Planning Target Volume Margin Assessment Using Daily Cone Beam Computed Tomography Image Verification in Prostate Cancer Patients

Introduction: Conformal radiation techniques are widely used in prostate cancer treatment as it improves the therapeutic ratio. However, inter- and intra-fraction variations remain challenging, which reflects on the planning target volume (PTV) margin. This study aimed to determine the benefit of daily Cone Beam Computed Tomography (CBCT) in reducing the  PTV margin. Material and Methods: ۵۱ patients over ۳ years were included in the study.  PTV was obtained by applying ۸mm in left-right (LR) and anterior (A), ۵mm in posterior (P) and ۸mm in superior-inferior (SI) directions of clinical target volumes (CTV). Pelvic bones of CBCT were matched with the planning CT scan and manually adjusted with soft tissue, assessing the total inter-fraction error. Values were registered in left-right (X), superior-inferior (Y), and anterior-posterior (Z) directions. Results: The median age was ۷۱ years and  ۸۴.۳% were in the high-risk group. The mean inter-fraction error (Mp) was obtained in all three principal axes (x, y, z). The majority had shifts ≤ ۰.۳cm. None recorded a shift >۱cm. The Random errors were ۰.۴۴cm in LR (X), ۰.۳۶cm in SI (Y) and ۰.۴۰cm in AP (Z) directions. The systematic errors were ۰.۰۵cm in LR (X), ۰.۰۴cm in SI (Y) and ۰.۰۴cm in AP (Z) directions. The PTV margin was calculated using van Herk’s formula and obtained as ۰.۶۸cm. Conclusion: Routine use of CBCT significantly reduces the random and systematic errors and ensures safer dose escalation with reduced PTV margin.

کلیدواژه ها:

Prostate Intensity Modulated Radiotherapy Cone ، Beam Computed Tomography