Dose/volume-response relations for rectal morbidity using planned and simulated motion-inclusive dose distributions

Area of Science:

• Radiation Oncology
• Medical Physics
• Clinical Oncology

Background:

• Internal motion of normal tissues in radiotherapy (RT) can impact dose-distribution predictions.
• Rectal motion is a significant factor in predicting rectal morbidity after RT.
• Simulating rectal motion is crucial for accurate treatment planning.

Purpose of the Study:

• To evaluate the impact of rectal motion on predicting rectal morbidity in prostate cancer patients.
• To compare the predictive power of planned versus motion-inclusive dose distributions.
• To assess the association between rectal dose and toxicity endpoints.

Main Methods:

• Two cohorts of prostate cancer patients (232 and 159 cases) received RT (70 and 74 Gy).
• Motion-inclusive dose distributions were simulated, incorporating random or systematic rectal motion.
• Six rectal morbidity endpoints were analyzed using planned and motion-inclusive doses, alongside a probit model.

Main Results:

• Differences between planned and motion-inclusive dose distributions were modest.
• Significant associations with rectal morbidity were found for four endpoints, mainly at high doses (>55 Gy).
• GI toxicity and rectal bleeding showed the strongest associations (Rs=0.12-0.21 and Rs=0.11-0.20, respectively).

Conclusions:

• Rectal motion, including random motion, did not significantly alter associations with rectal morbidity at high doses (>55 Gy).
• Planned and simulated motion-inclusive dose distributions yielded comparable predictive power for rectal morbidity.
• Future research should focus on patient-specific rectal motion descriptions for enhanced predictive accuracy.