International Journal of Radiation Oncology*Biology*Physics, 2009
Results: Although lung exhibited significant motion, the markers showed limited motion on fluoros... more Results: Although lung exhibited significant motion, the markers showed limited motion on fluoroscopy. The average marker motion on the fluoroscopy was 0.4 mm (range 0-2), 1.6 mm (0-4), and 1.6 mm (0-3) in LR, AP, and SI, respectively. Over a typical 6-minute treatment time, in LR, AP and SI directions, the average motion (. 120 fractions) was 1.3 mm (0-17), 1.1 mm (0-6) and 1 mm (0-11) based on bony matching, and were 3.5 mm (0-25), 2 mm (0-11), and 2 mm (0-18) based on the markers. The CBCT dosimetry analysis showed the CTV was adequately covered with both matching methods, indicating the current margin size is sufficient. On the other hand, the computational motion simulation showed that marker based setup reduced the planning margin. Conclusions: Breathing has limited effect on the TV motion during APBI. Seroma exhibits larger motion than what is otherwise believed based on bony matching. A seroma specific marker based or image registration based approach holds the potential to reduce margin size. As more patients are enrolled into this study, more definitive conclusions can be drawn for the magnitudes of both intra-fractional motion and planning margin reduction.
International Journal of Radiation Oncology*Biology*Physics, 2013
Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT V.J. Gonzalez, C. ... more Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT V.J. Gonzalez, C. Hullett, L. Burt, P. Rassiah-Szegedi, V. Sarkar, J.D. Tward, L.J. Hazard, J.Y. Huang, B.J. Salter, and D.K. Gaffney; Department of Radiation Oncology, University of Arizona, Tucson, AZ, College of Medicine, University of Arizona, Tucson, AZ, Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, Center for Neurosciences, Tucson, AZ
Purpose: 4D CT is now widely used in radiation therapy for generating accurate ITV's or for f... more Purpose: 4D CT is now widely used in radiation therapy for generating accurate ITV's or for facilitation of gated treatmentdelivery. It is, as yet, relatively unexplored for use as a potential tool for image guidance of SBRT of lung. Use of 4D imaging for image guidance in SBRT requires that we determine an acceptable method for fusing 2 4D data sets.Method and Materials: We compare five different manual and/or automatic 4D registration methods and present the comparison results for phantom and patient data: Individual phase‐to‐phase registration; Average of phase to phase; MIP‐to‐MIP; Average Intensity Projection; Auto‐segmentation with centroid; Manual GE SimMD methods. Phantom studies were performed using the CIRS Dynamic Thorax phantom (CIRS, Norfolk, VA). A 2‐cm target was set into motion with a periodic sinusoidal 3D motion inside the anthropomorphic phantom. The baseline motion envelope of the target for simulation day movement was 4.2 mm L/R, 6.0 mm A/P, and 14.0 mm I/S. The target was then re‐programmed to move with the same motion envelope, but shifted away from the simulation motion envelope centroid, for three scenarios: a) Axial (L/R and A/P) only shift; b) Longitudinal only shift; and c) combination of axial (L/R & A/P) and longitudinal shift. Results: Individual phase‐to‐phase fusions were within 2.4 mm for all phases, with some phases performing better than others. The average and AIP methods were seen to perform very similarly, and this seems reasonable when we consider that both are, essentially, averaging methods. The MIP‐to‐MIP and Manual fusion methods were least accurate, but still likely to be considered clinically acceptable. Conclusion: Multiple methods have been explored for registration of 2 4D data sets. The averaging methods were seen to perform best, but all performed within what would reasonably be considered clinically acceptable limits. The centroid method performed particularly well.
PURPOSE To present the techniques and preliminary outcomes of ultrasound-based image-guided inten... more PURPOSE To present the techniques and preliminary outcomes of ultrasound-based image-guided intensity-modulated radiotherapy (IG-IMRT) for pancreatic cancer. MATERIALS AND METHODS Retrospective analysis of 41 patients treated between November 2000 and March 2005 with IG-IMRT to mean total doses of 55 Gy (range, 45-64 Gy). We analyzed the clinical feasibility of IG-IMRT, dosimetric parameters, and outcomes, including acute gastrointestinal toxicity (RTOG grading). Survival was assessed for adenocarcinoma (n = 35) and other histologies. RESULTS Mean daily image-guidance corrective shifts were 4.8 +/- 4.3 mm, 7.5 +/- 7.2 mm, and 4.6 +/- 5.9 mm along the x-, y-, and z-axes, respectively (mean 3D correction vector, 11.7 +/- 8.4 mm). Acute upper gastrointestinal toxicity was grade 0-1 in 22 patients (53.7%), grade 2 in 16 patients (39%), and grade 3 in 3 patients (7.3%). Lower gastrointestinal toxicity was grade 0-1 in 32 patients (78%), grade 2 in 7 patients (17.1%), and grade 4 in 2 patients (4.9%). Treatment was stopped early in 4 patients following administration of 30 to 54 Gy. Median survival for adenocarcinoma histology was 10.3 months (18.6 months in patients alive at analysis; n = 8) with actuarial 1- and 2-year survivals of 38% and 25%, respectively. CONCLUSION Daily image-guidance during delivery of IMRT for pancreatic carcinoma is clinically feasible. The data presented support the conclusion that safety margin reduction and moderate dose escalation afforded by implementation of these new radiotherapy technologies yields preliminary outcomes at least comparable with published survival data.
Radiosurgery is a non-invasive alternative to brain surgery that uses a single focused applicatio... more Radiosurgery is a non-invasive alternative to brain surgery that uses a single focused application of high radiation to destroy intracerebral target tissues. A Gamma Knife delivers such treatments by using 201 cylindrically collimated cobalt-60 sources that are arranged in a hemispherical pattern and aimed to a common focal point. The accumulation of radiation at the focal point, called a “shot” due to the spherical nature of the dose distribution, is used to ablate (or destroy) target tissue in the brain. If the target is small and spherical, it is easily treated by choosing one of four available collimators (4, 8, 14, or 18 mm). For large, irregular targets, multiple shots are typically required to treat the entire lesion, and the process of determining the optimal arrangement and number of shots is complex. In this research, fast simulated annealing and a novel objective function are used to investigate the relationship between the number of shots and the quality of the resulting...
Purpose: Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siem... more Purpose: Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siemens' DirectDensity™ (DD) reconstruction algorithm, which allows scans of any kV setting to use the same calibration. This study demonstrates why DD scans should not be used in combination with DECT and quantifies the magnitude of potential errors in image quality and dose. Methods: A CatPhan 504 phantom was scanned with a dual-pass DECT and reconstructed with many different kernels, including several DD kernels. The HU values of various inserts were measured. The RANDO ® man phantom was also scanned. Bone was contoured and then histograms of the bone HU values were analyzed for Filtered-Backprojection (FBP) and DD reconstructions of the 80 and 140 kV scans, as well as several virtual, monoenergetic reconstructions generated from FBP and DD reconstructions. "Standard" dose distributions were calculated on several reconstructions of both phantoms for comparison. Results: The DD kernel overcorrected the high-Z material inserts relative to bone, giving an excessively low relative electron density (RED). A unique artifact was observed in the high density inserts of the CatPhan in the monoenergetic scans when utilizing a DD kernel, due to the overcorrection in the DD scan of the material, especially at lower kV. Conclusions: While DD and DECT perform as expected when used independently, errors from their combined use were demonstrated. Dose errors from misuse of the DD kernel with DECT post-processing were as large as 2.5%. The DECT post-processing was without value because the HU differences between low and high energy were removed by the DD kernel. When using DD and DECT, we recommend the use of a DD reconstruction of the high energy scan for the dose calculation, and use of a FBP filter for the low and high energy scans for the DECT postprocessing.
Abdominal compression has been shown to reduce the extent of lung tumor motion but the dosimetric... more Abdominal compression has been shown to reduce the extent of lung tumor motion but the dosimetric impact of the approach is still in need of investigation. The current work analyzes the impact of various changes in PTV volume on key metrics of the final dose distribution to normal lung. To add clinical perspective, we also provide NTCP calculations for grade 2+ pneumonitis for each case. For a total of seventeen cases, the original ITV/PTV was reduced by systematically varied amounts and SBRT plans using dynamic conformal arc and VMAT techniques were created. DVH analysis for the normal lung comparing the original plan to the one with the ITV reduced by up to 10 mm shows that the average reduction of V5, V20 and mean lung dose is 3.8%, 2.0% and 1.1 Gy, respectively, for the conformal arc plans. Corresponding values for the VMAT plans were 3.9%, 1.9% and 1.2 Gy respectively. The mean NTCP drop for the conformal arc plans was 2.0% while it was 1.9% for the VMAT plans. These results su...
Multiple commercial phantoms are now available for performing end-to-end QA testing for stereotac... more Multiple commercial phantoms are now available for performing end-to-end QA testing for stereotactic procedures. This project aims at directly comparing one of the newest phantoms on the market against a more established one by performing similar tests to determine whether results are similar and they can be used interchangeably. Both phantoms were used to evaluate the coincidence of radiation and laser isocenters of a linear accelerator. End-to-end dosimetric tests were also performed using both an ion chamber and film. As part of the testing, both phantoms were also evaluated in terms of their efficiency of setup as well as the time required to switch inserts for different tests. Results showed that the laser/radiation isocenter coincidence as determined from each phantom was highly correlated. Ion chamber results were within 0.5% of the expected values. Gamma (2%, 2mm) pass rates of corresponding films were within 2% between phantoms. These results show that both phantoms are cap...
This is a proof-of-principle study investigating the feasibility of using late gadolinium enhance... more This is a proof-of-principle study investigating the feasibility of using late gadolinium enhancement magnetic resonance imaging (LGE-MRI) to detect left atrium (LA) radiation damage. Methods and materials: LGE-MRI data were acquired for 7 patients with previous external beam radiation therapy (EBRT) histories. The enhancement in LA scar was delineated and fused to the computed tomography images used in dose calculation for radiation therapy. Dosimetric and normal tissue complication probability analyses were performed to investigate the relationship between LA scar enhancement and radiation doses. Results: The average LA scar volume for the subjects was 2.5 cm 3 (range, 1.2-4.1 cm 3 ; median, 2.6 cm 3). The overall average of the mean dose to the LA scar was 25.9 Gy (range, 5.8-49.2 Gy). Linear relationships were found between the amount of radiation dose (mean dose) (R 2 Z 0.8514, P Z .03) to the LA scar-enhanced volume. The ratio of the cardiac tissue change (LA scar/LA wall) also demonstrated a linear relationship with the level of radiation received by the cardiac tissue (R 2 Z 0.9787, P < .01). Last, the normal tissue complication probability analysis suggested a dose response function to the LA scar enhancement. Conclusions: With LGE-MRI and 3-dimensional dose mapping on the treatment planning system, it is possible to define subclinical cardiac damage and distinguish intrinsic cardiac tissue change from radiation induced cardiac tissue damage. Imaging myocardial injury secondary to EBRT using MRI may be a useful modality to follow cardiac toxicity from EBRT and help identify individuals who are more susceptible to EBRT damage. LGE-MRI may provide essential Conflicts of interest: None.
Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2016
We investigate the difference between surface matching and target matching for pelvic radiation i... more We investigate the difference between surface matching and target matching for pelvic radiation image guidance. The uniqueness of our study is that all patients have multiple CT-on-rails (CTOR) scans to compare to corresponding AlignRT images. Ten patients receiving pelvic radiation were enrolled in this study. Two simulation CT scans were performed in supine and prone positions for each patient. Body surface contours were generated in treatment planning system and exported to AlignRT to serve as reference images. During treatment day, the patient was aligned to treatment isocenter with room lasers, and then scanned with both CTOR and AlignRT. Image-guidance shifts were calculated for both modalities by com-parison to the simulation CT and the differences between them were analyzed for both supine and prone positions, respectively. These procedures were performed for each patient once per week for five weeks. The difference of patient displace-ment between AlignRT and CTOR was analy...
Medical dosimetry : official journal of the American Association of Medical Dosimetrists, Jan 16, 2016
To evaluate radiation dose delivered to pelvic lymph nodes, if daily Image Guided Radiation Thera... more To evaluate radiation dose delivered to pelvic lymph nodes, if daily Image Guided Radiation Therapy (IGRT) was implemented with treatment shifts based on the primary site (primary clinical target volume [CTV]). Our secondary goal was to compare dosimetric coverage with patient outcomes. A total of 10 female patients with gynecologic malignancies were evaluated retrospectively after completion of definitive intensity-modulated radiation therapy (IMRT) to their pelvic lymph nodes and primary tumor site. IGRT consisted of daily kilovoltage computed tomography (CT)-on-rails imaging fused with initial planning scans for position verification. The initial plan was created using Varian׳s Eclipse treatment planning software. Patients were treated with a median radiation dose of 45Gy (range: 37.5 to 50Gy) to the primary volume and 45Gy (range: 45 to 64.8Gy) to nodal structures. One IGRT scan per week was randomly selected from each patient׳s treatment course and re-planned on the Eclipse tre...
We have treated endobronchial carcinoma with intraluminal brachytherapy (ILBT) since 1997. The fi... more We have treated endobronchial carcinoma with intraluminal brachytherapy (ILBT) since 1997. The first choice of the treatment for endobronchial carcinoma is surgery, and ILBT is considered as a palliative treatment. However, it is not rare that patients have poor pulmonary function or multiple lesions. In those patients, ILBT combined with external beam radiation therapy (EBRT) might be useful as a curative treatment because of its less invasiveness. One issue of endobronchial ILBT is the uncertainty in dosimetric assessment when using X-ray films to calculate the dose distribution. Thus, we have performed CTbased dosimetric evaluation and evaluated its efficacy. Materials/Methods: Fifteen lesions of 12 endobronchial carcinoma patients treated with ILBT in 2000 to 2008 were retrospectively reviewed. Ten lesions were treated with combination of ILBT and EBRT. ILBT using high dose rate 192 iridium thin wire system was performed at a dose of 5 Gy/fraction. Dose prescribed points were mucosal surface (10mm for lesions in trachea, 7mm for lesions in main bronchus, 5mm for lesions in lobular and segmental bronchus and 3mm for lesions in sub-segmental bronchus lesions, all from the center of the source). CT based dosimetry was performed in the latest 1 patient. CT was scanned using the same couch of fluoroscopy in the treatment room and the dose distribution was calculated with PLATO (Nucletron). Results: The patient age at the beginning of radiation therapy ranged from 57 to 82 years. Seven lesions were roentgenographically occult endobronchial carcinomas, and three lesions were cancers of trachea. Seven patients had multiple cancers. ILBT were performed 1-5 times in 1-3 weeks (median total dose was 20 Gy). The dose of EBRT was 0-61 Gy in 0-34 fractions (median total dose was 40 Gy). Median follow-up time was 33 months. Two-year survival rate and local control rate were 90.9% and 68.1%, respectively. Local recurrences were observed in 3 lesions. Two patients died because of lung cancer (1) and other cancer (1). Toxicities greater than Grade 2 were not observed except Grade 3 dyspnea in 1 patient. In CT based dosimetric assessment, 95% of the clinical target volume receives more than 90% of the prescribed dose. Conclusions: ILBT combined with EBRT might be a treatment option in inoperable endobronchial carcinoma patients with tolerable toxicity. CT based dosimetry is a promising tool for sophisticated endobronchial ILBT.
International Journal of Radiation Oncology*Biology*Physics, 2009
Results: Although lung exhibited significant motion, the markers showed limited motion on fluoros... more Results: Although lung exhibited significant motion, the markers showed limited motion on fluoroscopy. The average marker motion on the fluoroscopy was 0.4 mm (range 0-2), 1.6 mm (0-4), and 1.6 mm (0-3) in LR, AP, and SI, respectively. Over a typical 6-minute treatment time, in LR, AP and SI directions, the average motion (. 120 fractions) was 1.3 mm (0-17), 1.1 mm (0-6) and 1 mm (0-11) based on bony matching, and were 3.5 mm (0-25), 2 mm (0-11), and 2 mm (0-18) based on the markers. The CBCT dosimetry analysis showed the CTV was adequately covered with both matching methods, indicating the current margin size is sufficient. On the other hand, the computational motion simulation showed that marker based setup reduced the planning margin. Conclusions: Breathing has limited effect on the TV motion during APBI. Seroma exhibits larger motion than what is otherwise believed based on bony matching. A seroma specific marker based or image registration based approach holds the potential to reduce margin size. As more patients are enrolled into this study, more definitive conclusions can be drawn for the magnitudes of both intra-fractional motion and planning margin reduction.
International Journal of Radiation Oncology*Biology*Physics, 2013
Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT V.J. Gonzalez, C. ... more Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT V.J. Gonzalez, C. Hullett, L. Burt, P. Rassiah-Szegedi, V. Sarkar, J.D. Tward, L.J. Hazard, J.Y. Huang, B.J. Salter, and D.K. Gaffney; Department of Radiation Oncology, University of Arizona, Tucson, AZ, College of Medicine, University of Arizona, Tucson, AZ, Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, Center for Neurosciences, Tucson, AZ
Purpose: 4D CT is now widely used in radiation therapy for generating accurate ITV's or for f... more Purpose: 4D CT is now widely used in radiation therapy for generating accurate ITV's or for facilitation of gated treatmentdelivery. It is, as yet, relatively unexplored for use as a potential tool for image guidance of SBRT of lung. Use of 4D imaging for image guidance in SBRT requires that we determine an acceptable method for fusing 2 4D data sets.Method and Materials: We compare five different manual and/or automatic 4D registration methods and present the comparison results for phantom and patient data: Individual phase‐to‐phase registration; Average of phase to phase; MIP‐to‐MIP; Average Intensity Projection; Auto‐segmentation with centroid; Manual GE SimMD methods. Phantom studies were performed using the CIRS Dynamic Thorax phantom (CIRS, Norfolk, VA). A 2‐cm target was set into motion with a periodic sinusoidal 3D motion inside the anthropomorphic phantom. The baseline motion envelope of the target for simulation day movement was 4.2 mm L/R, 6.0 mm A/P, and 14.0 mm I/S. The target was then re‐programmed to move with the same motion envelope, but shifted away from the simulation motion envelope centroid, for three scenarios: a) Axial (L/R and A/P) only shift; b) Longitudinal only shift; and c) combination of axial (L/R & A/P) and longitudinal shift. Results: Individual phase‐to‐phase fusions were within 2.4 mm for all phases, with some phases performing better than others. The average and AIP methods were seen to perform very similarly, and this seems reasonable when we consider that both are, essentially, averaging methods. The MIP‐to‐MIP and Manual fusion methods were least accurate, but still likely to be considered clinically acceptable. Conclusion: Multiple methods have been explored for registration of 2 4D data sets. The averaging methods were seen to perform best, but all performed within what would reasonably be considered clinically acceptable limits. The centroid method performed particularly well.
PURPOSE To present the techniques and preliminary outcomes of ultrasound-based image-guided inten... more PURPOSE To present the techniques and preliminary outcomes of ultrasound-based image-guided intensity-modulated radiotherapy (IG-IMRT) for pancreatic cancer. MATERIALS AND METHODS Retrospective analysis of 41 patients treated between November 2000 and March 2005 with IG-IMRT to mean total doses of 55 Gy (range, 45-64 Gy). We analyzed the clinical feasibility of IG-IMRT, dosimetric parameters, and outcomes, including acute gastrointestinal toxicity (RTOG grading). Survival was assessed for adenocarcinoma (n = 35) and other histologies. RESULTS Mean daily image-guidance corrective shifts were 4.8 +/- 4.3 mm, 7.5 +/- 7.2 mm, and 4.6 +/- 5.9 mm along the x-, y-, and z-axes, respectively (mean 3D correction vector, 11.7 +/- 8.4 mm). Acute upper gastrointestinal toxicity was grade 0-1 in 22 patients (53.7%), grade 2 in 16 patients (39%), and grade 3 in 3 patients (7.3%). Lower gastrointestinal toxicity was grade 0-1 in 32 patients (78%), grade 2 in 7 patients (17.1%), and grade 4 in 2 patients (4.9%). Treatment was stopped early in 4 patients following administration of 30 to 54 Gy. Median survival for adenocarcinoma histology was 10.3 months (18.6 months in patients alive at analysis; n = 8) with actuarial 1- and 2-year survivals of 38% and 25%, respectively. CONCLUSION Daily image-guidance during delivery of IMRT for pancreatic carcinoma is clinically feasible. The data presented support the conclusion that safety margin reduction and moderate dose escalation afforded by implementation of these new radiotherapy technologies yields preliminary outcomes at least comparable with published survival data.
Radiosurgery is a non-invasive alternative to brain surgery that uses a single focused applicatio... more Radiosurgery is a non-invasive alternative to brain surgery that uses a single focused application of high radiation to destroy intracerebral target tissues. A Gamma Knife delivers such treatments by using 201 cylindrically collimated cobalt-60 sources that are arranged in a hemispherical pattern and aimed to a common focal point. The accumulation of radiation at the focal point, called a “shot” due to the spherical nature of the dose distribution, is used to ablate (or destroy) target tissue in the brain. If the target is small and spherical, it is easily treated by choosing one of four available collimators (4, 8, 14, or 18 mm). For large, irregular targets, multiple shots are typically required to treat the entire lesion, and the process of determining the optimal arrangement and number of shots is complex. In this research, fast simulated annealing and a novel objective function are used to investigate the relationship between the number of shots and the quality of the resulting...
Purpose: Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siem... more Purpose: Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siemens' DirectDensity™ (DD) reconstruction algorithm, which allows scans of any kV setting to use the same calibration. This study demonstrates why DD scans should not be used in combination with DECT and quantifies the magnitude of potential errors in image quality and dose. Methods: A CatPhan 504 phantom was scanned with a dual-pass DECT and reconstructed with many different kernels, including several DD kernels. The HU values of various inserts were measured. The RANDO ® man phantom was also scanned. Bone was contoured and then histograms of the bone HU values were analyzed for Filtered-Backprojection (FBP) and DD reconstructions of the 80 and 140 kV scans, as well as several virtual, monoenergetic reconstructions generated from FBP and DD reconstructions. "Standard" dose distributions were calculated on several reconstructions of both phantoms for comparison. Results: The DD kernel overcorrected the high-Z material inserts relative to bone, giving an excessively low relative electron density (RED). A unique artifact was observed in the high density inserts of the CatPhan in the monoenergetic scans when utilizing a DD kernel, due to the overcorrection in the DD scan of the material, especially at lower kV. Conclusions: While DD and DECT perform as expected when used independently, errors from their combined use were demonstrated. Dose errors from misuse of the DD kernel with DECT post-processing were as large as 2.5%. The DECT post-processing was without value because the HU differences between low and high energy were removed by the DD kernel. When using DD and DECT, we recommend the use of a DD reconstruction of the high energy scan for the dose calculation, and use of a FBP filter for the low and high energy scans for the DECT postprocessing.
Abdominal compression has been shown to reduce the extent of lung tumor motion but the dosimetric... more Abdominal compression has been shown to reduce the extent of lung tumor motion but the dosimetric impact of the approach is still in need of investigation. The current work analyzes the impact of various changes in PTV volume on key metrics of the final dose distribution to normal lung. To add clinical perspective, we also provide NTCP calculations for grade 2+ pneumonitis for each case. For a total of seventeen cases, the original ITV/PTV was reduced by systematically varied amounts and SBRT plans using dynamic conformal arc and VMAT techniques were created. DVH analysis for the normal lung comparing the original plan to the one with the ITV reduced by up to 10 mm shows that the average reduction of V5, V20 and mean lung dose is 3.8%, 2.0% and 1.1 Gy, respectively, for the conformal arc plans. Corresponding values for the VMAT plans were 3.9%, 1.9% and 1.2 Gy respectively. The mean NTCP drop for the conformal arc plans was 2.0% while it was 1.9% for the VMAT plans. These results su...
Multiple commercial phantoms are now available for performing end-to-end QA testing for stereotac... more Multiple commercial phantoms are now available for performing end-to-end QA testing for stereotactic procedures. This project aims at directly comparing one of the newest phantoms on the market against a more established one by performing similar tests to determine whether results are similar and they can be used interchangeably. Both phantoms were used to evaluate the coincidence of radiation and laser isocenters of a linear accelerator. End-to-end dosimetric tests were also performed using both an ion chamber and film. As part of the testing, both phantoms were also evaluated in terms of their efficiency of setup as well as the time required to switch inserts for different tests. Results showed that the laser/radiation isocenter coincidence as determined from each phantom was highly correlated. Ion chamber results were within 0.5% of the expected values. Gamma (2%, 2mm) pass rates of corresponding films were within 2% between phantoms. These results show that both phantoms are cap...
This is a proof-of-principle study investigating the feasibility of using late gadolinium enhance... more This is a proof-of-principle study investigating the feasibility of using late gadolinium enhancement magnetic resonance imaging (LGE-MRI) to detect left atrium (LA) radiation damage. Methods and materials: LGE-MRI data were acquired for 7 patients with previous external beam radiation therapy (EBRT) histories. The enhancement in LA scar was delineated and fused to the computed tomography images used in dose calculation for radiation therapy. Dosimetric and normal tissue complication probability analyses were performed to investigate the relationship between LA scar enhancement and radiation doses. Results: The average LA scar volume for the subjects was 2.5 cm 3 (range, 1.2-4.1 cm 3 ; median, 2.6 cm 3). The overall average of the mean dose to the LA scar was 25.9 Gy (range, 5.8-49.2 Gy). Linear relationships were found between the amount of radiation dose (mean dose) (R 2 Z 0.8514, P Z .03) to the LA scar-enhanced volume. The ratio of the cardiac tissue change (LA scar/LA wall) also demonstrated a linear relationship with the level of radiation received by the cardiac tissue (R 2 Z 0.9787, P < .01). Last, the normal tissue complication probability analysis suggested a dose response function to the LA scar enhancement. Conclusions: With LGE-MRI and 3-dimensional dose mapping on the treatment planning system, it is possible to define subclinical cardiac damage and distinguish intrinsic cardiac tissue change from radiation induced cardiac tissue damage. Imaging myocardial injury secondary to EBRT using MRI may be a useful modality to follow cardiac toxicity from EBRT and help identify individuals who are more susceptible to EBRT damage. LGE-MRI may provide essential Conflicts of interest: None.
Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2016
We investigate the difference between surface matching and target matching for pelvic radiation i... more We investigate the difference between surface matching and target matching for pelvic radiation image guidance. The uniqueness of our study is that all patients have multiple CT-on-rails (CTOR) scans to compare to corresponding AlignRT images. Ten patients receiving pelvic radiation were enrolled in this study. Two simulation CT scans were performed in supine and prone positions for each patient. Body surface contours were generated in treatment planning system and exported to AlignRT to serve as reference images. During treatment day, the patient was aligned to treatment isocenter with room lasers, and then scanned with both CTOR and AlignRT. Image-guidance shifts were calculated for both modalities by com-parison to the simulation CT and the differences between them were analyzed for both supine and prone positions, respectively. These procedures were performed for each patient once per week for five weeks. The difference of patient displace-ment between AlignRT and CTOR was analy...
Medical dosimetry : official journal of the American Association of Medical Dosimetrists, Jan 16, 2016
To evaluate radiation dose delivered to pelvic lymph nodes, if daily Image Guided Radiation Thera... more To evaluate radiation dose delivered to pelvic lymph nodes, if daily Image Guided Radiation Therapy (IGRT) was implemented with treatment shifts based on the primary site (primary clinical target volume [CTV]). Our secondary goal was to compare dosimetric coverage with patient outcomes. A total of 10 female patients with gynecologic malignancies were evaluated retrospectively after completion of definitive intensity-modulated radiation therapy (IMRT) to their pelvic lymph nodes and primary tumor site. IGRT consisted of daily kilovoltage computed tomography (CT)-on-rails imaging fused with initial planning scans for position verification. The initial plan was created using Varian׳s Eclipse treatment planning software. Patients were treated with a median radiation dose of 45Gy (range: 37.5 to 50Gy) to the primary volume and 45Gy (range: 45 to 64.8Gy) to nodal structures. One IGRT scan per week was randomly selected from each patient׳s treatment course and re-planned on the Eclipse tre...
We have treated endobronchial carcinoma with intraluminal brachytherapy (ILBT) since 1997. The fi... more We have treated endobronchial carcinoma with intraluminal brachytherapy (ILBT) since 1997. The first choice of the treatment for endobronchial carcinoma is surgery, and ILBT is considered as a palliative treatment. However, it is not rare that patients have poor pulmonary function or multiple lesions. In those patients, ILBT combined with external beam radiation therapy (EBRT) might be useful as a curative treatment because of its less invasiveness. One issue of endobronchial ILBT is the uncertainty in dosimetric assessment when using X-ray films to calculate the dose distribution. Thus, we have performed CTbased dosimetric evaluation and evaluated its efficacy. Materials/Methods: Fifteen lesions of 12 endobronchial carcinoma patients treated with ILBT in 2000 to 2008 were retrospectively reviewed. Ten lesions were treated with combination of ILBT and EBRT. ILBT using high dose rate 192 iridium thin wire system was performed at a dose of 5 Gy/fraction. Dose prescribed points were mucosal surface (10mm for lesions in trachea, 7mm for lesions in main bronchus, 5mm for lesions in lobular and segmental bronchus and 3mm for lesions in sub-segmental bronchus lesions, all from the center of the source). CT based dosimetry was performed in the latest 1 patient. CT was scanned using the same couch of fluoroscopy in the treatment room and the dose distribution was calculated with PLATO (Nucletron). Results: The patient age at the beginning of radiation therapy ranged from 57 to 82 years. Seven lesions were roentgenographically occult endobronchial carcinomas, and three lesions were cancers of trachea. Seven patients had multiple cancers. ILBT were performed 1-5 times in 1-3 weeks (median total dose was 20 Gy). The dose of EBRT was 0-61 Gy in 0-34 fractions (median total dose was 40 Gy). Median follow-up time was 33 months. Two-year survival rate and local control rate were 90.9% and 68.1%, respectively. Local recurrences were observed in 3 lesions. Two patients died because of lung cancer (1) and other cancer (1). Toxicities greater than Grade 2 were not observed except Grade 3 dyspnea in 1 patient. In CT based dosimetric assessment, 95% of the clinical target volume receives more than 90% of the prescribed dose. Conclusions: ILBT combined with EBRT might be a treatment option in inoperable endobronchial carcinoma patients with tolerable toxicity. CT based dosimetry is a promising tool for sophisticated endobronchial ILBT.
Uploads
Papers by Bill Salter