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Treatment planning for protocol-based radiation therapy
241
Literature Reviews oped a simple method of calculating this isodose shift. It was shown that a shift technique based solely on geometrical correction for depth, which did not take into account differences in scatter between normally incident and oblique incident cases, gave reasonably accurate results for electron beams incident at an angle of 30”, but can lead to errors of 0.5 cm or more for isodose placement of beams at an incident angle of 60”. This study developed a correction factor to the method based solely on geometrical correction. A table of isodosc shift factors, dependent on beam energy and isodose line, was derived from measured data setting the angle of incidence to 60. It was argued and shown that the isodose shift factors should be valid for smaller angles of incidence. The largest error in the calculated depth was 1.9 mm, and the average error was less than 1 mm. It should be noted that the technique holds true only for the central portion of an electron beam and cannot be expected to give accurate results near beam edges. This technique was based on data acquired from a Varian Clinac 2500 accelerator, and verification should be made before it is used clinically to calculate obliquity corrections for electron beams from other accelerators.
MARCIA PRICE TREATMENT PLANNING FOR PROTOCOL-BASED RADIATION THERAPY Per Hahn,
M.D.,‘.3 Shlomo Shalev, Ph.D.,‘,2,3
David Viggars. Ph.D.’
and Pierre Therrien, B.Sc.’
Manitoba
Cancer Treatment and Research Foundation, 100 Olivia Street, Winnipeg, Man R3E 0V9, Canada; and Departments of 2Physics and ‘Radiology, University of Manitoba, Winnipeg, Manitoba, Canada
International Journal of‘Radiation Oncology, Biology, and Ph.v.sics, Vol. 18, April 1990. pp. 937-939.
Protocol studies are performed in which patients are assigned to alternative treatment regimens. Typically, the dosimetry specifications will define the maximal and minimal target doses, and maximal doses to specified critical normal structures; the success of the study will depend upon Ihe consistency and reliability with which these dose specifications are applied. We have investigated the use of dose-area histograms to ensure complete adherence to protocol dose specifications.
DOSIMETRIC ANALYSIS IN BRACHYTHERAPY OF ASYMETRIC FIELD ARC ROTATIONS
CARCINOMA OF THE CERVIX
Jatinder R. Paha, Ph.D., Komanduri M. Ayyangar, Ph.D., Nagalingam Suntharalingam, Ph.D., and Leslie Tupchong, M.D.
Leela Krishnan. M.S., M.D., Edmund P. Cytacki. Ph.D., Clifford D. Wolfe, B.A., R.T.. Eashwer K. Reddy, M.D., Linda S. Gemer, M.D., P.G.S., Giri, M.D., Stephen R. Smalley, M.D., and Richard G. Evans, Ph.D., M.D.
Department of Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA The British Journal
ofRadiology,
Vol. 62, No. 742,
October 1989 Treatment planning a target volume that surrounds a critical structure is very difficult. A method used in the past utilizes moving beam therapy with a secondary block in the field to shield the critical structure. The major drawback of this technique was significant transmission through the field shaping block. There also was a concern from the safety viewpoint of rotating the machine gantry with heavy blocks in place. The availability of independent motion of the collimator jaws on medical linear accelerators enables a photon field to be set with asymmetric portals. This means that the field center is offset from the radiation head rotational axis. Linear accelerators equipped with independent jaw motion allow easy implementation of asymmetric field arc rotations that are useful in the treatment of vertebral body and thyroid tumors. A doughnut-shaped isodose distribution is created by an asymmetric field arc rotation ideally suited for these target volumes with the spinal cord located in the central region. The only limitation of this technique is that the target volume can only be approximated by a cylinder whose axis is parallel to the long axis of the patient. This report presents the principle of beam summation for the generation of isodose curves for asymmetric field arc rotations. The accuracy of treatment planning software was experimentally verified with TLD chips and film.
Department of Radiation Oncology, The University of Kansas Medical Center, 39th and Rainbow Blvd., Kansas City, KS International Journal ofRadiation Oncology, Biology, and Physics, Vol 18, April 1990. pp. 965-970.
The dosimetry of intracavitary irradiation is complex, in that the optimum doses that can be delivered are dictated not only by the volume and extent oftumor, but also by the close vicinity of the small and large bowel, rectum, and bladder. An analysis was made of 50 intracavitary insertions of 137 Cesium, in which the Fletcher-Suit-Delcos applicators were used with three sources--the tandem, and one in each of the ovoids. The analysis of percent distribution of various sources to different reference points revealed that the dose to point A was equally contributed to by all sources: bladder and rectal doses were mainly contributed to by the lowermost uterine and ovoid sources.
AN INTERACTIVE SYSTEMFOR POINT DOSEOPTIMIZATION
George Starkschall, Ph.D.,* Gregory C. Henkelmann, M.D. and K. Kian Ang, M.D. The University of Texas M.D. Anderson Cancer Center, 15 15 Holcombe Blvd.. Houston. TX International Journal qfRadiation Oncology, Biology, and Physics, Vol. 18, April 1990. pp. 957-964.
Literature Reviews oped a simple method of calculating this isodose shift. It was shown that a shift technique based solely on geometrical correction for depth, which did not take into account differences in scatter between normally incident and oblique incident cases, gave reasonably accurate results for electron beams incident at an angle of 30”, but can lead to errors of 0.5 cm or more for isodose placement of beams at an incident angle of 60”. This study developed a correction factor to the method based solely on geometrical correction. A table of isodosc shift factors, dependent on beam energy and isodose line, was derived from measured data setting the angle of incidence to 60. It was argued and shown that the isodose shift factors should be valid for smaller angles of incidence. The largest error in the calculated depth was 1.9 mm, and the average error was less than 1 mm. It should be noted that the technique holds true only for the central portion of an electron beam and cannot be expected to give accurate results near beam edges. This technique was based on data acquired from a Varian Clinac 2500 accelerator, and verification should be made before it is used clinically to calculate obliquity corrections for electron beams from other accelerators.
MARCIA PRICE TREATMENT PLANNING FOR PROTOCOL-BASED RADIATION THERAPY Per Hahn,
M.D.,‘.3 Shlomo Shalev, Ph.D.,‘,2,3
David Viggars. Ph.D.’
and Pierre Therrien, B.Sc.’
Manitoba
Cancer Treatment and Research Foundation, 100 Olivia Street, Winnipeg, Man R3E 0V9, Canada; and Departments of 2Physics and ‘Radiology, University of Manitoba, Winnipeg, Manitoba, Canada
International Journal of‘Radiation Oncology, Biology, and Ph.v.sics, Vol. 18, April 1990. pp. 937-939.
Protocol studies are performed in which patients are assigned to alternative treatment regimens. Typically, the dosimetry specifications will define the maximal and minimal target doses, and maximal doses to specified critical normal structures; the success of the study will depend upon Ihe consistency and reliability with which these dose specifications are applied. We have investigated the use of dose-area histograms to ensure complete adherence to protocol dose specifications.
DOSIMETRIC ANALYSIS IN BRACHYTHERAPY OF ASYMETRIC FIELD ARC ROTATIONS
CARCINOMA OF THE CERVIX
Jatinder R. Paha, Ph.D., Komanduri M. Ayyangar, Ph.D., Nagalingam Suntharalingam, Ph.D., and Leslie Tupchong, M.D.
Leela Krishnan. M.S., M.D., Edmund P. Cytacki. Ph.D., Clifford D. Wolfe, B.A., R.T.. Eashwer K. Reddy, M.D., Linda S. Gemer, M.D., P.G.S., Giri, M.D., Stephen R. Smalley, M.D., and Richard G. Evans, Ph.D., M.D.
Department of Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA The British Journal
ofRadiology,
Vol. 62, No. 742,
October 1989 Treatment planning a target volume that surrounds a critical structure is very difficult. A method used in the past utilizes moving beam therapy with a secondary block in the field to shield the critical structure. The major drawback of this technique was significant transmission through the field shaping block. There also was a concern from the safety viewpoint of rotating the machine gantry with heavy blocks in place. The availability of independent motion of the collimator jaws on medical linear accelerators enables a photon field to be set with asymmetric portals. This means that the field center is offset from the radiation head rotational axis. Linear accelerators equipped with independent jaw motion allow easy implementation of asymmetric field arc rotations that are useful in the treatment of vertebral body and thyroid tumors. A doughnut-shaped isodose distribution is created by an asymmetric field arc rotation ideally suited for these target volumes with the spinal cord located in the central region. The only limitation of this technique is that the target volume can only be approximated by a cylinder whose axis is parallel to the long axis of the patient. This report presents the principle of beam summation for the generation of isodose curves for asymmetric field arc rotations. The accuracy of treatment planning software was experimentally verified with TLD chips and film.
Department of Radiation Oncology, The University of Kansas Medical Center, 39th and Rainbow Blvd., Kansas City, KS International Journal ofRadiation Oncology, Biology, and Physics, Vol 18, April 1990. pp. 965-970.
The dosimetry of intracavitary irradiation is complex, in that the optimum doses that can be delivered are dictated not only by the volume and extent oftumor, but also by the close vicinity of the small and large bowel, rectum, and bladder. An analysis was made of 50 intracavitary insertions of 137 Cesium, in which the Fletcher-Suit-Delcos applicators were used with three sources--the tandem, and one in each of the ovoids. The analysis of percent distribution of various sources to different reference points revealed that the dose to point A was equally contributed to by all sources: bladder and rectal doses were mainly contributed to by the lowermost uterine and ovoid sources.
AN INTERACTIVE SYSTEMFOR POINT DOSEOPTIMIZATION
George Starkschall, Ph.D.,* Gregory C. Henkelmann, M.D. and K. Kian Ang, M.D. The University of Texas M.D. Anderson Cancer Center, 15 15 Holcombe Blvd.. Houston. TX International Journal qfRadiation Oncology, Biology, and Physics, Vol. 18, April 1990. pp. 957-964.