Performance of a deformable image registration algorithm for CT and cone beam CT using physical multi-density geometric and digital anatomic phantoms.

PURPOSE: To study the accuracy of deformable registration algorithm for CT and cone beam CT (CBCT) using a combination of physical and digital phantoms. MATERIALS AND METHODS: The physical phantoms consisted of objects over a range of electron densities, shape and sizes. The system was tested for simple and complex scenarios including performance in the presence of metallic artefacts. Clinically present deformations were simulated using a set of five geometric and anatomic virtual phantoms. RESULTS: The system could not account for large changes in size, shape and Hounsfield units. Deformations of low intensity structures and small objects were highly inaccurate, and errors were prominent for volume reduction scenario than volume growth. The presence of artefacts did alter the performance of the algorithm. Objects of low density and that close to artefacts were affected the most. Overall, deformations to CBCT were poor. In virtual phantoms, the system could not handle gas pockets and deformation errors in inverse direction were higher than that in forward direction. CONCLUSION: The algorithm was tested for several non-clinical and clinical scenarios. The performance was acceptable for realistic and clinically present deformations. However, it is necessary to tread cautiously for structures with small volumes and large reductions in volume.

Auto-segmentation of head and neck organs at risk in radiotherapy and its dependence on anatomic similarity.

PURPOSE: The aim is to study the dependence of deformable based auto-segmentation of head and neck organs-at-risks (OAR) on anatomy matching for a single atlas based system and generate an acceptable set of contours. METHODS: A sample of ten patients in neutral neck position and three atlas sets consisting of ten patients each in different head and neck positions were utilized to generate three scenarios representing poor, average and perfect anatomy matching respectively and auto-segmentation was carried out for each scenario. Brainstem, larynx, mandible, cervical oesophagus, oral cavity, pharyngeal muscles, parotids, spinal cord, and trachea were the structures selected for the study. Automatic and oncologist reference contours were compared using the dice similarity index (DSI), Hausdroff distance and variation in the centre of mass (COM). RESULTS: The mean DSI scores for brainstem was good irrespective of the anatomy matching scenarios. The scores for mandible, oral cavity, larynx, parotids, spinal cord, and trachea were unacceptable with poor matching but improved with enhanced bony matching whereas cervical oesophagus and pharyngeal muscles had less than acceptable scores for even perfect matching scenario. HD value and variation in COM decreased with better matching for all the structures. CONCLUSION: Improved anatomy matching resulted in better segmentation. At least a similar setup can help generate an acceptable set of automatic contours in systems employing single atlas method. Automatic contours from average matching scenario were acceptable for most structures. Importance should be given to head and neck position during atlas generation for a single atlas based system.

Application of aSi-kVCBCT for Volume Assessment and Dose Estimation: An Offline Adaptive Study for Prostate Radiotherapy

Objective: The purpose of this study is to develop a method to estimate the dose using amorphous silicon detector panel cone beam computed tomography (aSi-kVCBCT) for the OARs and targets in prostate radiotherapy and to compare with the actual planned dose. Methods: The aSi-kVCBCT is used widely in radiotherapy to verify the patient position before treatment. The advancement in aSi-kVCBCT combined with adaptive software allows us to verify the dose distribution in daily acquired CBCT images. CBCT images from 10 patients undergoing radical prostate radiotherapy were included in this study. Patients received total dose of 65Gy in 25 fractions using volumetric modulated arc therapy (VMAT). aSi-kVCBCT scans were acquired before daily treatment and exported to smart adapt software for image adaptation. The planning CT is adapted to daily aSi-kVCBCT images in terms of HU mapping. The primary VMAT plans were copied on to the adapted planning CT images and dose was calculated using Anisotropic Analytic Algorithm (AAA). The DVH is then used to evaluate the volume changes of organs at risk (OAR), the actual dose received by OARs, CTV and PTV during a single fraction. Results: The normalized volume of the bladder and rectum ranged from 0.70­1.66 and 0.70­1.16 respectively. The cumulative mean Sorensen­Dice coefficient values of bladder and rectum were 0.89±0.04 and 0.79±0.06 respectively. The maximum dose differences for CTV and PTV were 2.5% and -4.7% and minimum were 0.1% and 0.1% respectively. Conclusion: The adapted planning CT obtained from daily imaging using aSi-kVCBCT and SmartAdapt® can be used as an effective tool to estimate the volume changes and dose difference in prostate radiotherapy.

Magnetic resonance image guidance in external beam radiation therapy planning and delivery.

The use of magnetic resonance (MR) imaging in radiation oncology is improving dramatically. This review article discusses the necessity of image guidance and how MR finds a significant place in radiotherapy planning and delivery. The challenges to and current solutions for an in-house MR simulation, dedicated MR simulator, estimation of electron density using MR image sets and development of MR-compatible treatment planning systems are presented. This article also reviews the feasibility, advantages and limitations of MR image-guided radiation therapy (MR-IGRT) and its drive toward the integration of radiation beams with MR technology. Specifications of Co-60 MR technology and three other MR-linac projects worldwide are presented. Online and real-time MR guidance is also discussed.

Is 5 mm MMLC suitable for VMAT-based lung SBRT? A dosimetric comparison with 2.5 mm HDMLC using RTOG-0813 treatment planning criteria for both conventional and high-dose flattening filter-free photon beams.

The aim of this study is to assess the suitability of 5 mm millennium multileaf collimator (MMLC) for volumetric-modulated arc therapy (VMAT)-based lung stereotactic body radiotherapy (SBRT). Thirty lung SBRT patient treatment plans along with their planning target volumes (ranging from 2.01 cc to 150.11 cc) were transferred to an inhomogeneous lung phantom and retrospectively planned using VMAT technique, along with the high definition multileaf collimator (HDMLC) and MMLC systems. The plans were evaluated using Radiation Therapy Oncology Group (RTOG-0813) treatment planning criteria for target coverage, normal tissue sparing, and treatment efficiency for both the MMLC and HDMLC systems using flat and flattening filter-free (FFF) photon beams. Irrespective of the target volumes, both the MLC systems were able to satisfy the RTOG-0813 treatment planning criteria without having any major deviation. Dose conformity was marginally better with HDMLC. The average conformity index (CI) value was found to be 1.069 ± 0.034 and 1.075 ± 0.0380 for HDMLC and MMLC plans, respectively. For the 6 MV FFF beams, the plan was slightly more conformal, with the average CI values of 1.063 ± 0.029 and 1.073 ± 0.033 for the HDMLC and MMLC plans, respectively. The high dose spillage was the maximum for 2 cc volume set (3% for HDMLC and 3.1% for MMLC). In the case of low dose spillage, both the MLCs were within the protocol of no deviation, except for the 2 cc volume set. The results from this study revealed that VMAT-based lung SBRT using 5 mm MMLC satisfies the RTOG-0813 treatment planning criteria for the studied target size and shapes.

Feasibility study of deep inspiration breath-hold based volumetric modulated arc therapy for locally advanced left sided breast cancer patients.

BACKGROUND: The purpose of this study was to assess the feasibility of deep inspiration breath-hold (DIBH) based volumetric modulated arc therapy (VMAT) for locally advanced left sided breast cancer patients undergoing radical mastectomy. DIBH immobilizes the tumor bed providing dosimetric benefits over free breathing (FB). MATERIALS AND METHODS: Ten left sided post mastectomy patients were immobilized in a supine position with both the arms lifted above the head on a hemi-body vaclock. Two thermoplastic masks were prepared for each patient, one for normal free breathing and a second made with breath-hold to maintain reproducibility. DIBH CT scans were performed in the prospective mode of the Varian real time position management (RPM) system. The planning target volume (PTV) included the left chest wall and supraclavicular nodes and PTV prescription dose was 5000cGy in 25 fractions. DIBH-3DCRT planning was performed with the single iso-centre technique using a 6MV photon beam and the field-in-field technique. VMAT plans for FB and DIBH contained two partial arcs (179o-300oCCW/CW). Dose volume histograms of PTV and OAR's were analyzed for DIBH-VMAT, FB-VMAT and DIBH-3DCRT. In DIBH mode daily orthogonal (0o and 90o) KV images were taken to determine the setup variability and weekly twice CBCT to verify gating threshold level reproducibility. RESULTS: DIBH-VMAT reduced the lung and heart dose compared to FB-VMAT, while maintaining similar PTV coverage. The mean heart V30Gy was 2.3% ±2.7, 5.1% ±3.2 and 3.3% ±7.2 and for left lung V20Gy was 18.57% ±2.9, 21.7% ±3.9 and 23.5% ±5.1 for DIBH-VMAT, FB-VMAT and DIBH-3DCRT respectively. CONCLUSIONS: DIBH-VMAT significantly reduced the heart and lung dose for left side chest wall patients compared to FB-VMAT. PTV conformity index, homogeneity index, ipsilateral lung dose and heart dose were better for DIBH-VMAT compared to DIBH-3DCRT. However, contralateral lung and breast volumes exposed to low doses were increased with DIBH-VMAT.

Critical appraisal of the accuracy of Acuros-XB and Anisotropic Analytical Algorithm compared to measurement and calculations with the compass system in the delivery of RapidArc clinical plans.

BACKGROUND: The accuracy of the two dose calculation engines available for RapidArc planning (both released for clinical use) is investigated in comparison to the COMPASS data. METHODS: Two dose calculation algorithms (Acuros-XB and Anisotropic Analytic Algorithm (AAA)) were used to calculate RA plans and compared to calculations with the Collapsed Cone Convolution algorithm (CC) from the COMPASS system (IBA Dosimetry). CC calculations, performed on patient data, are based on experimental fluence measurements with a 2D array of ion chambers mounted on the linac head. The study was conducted on clinical cases treated with RA. Five cases for each of the following groups were included: Brain, Head and Neck, Thorax, Pelvis and stereotactic body radiation therapy for hypo-fractionated treatments with small fields. COMPASS measurements were performed with the iMatrixx-2D array. RapidArc plans were optimized for delivery using 6MV photons from a Clinac-iX (Varian, Palo Alto, USA). RESULTS: For almost all parameters, the better agreement was between Acuros-XB and COMPASS independently from the anatomical site and fractionation. The same result was obtained from the mean dose difference per organ with Acuros-CC average differences below 0.5% while for AAA-CC data, average deviations exceeded 0.5% and in the case of the pelvis 1%. Relevance of observed differences determined with the 3D gamma analysis resulted in a pass rate exceeding 99.5% for Acuros-CC and exceeding 97.5% for AAA-CC. CONCLUSIONS: This study demonstrated that i) a good agreement exists between COMPASS-CC calculations based on measured fluences with respect to dose distributions obtained with both Acuros-XB and AAA algorithms; ii) 3D dose distributions reconstructed from actual delivery coincide very precisely with the planned data; iii) a slight preference in favor of Acuros-XB was observed suggesting the preference for this algorithm in clinical applications.

Objectifying specific and nonspecific effects of acupuncture: a double-blinded randomised trial in osteoarthritis of the knee.

Introduction. Acupuncture was recently shown to be effective in the treatment of knee osteoarthritis. However, controversy persists whether the observed effects are specific to acupuncture or merely nonspecific consequences of needling. Therefore, the objective of this study is to determine the efficacy of different acupuncture treatment modalities. Materials and Methods. We compared between three different forms of acupuncture in a prospective randomised trial with a novel double-blinded study design. One-hundred and sixteen patients aged from 35 to 82 with osteoarthritis of the knee were enrolled in three study centres. Interventions were individualised classical/ modern semistandardised acupuncture and non-specific needling. Blinded outcome assessment comprised knee flexibility and changes in pain according to the WOMAC score. Results and Discussion. Improvement in knee flexibility was significantly higher after classical Chinese acupuncture (10.3 degrees; 95% CI 8.9 to 11.7) as compared to modern acupuncture (4.7 degrees; 3.6 to 5.8). All methods achieved pain relief, with a patient response rate of 48 percent for non-specific needling, 64 percent for modern acupuncture, and 73 percent for classical acupuncture. Conclusion. This trial establishes a novel study design enabling double blinding in acupuncture studies. The data suggest a specific effect of acupuncture in knee mobility and both non-specific and specific effects of needling in pain relief.