The effectiveness of immobilization during prostate irradiation

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Accurate patient positioning is crucial for effective external beam radiation therapy (EBRT).
• Variability in daily setup can lead to under- or over-dosing of the target volume and surrounding organs at risk.
• Immobilization devices aim to reduce setup inconsistencies during fractionated radiotherapy.

Purpose of the Study:

• To assess the impact of a custom-made hemibody foam cradle on patient setup reproducibility.
• To evaluate its effect on isocenter shifts during prostate cancer radiation treatment.

Main Methods:

• A cohort of 74 prostate cancer patients undergoing EBRT were analyzed.
• Forty-four patients used a custom hemibody foam cradle for immobilization.
• Weekly port films were reviewed retrospectively to quantify isocenter shifts, comparing immobilized to non-immobilized groups.

Main Results:

• Patients using the foam cradle showed a trend towards improved overall setup reproducibility (17.4% vs. 23.1% isocenter shifts).
• A statistically significant reduction in anterior-posterior isocenter shifts was observed in the immobilized group (5.1% vs. 12.6%, p < 0.05).
• No significant improvement was noted in cephalad-caudal or right-left directions.

Conclusions:

• The custom hemibody foam cradle enhances patient setup reproducibility during prostate cancer radiotherapy.
• This immobilization technique is now routinely used and recommended for pelvic radiotherapy.
• It is particularly beneficial for dose escalation strategies to minimize radiation to the bladder and rectum.