Assessment of Volumetric and Dosimetric Variations for Image Guided Stereotactic Body Radiation Therapy Treatment

Abstract

Purpose/Objective(s)Current 2D X-ray image has allowed for fast and accurate target localization and patient positioning in prostate stereotactic body radiation therapy (SBRT), the temporal and volumetric variations need to be assessed. The purpose of the work is to investigate the amount of interfraction anatomic changes (using 3D cone beam image) and the consequential dosimetric variations based on a group of previously treated prostate SBRT for continuous quality improvement in clinical practice.Materials/Method81 localized prostate cancer patients treated between 2010 through 2013 were retrospectively analyzed. All patients went through SBRT treatment on a robotic radiosurgery accelerator with the prescription dose of 40 Gy in 5 fractions to the planning target volume (PTV). The SBRT treatment plans were created on a treatment planning system using rotational IMRT technique with PTV margin of 3-4 mm. For better visualization and localization purposes, three fiducial markers were implanted into the prostate to ensure proper patient alignment. Prior to each treatment delivery, a set of ExacTrac 2D kV images was acquired, and the patient setup corrections were made according to the fusion of fiducial markers. In addition, a 3D kilovoltage cone beam CT (kVCBCT) scan was performed to further verify the correct patient alignment and to monitor the volume variations for the bladder and rectum. Each kVCBCT scan was then registered to the corresponding planning CT using an automated deformable image fusion tool; the daily and composite accumulation doses to the PTV, bladder and rectum were assessed using the deformable registration algorithm.ResultsA total of 195 kVCBCT images for a subset of 39 prostate cases were analyzed and compared with the planning volume and planning dosimetric endpoints. We found large interfraction geometric and dosimetric variations in the rectum and bladder throughout the course of the prostate SBRT treatment. The fractions in which the actual treatment volumes differed from the original planning volumes by at least 50% were 18% for rectums and 37.4% for bladders. Compared to the plan, the maximum cumulative doses varied up to 24% for the rectum and the mean cumulative doses varied up to 63% for the bladder. On average, the mean PTV doses (normalized to the plan) were 0.92±0.17.ConclusionsVolumetric kVCBCT scans revealed dramatic bladder and rectum volumatric variations throughout the course of prostate SBRT treatments. Consequently, the delivered dose distributions greatly deviated from the original planned doses. Systematic evaluation and proper management of interfraction changes in organ anatomy are necessary in order to minimize dosimetric perturbations and to ensure better clinical outcomes in prostate SBRT treatments. Purpose/Objective(s)Current 2D X-ray image has allowed for fast and accurate target localization and patient positioning in prostate stereotactic body radiation therapy (SBRT), the temporal and volumetric variations need to be assessed. The purpose of the work is to investigate the amount of interfraction anatomic changes (using 3D cone beam image) and the consequential dosimetric variations based on a group of previously treated prostate SBRT for continuous quality improvement in clinical practice. Current 2D X-ray image has allowed for fast and accurate target localization and patient positioning in prostate stereotactic body radiation therapy (SBRT), the temporal and volumetric variations need to be assessed. The purpose of the work is to investigate the amount of interfraction anatomic changes (using 3D cone beam image) and the consequential dosimetric variations based on a group of previously treated prostate SBRT for continuous quality improvement in clinical practice. Materials/Method81 localized prostate cancer patients treated between 2010 through 2013 were retrospectively analyzed. All patients went through SBRT treatment on a robotic radiosurgery accelerator with the prescription dose of 40 Gy in 5 fractions to the planning target volume (PTV). The SBRT treatment plans were created on a treatment planning system using rotational IMRT technique with PTV margin of 3-4 mm. For better visualization and localization purposes, three fiducial markers were implanted into the prostate to ensure proper patient alignment. Prior to each treatment delivery, a set of ExacTrac 2D kV images was acquired, and the patient setup corrections were made according to the fusion of fiducial markers. In addition, a 3D kilovoltage cone beam CT (kVCBCT) scan was performed to further verify the correct patient alignment and to monitor the volume variations for the bladder and rectum. Each kVCBCT scan was then registered to the corresponding planning CT using an automated deformable image fusion tool; the daily and composite accumulation doses to the PTV, bladder and rectum were assessed using the deformable registration algorithm. 81 localized prostate cancer patients treated between 2010 through 2013 were retrospectively analyzed. All patients went through SBRT treatment on a robotic radiosurgery accelerator with the prescription dose of 40 Gy in 5 fractions to the planning target volume (PTV). The SBRT treatment plans were created on a treatment planning system using rotational IMRT technique with PTV margin of 3-4 mm. For better visualization and localization purposes, three fiducial markers were implanted into the prostate to ensure proper patient alignment. Prior to each treatment delivery, a set of ExacTrac 2D kV images was acquired, and the patient setup corrections were made according to the fusion of fiducial markers. In addition, a 3D kilovoltage cone beam CT (kVCBCT) scan was performed to further verify the correct patient alignment and to monitor the volume variations for the bladder and rectum. Each kVCBCT scan was then registered to the corresponding planning CT using an automated deformable image fusion tool; the daily and composite accumulation doses to the PTV, bladder and rectum were assessed using the deformable registration algorithm. ResultsA total of 195 kVCBCT images for a subset of 39 prostate cases were analyzed and compared with the planning volume and planning dosimetric endpoints. We found large interfraction geometric and dosimetric variations in the rectum and bladder throughout the course of the prostate SBRT treatment. The fractions in which the actual treatment volumes differed from the original planning volumes by at least 50% were 18% for rectums and 37.4% for bladders. Compared to the plan, the maximum cumulative doses varied up to 24% for the rectum and the mean cumulative doses varied up to 63% for the bladder. On average, the mean PTV doses (normalized to the plan) were 0.92±0.17. A total of 195 kVCBCT images for a subset of 39 prostate cases were analyzed and compared with the planning volume and planning dosimetric endpoints. We found large interfraction geometric and dosimetric variations in the rectum and bladder throughout the course of the prostate SBRT treatment. The fractions in which the actual treatment volumes differed from the original planning volumes by at least 50% were 18% for rectums and 37.4% for bladders. Compared to the plan, the maximum cumulative doses varied up to 24% for the rectum and the mean cumulative doses varied up to 63% for the bladder. On average, the mean PTV doses (normalized to the plan) were 0.92±0.17. ConclusionsVolumetric kVCBCT scans revealed dramatic bladder and rectum volumatric variations throughout the course of prostate SBRT treatments. Consequently, the delivered dose distributions greatly deviated from the original planned doses. Systematic evaluation and proper management of interfraction changes in organ anatomy are necessary in order to minimize dosimetric perturbations and to ensure better clinical outcomes in prostate SBRT treatments. Volumetric kVCBCT scans revealed dramatic bladder and rectum volumatric variations throughout the course of prostate SBRT treatments. Consequently, the delivered dose distributions greatly deviated from the original planned doses. Systematic evaluation and proper management of interfraction changes in organ anatomy are necessary in order to minimize dosimetric perturbations and to ensure better clinical outcomes in prostate SBRT treatments.