Radiobiological corrections of dose-volume histograms for treatment gap calculations
PO-1513
Abstract
Radiobiological corrections of dose-volume histograms for treatment gap calculations
Authors: Katie O'Shea1, Margaret Moore2, Linda Coleman2
1National University of Ireland Galway, Department of Physics, Galway, Ireland; 2University Hospital Galway, Department of Medical Physics & Clinical Engineering, Galway, Ireland
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Purpose or Objective
Unscheduled treatment interruptions to radiotherapy treatments lead to a decrease in the TCP due to dose lost to ongoing rapid cell repopulation. The dose lost to a treatment gap must be compensated for to prevent an extension onto the patient’s overall treatment time and to re-gain the original TCP. This was the case during the Irish Health Service Executive (HSE) cyberattack of May 2021 which resulted in radiotherapy patients experiencing treatment gaps of up to 12 days. Current treatment gap calculations are performed with a point-dose for the PTV and the OARs, using the prescribed dose to the PTV. This can overestimate the dose to the OARs by assuming all OARs receive the prescription dose.
Material and Methods
An in-house tool EQD2VH was created in Python to perform treatment gap calculations using the DVH information provided in the RT Dose DICOM files. The physical dose in each dose bin was converted into EQD2 while accounting for cell repopulation in the PTV. This provided a 2D representation of treatment gap calculations in comparison to the 1D point-dose method. The tool was evaluated using five Category 1 patients (head, neck, and lung cancer patients) who were receiving radiotherapy treatments when the cyberattack occurred. Compensation plans were created for these patients using Royal College of Radiologists (RCR) methodology to evaluate the use of EQD2VH as a clinical aid.
Results
The 2D representation of treatment gap calculations for the PTV and OARs provided a better representation of each compensation option in comparison to the 1D point-dose calculation method. EQD2VH provided a visual analysis of each plan to each individual structure and was used as a tool to find a balance between the dose to the PTV and the OARs. The DVH statistics provided by EQD2VH were used for comparisons with dose constraints.
Conclusion
The results demonstrated EQD2VH's potential as a clinical aid to assist Radiation Oncologists in determining the most suitable compensation options for all categories of patients after a treatment gap. It provided a visual and quantitative analysis of the compensation options to each individual structure while accounting for repopulation effects in the tumour, and provided a higher accuracy of results than the point-dose calculation methods.