Comparison of two head and neck immobilization systems

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Immobilization Techniques

Background:

• Accurate patient positioning is crucial for effective fractionated radiotherapy.
• Traditional head and neck immobilization systems using foam supports and casting strips were replaced by customized mask-based devices.
• The study aimed to evaluate the impact of this transition on patient setup reproducibility.

Purpose of the Study:

• To analyze the impact of a customized mask-based immobilization system on patient setup reproducibility.
• To compare the accuracy of patient positioning using a mask system versus a strip system for head and neck and brain tumors.
• To assess the influence of immobilization system fixation to the treatment couch on setup accuracy.

Main Methods:

• Retrospective analysis of patient positioning data from 1989-1995.
• Comparison of a strip immobilization system (1989-1991) with a mask system (1991-1995).
• Analysis of isocenter shifts from port films taken on 4 MV and >= 6 MV accelerators, with varying fixation methods.

Main Results:

• On >= 6 MV accelerators where both systems were fixed to the couch, the mask system showed significantly fewer isocenter shifts (6.2%) compared to the strip system (16.1%; p=0.002).
• This improvement was most pronounced in routine daily setup films.
• The mask system's accuracy was dependent on fixation to the treatment couch, with higher shift rates on the 4-MV unit where it was not fixed.

Conclusions:

• The customized mask immobilization system, when secured to the treatment couch, offers improved patient setup accuracy over the previous strip system.
• Enhanced accuracy in daily patient setup can potentially improve the therapeutic ratio in radiotherapy.
• This leads to a greater likelihood of tumor control and a reduced risk of normal tissue complications.