ABSTRACT
PURPOSE: In external beam radiotherapy, the presence of metal implants such as hip prostheses causes significant streak artifacts in planning images, thus affecting the accuracy of target and critical organ delineation. The purpose of this study is to evaluate the improvement of image quality and impact on accuracy of dose calculation by using a commercially available metal artifact reduction (MAR) algorithm. METHODS: Nine patients were selected for this study, including 5 patients with unilateral hip prostheses for orthopedic irradiation, and 4 patients with unilateral or bilateral hip prostheses for prostate cancer treatment. For each patient, simulation CT image was reconstructed with and without MAR correction. Contours of the prostate, bladder and rectum were delineated on both images by an experienced physician for the prostate patients. The difference of contours between MAR corrected and un-corrected images was quantified by an overlap index, and dose calculation accuracy was evaluated for both target and critical organs. RESULTS: For orthopedic patients, dose difference between MAR corrected and un-corrected images was negligible: 0.1±0.1% for maximum dose and 0.8±1.8% for dose at isocenter. For prostate patients, no significant dosimetric difference was observed between MAR corrected and un-corrected images if same contours were used in the treatment planning. For the PTV, the average dose variation in D99 was 0.9±0.6%. The dose differences in D50 of the bladder and rectum were 1.0±0.8% and 0.4±0.3%, respectively. The average overlap index of prostate between the two images was 0.86±0.12 for patients with bilateral hip replacements. Substantial changes in the dose-volume-histograms were observed if different contours were used in the treatment planning. CONCLUSIONS: The commercial MAR algorithm can improve the image quality dramatically and the MAR corrected images do not affect dose calculation accuracy. The improvement of accuracy in organ delineation provides significant dosimetric advantage. Philips Healthcare.
ABSTRACT
PURPOSE: The purpose of this work is to evaluate the accuracy of a three-dimensional surface based optical imaging device for treatment setup of breast patients. A commercial system has been used to acquire live surface contour data, which are registered with a reference surface contour for setup corrections. This work is to investigate the accuracy of this system when compared with conventional portal images. METHODS: The system was clinically applied to twenty breast cancer patients receiving radiotherapy treatment. For each patient, conventional portal imaging before the first fraction was acquired and approved by clinicians. After approval of portal images, a reference surface contour was acquired. This reference contour was subsequently used to guide daily patient setup followed by weekly portal images. A total of 89 sets of portal images were acquired for these patients. On days when portal images were taken, optical images were used to guide for initial patient setup, then portal images were taken and evaluated in order to make direct comparison between the optical imaging system and the conventional portal images. RESULTS: Among 89 sets of portal images taken after optical imaging guidance, 11 (12%) sets of portal images required further adjustments in order to achieve clinically acceptable criteria. The average vector adjustments for these 11 fractions were 0.65 cm ± 0.30 cm. Average vector shifts made according to the optical imaging for all fractions of 20 patients was 0.66 ± 0.33 cm. CONCLUSIONS: Our data show that the commercial optical system can improve the accuracy of treatment setup for breast patients without additional radiation exposure. The observed discrepancy between the portal images and optimal images requires further investigation. The optical imaging guidance can be routinely used between normally scheduled portal imaging.
ABSTRACT
PURPOSE: Stereotactic body radiotherapy has been an efficacious treatment modality for early stage non-small cell lung cancer. The accuracy of dose calculations is in question due to the presence of inhomogeneity. It was required in several clinical trials to calculate dose without heterogeneity correction. However, to better correlate the outcomes with the planned dose, accurate dose calculation with heterogeneity correction is highly desirable. METHODS: We compared the recalculated dose with Monte Carlo (MC) algorithm to the original Pencil Beam (PB) calculations for clinical lung SBRT plans. Thirty-one clinical plans that followed protocol guidelines were retrospectively investigated. Dosimetric parameters D1, D95 and D99 for the PTV and D1 for organs at risk were compared. Correlations of mean lung dose and V20 of lungs between two calculations were investigated. RESULTS: Compared to the PB calculations without heterogeneity correction in clinical plans, we found that in terms of D95 of PTV, (1) the two calculations resulted in similar D95 for edge tumors with volumes greater than 25.1cc; (2) an average overestimation of 5% in PB calculations for edge tumors with volumes less than 25.1cc; and (3) an average overestimation of 9% or underestimation of 3% in PB calculations for island tumors with volumes smaller or greater than 22.6 cc, respectively. With heterogeneity correction, the PB calculation resulted in an average reduction of 23.8% and 15.3% in D95 for island and edge lesions respectively compared to the MC calculation. For organs at risks, no clinical meaningful differences were found among all the comparisons. Excellent correlations for mean dose and V20 of lungs were observed between the two calculations. CONCLUSIONS: Using a single scaling factor to account for the differences in using heterogeneity correction may not be sufficient. To understand dose-response relation in Lung SBRT, accurate dose calculation such as the Monte Carlo algorithms is highly recommended.
ABSTRACT
PURPOSE: To complete a CBCT for a treatment using ABC, multiple breath hold (BH) (>3) were used due to the slow gantry rotation and the short BH period. Inter-BH tumor position variability may introduce distortion in the reconstructed images. This study aims to determine a threshold of the inter-BH scan displacement so that the inconsistency can be identified from the CBCT images. METHODS: A numerical phantom was constructed to represent the thorax region of a human body. To simulate the inter-BH displacements, known magnitudes of motion (s = 0, 1, 3, 5 mm) along the longitudinal direction were introduced for the 'tumor' and 'diaphragm' in the phantom. Two different irregular motion patterns (s1=s3=/=s2 and s1=/=s2=/=s3) during CBCT scans were tested. Furthermore, a physical phantom with a movable insert was scanned using a commercial CBCT system. The insert of the phantom was programmed to move in the longitudinal direction according to the same motion patterns as designed in the numerical simulations. Subsequently, nine CBCT's in 'half-fan' mode for the physical phantom were acquired with the insert in various positions. These CBCT images were then fused to the reference CT by aligning to either the body of the phantom or the 'tumor' inside the insert. RESULTS: Based on numerical simulation, position variation >1mm can be observed from the reconstructed CBCT images. Based on acquired CBCTs of the physical phantom, position variations of >3mm or 5mm were observed, depending on the motion pattern during the data acquisition. Because of the use of half-fan mode, we observed the order of position displacements of the tumor during CBCT acquisition drastically affected the outcome of imaging registration. CONCLUSIONS: Using ABC device, the inter-BH variability during a CBCT acquisition affects accuracy of tumor localization. A patient individualized planning margin might be necessary to account for this effect.
ABSTRACT
A retrospective randomized paired study was performed of 200 electively induced labor by means of artificial rupture of membranes and oxytocin infusion and 200 spontaneous labor. It was found that labor length was significantly shorter (p < 0.5) in the study group tan the control group (2.02 +/- 3 h and 6.2 +/- 3 h respectively). Delivery was accomplished in the majority of the induced group (50.2%) between 12:00 and 17:59 h (p < 0.001), while in the control group it occurred randomly during the 24 hours (p > 0.05).
