Kevin Bylund

Analysis of Interfraction Prostate Motion Using Megavoltage Cone Beam Computed Tomography

PURPOSE Determine the degree of interfraction prostate motion and its components measured by using daily megavoltage (MV) cone beam computed tomography (CBCT) imaging. METHODS AND MATERIALS A total of 984 daily MV CBCT images from 24 patients undergoing definitive intensity-modulated radiotherapy for localized prostate cancer were analyzed retrospectively. Pretreatment couch shifts, based on physician registration of MV CBCT to planning CT data sets, were used as a measure of daily interfraction motion. Off-line bony registration was performed to separate bony misalignment from internal organ motion. Interobserver and intraobserver variation studies were performed on 20 MV CBCT images. RESULTS Mean interfraction prostate motion was 6.7 mm, with the greatest single-axis deviation in the anterior-posterior (AP) direction. The largest positional inaccuracy was accounted for by systematic deviations in bony misalignment, whereas random deviations occurred from bony misalignment and internal prostate motion. In the aggregate, AP motion did not correlate with days elapsed since beginning therapy or on average with rectal size at treatment planning. Interobserver variation was greatest in the AP direction, decreased in experienced observers, and further decreased in intraobserver studies. Mean interfraction motion during the first 6 days of therapy, when used as a subsequent offset, reduced acceptable AP planning target volume margins by 50%. CONCLUSION The MV CBCT is a practical direct method of daily localization that shows significant interfraction motion with respect to conventional three-dimensional conformal and intensity-modulated radiotherapy margins, similar to that measured in other modalities.

Real-time sonoelastography of hepatic thermal lesions in a swine model

Sonoelastography has been developed as an ultrasound-based elasticity imaging technique. In this technique, external vibration is induced into the target tissue. In general, tissue stiffness is inversely proportional to the amplitude of tissue vibration. Imaging tissue vibration will provide the elasticity distribution in the target region. This study investigated the feasibility of using real-time sonoelastography to detect and estimate the volume of thermal lesions in porcine livers in vivo. A total of 32 thermal lesions with volumes ranging from 0.2to5.3cm3 were created using radiofrequency ablation (RFA) or high-intensity focused ultrasound (HIFU) technique. Lesions were imaged using sonoelastography and coregistered B-mode ultrasound. Volumes were reconstructed from a sequence of two-dimensional scans. The comparison of sonoelastographic measurements and pathology findings showed good correlation with respect to the area of the lesions (r2=0.8823 for RFA lesions, r2=0.9543 for HIFU lesions). In addition, good correspondence was found between three-dimensional sonoelastography and gross pathology (3.6% underestimate), demonstrating the feasibility of sonoelastography for volume estimation of thermal lesions. These results support that sonoelastography outperforms conventional B-mode ultrasound and could potentially be used for assessment of thermal therapies.

Bladder cancer in the elderly patient: challenges and solutions

Bladder cancer (BC) is an age-associated malignancy with increased prevalence in the elderly population. Elderly patients are a vulnerable population at increased risk for treatment-related toxicity secondary to medical comorbidities and geriatric syndromes. As a result, this population has been historically undertreated and suffers worse disease-specific outcomes than younger patients with BC. Recognition of this disparity has led to efforts to individualize treatment decisions based on functional status rather than chronologic age in an effort to optimize the use of curative therapies for the fit elderly and modify treatments to reduce the risk of toxicity and disease-related morbidity in vulnerable or frail patients. The comprehensive geriatric assessment is a decision framework that helps to balance underlying health considerations and risks of therapy with aggressiveness of the cancer. Development of systemic therapies with increased efficacy against BC and reduced toxicity are eagerly awaited, as are techniques and interventions to reduce the morbidity from surgery and radiation for patients with BC.

Measurement of thermally ablated lesions in sonoelastographic images using level set methods

The capability of sonoelastography to detect lesions based on elasticity contrast can be applied to monitor the creation of thermally ablated lesion. Currently, segmentation of lesions depicted in sonoelastographic images is performed manually which can be a time consuming process and prone to significant intra- and inter-observer variability. This work presents a semi-automated segmentation algorithm for sonoelastographic data. The user starts by planting a seed in the perceived center of the lesion. Fast marching methods use this information to create an initial estimate of the lesion. Subsequently, level set methods refine its final shape by attaching the segmented contour to edges in the image while maintaining smoothness. The algorithm is applied to in vivo sonoelastographic images from twenty five thermal ablated lesions created in porcine livers. The estimated area is compared to results from manual segmentation and gross pathology images. Results show that the algorithm outperforms manual segmentation in accuracy, inter- and intra-observer variability. The processing time per image is significantly reduced.

Split-Course Palliative Radiotherapy for Advanced Non-small Cell Lung Cancer

Purpose: Palliative chest radiotherapy (RT) for lung malignancies is effective in relieving serious chest symptoms from tumor bleeding or mass effect on major airways, vessels, and nerves. Albeit an important subject, there is a lack of consensus for an optimal palliative RT regimen. We report the outcomes of a split-course palliative chest RT, a frequently used schema at our institution. Methods and Materials: Records of 140 patients treated between 1995 and 2006 were reviewed. Treatment was prescribed to an initial 25 Gy in 10 fractions through anterior-posterior/posterior-anterior beam arrangements. After a 2-week rest period, patients were selected to receive an additional 10 Gy (anterior-posterior/posterior-anterior) followed by off-cord beams to a final dose of 50 to 62.5 Gy. Symptom relief and toxicity during RT and after completion of RT were assessed from clinician notes and patient-reported symptom inventory forms. Second, the impact on survival was assessed. Results: Symptomatic relief was observed in 52 to 84% of patients with durable palliation in 58%. There were no grade 3 to 5 toxicities. Grades 1 and 2 esophagitis and pneumonitis were observed in 34 and 8% patients, respectively. Median survival was 5 months. Conclusions: A majority of patients experienced symptomatic improvement. The built-in 2-week break allowed for selection of patients for high-dose palliative radiation and balanced treatment benefits with potential side effects. Cancer survival was not adversely affected by treatments in this population with mostly advanced disease. This regimen is a viable option for patients who cannot tolerate a protracted, uninterrupted course of treatment.

Soft Tissue Sarcoma in the Setting of Chronic Cutaneous Graft Versus Host Disease After Allogenic Bone Marrow Transplantation

Second primary cancers are approximately 2.1–2.8 times more common in survivors of bone marrow transplant than in the age-matched general population. We describe a patient who developed high-grade sarcoma in two disparate sites that were clinically involved by chronic cutaneous graft versus host disease (GVHD). This occurred 3.5 years after bone marrow transplant for acute myelogenous leukemia (AML). This suggests that malignant sarcomas may develop in the setting of chronic GVHD, and close surveillance of GVHD-related nodules is warranted.

P1C-4 Real-Time Semi-Automatic Segmentation of Hepatic Radiofrequency Ablated Lesions in an In Vivo Porcine Model Using Sonoelastography

Radiofrequency ablation (RFA) is a minimally invasive thermal therapy that is under investigation as an alternative to surgery for treating liver tumors. Currently, there is a need to monitor the process of lesion creation to guarantee complete treatment of the diseased tissue. In a previous study, sonoelastography was used to detect and measure RFA lesions during exposed liver experiments in a porcine model in vivo. Manual outlining of these lesions in the sonoelastographic images is challenging due to a lack of boundary definition and artifacts formed by respiratory motion and perfusion. As a result, measuring the lesions becomes a time-consuming process with high variability. This work introduces a semi-automatic segmentation algorithm for sonoelastographic data based on level set methods. This algorithm aims to reduce the variability and processing time involved in manual segmentation while maintaining comparable results. For this purpose, eleven RFA lesions are created in five porcine livers exposed through a midline incision. Three independent observers perform manual and semi-automatic measurements on the in vivo sonoelastographic images. These results are compared to measurements from gross pathology. In addition, we assess the feasibility of performing sonoelastograhic measurements transcutaneously. The procedure previously described is repeated with three more lesions without exposing the liver. Overall, the semi-automatic algorithm outperforms manual segmentation in accuracy, speed, and repeatability. These results suggest that sonoelastography in combination with the segmentation algorithm has the potential to be used as a complementary technique to conventional ultrasound for thermal ablation monitoring and follow-up imaging.

Is there a subset of patients with recurrent cancer in the vagina who are not candidates for interstitial brachytherapy that can be treated with multichannel vaginal brachytherapy using graphic optimization

Purpose To evaluate recurrent vaginal cancer treated with vaginal brachytherapy (VBT) using graphic optimization in patients not amenable to surgery and interstitial brachytherapy (ISBT). Material and methods We retrospectively reviewed the records of 5 patients with recurrent cancer in the vagina that were deemed not to be good candidates for ISBT implant because of medical reasons. All patients received computed tomography/magnetic resonance imaging (CT/MRI) based evaluation in addition to a detailed clinical examination, and were noted to have recurrent nodules in the vagina with size ranging from 10-25 mm. Four of the 5 patients had recurrent disease in the vaginal apex, whereas one patient had recurrence in the lateral vaginal wall. Subsequently, all patients were treated with external beam radiation therapy (EBRT) followed by multichannel vaginal cylinder (MVC)-based VBT using graphic optimization for shaping the isodose to improve the clinical target volume (CTV) coverage, as well as to spare the organs at risk (OAR). The dose to the bladder and rectum with regard to 0.1 cc, 1 cc, and 2 cc were recorded. Results Median age of the patients was 78 years (range 58-86 years). Thickness of the lesions before VBT ranged from 6-15 mm. All patients were followed up with MRI at 3 months. All patients but one demonstrated complete clinical/ radiological response of the tumor. No patient had any grade III/IV toxicity at 24 months. Conclusions MVC-based VBT using graphic optimization is safe and yields favorable results if used judiciously.

7-Benzylidine-7-Dehydronaltrexone

7-Benzylidine-7-dehydronaltrexone (BNTX) is the first discovered nonpeptide opioid receptor antagonist that reportedly has high selectivity for delta-1-opioid receptor sites. [ 3 H]BNTX is used as a probe for delta-1-opioid receptors.

TU-EE-A1-02: Validation of Treatment Planning and Delivery in Conventional Linear Accelerator Without Flattening Filter

Purpose: The purpose of this study was to compare planning and delivery accuracy of IMRT on a conventional linac with and without the flattening filter. Method and Materials: The 6 MV x‐ray beam of a Siemens Oncor linac was modified by removing the flattening filter, enabling dose rates of 1000 MU/min, and modeled within a commercial treatment planning system. IMRT treatment plans created with the flattening filter (F) were reoptimized with equivalent segments and computed for the beam model without the filter (NF) on 10 clinical head‐and‐neck cases. All plans (F and NF) were compared for equivalence and delivered to phantoms; treatment time and dose agreement with planning system were determined. Results: Dose distributions are similar between the two beam lines, and clinically reasonable plans were created despite the absence of the flattening filter. PTV hot spots were <0.5% hotter and cold spots were <0.5% colder for the (NF) plan. Similarly, all other ROIs investigated were within 1% for hot spots and cold spots. On average NF plans required 15% more MU, but delivered treatments were shorter (9 min vs 11 min). Dosimetric differences between computed and ion chamber measurements were similar (−1.7%+/−1.3% − F) and (1.7%+/−1.9% − NF). The number of pixels meeting gamma map criteria of 3%/3mm, 5%/5mm, and 7%/7mm were statistically equivalent (p = 0.6): [88.5%, 96.8%, and 97.8% (NF)], [87.8%, 96.6%, and 97.9% (F)]. Conclusion: The planning system was able to generate equivalent plans, and measured dose distributions in ion chamber and film show no difference between beam models with or without the flattening filter. At the higher dose rate, overall treatment times were reduced and could be applied to gating and hypofractionation. Conflict of Interest: Research supported by industrial grant from Siemens Medical Solutions.