Synchronized dynamic dose reconstruction

• Published in: Medical physics (Lancaster) Vol. 34; no. 1; pp. 91 - 102
• Main Authors: Litzenberg, Dale W., Hadley, Scott W., Tyagi, Neelam, Balter, James M., Ten Haken, Randall K., Chetty, Indrin J.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-01-2007
• Subjects: Ancillary equipment; Body Burden; Collimation; COLLIMATORS; Computed tomography; delivered dose; DOSIMETRY; Dosimetry/exposure assessment; Error analysis; ERRORS; Image registration; Intensity modulated radiation therapy; intensity modulation; intra-fraction motion; Kinematics; Medical imaging; Medical treatment planning; MODULATION; Monte Carlo; MONTE CARLO METHOD; Movement; Multileaf collimators; PATIENTS; PHANTOMS; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; radiation therapy; Radiometry - methods; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Conformal - methods; Real time information delivery; real-time tracking; Relative Biological Effectiveness; Reproducibility of Results; Sensitivity and Specificity; Treatment strategy; Wedges and compensators; real-time tracking; Monte Carlo; delivered dose; intra-fraction motion
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2388157

Variations in target volume position between and during treatment fractions can lead to measurable differences in the dose distribution delivered to each patient. Current methods to estimate the ongoing cumulative delivered dose distribution make idealized assumptions about individual patient motion based on average motions observed in a population of patients. In the delivery of intensity modulated radiation therapy (IMRT) with a multi-leaf collimator (MLC), errors are introduced in both the implementation and delivery processes. In addition, target motion and MLC motion can lead to dosimetric errors from interplay effects. All of these effects may be of clinical importance. Here we present a method to compute delivered dose distributions for each treatment beam and fraction, which explicitly incorporates synchronized real-time patient motion data and real-time fluence and machine configuration data. This synchronized dynamic dose reconstruction method properly accounts for the two primary classes of errors that arise from delivering IMRT with an MLC: (a) Interplay errors between target volume motion and MLC motion, and (b) Implementation errors, such as dropped segments, dose over/under shoot, faulty leaf motors, tongue-and-groove effect, rounded leaf ends, and communications delays. These reconstructed dose fractions can then be combined to produce high-quality determinations of the dose distribution actually received to date, from which individualized adaptive treatment strategies can be determined.