Faculty Bibliography

Purpose: In-vivo dosimetry for conventional total body irradiation (TBI) utilize point detectors placed along the patient surface to confirm the delivered dose matches prescription dose. However, in the volumetrically modulated arc therapy (VMAT) approach to TBI, the electronic portal imager device (EPID) can be utilized to acquire a 2-dimensional transmission fluence plane. This work explores the relationship between patient setup accuracy with transit in-vivo dosimetry.
Method(s): A total of 192 fields were investigated. Each VMAT plan consisted of four isocenters: head, chest, abdomen, and pelvis. Prior to treatment, the patient was imaged at the head, pelvis, and chest. Optimal couch shifts were determined for each isocenter under image guidance. The optimal IGRT shifts were determined using an inhouse application that minimized dose deviation using criteria established through plan uncertainty analysis performed in Eclipse. Translational couch residuals were recorded and defined as the difference in the global shift calculated and the optimal couch position with shifts. Transit dosimetry was measured per arc, and analyzed using SNC PerFRACTION with a gamma criteria of 10%/5mm, 5%/5mm, and 5%/7mm.
Result(s): Based on plan uncertainty analysis, clinical threshold for couch residuals were set to 7 mm (5 mm for chest isocenter) as there would be minimal impact on target coverage and organ sparing at those levels. Transit dosimetry showed that the average pass rate across all fields was 99.6%, 97.0%, and 99.2% for 10%/5mm, 5%/5mm, and 5%/7mm gamma criteria, respectively. Pearson correlation tests showed that there was weak correlation between gamma criteria and couch residuals. At stringent 3%/5mm gamma criteria, moderate correlation was found between lateral couch residuals for the head and chest and the head and chest arc analysis.
Conclusion(s): Transit dosimetry showed high pass rates using our couch residual tolerances, which confirmed the plan uncertainty analysis performed during treatment planning

The purpose of this work is to establish an automated approach for a multiple isocenter volumetric arc therapy (VMAT)-based TBI treatment planning approach. Five anonymized full-body CT imaging sets were used. A script was developed to automate and standardize the treatment planning process using the Varian Eclipse v15.6 Scripting API. The script generates two treatment plans: a head-first VMAT-based plan for upper body coverage using four isocenters and a total of eight full arcs; and a feet-first AP/PA plan with three isocenters that covers the lower extremities of the patient. PTV was the entire body cropped 5 mm from the patient surface and extended 3 mm into the lungs and kidneys. Two plans were generated for each case: one to a total dose of 1200 cGy in 8 fractions and a second one to a total dose of 1320 cGy in 8 fractions. Plans were calculated using the AAA algorithm and 6 MV photon energy. One plan was created and delivered to an anthropomorphic phantom containing 12 OSLDs for in-vivo dose verification. For the plans prescribed to 1200 cGy total dose the following dosimetric results were achieved: median PTV V100% = 94.5%; median PTV D98% = 89.9%; median lungs Dmean = 763 cGy; median left kidney Dmean = 1058 cGy; and median right kidney Dmean = 1051 cGy. For the plans prescribed to 1320 cGy total dose the following dosimetric results were achieved: median PTV V100% = 95.0%; median PTV D98% = 88.7%; median lungs Dmean = 798 cGy; median left kidney Dmean = 1059 cGy; and median right kidney Dmean = 1064 cGy. Maximum dose objective was met for all cases. The dose deviation between the treatment planning dose and the dose measured by the OSLDs was within ±4%. In summary, we have demonstrated that scripting can produce high-quality plans based on predefined dose objectives and can decrease planning time by automatic target and optimization contours generation, plan creation, field and isocenter placement, and optimization objectives setup.

ABSTRACT/UNASSIGNED:Renal echo planar diffusion tensor imaging (DTI) has clinical potential but suffers from geometric distortion. We evaluated feasibility of reversed gradient distortion correction in 10 diabetic patients and 6 volunteers. Renal area, apparent diffusion coefficient, fractional anisotropy, and tensor eigenvalues were measured on uncorrected and distortion-corrected DTI. Corrected DTI correlated better than uncorrected DTI (r = 0.904 vs 0.840, P = 0.002) with reference anatomic T2-weighted imaging, with no significant difference in DTI metrics.

We describe a model case of unplanned pregnancy during radiation therapy to the chest wall and peripheral lymphatics for breast cancer. We use the Morbidity and Mortality Conference format to demonstrate how radiation oncology departments should evaluate and manage this situation.

The purpose of this feasibility study is to develop a fully automated procedure capable of generating treatment plans with multiple fractionation schemes to improve speed, robustness, and standardization of plan quality. A fully automated script was implemented for spinal stereotactic radiosurgery/stereotactic body radiation therapy (SRS/SBRT) plan generation using Eclipse v15.6 API. The script interface allows multiple dose/fractionation plan requests, planning target volume (PTV) expansions, as well as information regarding distance/overlap between spinal cord and targets to drive decision-making. For each requested plan, the script creates the course, plans, field arrangements, and automatically optimizes and calculates dose. The script was retrospectively applied to ten computed tomography (CT) scans of previous cervical, thoracic, and lumbar spine SBRT patients. Three plans were generated for each patient - simultaneous integrated boost (SIB) 1800/1600 cGy to gross tumor volume (GTV)/PTV in one fraction; SIB 2700/2100 cGy to GTV/PTV in three fractions; and 3000 cGy to PTV in five fractions. Plan complexity and deliverability patient-specific quality assurance (QA) was performed using ArcCHECK with an Exradin A16 chamber inserted. Dose objectives were met for all organs at risk (OARs) for each treatment plan. Median target coverage was GTV V100% = 87.3%, clinical target volume (CTV) V100% = 95.7% and PTV V100% = 88.0% for single fraction plans; GTV V100% = 95.6, CTV V100% = 99.6% and PTV V100% = 97.2% for three fraction plans; and GTV V100% = 99.6%, CTV V100% = 99.1% and PTV V100% = 97.2% for five fraction plans. All plans (n = 30) passed patient-specific QA (>90%) at 2%/2 mm global gamma. A16 chamber dose measured at isocenter agreed with planned dose within 3% for all cases. Automatic planning for spine SRS/SBRT through scripting increases efficiency, standardizes plan quality and approach, and provides a tool for target coverage comparison of different fractionation schemes without the need for additional resources.

Purpose: For the Cyberknife (Accuray Inc. Sunnyvale CA) stereotactic radiosurgery and stereotactic body radiotherapy treatment unit, a series of collimating cones are used with diameters ranging from 5 mm to 60 mm. The measurement of output factors (OFs) in these small radiation fields is challenging due to limitations in detector size. Currently multiple detectors are used for the measurement of output factors, but if not water equivalent, Monte Carlo corrections are required. The Exradin W2 (Standard Imaging Inc., Middleton, WI) plastic scintillation device (PSD) has an active volume of 0.0008 cm³ and is water equivalent. This work reports OFs and scanning data measured by the W2 PSD and a diode in Cyberknife.
Method(s): A Cyberknife M6 and a W2 PSD in a MP3 water phantom (PTW, Freiberg, Germany) were used to take TPR, profile, and OF measurements. The W2 comes with a specialized electrometer, MAX SD, used to measure the Cerenkov light ratio using the manufacturer's recommendation. Profiles, tissue phantom ratios (TPR), and OF values were taken using the clinically relevant (5, 7.5 and 10) mm cones, with OFs normalized to the 60 mm cone and scanning measurements normalized to maximum dose. All results were compared with PTW 60018 diode measurements taken during commissioning.
Result(s): The W2 scintillator required the slowest scan speed (0.1 mm/s) in order to eliminate noise, and TPR data was smoothed using a moving average filter. Comparison between diode and W2 profiles and TPR data showed good agreement. Monte Carlo adjusted diode OFs and W2 measured OFs were within 2.6%.
Conclusion(s): This work demonstrated the feasibility of using a water equivalent, small volume commercial W2 PSD in Cyberknife. Scanning data was near equivalent, but showed significant noise and required smoothing. W2 measured OFs agreed with MC-corrected diode measurements taken during commissioning