiol.,1966,39:559.
20 Day M. J., Aird E. G. A. Central axis depth dose data for use in radiotherapy. Br. J. Radiol., 1996, 25: 258-260.
21 Bjarngard B. E., Petti P. L. Description of the scatter component in photon beam data. Phys. Meal. Biol., 1988, 33: 21-32.
22 Nizin P. S. Geometrical aspects of scatter-to-primary ratio and primary dose. Med. Phys., 1991, 18: 153-160.
23 Van De Geijn J. The computation of two and three dimensional dose distributions in Cobalt-60 teletherapy. Br. J. Radiol., 1965, 38: 369.
24 Chui CS, Mohan R. Off-center ratios for three-dimensional dose calculations. Med. Phys. 1986, 13: 409-412.
25 Knoos K., Wittgren L. Which depth dose should be used for dose planning when
wedge filters are used to modify the photon beam. Phys. Med. Biol., 1991, 36: 255-267.
26 Pascal Storchi, Evert Woudstra. Calculation models for determining the absorbed dose in water phantoms in off-axis planes of rectangular fields of open and wedged photon beams. Phys. Med. Biol., 1995, 40: 511-527.
27 Chui C. S., Losasso T. Beam profiles along the nonwedged direction for large wedged fields. Med. Phy., 1994, 21(11): 1685-1690.
28 Loshek D. D., Keller K. A. Beam profile generator for asymmetric fields. Med. Phys., 1988, 15: 604-610.
29 Thomas S. J., Thomas R. L. A beam generation algorithm for linear accelerators with independent collimators. Phy. Med. Biol., 1990, 35(3): 325-332.
30 M. J. Day, E. G. A. Aird. The equivalent field method for dose determination in rectangular fields. Br. J. Radiol. Suppl., 1983, 17: 105-114.
31 Morris T., Bengt E. B. Equivalent squares of irregular photon fields. Med. Phys., 1992, 20(4): 1229-1232.
32 Cunningham J. R., Shrivastava P. N. Program IRREG-calculation of dose from irregularly shaped radiation beams. Prog. Biomed., 1972, 2: 192.
33 Steidley K. D., Gamper C. A Clarson's sector integration routine for personal computer. Med. Phys., 1994, 21(1): 61-64.
34 Mohan R., Chui C. S. Validity of concept of separating primary and scatter dose. Med. Phys., 1985, 12: 726-730.
35 Lei D. Almon S. A pencil beam photon dose algorithm for stereotactic radiosurgey using a miniature multifleaf collimator. Med. Phys., 1998, 25(6): 841-850.
36 Bevington P. R. Data reduction and error analysis for the physics science. McGraw-Hill, NeW York, 1969.
37 Ernest Mah, John A. Experimental evaluation of a 2D and 3D electron pencil
beam algorithm. Phys. Med. Biol., 1989, 34(9): 1179-1194.
38 Chui C. S., Mohan R. Extraction of pencil beam kernels by the deconvolution method. Med. Phys., 1988, 15(2): 138-144.
39 D. Jette, A. Pagnamenta, L. H. Lanzel, and M. Rozenfeld. The application of multiple scattering theory to therapeutic electron dosimetry. Med. Phys., 1983, 10: 141.
2 Bently RE, Milan J. An interactive digital computer system for radiotherapy treatment planning. Br. J. Radiol., 1971, 44: 307-317.
3 Weinkam J., Sterling T. A Versatile system for three dimensional radiation dose computation and display. RTP. Comput. Prog. Biomed., 1972, 2: 178-191.
4 Ira J. Kalet. Multiview three-dimensional treatment planning. Front. Radiat. Ther. Oncol., 1987, 21: 33-43.
5 ICRU. Report 24. Determination of absorbed dose in a patient irradiated by beams of X or Gamma rays in radiotherapy procedures. 1976.
6 BJR. Central axis depth dose data for use in radiotherapy. Br. J. Radiol. Suppl. No. 17; 1983
7 Milan J., Bentley R. E. The storage and manipulation of radiation-dose data in a small digital computer. Br. J. Radiol., 1974, 47: 115-121.
8 Meredith W. J., Neary G. J. The production of isodose curves and calculation of energy absorption from standard depth dose data. Br. J. Radiol., 1944, 17: 75-126.
9 Cunningham J. R. Scatter-air ratios. Phys. Med. Biol., 1972, 17: 42-51.
10 Johns H. E., Cunningham J. R. The physics of radiology, 4th Edition. Springfield, 1983.
11 Paul J. M., Koch R. F. Characteristics of mevatron 77 15-MV photon beam. Med. Phys., 1983, 10: 237.
12 Clarson J. R. A note on depth doses in fields of irregular shape. Br. J. Radiol., 1941, 14: 265.
13 Day M. J. A note on the calculation of dose in fields of irregular shape. Br. J. Radiol., 1941, 14: 265.
14 Haywood J. K., Bomford C. K. A less empirical method of representing megavoltage beams for use in rapid radiotherapy dose calculations. Br. J. Radiol., 1979, 52: 709.
15 Ulam S. M., Von Neumann J. On combination of stochastic and deterministic processes. Bull. Amer. Math. Soc., 1947, 53: 1120.
16 Goldberger M. L. The interaction of high energy neutrons and heavy nuclei. Phys. Rev., 1948, 72: 1269-1277.
17 Webb S. The absorbed dose in the vicinity of an interface between two media irradiated by a Co-60 source. Br. J. Radiol., 1979, 52, 962.
18 Mohan R., Chui C. S. Use of fast Fourier transforms in calculating dose distributions for irregular shaped fields for three dimensional treatment planning. Med. Phys., 1987, 14(1): 70-77.
19 Worthy B. Equivalent square of rectangular fields. Br. J. Radiol.,1966,39:559.
20 Day M. J., Aird E. G. A. Central axis depth dose data for use in radiotherapy. Br. J. Radiol., 1996, 25: 258-260.
21 Bjarngard B. E., Petti P. L. Description of the scatter component in photon beam data. Phys. Meal. Biol., 1988, 33: 21-32.
22 Nizin P. S. Geometrical aspects of scatter-to-primary ratio and primary dose. Med. Phys., 1991, 18: 153-160.
23 Van De Geijn J. The computation of two and three dimensional dose distributions in Cobalt-60 teletherapy. Br. J. Radiol., 1965, 38: 369.
24 Chui CS, Mohan R. Off-center ratios for three-dimensional dose calculations. Med. Phys. 1986, 13: 409-412.
25 Knoos K., Wittgren L. Which depth dose should be used for dose planning when
wedge filters are used to modify the photon beam. Phys. Med. Biol., 1991, 36: 255-267.
26 Pascal Storchi, Evert Woudstra. Calculation models for determining the absorbed dose in water phantoms in off-axis planes of rectangular fields of open and wedged photon beams. Phys. Med. Biol., 1995, 40: 511-527.
27 Chui C. S., Losasso T. Beam profiles along the nonwedged direction for large wedged fields. Med. Phy., 1994, 21(11): 1685-1690.
28 Loshek D. D., Keller K. A. Beam profile generator for asymmetric fields. Med. Phys., 1988, 15: 604-610.
29 Thomas S. J., Thomas R. L. A beam generation algorithm for linear accelerators with independent collimators. Phy. Med. Biol., 1990, 35(3): 325-332.
30 M. J. Day, E. G. A. Aird. The equivalent field method for dose determination in rectangular fields. Br. J. Radiol. Suppl., 1983, 17: 105-114.
31 Morris T., Bengt E. B. Equivalent squares of irregular photon fields. Med. Phys., 1992, 20(4): 1229-1232.
32 Cunningham J. R., Shrivastava P. N. Program IRREG-calculation of dose from irregularly shaped radiation beams. Prog. Biomed., 1972, 2: 192.
33 Steidley K. D., Gamper C. A Clarson's sector integration routine for personal computer. Med. Phys., 1994, 21(1): 61-64.
34 Mohan R., Chui C. S. Validity of concept of separating primary and scatter dose. Med. Phys., 1985, 12: 726-730.
35 Lei D. Almon S. A pencil beam photon dose algorithm for stereotactic radiosurgey using a miniature multifleaf collimator. Med. Phys., 1998, 25(6): 841-850.
36 Bevington P. R. Data reduction and error analysis for the physics science. McGraw-Hill, NeW York, 1969.
37 Ernest Mah, John A. Experimental evaluation of a 2D and 3D electron pencil
beam algorithm. Phys. Med. Biol., 1989, 34(9): 1179-1194.
38 Chui C. S., Mohan R. Extraction of pencil beam kernels by the deconvolution method. Med. Phys., 1988, 15(2): 138-144.
39 D. Jette, A. Pagnamenta, L. H. Lanzel, and M. Rozenfeld. The application of multiple scattering theory to therapeutic electron dosimetry. Med. Phys., 1983, 10: 141.