Which failures do patient-specific quality assurance systems need to catch?

Background: The Joint AAPM-ESTRO TG-360 is developing a quantitative framework to evaluate treatment verification systems used for patient-specific quality assurance (PSQA). A subgroup was commissioned to determine which potential failure modes had the greatest risk to treatment quality and safety, and therefore should be evaluated as part of the PSQA verification.

Purpose: To create an extensive database of potential radiotherapy failure modes that should be detected by PSQA and to determine their relative importance for maximizing treatment quality.

A structured FMEA approach to optimizing combinations of plan-specific quality assurance techniques for IMRT and VMAT QA.

Background: Many commercial tools are available for plan-specific quality assurance (QA) of radiotherapy plans, with their functionality assessed in isolation. However, multiple QA tools are required to review the full range of potential errors. It is important to assess their effectiveness in combination with each other to look for ways to both streamline the QA process and to make certain that errors of high impact and/or high occurrence are caught before reaching patient treatment.

Accuracy and efficiency of image-guided radiation therapy (IGRT) for preoperative partial breast radiosurgery.

Objective: To analyze and evaluate accuracy and efficiency of IGRT process for preoperative partial breast radiosurgery.

Methods: Patients were initially setup with skin marks and 5 steps were performed: (1) Initial orthogonal 2D kV images, (2) pre-treatment 3D CBCT images, (3) verification orthogonal 2D kV images, (4) treatment including mid-treatment 2D kV images (for the final 15 patients only), and (5) post-treatment orthogonal 2D kV or 3D CBCT images. Patient position was corrected at each step to align the biopsy clip and to verify surrounding soft tissue positioning.

AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs.

Thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSLD) are practical, accurate, and precise tools for point dosimetry in medical physics applications. The charges of Task Group 191 were to detail the methodologies for practical and optimal luminescence dosimetry in a clinical setting. This includes: (a) to review the variety of TLD/OSLD materials available, including features and limitations of each; (b) to outline the optimal steps to achieve accurate and precise dosimetry with luminescent detectors and to evaluate the uncertainty induced when less rigorous procedures are used; (c) to develop consensus guidelines on the optimal use of luminescent dosimeters for clinical practice; and (d) to develop guidelines for special medically relevant uses of TLDs/OSLDs such as mixed photon/neutron field dosimetry, particle beam dosimetry, and skin dosimetry.

Quantitative Approach to Failure Mode and Effect Analysis for Linear Accelerator Quality Assurance.

Purpose: To determine clinic-specific linear accelerator quality assurance (QA) TG-142 test frequencies, to maximize physicist time efficiency and patient treatment quality.

Methods And Materials: A novel quantitative approach to failure mode and effect analysis is proposed. Nine linear accelerator-years of QA records provided data on failure occurrence rates.

Diode-based transmission detector for IMRT delivery monitoring: a validation study.

The purpose of this work was to evaluate the potential of a new transmission detector for real-time quality assurance of dynamic-MLC-based radiotherapy. The accuracy of detecting dose variation and static/dynamic MLC position deviations was measured, as well as the impact of the device on the radiation field (surface dose, transmission). Measured dose variations agreed with the known variations within 0.

Comparison of 2D and 3D gamma analyses.

Purpose: As clinics begin to use 3D metrics for intensity-modulated radiation therapy (IMRT) quality assurance, it must be noted that these metrics will often produce results different from those produced by their 2D counterparts. 3D and 2D gamma analyses would be expected to produce different values, in part because of the different search space available. In the present investigation, the authors compared the results of 2D and 3D gamma analysis (where both datasets were generated in the same manner) for clinical treatment plans.

Investigation of sliced body volume (SBV) as respiratory surrogate.

The purpose of this study was to evaluate the sliced body volume (SBV) as a respiratory surrogate by comparing with the real-time position management (RPM) in phantom and patient cases. Using the SBV surrogate, breathing signals were extracted from unsorted 4D CT images of a motion phantom and 31 cancer patients (17 lung cancers, 14 abdominal cancers) and were compared to those clinically acquired using the RPM system. Correlation coefficient (R), phase difference (D), and absolute phase difference (D(A)) between the SBV-derived breathing signal and the RPM signal were calculated.

A quality assurance method that utilizes 3D dosimetry and facilitates clinical interpretation.

Purpose: To demonstrate a new three-dimensional (3D) quality assurance (QA) method that provides comprehensive dosimetry verification and facilitates evaluation of the clinical significance of QA data acquired in a phantom. Also to apply the method to investigate the dosimetric efficacy of base-of-skull (BOS) intensity-modulated radiotherapy (IMRT) treatment.

Methods And Materials: Two types of IMRT QA verification plans were created for 6 patients who received BOS IMRT.

Comparison of 3D conformal breast radiation treatment plans using the anisotropic analytical algorithm and pencil beam convolution algorithm.

Purpose: To investigate (1) dosimetric differences between plans calculated using the anisotropic analytical algorithm (AAA) and pencil beam convolution (PBC) algorithm, (2) the plan quality achieved using AAA compared to PBC based on dosimetric parameters and (3) discrepancies with an independent MU verification calculation for breast treatment planning.

Materials And Methods: This study included 10 lumpectomy (Group I) and 10 mastectomy (Group II) cases. Target volumes were defined as breast for Group I and chest-wall for Group II based on the isodose distribution of PBC plans in order to evaluate plans.

Volumetric-modulated arc therapy: effective and efficient end-to-end patient-specific quality assurance.

Purpose: To explore an effective and efficient end-to-end patient-specific quality-assurance (QA) protocol for volumetric modulated arc radiotherapy (VMAT) and to evaluate the suitability of a stationary radiotherapy QA device (two-dimensional [2D] ion chamber array) for VMAT QA.

Methods And Materials: Three methods were used to analyze 39 VMAT treatment plans for brain, spine, and prostate: ion chamber (one-dimensional absolute, n = 39), film (2D relative, coronal/sagittal, n = 8), and 2D ion chamber array (ICA, 2D absolute, coronal/sagittal, n = 39) measurements. All measurements were compared with the treatment planning system dose calculation either via gamma analysis (3%, 3- to 4-mm distance-to-agreement criteria) or absolute point dose comparison.

6D image guidance for spinal non-invasive stereotactic body radiation therapy: Comparison between ExacTrac X-ray 6D with kilo-voltage cone-beam CT.

Purpose: To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT).

Materials And Methods: In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac X-ray 6D and CBCT to test the accuracy of the imaging systems.

Performance evaluation of automatic anatomy segmentation algorithm on repeat or four-dimensional computed tomography images using deformable image registration method.

Purpose: Auto-propagation of anatomic regions of interest from the planning computed tomography (CT) scan to the daily CT is an essential step in image-guided adaptive radiotherapy. The goal of this study was to quantitatively evaluate the performance of the algorithm in typical clinical applications.

Methods And Materials: We had previously adopted an image intensity-based deformable registration algorithm to find the correspondence between two images.

Dosimetric effect of translational and rotational errors for patients undergoing image-guided stereotactic body radiotherapy for spinal metastases.

Purpose: To investigate the dosimetric effects of translational and rotational patient positioning errors on the treatment of spinal and paraspinal metastases using computed tomography image-guided stereotactic body radiotherapy. The results of this study provide guidance for the treatment planning process and recognition of the dosimetric consequences of daily patient treatment setup errors.

Methods And Materials: The data from 20 patients treated for metastatic spinal cancer using image-guided stereotactic body radiotherapy were investigated in this study.

Daily bone alignment with limited repeat CT correction rivals daily ultrasound alignment for prostate radiotherapy.

Purpose: To compare the effectiveness of daily ultrasound (US)- and computed tomography (CT)-guided alignments with an off-line correction protocol using daily bone alignment plus a correction factor for systematic internal prostate displacement (CF(ID)).

Methods And Materials: Ten prostate cancer patients underwent CT scans three times weekly using an integrated CT-linear accelerator system, followed by alignment using US for daily radiotherapy. Intensity-modulated radiotherapy plans were designed with our current clinical margins.

Quantification of prostate and seminal vesicle interfraction variation during IMRT.

Purpose: To quantify the interfraction variability in prostate and seminal vesicle (SV) positions during a course of intensity-modulated radiotherapy (IMRT) using an integrated computed tomography (CT)-linear accelerator system and to assess the impact of rectal and bladder volume changes.

Methods And Materials: We studied 15 patients who had undergone IMRT for prostate carcinoma. Patients had one pretreatment planning CT scan followed by three in-room CT scans per week using a CT-on-rails system.

Parotid gland dose in intensity-modulated radiotherapy for head and neck cancer: is what you plan what you get?

Purpose: To quantify the differences between planned and delivered parotid gland and target doses, and to assess the benefits of daily bone alignment for head and neck cancer patients treated with intensity-modulated radiotherapy (IMRT).

Methods And Materials: Eleven head and neck cancer patients received two CT scans per week with an in-room CT scanner over the course of their radiotherapy. The clinical IMRT plans, designed with 3-mm to 4-mm planning margins, were recalculated on the repeat CT images.

The effect of dental artifacts, contrast media, and experience on interobserver contouring variations in head and neck anatomy.

Objectives: To investigate interobserver variability in the delineation of head-and-neck (H&N) anatomic structures on CT images, including the effects of image artifacts and observer experience.

Methods: Nine observers (7 radiation oncologists, 1 surgeon, and 1 physician assistant) with varying levels of H&N delineation experience independently contoured H&N gross tumor volumes and critical structures on radiation therapy treatment planning CT images alongside reference diagnostic CT images for 4 patients with oropharynx cancer. Image artifacts from dental fillings partially obstructed 3 images.

Dosimetric comparison of four target alignment methods for prostate cancer radiotherapy.

Purpose: The aim of this study was to compare the dosimetric consequences of 4 treatment delivery techniques for prostate cancer patients treated with intensity-modulated radiotherapy (IMRT).

Methods And Materials: During an 8-week course of radiotherapy, 10 patients underwent computed tomography (CT) scans 3 times per week (243 total) before daily treatment with a CT-linear accelerator. Treatment delivery was simulated by realigning a fixed-margin treatment plan on each CT scan and calculating doses.

Reducing radiation exposure from survey CT scans.

Objective: The purpose of this study was to focus attention on the technique factors commonly used in survey CT scans (e.g., scout, topogram, or pilot scans) to measure the radiation exposure from typical survey CT scans, to compare their exposure to that of typical chest radiographs, and to explore methods for radiation exposure reduction.

Validation of an accelerated 'demons' algorithm for deformable image registration in radiation therapy.

A greyscale-based fully automatic deformable image registration algorithm, originally known as the 'demons' algorithm, was implemented for CT image-guided radiotherapy. We accelerated the algorithm by introducing an 'active force' along with an adaptive force strength adjustment during the iterative process. These improvements led to a 40% speed improvement over the original algorithm and a high tolerance of large organ deformations.

An automatic CT-guided adaptive radiation therapy technique by online modification of multileaf collimator leaf positions for prostate cancer.

Purpose: To propose and evaluate online adaptive radiation therapy (ART) using in-room computed tomography (CT) imaging that detects changes in the target position and shape of the prostate and seminal vesicles (SVs) and then automatically modifies the multileaf collimator (MLC) leaf pairs in a slice-by-slice fashion.

Methods And Materials: For intensity-modulated radiation therapy (IMRT) using a coplanar beam arrangement, each MLC leaf pair projects onto a specific anatomic slice. The proposed strategy assumes that shape deformation is a function of only the superior-inferior (SI) position.

Quantification of volumetric and geometric changes occurring during fractionated radiotherapy for head-and-neck cancer using an integrated CT/linear accelerator system.

Purpose: Many patients receiving fractionated radiotherapy (RT) for head-and-neck cancer have marked anatomic changes during their course of treatment, including shrinking of the primary tumor or nodal masses, resolving postoperative changes/edema, and changes in overall body habitus/weight loss. We conducted a pilot study to quantify the magnitude of these anatomic changes with systematic CT imaging.

Methods And Materials: Fourteen assessable patients were enrolled in this pilot study.