Résumé:
Purpose: Tomotherapy relies heavily on consistent patient preparation to ensure accurate
treatment delivery. This study assesses the effectiveness of a preparation protocol
by analyzing variations in bladder and evaluating impact of poor preparations among
patients undergoing tomotherapy.
Methods: This study involved two study cases focused on prostate tomotherapy. The
first case included 10 patients who received hypofractionated treatment whose dose volumes
were computed for each fraction by experienced physicists using the TomoTherapy
planning system. Bladder contours and dose computations were performed by supervised
medical physicist students which involved contouring the bladder across multiple
MegaVoltage Computed Tomography (MVCT) scans, yielding over 200 bladder contours
using RayStation™ and Planned Adaptive™. The second case surveyed 24 patients on
treatment preparation. Computed Tomography (CT) images from treatment sessions
were registered with planning CT. Bladder contours were contoured and were used to
calculate verification doses in Planned Adaptive™. Summation doses were assessed and
compared to planning doses using Dose-volume histograms (DVHs). Exported summation
doses, planning doses, CT images, and contours were analyzed using Python. The analysis
included computing bladder volumes, constructing DVHs, and performing regression
analyses to explore correlations among parameters.
Results: All patients, except one, exhibited significant dose volume inter-fraction differences
between initial planning and poor preparation, both in low and high dose regions.
Re-preparations significantly reduced these differences. Some planning preparations could
have matched the optimal preparations.
Dose volume metrics showed an average inter-fraction difference, with bladder volume
increases of 18.48% at 2.04 Gy, 13.68% at 2.43 Gy, and 1.2% at 3 Gy. Comparing bladder
volumes, there was a 53.5% decrease between planning and poor preparations, and
re-preparations increased bladder volume by 8.09%, while optimal preparations increased
it by 30.39%.
An exponential regression model given by the expression D
mean
= 2.09e
explained
77.33% of the variance in the mean bladder dose.
Summation dose indicated six patients with DVH metrics exceeding planning, with two
exceeding constraints, while three had met the constraints. One patient had alternating
DVH metrics, and one of the patients benefited from re-preparations that lowered metrics
below constraints. A linear increase in the number of acceptable poor preparations was
observed with increasing planning bladder volume, becoming fully acceptable at 398.61
−0.005V cubic centimeters (cc).
Due to missing bladder volume data in the second study case, the sample size was smaller
than expected, with only 2 out of 28 samples having complete data. High variance in
bladder filling patterns was observed, with an R2 score of 0.1724, not aligning with the
expected pattern.
Conclusion: The results demonstrated that all well-prepared patients met the treatment
constraints. Other findings showed that thorough bladder preparation before planning is
crucial, as it significantly impacts the effectiveness and accuracy of subsequent treatments.