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Optimization of beam‐orientations in conformal radiotherapy treatment planning
Author(s) -
Rowbottom Carl Graham
Publication year - 1999
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598642
Subject(s) - medicine , radiation therapy , isocenter , radiation treatment planning , cohort , esophagus , orientation (vector space) , nuclear medicine , beam (structure) , radiology , surgery , mathematics , physics , optics , geometry
Traditionally, human planners have devised the treatment parameters used in radiotherapy treatment plans via a manually iterative process. Computer “optimization” algorithms have been shown to improve treatment plans as they can explore much more of the search space in a relatively short time. This thesis examines beam‐orientation computer “optimization” in radiotherapy treatment planning. New techniques were developed and a comparison was performed between treatment plans with “standard,” fixed beam‐orientations and treatment plans with “optimized” beam‐orientations for patients with cancer of the prostate, esophagus, and brain. A cohort of patients was considered in each group to avoid bias from a specific patient geometry. In the case of the patient cohort with cancer of the prostate, a coplanar beam‐orientation “optimization” scheme led to an average increase in the tumor control probability (TCP) of (5.7±1.4)% compared to the standard plans after the dose to the isocenter had been scaled to produce a rectal normal tissue complication probability (NTCP) of 1%. For the patient cohort with cancer of the esophagus, the beam‐orientation “optimization” scheme reduced the average lung NTCP by (0.7±0.2)% at the expense of a modest increase in the average spinal cord NTCP of (0.1±0.2)%. A noncoplanar beam‐orientation “optimization” scheme was tested using five patients with tumors of the brain. The scheme reduced the mean orbit doses by (19±4)%, when averaged over the patient cohort. The optic‐nerve mean and maximum doses were reduced by (11±5)% and (12±1)%, respectively. In conclusion, “optimization” of coplanar beam‐orientations led to improved treatment plans, but improvements were relatively modest compared to those from the “optimization” of noncoplanar beam‐orientations.