Optimization of tomotherapy treatment planning for patients with bilateral hip prostheses

Abstract

BackgroundTo determine the effect of different imaging options and the most efficient imaging strategy for treatment planning of patients with hip prostheses.MethodsThe planning kilovoltage CT (kVCT) and daily megavoltage CT (MVCT) studies for three prostate cancer patients with bilateral hip prostheses were used for creating hybrid kVCT/MVCT image sets. Treatment plans were created for kVCT images alone, hybrid kVCT/MVCT images, and MVCT images alone using the same dose prescription and planning parameters. The resulting dose volume histograms were compared. The orthopedic metal artifact reduction (O-MAR) reconstruction tool for kVCT images and different MVCT options were investigated with a water tank fit with double hip prostheses. Treatment plans were created for all imaging options and calculated dose was compared with the one measured by a pin-point ion chamber.ResultsOn average for three patients, the D35% for the bladder was 8% higher in plans based on MVCT images and 7% higher in plans based on hybrid images, compared to the plans based on kVCT images alone. Likewise, the D35% for the rectum was 3% higher than the kVCT based plan for both hybrid and MVCT plans. The average difference in planned D99% in the PTV compared to kVCT plans was 0.9% and 0.1% for MVCT and hybrid plans, respectively. For the water tank with hip prostheses phantom, the kVCT plan with O-MAR correction applied showed better agreement between the measured and calculated dose than the original image set, with a difference of -1.9% compared to 3.3%. The measured doses for the MVCT plans were lower than the calculated dose due to image size limitations. The best agreement was for the kVCT/MVCT hybrid plans with the difference between calculated and measured dose around 1%.ConclusionMVCT image provides better visualization of patient anatomy and hybrid kVCT/MVCT study enables more accurate calculations using updated MVCT relative electron density calibration.

Approaches to reducing photon dose calculation errors near metal implants

“…A limitation of this study is that other approaches to improving calculation accuracy for patients with metal implants, namely the use of other calculation methods (e.g., Monte Carlo 34 and Grid-Based Boltzmann Solvers 35 ) and MV imaging, 36 were not investigated. Another limitation is that in our evaluation of various commercial artifact reduction algorithms we chose clinical cases in which treatment beams traverse metal implants.…”

ACR Appropriateness Criteria ® external beam radiation therapy treatment planning for clinically localized prostate cancer, part I of II

“…Although challenging, IMRT planning is feasible in a patient with bilateral hip prostheses, 127 and class solutions have been proposed 128, 129. Megavoltage CT imaging, if available, may provide better imaging of pelvic anatomy and may be useful as a tool for electron density calibration during EBRT planning 130, 131. There is some limited evidence that MRI scanning may also be helpful for target delineation for patients with bilateral hip prostheses 132, 133.…”

“… 128 , 129 Megavoltage CT imaging, if available, may provide better imaging of pelvic anatomy and may be useful as a tool for electron density calibration during EBRT planning. 130 , 131 There is some limited evidence that MRI scanning may also be helpful for target delineation for patients with bilateral hip prostheses. 132 , 133 EBRT planning requires careful collaboration among radiation oncologists, physicists, and dosimetrists and should include recognition of the uncertainty in target volume definition and dose calculations.…”

Modeling of kyphoplasty cement for accurate dose calculations

“…Other authors have shown that CT scans acquired with MV-range energy spectra can provide a more accurate representation of the effect on megavoltage treatment beam interactions with dense objects. 14,15 This is not a practical alternative in most clinics, hence the need for a material assignment methodology based on commonly available kV-range CT datasets.…”