Sean L. Berry

Proton beam radiation therapy results in significantly reduced toxicity compared with intensity-modulated radiation therapy for head and neck tumors that require ipsilateral radiation

BACKGROUND As proton beam radiation therapy (PBRT) may allow greater normal tissue sparing when compared with intensity-modulated radiation therapy (IMRT), we compared the dosimetry and treatment-related toxicities between patients treated to the ipsilateral head and neck with either PBRT or IMRT. METHODS Between 01/2011 and 03/2014, 41 consecutive patients underwent ipsilateral irradiation for major salivary gland cancer or cutaneous squamous cell carcinoma. The availability of PBRT, during this period, resulted in an immediate shift in practice from IMRT to PBRT, without any change in target delineation. Acute toxicities were assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. RESULTS Twenty-three (56.1%) patients were treated with IMRT and 18 (43.9%) with PBRT. The groups were balanced in terms of baseline, treatment, and target volume characteristics. IMRT plans had a greater median maximum brainstem (29.7 Gy vs. 0.62 Gy (RBE), ​P < 0.001), maximum spinal cord (36.3 Gy vs. 1.88 Gy (RBE), ​P < 0.001), mean oral cavity (20.6 Gy vs. 0.94 Gy (RBE), ​P < 0.001), mean contralateral parotid (1.4 Gy vs. 0.0 Gy (RBE), P<0.001), and mean contralateral submandibular (4.1 Gy vs. 0.0 Gy (RBE), ​P < 0.001) dose when compared to PBRT plans. PBRT had significantly lower rates of grade 2 or greater acute dysgeusia (5.6% vs. 65.2%, P<0.001), mucositis (16.7% vs. 52.2%, P=0.019), and nausea (11.1% vs. 56.5%, P=0.003). CONCLUSIONS The unique properties of PBRT allow greater normal tissue sparing without sacrificing target coverage when irradiating the ipsilateral head and neck. This dosimetric advantage seemingly translates into lower rates of acute treatment-related toxicity.

A field size specific backscatter correction algorithm for accurate EPID dosimetry.

PURPOSE Portal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed. METHODS A series of open field dose images were obtained for field sizes ranging from 2×2 to 30×40cm2. Each image was analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered. These include the use of discrete FS specific correction matrices and the use of a single generalized equation. The efficacy of each approach was tested on the clinical dosimetric images for ten patients, 49 treatment fields. The fields were evaluated to determine whether there was an improvement in the dosimetric result over the commercial vendors current algorithm. RESULTS It was found that backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is approximately 3.6% for 10×10 and 12.5×12.5cm2 field sizes. The asymmetry decreased with increasing FS to approximately 0.6% for fields larger than 30×30cm2. The dosimetric comparison between the measured and predicted dose images was significantly improved (p⪡.001) when a FS specific backscatter correction was applied. The average percentage of points passing a 2%, 2 mm gamma criteria increased from 90.6% to between 96.7% and 97.2% after the proposed methods were employed. CONCLUSIONS The error observed in a measured portal dose image depends on how much its FS differs from the 30×40cm2 calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the methods presented within this investigation.

Evaluating inter-campus plan consistency using a knowledge based planning model.

BACKGROUND AND PURPOSE We investigate whether knowledge based planning (KBP) can identify systematic variations in intensity modulated radiotherapy (IMRT) plans between multiple campuses of a single institution. MATERIAL AND METHODS A KBP model was constructed from 58 prior main campus (MC) esophagus IMRT radiotherapy plans and then applied to 172 previous patient plans across MC and 4 regional sites (RS). The KBP model predicts DVH bands for each organ at risk which were compared to the previously planned DVHs for that patient. RESULTS RS1s plans were the least similar to the model with less heart and stomach sparing, and more variation in liver dose, compared to MC. RS2 produced plans most similar to those expected from the model. RS3 plans displayed more variability from the model prediction but overall, the DVHs were no worse than those of MC. RS4 did not present any statistically significant results due to the small sample size (n=11). CONCLUSIONS KBP can retrospectively highlight subtle differences in planning practices, even between campuses of the same institution. This information can be used to identify areas needing increased consistency in planning output and subsequently improve consistency and quality of care.

Implementation of EPID transit dosimetry based on a through‐air dosimetry algorithm

PURPOSE A method to perform transit dosimetry with an electronic portal imaging device (EPID) by extending the commercial implementation of a published through-air portal dose image (PDI) prediction algorithm Van Esch et al. [Radiother. Oncol. 71, 223-234 (2004)] is proposed and validated. A detailed characterization of the attenuation, scattering, and EPID response behind objects in the beam path is used to convert through-air PDIs into transit PDIs. METHODS The EPID detector response beyond a range of water equivalent thicknesses (0-35 cm) and field sizes (3×3 to 22.2×29.6 cm(2)) was analyzed. A constant air gap between the phantom exit surface and the EPID was utilized. A model was constructed that accounts for the beams attenuation along the central axis, the presence of phantom scattered radiation, the detectors energy dependent response, and the difference in EPID off-axis pixel response relative to the central pixel. The efficacy of the algorithm was verified by comparing predicted and measured PDIs for IMRT fields delivered through phantoms of increasing complexity. RESULTS The expression that converts a through-air PDI to a transit PDI is dependent on the objects thickness, the irradiated field size, and the EPID pixel position. Monte Carlo derived narrow-beam linear attenuation coefficients are used to model the decrease in primary fluence incident upon the EPID due to the objects presence in the beam. This term is multiplied by a factor that accounts for the broad beam scatter geometry of the linac-phantom-EPID system and the detectors response to the incident beam quality. A 2D Gaussian function that models the nonuniformity of pixel response across the EPID detector plane is developed. For algorithmic verification, 49 IMRT fields were repeatedly delivered to homogeneous slab phantoms in 5 cm increments. Over the entire set of measurements, the average area passing a 3%∕3mm gamma criteria slowly decreased from 98% for no material in the beam to 96.7% for 35 cm of material in the beam. The same 49 fields were delivered to a heterogeneous slab phantom and on average, 97.1% of the pixels passed the gamma criteria. Finally, a total of 33 IMRT fields were delivered to the anthropomorphic phantom and on average, 98.1% of the pixels passed. The likelihood of good matches was independent of anatomical site. CONCLUSIONS A prediction of the transit PDI behind a phantom or patient can be created for the purposes of treatment verification via an extension of the Van Esch through-air PDI algorithm. The results of the verification measurements through phantoms indicate that further investigation through patients during their treatments is warranted.

Interobserver variability in radiation therapy plan output: Results of a single-institution study

PURPOSE We investigated the sources of variability in radiation therapy treatment plan output between planners within a single institution. METHODS AND MATERIALS Forty treatment planners across 5 campuses of an institution created a plan on the same thoracic esophagus patient computed tomography scan and structure set. Plans were scored and ranked based on the planners adherence to an ordered list of target dose coverage and normal tissue evaluation criteria. A runs test was used to identify whether any of the studied planner qualities influenced the ranking. Spearman rank correlation was used to investigate whether plan score correlated with years of experience or planned monitor units. RESULTS The distribution of scores, ranging from 80.24 to 135.89, was negatively skewed (mean, 128.7; median, 131.5). No statistically significant relationship between plan score and campus (P = .193), job title (P = .174), previous outside experience (P = .611), or number of gantry angles (P = .156) was discovered. No statistical correlation between plan score and monitor unit or years of experience was found. CONCLUSIONS Despite clear and established critical organ dose criteria and well-documented planning guidelines, planning variation still occurs, even among members of the same institution. Because plan consistency does not seem to significantly correlate with experience, career path, or campus, investigation into alternate methods beyond additional education and training to reduce this variation, such as knowledge-based planning or advanced optimization techniques, is necessary.

High-dose hypofractionated radiotherapy is effective and safe for tumors in the head-and-neck

OBJECTIVES High-dose, hypofractionated radiotherapy (HFRT) is sometimes used to treat malignancy in the head-and-neck (HN), both in the curative and palliative setting. Its safety and efficacy have been reported in small studies and are still controversial. MATERIALS AND METHODS We retrospectively evaluated the outcomes and toxicities of HFRT, including ultra-high-dose fractionation schemes (⩾8Gray per fraction), for HN malignancies. RESULTS A total of 62 sites of measurable gross disease in 48 patients were analyzed. The median follow-up was 54.3months among five survivors and 6.0months in the remaining patients. Median RT dose was 30Gray in 5 fractions; 20/62 lesions (32%) received dose-per-fraction of ⩾8Gray. Overall response rate at first follow-up was 79%. One-year local-progression free rate was 50%. On multivariate analysis for locoregional control, dose-per-fraction ⩾6Gray was associated with control (p=0.04) and previous radiation was associated with inferior control (p=0.04). Patients who achieved complete response to RT had longer survival than those who did not (p=0.01). Increased toxicity rates were not observed among patients treated with dose-per-fraction ⩾8Gray; only re-irradiation increased toxicity rates. CONCLUSION Despite the poor prognostic features noted in this cohort of patients with HN malignancies, HFRT was associated with high response rates, good local control, and acceptable toxicity. Sites that were treated with 6Gray per fraction or higher and had not been previously irradiated had the best disease control. A prospective trial is warranted to further refine the use and indications of HFRT in this setting.

SU‐GG‐T‐188: A Field Size Specific Backscatter Correction Algorithm for Accurate EPID Dosimetry

PURPOSE Portal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed. METHODS A series of open field dose images were obtained for field sizes ranging from 2 x 2 to 30 x 40 cm2. Each image was analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered. These include the use of discrete FS specific correction matrices and the use of a single generalized equation. The efficacy of each approach was tested on the clinical dosimetric images for ten patients, 49 treatment fields. The fields were evaluated to determine whether there was an improvement in the dosimetric result over the commercial vendors current algorithm. RESULTS It was found that backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is approximately 3.6% for 10 x 10 and 12.5 x 12.5 cm2 field sizes. The asymmetry decreased with increasing FS to approximately 0.6% for fields larger than 30 x 30 cm2. The dosimetric comparison between the measured and predicted dose images was significantly improved (p << .001) when a FS specific backscatter correction was applied. The average percentage of points passing a 2%, 2 mm gamma criteria increased from 90.6% to between 96.7% and 97.2% after the proposed methods were employed. CONCLUSIONS The error observed in a measured portal dose image depends on how much its FS differs from the 30 x 40 cm2 calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the methods presented within this investigation.

Five years’ experience with a customized electronic checklist for radiation therapy planning quality assurance in a multicampus institution

INTRODUCTION An electronic checklist has been designed with the intention of reducing errors while minimizing user effort in completing the checklist. We analyze the clinical use and evolution of the checklist over the past 5 years and review data in an incident learning system (ILS) to investigate whether it has contributed to an improvement in patient safety. METHODS AND MATERIALS The checklist is written as a standalone HTML application using VBScript. User selection of pertinent demographic details limits the display of checklist items only to those necessary for the particular clinical scenario. Ten common clinical scenarios were used to illustrate the difference between the maximum possible number of checklist items available in the code versus the number displayed to the user at any one time. An ILS database of errors and near misses was reviewed to evaluate whether the checklist influenced the occurrence of reported events. RESULTS Over 5 years, the number of checklist items available in the code nearly doubled, whereas the number displayed to the user at any one time stayed constant. Events reported in our ILS related to the beam energy used with pacemakers, projection of anatomy on digitally reconstructed radiographs, orthogonality of setup fields, and field extension beyond match lines, did not recur after the items were added to the checklist. Other events related to bolus documentation and breakpoints continued to be reported. CONCLUSION Our checklist is adaptable to the introduction of new technologies, transitions between planning systems, and to errors and near misses recorded in the ILS. The electronic format allows us to restrict user display to a small, relevant, subset of possible checklist items, limiting the planner effort needed to review and complete the checklist.

WE-H-BRC-07: Validation of a Commercial Atlas Based Auto-Segmentation Package For Automated Contour Quality Control

PURPOSE To investigate whether a commercial atlas based auto-segmentation (ABAS) package can be used for automated review and quality control (QC) of physician segmentations, and if so, to determine action levels for future clinical implementation. METHODS 42 head and neck cancer (HNC) patient plan CT scans with manually defined expert physician organ at risk (OAR) segmentations were retrospectively identified. Five representative patients were selected as ABAS models and were subsequently applied to each of the remaining 37 studies, resulting in 5 auto-segmentations (AS) per patient. The similarity metric (SM) generated by the ABAS package to describe the anatomical similarity of the CT scan to be segmented against that of the atlas CT was recorded for each AS. A simultaneous truth and performance level (STAPLE) consensus contour was created from the 5 AS on each patient. Each individual AS and the STAPLE were compared to the existing expert manual segmentation using the Hausdorff Distance (HD) and Dice similarity coefficient (DSC). RESULTS Software-based SM is not indicative of AS accuracy. STAPLE significantly improved AS quality over the results averaged from individual ABAS for 7 of 8 OARs. DSC values (mean ± 1 standard deviation) for STAPLE compared to the expert segmentations are comparable to the literature for the parotids (0.74 ± 0.10), mandible (0.80 ± 0.07), and submandibular glands (0.68 ± 0.10) but is poor at delineating the brachial plexus (0.32 ± 0.08) and larynx (0.61 ± 0.15). CONCLUSION Automated QC of manually delineated HNC OARs can be achieved with a STAPLE consensus contour constructed from 5 ABAS. Parotid, mandible, and submandibular gland structures can be flagged for manual review and user intervention if the DSC and HD exceed the action levels defined during the commissioning process. Further investigation is necessary to improve the AS results for the brachial plexus and larynx. Sean Berry, Harini Veeraraghavan, and Margie Hunt hold grants from Varian Medical Systems unrelated to this project.

Proton Radiation Therapy for Local Control in a Case of Osteosarcoma of the Neck

A 33-year-old man with symptomatic, unresectable osteosarcoma of the neck experienced disease progression despite treatment with multiple systemic agents. Given the tumor location, adjacent to the spinal cord and encasing the brachial plexus, proton beam therapy was recommended instead of conventional photon radiation therapy. The treatment was delivered in 3 weekly 10 cobalt-gray equivalents fractions, and there was minimal associated toxicity. There has been significant improvement in the patients presenting symptoms as well as radiologically stable disease at 1 year. A photon intensity-modulated radiation therapy plan was created retrospectively for dosimetric comparison and demonstrated noninferiority, thereby highlighting the need for judicious use of proton therapy in certain cases.