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Deformable Contour Propagation in Adaptive Replanning for Cancers of the Head and Neck
Poster Viewing Abstracts S709
Volume 87 Number 2S Supplement 2013 The dosimetric impact of IC is smaller compared to EC, and is less dependent on arc length. Author Disclosure: J. Ye: None. H. Liu: None. J. Kim: None. J. Deng: None. Z. Chen: None.
3324 Optimizing CT Acquisition for Prostate Cancer Radiation Treatment Planning and Delivery G. Chen, A. Tai, F. Liu, C. Lawton, and A. Li; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): CT acquisition protocols are usually established based on diagnostic purpose with major emphasis on imaging dose, thus, are not necessarily optimized for radiation therapy (RT) planning and delivery, where slightly increased imaging dose in exchange for improved soft tissue contrast may be justified (e.g., prostate SBRT). In this work, we investigate the impact of CT data acquisition parameters on image quality for treatment planning and delivery guidance in prostate cancer RT. Materials/Methods: A CT scanner installed inside a linac room (i.e., CTon-rails) was used. Various CT acquisition parameters (e.g., tube voltage and current, rotation time, pitch, imaging dose control methods) and reconstruction algorithms were first tested on a phantom then on patients. A cylindrical phantom 32 cm in diameter with two plugs of relative electron densities of 1.05 and 0.96 was scanned using a predefined CT protocol (120 kVp, 250 mAs, CareDose off) routinely used for daily IGRT of prostate RT. This protocol leads to a CTDIvol of 17 mGy for a typical prostate case. The phantom was scanned with a series of customized protocols with different parameter sets (e.g., tube voltage of 100, 120, 130 and 140 kVp with effective exposure of 250-1800 mAs). The phantom images obtained were compared and evaluated, and a set of parameters that results in optimal image quality (soft tissue contrast) was used to create an image quality enhancement protocol (IQEP) which was then used to scan selected prostate cancer patients as a part of their regular IGRT procedure. For each patient, no more than two sets of CTs were acquired using the IQEP. The CT data were reconstructed using various available reconstruction algorithms from the vendor. The image quality of the obtained CTs was assessed with (1) accuracy and reproducibility of auto-segmentation for the prostate gland using a tool and (2) intra- and inter-variability of manual contouring of the prostate gland by 10 observers. Results: The phantom data shows that the contrast to noise ratio (CNR) increased with appropriate combinations of mAs and kVp. The dose weighted CNR peaked around 1000 mAs with 120 kVp for the 1.05 electron density plug and 100 kVp for the 0.96 electron density plug. kVp < 100 increased imaging noise. Visual inspection of the CTs obtained with IQEP of 100 kVp and 987 mAs (a CTDIvol of around 50 mGy) showed improved visibility of the prostate gland boundary. This improvement was supported by the reduced intra- and inter-variability of manual contouring. Conclusions: The CT protocols may be optimized for radiation therapy to improve soft tissue contrast, thus, improving the accuracy of target/organ delineation and treatment delivery. If the optimized protocol is used with in-room CT for IGRT, the slightly increased imaging dose is comparable to other IGRT modalities. Author Disclosure: G. Chen: None. A. Tai: None. F. Liu: None. C. Lawton: None. A. Li: None.
3325 Deformable Contour Propagation in Adaptive Replanning for Cancers of the Head and Neck J. Pasha, J.L. Ducote, V. Sehgal, P. Daroui, J.V. Kuo, N.S. Ramsinghani, and J.C. Wong; University of California, Irvine, Orange, CA Purpose/Objective(s): To assess the utility of deformable image registration and automatic re-contouring of target volumes in the head and neck for adaptive re-planning.
Materials/Methods: All head and neck cancer patients who underwent adaptive re-planning over the past one year at our institution were identified and included in this retrospective study. All patients had an initial planning CT scan and one additional re-planning CT scan done at a subsequent time during the course of radiation therapy for adaptive replanning purposes. Indications for re-planning were based on any change in the patient’s anatomy during the course of radiation treatment such as a significant tumor response or weight loss. All plans were contoured by the same physician (JP), and volumes contoured included the GTV and elective lymph node regions on both the initial planning CT scan as well as on the re-planning CT scan. Subsequently, a multi-modality image registration and contouring software was used to deformably propagate contours from initial planning CT scan to the re-planning CT scan. The software-propagated contours were then compared with the physiciandrawn contours using the Dice Similarity Coefficient (DSC). Results: Twelve patients (six male and six female) with various head and neck cancers were identified for this study. The patients’ had the following tumor types: tonsillar carcinoma (4), base of tongue carcinoma (3), thyroid carcinoma (1), maxillary sinus carcinoma (1), soft palate carcinoma (1), lymphoma (1) and nasopharyngeal carcinoma (1). The median overall DSC value for both the Gross Tumor Volumes (GTV) and elective nodal volumes was 0.771. The median DSC computed separately for the GTV and nodal volumes was 0.722 and 0.797 respectively. It has been suggested in literature that a DSC value greater than 0.700 in is indicative of a good overlap. Our findings of an overall DSC value of 0.771 are in agreement with results described in the literature. Conclusions: The results of this study suggest that contours derived from prior scans of the same patient may be reliably propagated to the replanning CT scan. The approach used in this study obviates the need for a large patient database as used in current atlas- based automatic segmentation modules. Author Disclosure: J. Pasha: None. J.L. Ducote: None. V. Sehgal: None. P. Daroui: None. J.V. Kuo: None. N.S. Ramsinghani: None. J.C. Wong: None.
3326 Adaptive Dose Recalculation and In Vivo Dosimetry as Clinical Tools to Tailor Daily IGRT: Experience After 100,000 Fractions Delivered G. Olivera,1 W. Lu,1 D. Parnell,1 X. Mo,1 M. Chen,1 D. Dsoretz,2 S.E. Finkelstein,3 E. Fernandez,4 C. Mantz,2 and D. Galmarini2; 121st Century Oncology, Madison, WI, 221st Century Oncology, Fort Myers, FL, 3 21st Century Oncology, Scottsdale, AZ, 421st Century Oncology, Plantation, FL Purpose/Objective(s): In our network of radiation therapy clinics distributed over multiple states, over 2,300 treatment fractions are delivered daily. To serve the Quality Assurance needs of this widespread, high volume network, we concluded that automatic tools to assess treatment delivery quality are paramount. Therefore, an in-house system operating in the background of normal clinic workflows was developed to flag and evaluate treatment quality during delivery using in vivo verification (IV), in vivo dosimetry (ID) and adaptive dose recalculation (ADR). The system’s flagging function prompts different actions from medical physics, physicians, dosimetrists and therapists. Herein, we summarize the result of this system for approximately 100,000 daily fractions delivered using linear accelerators (LA) and tomotherapy (TT). Materials/Methods: In vivo verification at the treatment time is performed via accessing sensors/detectors from LA and TT to compare planned values to the actual reading during treatment delivery. The exit detector is used to perform ID and dose reconstruction. Adaptive dose recalculation is now being performed for some of the anatomical sites by computing the dose on the daily setup CT (whenever available). Daily contours sets are generated using deformable registration and doses are accumulated by warping daily doses to the planning CT using deformation vectors fields.
Volume 87 Number 2S Supplement 2013 The dosimetric impact of IC is smaller compared to EC, and is less dependent on arc length. Author Disclosure: J. Ye: None. H. Liu: None. J. Kim: None. J. Deng: None. Z. Chen: None.
3324 Optimizing CT Acquisition for Prostate Cancer Radiation Treatment Planning and Delivery G. Chen, A. Tai, F. Liu, C. Lawton, and A. Li; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): CT acquisition protocols are usually established based on diagnostic purpose with major emphasis on imaging dose, thus, are not necessarily optimized for radiation therapy (RT) planning and delivery, where slightly increased imaging dose in exchange for improved soft tissue contrast may be justified (e.g., prostate SBRT). In this work, we investigate the impact of CT data acquisition parameters on image quality for treatment planning and delivery guidance in prostate cancer RT. Materials/Methods: A CT scanner installed inside a linac room (i.e., CTon-rails) was used. Various CT acquisition parameters (e.g., tube voltage and current, rotation time, pitch, imaging dose control methods) and reconstruction algorithms were first tested on a phantom then on patients. A cylindrical phantom 32 cm in diameter with two plugs of relative electron densities of 1.05 and 0.96 was scanned using a predefined CT protocol (120 kVp, 250 mAs, CareDose off) routinely used for daily IGRT of prostate RT. This protocol leads to a CTDIvol of 17 mGy for a typical prostate case. The phantom was scanned with a series of customized protocols with different parameter sets (e.g., tube voltage of 100, 120, 130 and 140 kVp with effective exposure of 250-1800 mAs). The phantom images obtained were compared and evaluated, and a set of parameters that results in optimal image quality (soft tissue contrast) was used to create an image quality enhancement protocol (IQEP) which was then used to scan selected prostate cancer patients as a part of their regular IGRT procedure. For each patient, no more than two sets of CTs were acquired using the IQEP. The CT data were reconstructed using various available reconstruction algorithms from the vendor. The image quality of the obtained CTs was assessed with (1) accuracy and reproducibility of auto-segmentation for the prostate gland using a tool and (2) intra- and inter-variability of manual contouring of the prostate gland by 10 observers. Results: The phantom data shows that the contrast to noise ratio (CNR) increased with appropriate combinations of mAs and kVp. The dose weighted CNR peaked around 1000 mAs with 120 kVp for the 1.05 electron density plug and 100 kVp for the 0.96 electron density plug. kVp < 100 increased imaging noise. Visual inspection of the CTs obtained with IQEP of 100 kVp and 987 mAs (a CTDIvol of around 50 mGy) showed improved visibility of the prostate gland boundary. This improvement was supported by the reduced intra- and inter-variability of manual contouring. Conclusions: The CT protocols may be optimized for radiation therapy to improve soft tissue contrast, thus, improving the accuracy of target/organ delineation and treatment delivery. If the optimized protocol is used with in-room CT for IGRT, the slightly increased imaging dose is comparable to other IGRT modalities. Author Disclosure: G. Chen: None. A. Tai: None. F. Liu: None. C. Lawton: None. A. Li: None.
3325 Deformable Contour Propagation in Adaptive Replanning for Cancers of the Head and Neck J. Pasha, J.L. Ducote, V. Sehgal, P. Daroui, J.V. Kuo, N.S. Ramsinghani, and J.C. Wong; University of California, Irvine, Orange, CA Purpose/Objective(s): To assess the utility of deformable image registration and automatic re-contouring of target volumes in the head and neck for adaptive re-planning.
Materials/Methods: All head and neck cancer patients who underwent adaptive re-planning over the past one year at our institution were identified and included in this retrospective study. All patients had an initial planning CT scan and one additional re-planning CT scan done at a subsequent time during the course of radiation therapy for adaptive replanning purposes. Indications for re-planning were based on any change in the patient’s anatomy during the course of radiation treatment such as a significant tumor response or weight loss. All plans were contoured by the same physician (JP), and volumes contoured included the GTV and elective lymph node regions on both the initial planning CT scan as well as on the re-planning CT scan. Subsequently, a multi-modality image registration and contouring software was used to deformably propagate contours from initial planning CT scan to the re-planning CT scan. The software-propagated contours were then compared with the physiciandrawn contours using the Dice Similarity Coefficient (DSC). Results: Twelve patients (six male and six female) with various head and neck cancers were identified for this study. The patients’ had the following tumor types: tonsillar carcinoma (4), base of tongue carcinoma (3), thyroid carcinoma (1), maxillary sinus carcinoma (1), soft palate carcinoma (1), lymphoma (1) and nasopharyngeal carcinoma (1). The median overall DSC value for both the Gross Tumor Volumes (GTV) and elective nodal volumes was 0.771. The median DSC computed separately for the GTV and nodal volumes was 0.722 and 0.797 respectively. It has been suggested in literature that a DSC value greater than 0.700 in is indicative of a good overlap. Our findings of an overall DSC value of 0.771 are in agreement with results described in the literature. Conclusions: The results of this study suggest that contours derived from prior scans of the same patient may be reliably propagated to the replanning CT scan. The approach used in this study obviates the need for a large patient database as used in current atlas- based automatic segmentation modules. Author Disclosure: J. Pasha: None. J.L. Ducote: None. V. Sehgal: None. P. Daroui: None. J.V. Kuo: None. N.S. Ramsinghani: None. J.C. Wong: None.
3326 Adaptive Dose Recalculation and In Vivo Dosimetry as Clinical Tools to Tailor Daily IGRT: Experience After 100,000 Fractions Delivered G. Olivera,1 W. Lu,1 D. Parnell,1 X. Mo,1 M. Chen,1 D. Dsoretz,2 S.E. Finkelstein,3 E. Fernandez,4 C. Mantz,2 and D. Galmarini2; 121st Century Oncology, Madison, WI, 221st Century Oncology, Fort Myers, FL, 3 21st Century Oncology, Scottsdale, AZ, 421st Century Oncology, Plantation, FL Purpose/Objective(s): In our network of radiation therapy clinics distributed over multiple states, over 2,300 treatment fractions are delivered daily. To serve the Quality Assurance needs of this widespread, high volume network, we concluded that automatic tools to assess treatment delivery quality are paramount. Therefore, an in-house system operating in the background of normal clinic workflows was developed to flag and evaluate treatment quality during delivery using in vivo verification (IV), in vivo dosimetry (ID) and adaptive dose recalculation (ADR). The system’s flagging function prompts different actions from medical physics, physicians, dosimetrists and therapists. Herein, we summarize the result of this system for approximately 100,000 daily fractions delivered using linear accelerators (LA) and tomotherapy (TT). Materials/Methods: In vivo verification at the treatment time is performed via accessing sensors/detectors from LA and TT to compare planned values to the actual reading during treatment delivery. The exit detector is used to perform ID and dose reconstruction. Adaptive dose recalculation is now being performed for some of the anatomical sites by computing the dose on the daily setup CT (whenever available). Daily contours sets are generated using deformable registration and doses are accumulated by warping daily doses to the planning CT using deformation vectors fields.