J Cao

Treatment-related acute esophagitis for patients with locoregionally advanced non-small cell lung cancer treated with involved-field radiotherapy and concurrent chemotherapy.

Purpose:To explore the incidence and risk factors for treatment-related acute esophagitis associated with involved-field radiation therapy (RT) delivered concurrently with chemotherapy for patients with locoregionally advanced non–small cell lung cancer. Materials and Methods:Forty-nine consecutive patients diagnosed with locoregionally advanced non–small cell lung cancer were treated using involved-field RT. Radiotherapy target volumes included the primary lung tumor and involved mediastinal lymphadenopathy as defined on imaging studies including computed tomography of the chest and [18F] fluorodeoxyglucose-positron emission tomography/computed tomography. The patients were treated to a median total dose of 63 Gy (range, 55.8 to 74 Gy) using daily fractions of 1.8 or 2.0 Gy. No elective radiotherapy of mediastinal lymph nodes was used. Concurrent platinum-based chemotherapy was delivered to all patients. Treatment-related toxicity was evaluated during the course of RT and subsequent follow-up visits. Results:Thirty-one (63%) patients were female and 18 (37%) were male. Median age at the time of diagnosis was 68 years (range, 36 to 83 y). Thirty-one patients (63%) developed treatment-related acute esophagitis: 24 patients (49%) grade 2 and 7 (14%) patients grade 3 esophagitis, with the peak occurring during the seventh week of radiotherapy. No grade ≥4 esophagitis was seen in this cohort. Eighteen patients (37%) did not develop radiation-induced esophagitis associated with their course of chemoradiotherapy. In the univariate analysis, age at the time of diagnosis, radiation dose per fraction, and total volume of the esophagus were significantly associated with the risk of acute esophagitis. Increasing age reduced the risk of acute esophagitis (odds ratio [OR] for 10-y increase=0.40) as did increasing total esophagus volume (OR for 10-U increase=0.27). Dose per fraction of 1.8 Gy was associated with lower risk of acute esophagitis when compared with dose per fraction of 2 Gy (OR=0.19). Marginal associations were observed for all of the volume variables. Higher volume variable values had a nonsignificant association with an increase in risk of acute esophagitis. However, only the total volume of the esophagus (P=0.0032) and larger dose per fraction (2 vs. 1.8 Gy) (P=0.011) remained significantly associated with higher risk of developing grade ≥2 acute esophagitis in the multivariate analysis. Conclusions:Higher risk of grade ≥2 treatment-related esophagitis was associated with lower total esophageal volume and higher radiotherapy dose per fraction and should be taken into consideration during patient treatment planning. Inclusion of total esophageal volume and dose per fraction into future clinical protocols may further help our understanding of treatment-related esophagitis and enable the development of novel preventative approaches.

Commissioning and implementation of an implantable dosimeter for radiation therapy

In this article we describe commissioning and implementation procedures for the Dose Verification System (DVS) with permanently implanted in vivo wireless, telemetric radiation dosimeters for absolute dose measurements. The dosimeter uses a semiconductor device called a metal–oxide semiconductor field‐effect transistor (MOSFET) to measure radiation dose. A MOSFET is a transistor that is generally used for amplifying or switching electronic signals. The implantable dosimeter was implemented with the goal of verifying the dose delivered to radiation therapy patients. For the purpose of acceptance testing, commissioning, and clinical implementation and to evaluate characteristics of the dosimeter, the following tests were performed: 1) temperature dependence, 2) reproducibility, 3) field size dependence, 4) postirradiation signal drift, 5) dependence on average dose rate, 6) linearity test, 7) angular dependence (different gantry angle position), 8) angular dependence (different DVS angle position), 9) dose rate dependence, 10) irradiation depth dependence, 11) effect of cone‐beam exposure to the dosimeter, and 12) multiple reading effect. The dosimeter is not currently calibrated for use in the kV range; nonetheless, the effect of the cone‐beam procedure on the MOSFET dosimeter was investigated. Phantom studies were performed in both air and water using an Elekta Synergy S Beam‐Modulator linear accelerator. Commissioning and clinical implementation for prostate cancer patients receiving external‐beam radiation therapy were performed in compliance with the general recommendations given for in vivo dosimetry devices. The reproducibility test in water at human body temperature (37°C) showed a 1.4% absolute difference, with a standard deviation of 5.72 cGy (i.e., SD=2.9%). The constancy test shows that the average readings at room temperature were 3% lower compared to the readings at human body temperature, with a SD=2%. Measurements were not dependent upon field size. Due to postirradiation signal drift, the following corrections are suggested: −2.8%, −2%, 0.5%, and 2.5% for the readings taken after 0.5, 1, 5, or 10 min, respectively. Different gantry angles did not influence the readings. The maximum error was less than 1% with a maximum SD=3.61cGy (1.8%) for the gantry angle of 45°. However, readings are dependent on the dosimeter orientation. The average dose reading was 7.89 cGy (SD=1.46cGy) when CBCT imaging was used for the pelvis protocol, and when postirradiation measurement was taken at 2.5 min (expected 2–3 cGy). The clinical implementation of the implantable MOSFET dosimeters for prostate cancer radiation therapy is described. Measurements performed for commissioning show that the dosimeter, if used within specifications, provides sufficient accuracy for its intended use in clinical procedures. The postradiation signal drift, temperature dependence, variation of reproducibility, and rotational isotropy could be encountered if the dosimeter is used outside the manufacturers specifications. The dosimeter can be used as a tool for quantifying dose at depth, as well as to evaluate adherence between planned doses and the delivered doses. Currently, the system is clinically implemented with ±7% tolerance. PACS numbers: 87.53.‐j; 87.55.‐x

Determination of internal target volume using selective phases of a 4-dimensional computed tomography scan

PURPOSE Internal target volume (ITV) is frequently determined by contouring of gross tumor volumes (GTV) on 10 phases of a 4-dimensional computed tomography (4DCT) study set for lung cancer radiotherapy. This study aimed to investigate the possibility of generating ITV by using selective phases of a 4DCT scan. METHODS AND MATERIALS The 4DCT scans of 20 patients with lung cancer were included in this study. GTVs were contoured on 10 phases in Focal4D (CMS, St Louis, MO). Different ITVs were derived by encompassing volumes of contours from selective phases. ITV10 was the combination of GTVs on all of the 10 phases and served as the gold standard volume. All of the other ITVs were smaller and within ITV10. The ratios of the volumes of these ITVs to ITV10 were calculated and used as a criterion to determine the similarity of different ITVs to ITV10. ITV2 represented the ITV derived by using end-inhalation and end-exhalation (0% + 50%). ITV3E was derived from contouring the 3 phases at end-inhalation, mid-exhalation, and end-exhalation (0% + 20% + 50%). ITV3I was derived from contouring the 3 phases at end-inhalation, mid-inhalation, and end-exhalation (0% + 70% + 50%). ITV4 was derived by contouring the 4 phases at end-inhalation, mid-inhalation, end-exhalation, and mid-exhalation (0% + 20% + 50% + 70%). ITV6E was derived from contouring the 6 consecutive phases during exhalation (0% + 10% + 20% + 30% + 40% + 50%). ITV6I was derived from contouring the 6 consecutive phases during inhalation (50% + 60% + 70% + 80% + 90% + 0%). The volumes of ITVs were calculated and compared. RESULTS ITV6I showed excellent agreement with ITV10 (volume ratio ITV6I/ITV10 = 0.975). ITV4 and ITV6E showed good agreement with ITV10 (ITV6E/ITV10 = 0.939, ITV4/ITV10 = 0.944). The volume ratios ITV3I/ITV10 and ITV3E/ITV10 were 0.927 and 0.906, respectively. ITV2 did not agree well with ITV10 (ITV2/ITV10 = 0.888). CONCLUSIONS Contouring all phases during inhalation provides a good estimate of the ITV. However, the ITV may be underestimated if only contouring on 2 extreme phases.

Impact of transrectal ultrasound- and computed tomography-based seed localization on postimplant dosimetry in prostate brachytherapy

PURPOSE To study the impact of seed localization, as performed by different observers using linked (125)I seeds, on postimplant dosimetry in prostate brachytherapy and, to compare transrectal ultrasound (TRUS)-based with CT-based approach for the dosimetric outcomes. METHODS AND MATERIALS Nineteen permanent prostate implants were conducted using linked (125)I seeds. Postimplant TRUS and CT images were acquired and prostate glands were, after implantation, delineated on all images by a single oncologist, who had performed all 19 seeding procedures. Six observers independently localized the seeds on both TRUS and CT images, from which the principle dosimetric parameters V(100) (volume of prostate that received the prescribed dose), V(150) (volume of prostate that received 150% of the prescribed dose), and D(90) (minimal dose delivered to 90% of the prostate) were directly calculated for each patient. A single-factor analysis of variance was first applied to determine interobserver variability in seed localization. A nonparametric comparison of the approach using TRUS and CT was then carried out by the Wilcoxon paired-sample test. RESULTS Analysis from the analysis of variance for TRUS showed that the null hypothesis for equal means, could not be rejected for all six observers based on a significance level alpha=0.05. TRUS-based and CT-based approaches were then cross compared by the Wilcoxon paired-sample test, which suggested that the null hypothesis was insignificant for V(100) and D(90), but was significant for V(150). CONCLUSIONS Both TRUS- and CT-imaging modalities provided indistinguishable postimplant dosimetry results as far as V(100) and D(90) were concerned. There was comparable observer independence between TRUS- and CT-based seed localization for linked-seed implant procedures. With other advantages that TRUS-imaging modality had over CT in the evaluation of postimplant dosimetry, TRUS would be a preferred choice in conjunction with linked seeds for intraoperative procedures in prostate brachytherapy.

SU‐E‐T‐408: Evaluation of the Type and Frequency of Variations Discovered During Routine Secondary Patient Chart Review

Purpose: Desire to improve efficiency and throughput inspired a review of our physics chart check procedures. Departmental policy mandates plan checks pre-treatment, after first treatment and weekly every 3–5 days. This study examined the effectiveness of the “after first” check with respect to improving patient safety and clinical efficiency. Type and frequency of variations discovered during this redundant secondary review was examined over seven months. Methods: A community spreadsheet was created to record variations in care discovered during chart review following the first fraction of treatment and before the second fraction (each plan reviewed prior to treatment). Entries were recorded from August 2014 through February 2015, amounting to 43 recorded variations out of 906 reviewed charts. The variations were divided into categories and frequencies were assessed month-to-month. Results: Analysis of recorded variations indicates an overall variation rate of 4.7%. The initial rate was 13.5%; months 2–7 average 3.7%. The majority of variations related to discrepancies in documentation at 46.5%, followed by prescription, plan deficiency, and dose tracking related variations at 25.5%, 12.8%, and 12.8%, respectively. Minor variations (negligible consequence on patient treatment) outweighed major variations 3 to 1. Conclusion: This work indicates that this redundant secondary check is effective. The first month spike in rates could be due to the Hawthorne/observer effect, but the consistent 4% variation rate suggests the need for periodical re-training on variations noted as frequent to improve awareness and quality of the initial chart review process, which may lead to improved treatment quality, patient safety and increased clinical efficiency. Utilizing these results, a continuous quality improvement process following Deming’s Plan-Do-Study-Act (PDSA) methodology was generated. The first iteration of this PDSA was adding a specific dose tracking checklist item in the pre-treatment plan check assessment; the ramification of which will be assessed in future data.

SU‐E‐T‐136: Measure the Actual Radiation Dose Delivered for Prostate IMRT Treatment Using An Implantable MOSFET Dosimeter

Purpose: To report the initial clinical experience using an in‐vivo, implantable metal oxide semiconductors field effect transistors(MOSFET)dosimeters for the daily dose verification of prostate IMRTtreatment.Methods: The dose verification system (DVS) from Sicel Technologies was used to measure the actual dose delivered for prostate IMRT patients. Fifteen patients (10 prostate IMRT; 5 Sequential IMRT, pelvis then prostate) were implanted with two DVS dosimeters in the prostate gland: one on the right and the other on the left. The location of the DVS dosimeters were identified on the CTimages and the expected doses were calculated. The measured readings of the dosimeters were compared to the expected dose values. Daily orthogonal portal film or CBCT was used for patient setup.Results: The average difference between predicted and measured doses was 1.1% for all 15 patients (30 dosimeters) over the whole course of treatment. The range of the difference between the measured cumulative doses to the planned doses for the whole treatment course was from −5.3% to 5.1%. For three out of fifteen patients, a new plan was created as the measured doses disagreed with the expected value for the original plans. For those three patients, the difference between measured and the predicted doses was as large as 11.3%. The discrepancies were much smaller after replanning. The average dosimeter measurement for the nine prostate IMRTtreatment (exclude one prostate IMRT patient who had been re‐planned) over the course of treatment was decreasing signifying a possible decrease in the sensitivity of the dosimeters Conclusions: This study demonstrated DVS dosimeters could provide valuable information about actual dose delivered and actual dose fluctuations of the daily treatment. The DVS dosimeters could serve as a patient specific quality assurance and guidance for adaptive radiation therapy.

SU‐E‐T‐233: Commissioning of An Implantable Dosimeter for External Beam Radiation Therapy

Purpose: To commission a Dose Verification System (DVS) with permanently implanted in vivo dosimeters. To acquire and evaluate sufficient data for establishing standard of quality in a clinical setting.Methods: DVS is permanent implantable wireless radiation sensor based on MOSFET for absolute dosemeasurements. To evaluate characteristics of dosimeter, following tests were performed: temperature dependence, reproducibility, field size dependence, post‐irradiation signal drift, dependence on average dose‐rate, linearity test, angular dependence, dose‐rate dependence, irradiation depth dependence and a multiple reading effect. Dosimeter is not currently calibrated for use in kV range. Nonetheless, effects of conebeam CT(CBCT) imaging to dosimeter were investigated. Phantom studies were performed in both air and water using an Elekta Synergy‐S Beam‐Modulator linear accelerator. Results: DVS dosimeters have been calibrated to be used at 37C. Reproducibility tests were performed at room temperature. Readings were −3.2% low (SD=2.5%, or 5.06cGy for 200cGy delivered). Same tests in water at human body temperature showed 1.5% absolute difference, with a similar deviation (SD=2.85%). It was observed that measurement signal decayed significantly with time post‐irradiation, from +3% after 0.5min to −3.5% after 10min. Dose linearity was within 2% for absorbed total dose of 75Gy. Signal rapidly decayed after total dose of 82Gy. Angular dependence was −0.3% (SD=2.31%). Readings decreased with increase in depth, about 0.3%/cm. No filed size and dose‐rate difference were observed. Average dose reading due to CBCTimaging using the pelvis protocol was 7.89cGy (SD=1.46cGy) Conclusions: Extensive acceptance and commissioning measurements have shown considerable post‐radiation signal drift, temperature dependence, reproducibility variation, and rotational isotropy. This process confirmed manufacturers stated performance and provided baseline QA necessary to implement DVS clinically. System is currently implemented with ±7% tolerance. Dosimeter can be used to quantify dose at depth, as well as to evaluate adherence between dose from treatment plan and daily delivery.

SU‐E‐T‐291: How Many Sets of Four‐Dimensional Computed Tomography (4DCT) Images Are Needed to Determine the Internal Target Volume (ITV) for Lung Radiation Therapy?

Purpose: For the treatment of patients with lungcancer, internal target volume (ITV) is frequently determined by contouring of gross tumor volumes (GTV) on 10 phases of a four‐dimensional computed tomography (4DCT) scan. This study investigated the possibility of generating ITV by using selective phases of a 4DCT scan. Methods: The 4DCT scans of 20 patients with lungcancer were included in this study. GTVs were contoured on all 10 phases in Focal4D (CMS, St. Louis, MO). Different ITVs were derived by encompassing volumes of contours from selective phases. ITV10 was derived from contouring GTV on all 10 phases and served as the gold standard. All the other ITVs were smaller and within ITV10. The ratios of the volume of ITVs to ITV10 were calculated and used as a criterion to determine the similarity of ITVs to ITV10. ITV2 represented the ITV derived by using end of inhalation and end of exhalation (0%+50%). ITV3E was derived from contouring the three phases at end‐inhalation, mid‐exhalation, end‐exhalation (0%+20%+50%). ITV3I was derived from contouring the three phases at end‐inhalation, mid‐inhalation, end‐exhalation (0%+70%+50%). ITV4 was created by contouring the fours phases at end‐inhalation, mid‐inhalation, end‐exhalation, mid‐exhalation (0%+20%+50%+70%). ITV6E was derived from contouring the six consecutive phases during exhalation (0%+10%+20%+30%+40%+50%). ITV6I was derived from contouring the six consecutive phases during inhalation (50%+60%+70%+80%+90%+0%). Results: ITV6I showed excellent agreement with ITV10 (Volume ratio ITV6I/ITV10=0.975). ITV4 and ITV6E showed good agreement with ITV10 (ITV6E/ITV10=0.939, ITV4/ITV10=0.944). The volume ratio ITV3I/ITV10 and ITV3E/ITV10 was 0.927 and 0.906 respectively. ITV2 did not agree well with ITV10 (ITV2/ITV10 =0.888). Conclusions: Contouring all phases during inhalation will give a good estimate of the internal target volume, while helping to minimize the clinical load and work time during treatment planning. However, the ITV will be underestimated if only contouring on two extreme phases.

SU-GG-T-48: Impact of Seed Localization On Post-Implant Dosimetry in Prostate Brachytherapy

Purpose: To study the impact of seed localization, as performed by different observers using linked I‐125 seeds, on post‐implant dosimetry in prostate brachytherapy and to compare TRUS‐based with CT‐based approach for the dosimetric outcomes. Method and Materials: Permanent prostate implant is conducted using linked I‐125 seeds. Both post‐implant TRUS and CTimages were acquired and the prostate glands were delineated on each of those images by a single oncologist, who performed the seeding procedures for all 19 patients under study. Six observers then independently localized the seeds on both TRUS and CTimages, based on which the principle dosimetric parameters V100, V150 and D90 were directly calculated for each patient. A single‐factor analysis of variance (ANOVA) is first applied to determine inter‐observer variability in seed localization. A non‐parametric comparison of the approach using the two imaging modalities, TRUS and CT, is then carried out by the Wilcoxon paired‐sample test. Results: Analysis from the ANOVA for TRUS (V100: P=0.655; V150: P=0.994; D90: P=0.734) and CT (V100: P=0.901; V150: P=0.999; D90: P=0.99) shows that the null hypothesis for equal means, cannot be rejected for all six observers based on a significance level α=0.05. TRUS‐based and CT‐based approaches are then cross‐compared by the Wilcoxon paired‐sample test, which suggests that the null hypothesis is not rejectable for V100 and D90, but is for V150. Conclusion: Both TRUS and CTimaging modalities provide indistinguishable post‐implant dosimetry results as far as V100 and D90 are concerned. TRUS‐based seed localization has comparable observer independence as CT‐based seed localization for linked‐seed implant procedures. In view of other advantages that TRUSimaging modality has over CT in the evaluation of post‐implant dosimetry,TRUS can therefore be an alternative gold standard to CT and would be a preferred choice together with linked‐seed for intra‐operative procedures ins prostate brachytherapy.

SU‐GG‐T‐20: Dosimetric Analysis and Comparison of Cesium‐131 and Iodine‐125 for Permanent Prostate Brachytherapy

Purpose: To perform a dosimetric analysis and comparison of Cesium‐131 and Iodine‐125 for permanent prostate brachytherapy.Method and Materials:TRUS prostate volume studies of 30 patients treated in our institution with a wide range of prostate size were included in this study. The average gland size was 31.13cc (from 15.22cc to 51.49cc). Treatment plans were generated using Variseed 7.1 with both Cesium‐131 (with an activity of 2.1U, prescription of 115 Gy) and Iodine‐125 (with an activity of 0.521U, prescription of 145 Gy). Prostate, rectum, urethra were contoured by the same radiation oncologist. The Auto Source Placement tool of the software was first used to create treatment plans for both Cesium‐131 and Iodine‐125. The plans were then adjusted to meet the treatment goals and achieve the same dose coverage (V100, V90, D90) of the prostate for both isotopes. The dose to the prostate (V100, V90, V80, D90), rectum (RV100, RD10), urethra (UD10), and dose inhomogeneity (V150, V200) were reported. Results: For 30 patients, the average of V100, V90, V80, D90 for the prostate was 98.58%, 99.46%, 99.95%, 134.7 Gy and 98.49%, 99.57%, 99.87%, 170.4 Gy for Cesium‐131 and Iodine‐125 respectively. V200 and V150 of prostate were 22.06%, 49.20% for Cesium‐131, and 22.57%, 51.38% for Iodine. UD10 and RD10 were 81.17%, 127.79% of the prescription for Cesium‐131, and 82.58%, 129.44% of the prescription for Iodine. There was a decrease of 27.5% rectum RV100 (0.24cc for Cesium, and 0.33 for Iodine, with a p‐value of 0.05) when planning for Cesium‐131 as compared to Iodine‐125. Conclusion: Cesium‐131 prostate brachytherapy can provide a homogeneous dose distribution, dose coverage compared with Iodine‐125 seeds implant, while reducing the overall dose to the rectum. Large volume of patient studies is needed to validate this statement.