Nonuniform Planning Target Volume Margins for Prostate Bed on the Basis of Surgical Clips on Daily Cone Beam Computed Tomography.

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Purpose:We hypothesized that the interfraction motions of the superior and inferior prostate beds differ and therefore require different margins. In this study, we used daily cone beam computed tomography (CBCT) to evaluate the motion of postprostatectomy surgical clips (separated to superior and inferior portions) within the planning target volume (PTV) to derive data-driven PTV margins. Methods and Materials:Our study cohort included consecutive patients with identifiable surgical clips undergoing prostate bed irradiation with daily CBCT image guidance. We identified and contoured the clips within the PTV on the planning computed tomography and CBCT scans. All CBCT scans were registered to the planning computed tomography scan on the basis of pelvic bony structures. The superior border of the pubic symphysis was used to mark the division between the superior and inferior portions. Results:Eleven patients with 263 CBCT scans were included in the cohort. In the left-right direction, the global mean M, systematic error Σ, and residue error σ were 0.02, 0.03, and 0.16 cm, respectively, for superior clips, and 0.00, 0.03, and 0.03 cm, respectively, for inferior clips. In the anterior-posterior direction, the corresponding values were M = 0.01, Σ = 0.25, and σ= 0.37, respectively, for superior, and M = 0.08, Σ= 0.13, σ= 0.15, respectively, for inferior. In the superior-inferior direction, the values were M =-0.06, Σ= 0.23, and σ= 0.27, respectively, for superior, and M =-0.01, Σ= 0.21, σ= 0.20, respectively, for inferior. The results of the 2-tailed F tests showed that the anterior-posterior motion is statistically different between the superior and inferior portions in the anterior-posterior direction. There is no statistical difference in the superior-inferior and lateral directions. Therefore, we propose a set of nonuniform PTV margins (based on the formula 2.5 Σ+ 0.7σ) as 0.2 cm for all prostate beds in the left-right direction, 0.7 cm for all in superior-inferior, and 0.9 to 0.4 for superior-inferior in the anterior-posterior direction. Conclusions:The difference in motion between the superior and inferior portions of the prostate bed is statistically insignificant in the left-right and superior-inferior directions, but statistically significant in the anterior-posterior direction, which warrants a nonuniform PTV margin scheme.






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Song, Haijun, Joseph K Salama, William Robert Lee and Qiuwen Wu (2019). Nonuniform Planning Target Volume Margins for Prostate Bed on the Basis of Surgical Clips on Daily Cone Beam Computed Tomography. Advances in radiation oncology, 4(1). pp. 186–190. 10.1016/j.adro.2018.09.014 Retrieved from

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Joseph Kamel Salama

Professor of Radiation Oncology

I have the privilege to be the Chief of the Durham VA Radiation Oncology Service, where I care for veterans who have served our country. I am a dedicated educator, serving as the Residency Program Director for the Duke Radiation Oncology Residency Program.  I am also a cancer researcher developing novel treatment techniques for patients with head and neck cancer, lung cancer, prostate cancer, and those limited metastatic disease, and integration of these treatments with drug therapies. 


W. Robert Lee

Professor of Radiation Oncology

Prostate cancer, Intensity-modulated radiation therapy (IMRT), Image-guided radiation therapy (IGRT), Stereotactic Body Radiation Therapy (SBRT), Prostate HDR and LDR Brachytherapy, Quality of Life, Educational Technology

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