A cone beam CT-Based Study for Clinical Target Definition Using Pelvic Anatomy During Postprostatectomy Radiotherapy

Area of Science:

• Radiation Oncology
• Medical Imaging
• Prostate Cancer Treatment

Background:

• Online image-guided radiation therapy (IGRT) lacks standardized target volume definition guidelines post-radical prostatectomy (RP).
• Accurate target volume definition is crucial for effective and safe radiotherapy after RP.

Purpose of the Study:

• To utilize cone beam CT (CBCT) imaging to gather data for defining target volumes in post-RP IGRT.
• To establish evidence-based margins for image-guided radiotherapy following prostatectomy.

Main Methods:

• Analyzed CBCT images from 10 patients undergoing post-RP radiation therapy (RT).
• Compared bladder and rectal volumes on CBCT with planning CT (CT(ref)) to approximate the prostatic fossa.
• Calculated anterior and posterior planning target volume margins based on observed bladder and rectal motion using ICRU report 71 guidelines.

Main Results:

• Rectal and bladder borders were identifiable in 94% of 176 CBCT scans.
• Mean bladder posterior wall position shifted anteriorly (0.1–1.5 mm) and mean rectum anterior wall position shifted posteriorly (1.6–2.7 mm) relative to CT(ref).
• Calculated anterior margins ranged from 5.9–7.1 mm (bladder motion), and posterior margins ranged from 8.6–10.2 mm (rectal motion).

Conclusions:

• CBCT imaging reliably defines normal tissue anatomy during post-RP RT.
• Interfraction motion of the bladder and rectum was quantified, providing essential data for image-guided RT.
• The findings support the development of improved post-RP RT techniques utilizing image guidance.