Helical tomotherapy with dynamic running-start-stop delivery compared to conventional tomotherapy delivery

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Helical tomotherapy (HT) offers superior dose uniformity but faces challenges in balancing longitudinal dose conformity and beam-on time (BOT) due to fixed jaw limitations.
• The dynamic running-start-stop (RSS) delivery technique was developed to address these limitations by allowing variable jaw openings.

Purpose of the Study:

• To compare the dosimetric performance of dynamic RSS delivery versus conventional fixed jaw HT delivery.
• To evaluate the impact of RSS on treatment time, target dose conformity, and organ-at-risk sparing.

Main Methods:

• Twenty patient cases (16 common, 4 whole brain with hippocampus avoidance) were analyzed.
• Helical tomotherapy plans were created using fixed jaw widths (HT2.5, HT1.0) and compared with RSS plans using larger jaw presets (RSS5.0, RSS2.5).
• Dosimetric indices, BOT, and monitor units were compared between the two delivery techniques.

Main Results:

• RSS with larger jaws (RSS5.0) reduced average BOT by nearly 50% compared to HT2.5, with comparable target dose homogeneity for common sites.
• RSS demonstrated superior normal tissue sparing in brain, head and neck, lung, and prostate cases.
• For complex whole brain cases, RSS2.5 showed degraded target homogeneity compared to HT1.0.

Conclusions:

• Dynamic RSS delivery with larger jaw widths enhances treatment speed and cranial-caudal dose conformity in helical tomotherapy.
• RSS provides comparable target coverage to fixed jaw HT for standard cancer sites.
• Complex target geometries may require careful planning with RSS to avoid compromising target homogeneity.