Estimates of whole-body dose equivalent produced by beam intensity modulated conformal therapy.

PURPOSE To estimate the dose delivered to patients by photons and neutrons outside the radiation fields when beam intensity modulation conformal radiotherapy is given. These estimates are then used to compute the risk of secondary cancers as a sequela of the radiation therapy. MATERIALS AND METHODS The x-ray and neutron leakage accompanying two beam-intensity modulation techniques delivered by currently available linear accelerators were estimated for 6-MV, 18-MV, and 25-MV x-ray energies. Estimates of whole-body dose equivalents were determined using leakage measurements reported in the literature and treatment parameters derived for two modulated beam-intensity conformal therapy techniques. Risk values recommended by the National Council on Radiation Protection and Measurements (NCRP) were used to estimate the resulting risk of fatal radiation-induced cancer for 70.00 Gy prescribed tumor doses. RESULTS The computed worst-case risks of secondary cancers increased in the range from 1.00% for 6-MV x-rays to 24.4% for 25-MV x-rays. CONCLUSIONS Careful consideration should be made of the risks associated with secondary whole-body radiation before implementation of beam intensity modulated conformal therapy at x-ray energies greater than 10 MV.

[1]  C. Orton.  Progress in medical radiation physics , 1982 .

[2]  Robert J. Shalek,et al.  Fetal Dose from Radiotherapy with Photon Beams , 1995 .

[3]  E. Hall,et al.  Photoneutrons from medical linear accelerators--radiobiological measurements and risk estimates. , 1995, International journal of radiation oncology, biology, physics.

[4]  A Brahme,et al.  Solution of an integral equation encountered in rotation therapy. , 1982, Physics in medicine and biology.

[5]  R Svensson,et al.  An analytical solution for the dynamic control of multileaf collimators. , 1994, Physics in medicine and biology.

[6]  S. Webb.  Optimization by simulated annealing of three-dimensional, conformal treatment planning for radiation fields defined by a multileaf collimator: II. Inclusion of two-dimensional modulation of the x-ray intensity. , 1992, Physics in medicine and biology.

[7]  D. Convery,et al.  The generation of intensity-modulated fields for conformal radiotherapy by dynamic collimation , 1992 .

[8]  W Schlegel,et al.  Dynamic X-ray compensation for conformal radiotherapy by means of multi-leaf collimation. , 1994, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[9]  T. J. Davy.  Physical Aspects of Conformation Therapy Using Computer-Controlled Tracking Units , 1985 .

[10]  P. Schonken,et al.  Health effects of exposure to low levels of ionizing radiation , 1991 .

[11]  S. Webb.  Optimizing the planning of intensity-modulated radiotherapy. , 1994, Physics in medicine and biology.

[12]  T. Bortfeld,et al.  X-ray field compensation with multileaf collimators. , 1994, International journal of radiation oncology, biology, physics.

[13]  R Mohan,et al.  The biological basis for conformal three-dimensional radiation therapy. , 1991, International journal of radiation oncology, biology, physics.

[14]  Chee-Wai Cheng,et al.  Three-dimensional treatment planning , 1992 .

[15]  J O Deasy,et al.  Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy. , 1993, Medical physics.

[16]  S. Webb.  Optimization by simulated annealing of three-dimensional conformal treatment planning for radiation fields defined by a multileaf collimator. , 1991, Physics in medicine and biology.

[17]  S. Spirou,et al.  Generation of arbitrary intensity profiles by dynamic jaws or multileaf collimators. , 1994, Medical physics.

[18]  C R Blackwell,et al.  Fetal dose from radiotherapy with photon beams: report of AAPM Radiation Therapy Committee Task Group No. 36. , 1995, Medical physics.

[19]  A. B. Brill,et al.  NCRP Report No. 116, Limitation of Exposure to Ionizing Radiation National Council on Radiation Protection, Bethesda, MD, 88 pages, $22.50 , 1994 .

[20]  A Brahme,et al.  Shaping of arbitrary dose distributions by dynamic multileaf collimation. , 1988, Physics in medicine and biology.

[21]  S Takahashi,et al.  Conformation radiotherapy. Rotation techniques as applied to radiography and radiotherapy of cancer. , 1965, Acta radiologica: diagnosis.