Author: María Fernández, Inés Flores, Nuria Montero, Manuel Ruiz, Francisco San Miguel 👨🔬
Affiliation: Hospital Central de la Defensa 'Gómez Ulla', Hospital Central de la Defensa "Gomez Ulla", CSVE, Hospital Central de la Defensa 'Gómez Ulla', CSVE 🌍
Purpose:
During external radiotherapy treatments in the prostate, there can be PTV movements between fractions and during each treatment fraction. In a typical prostate treatment in our institution, the patient is positioned using cone beam CT at the beginning of each session, correcting possible PTV movements between fractions. Nevertheless, the position of the prostate during treatment is influenced by rectal activity, bladder filling, and involuntary muscle movements, which can lead to different movement patterns. These intrafraction movements can occur in any direction and may result in an incorrect treatment of the PTV.
The aim of this study is to analyze how this non- corrected intrafraction movement affects the dosimetry of the treatment through experimental measurements.
Methods:
Ten prostate patients have been analyzed, receiving a total dose of 70 Gy in 25 fractions. All treatments were delivered using the VMAT technique with 6 MV. The treatment planning system used was Monaco (Elekta), and the treatments were delivered using an Elekta Versa HD linear accelerator.
To carry out the experimental measurements, the Scandidos Delta 4 detector was used in combination with the Scandidos Hexamotion system. Four different movement patterns have been simulated that represent typical movements observed in prostate treatments using the Calypso and Radixact Systems. Since any of the patterns can occur during any fraction in any patient, all four models have been studied for each analyzed patient through a gamma analysis with a criterion of 2% global dose and 2 mm, comparing the results obtained with the static case.
Results:
The stable movement and continuous drift patterns do not seem to significantly affect the gamma analysis. On the other hand, the erratic and high-frequency patterns considerably compromise the treatment dosimetry.
Conclusion:
It is crucial to use intrafraction motion management on prostate treatments.