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Updated: Jun 15, 2026
A New Technique for Treating Low-risk Prostate Cancer—Super Active Surveillance
Published on: November 7, 2025
Impact of anatomical interventions on the localization of post-prostatectomy cancer patients
Quentin Diot1, Christine Olsen, Brian Kavanagh
1Department of Radiation Oncology, University of Colorado Denver, Aurora, Colorado 80045, USA.
Purpose:
Anatomical deformations of prostate-bed, rectum, and bladder can compromise the targeting accuracy in post-prostatectomy cancer patients. In this work, the impact of anatomical interventions on the localization data from post-prostatectomy patients who received image-guided IMRT was analyzed.
Methods:
Patients were localized daily with online kilovoltage cone-beam computed tomography (kV-CBCT). The target and the organs at risk (OARs) positional and volumetric changes were evaluated and couch shifts were applied. For patients with large target or OAR volumetric changes, quantified by either a rectal or bladder wall displacement of >5 mm on the CBCT sagittal images compared to the planning CT, repeated localization CBCT scans were performed following an interventional procedure. The procedure involves insertion of a catheter to deflate the rectum, evacuation of stools, and/or adjustment of bladder filling. The required shifts were then evaluated, and the IMRT treatment was subsequently delivered after proper patient positioning. The pre- and post-intervention shifts were compared in the lateral [left-right (LR)], longitudinal [superior-inferior (SI)], and vertical [anterior-posterior (AP)] directions. The percentage of shifts larger than 5 mm in all directions was also compared. Clinical target volume to planning target volume (CTV-to-PTV) expansion margins were estimated based on the pre- and post-intervention localization data.
Results:
Intervention was performed on all patients (n=17) treated between October 2008 and March 2009. The number of interventions ranged from 2 to 12 with a median number of 5, resulting in a total of 96 pairs of pre- and post-intervention shifts. The mean value (sigma) and standard deviation (sigma) of the shifts from pre- versus post-intervention data were LR, 0.0 +/- 3.0 mm vs. 0.5 +/- 2.8 mm; SI, 0.2 +/- 3.1 mm vs. -1.0 +/- 2.1 mm; and AP, -2.6 +/- 5.8 mm vs. 1.7 +/- 3.9 mm. The mean 3D shift distance was 7.0 +/- 3.1 mm vs. 5.0 +/- 2.6 mm. The percentage of pre-intervention shifts larger than 5 mm were 7%, 7%, and 45% in the LR, SI, and AP directions, respectively, compared to 8%, 4%, and 21% for post-intervention. Localization data from pre- and post-intervention procedures suggest that treatments that do not include intervention to correct for rectum/bladder anatomical variations require an additional 3.3 mm CTV-to-PTV margin.
Conclusions:
Anatomical interventions reduced the localization errors arising from large volume and shape changes in the rectum and/or bladder compared to treatments without interventions.
Insights
Anatomical interventions significantly reduce localization errors in post-prostatectomy patients undergoing image-guided intensity-modulated radiation therapy (IMRT). These interventions improve targeting accuracy by managing rectal and bladder volume changes, leading to smaller margins and safer treatments.
Area of Science:
- Radiation oncology
- Medical physics
- Anatomical imaging
Background:
- Anatomical variations in the prostate-bed, rectum, and bladder can significantly impact the accuracy of radiation targeting in post-prostatectomy cancer patients.
- Image-guided intensity-modulated radiation therapy (IMRT) relies on precise patient alignment to deliver effective treatment.
Purpose of the Study:
- To analyze the impact of anatomical interventions on localization accuracy in post-prostatectomy patients receiving image-guided IMRT.
- To quantify the reduction in localization errors and assess the effect on planning margins.
Main Methods:
- Daily online kilovoltage cone-beam computed tomography (kV-CBCT) was used for patient localization.
- Interventional procedures (e.g., catheterization, stool evacuation, bladder adjustment) were performed for significant rectal/bladder volume changes (>5 mm displacement).
- Pre- and post-intervention shifts were compared, and clinical target volume (CTV) to planning target volume (PTV) margins were estimated.
Main Results:
- Interventions were performed on all 17 patients, with a median of 5 interventions per patient.
- Mean 3D shift distance decreased from 7.0 ± 3.1 mm pre-intervention to 5.0 ± 2.6 mm post-intervention.
- The percentage of shifts >5 mm decreased significantly in the anterior-posterior direction (45% to 21%) and slightly in other directions.
Conclusions:
- Anatomical interventions effectively reduce localization errors caused by rectal and bladder volume/shape changes.
- Treatments without these interventions necessitate an additional 3.3 mm CTV-to-PTV margin.
- These findings support the routine use of anatomical interventions to enhance targeting accuracy in image-guided IMRT for post-prostatectomy patients.
