Susan Richardson

Dosimetric effects of air pockets around high-dose rate brachytherapy vaginal cylinders.

PURPOSE Most physicians use a single-channel vaginal cylinder for postoperative endometrial cancer brachytherapy. Recent published data have identified air pockets between the vaginal cylinders and the vaginal mucosa. The purpose of this research was to evaluate the incidence, size, and dosimetric effects of these air pockets. METHODS AND MATERIALS 25 patients receiving postoperative vaginal cuff brachytherapy with a high-dose rate vaginal cylinders were enrolled in this prospective data collection study. Patients were treated with 6 fractions of 200 to 400 cGy per fraction prescribed at 5 mm depth. Computed tomography simulation for brachytherapy treatment planning was performed for each fraction. The quantity, volume, and dosimetric impact of the air pockets surrounding the cylinder were quantified. RESULTS In 25 patients, a total of 90 air pockets were present in 150 procedures (60%). Five patients had no air pockets present during any of their treatments. The average number of air pockets per patient was 3.6, with the average total air pocket volume being 0.34 cm(3) (range, 0.01-1.32 cm(3)). The average dose reduction to the vaginal mucosa at the air pocket was 27% (range, 9-58%). Ten patients had no air pockets on their first fraction but air pockets occurred in subsequent fractions. CONCLUSION Air pockets between high-dose rate vaginal cylinder applicators and the vaginal mucosa are present in the majority of fractions of therapy, and their presence varies from patient to patient and fraction to fraction. The existence of air pockets results in reduced radiation dose to the vaginal mucosa.

A new method of anatomically conformal vaginal Cuff HDR brachytherapy

OBJECTIVE HDR brachytherapy to the vaginal cuff using rigid intracavitary cylinders has a limited capacity to adapt to patient-specific anatomy. This study describes the use and dosimetry of a new method of anatomically conformal post-operative vaginal cuff HDR brachytherapy using an intra-vaginal balloon applicator. METHODS Thirty consecutive patients with endometrial carcinoma underwent a hysterectomy and received adjuvant HDR brachytherapy in 6 weekly fractions using an intra-vaginal balloon. Optimal distension of the balloon to conform to the vaginal cuff was clinically determined to achieve complete balloon surface apposition with the vaginal mucosa and was confirmed radiographically. Radiation dose was prescribed to the vaginal mucosa and brachytherapy CT simulation was performed to optimize the irradiation dose in 3-D. RESULTS 180 brachytherapy procedures were performed. The mean volume of balloon distension was 47.3 cc (range 20.8-83.8 cc; +/-11.3 cc). The mean dose from brachytherapy to the 2 cc volume of the bladder and rectum was 48.6% and 71.1% of the prescribed vaginal mucosal dose, respectively. Bladder and rectal doses increased as a function of balloon volume. 100% of the prescribed dose covered an average of 95.6% of the vaginal cuff. There were no acute complications or vaginal cuff recurrences at a mean follow-up of 13 months. CONCLUSIONS Post-operative vaginal cuff HDR brachytherapy using an intra-vaginal balloon applicator which conforms to the individual patients vaginal cuff provides excellent radiation dose coverage of the vaginal mucosa with acceptable doses to the bladder and rectum.

A 2-year review of recent Nuclear Regulatory Commission events: What errors occur in the modern brachytherapy era?

PURPOSE To perform a retrospective analysis of recently reported brachytherapy errors to the Nuclear Regulatory Commission and to compare with historical trends. METHODS All events reported in the 2-year period from January 1, 2009 to December 31, 2010 were categorized and analyzed. The 4 main areas of dose delivery were Gamma Knife radiosurgery, therapeutic radiopharmaceutical administration, high-dose-rate brachytherapy, and low-dose-rate brachytherapy. The different types of errors were wrong site, wrong dose, unintended exposure, lost or leaking source, or other. The causes of events were specified as the following: communication errors, equipment malfunction, human error, lack of training, or miscellaneous. RESULTS One hundred and forty-seven events were found in the 2-year period. This error reporting rate far surpasses previous reports. The greatest number of events reported was for low-dose-rate brachytherapy, and the most common cause of error was human error. Wrong dose was the error that occurred most often, followed by wrong site. CONCLUSIONS Very simple treatment errors, such as wrong patient, or wrong side of patient treated, are still occurring. Newer, complex deliveries such as high-dose-rate partial breast irradiation and low-dose-rate prostate brachytherapy also had a large number of events reported in this sampling. This report can help institutions establish needs for quality assessment and quality control processes.

Dosimetric effects of an air cavity for the SAVI™ partial breast irradiation applicator

PURPOSE To investigate the dosimetric effect of the air inside the SAVI™ partial breast irradiation device. METHODS The authors have investigated how the air inside the SAVI™ partial breast irradiation device changes the delivered dose from the homogeneously calculated dose. Measurements were made with the device filled with air and water to allow comparison to a homogenous dose calculation done by the treatment planning system. Measurements were made with an ion chamber, TLDs, and film. Monte Carlo (MC) simulations of the experiment were done using the EGSnrc suite. The MC model was validated by comparing the water-filled calculations to those from a commercial treatment planning system. RESULTS The magnitude of the dosimetric effect depends on the size of the cavity, the arrangement of sources, and the relative dwell times. For a simple case using only the central catheter of the largest device, MC results indicate that the dose at the prescription point 1 cm away from the air-water boundary is about 9% higher than the homogeneous calculation. Independent measurements in a water phantom with a similar air cavity gave comparable results. MC simulation of a realistic multidwell position plan showed discrepancies of about 5% on average at the prescription point for the largest device. CONCLUSIONS The dosimetric effect of the air cavity is in the range of 3%-9%. Unless a heterogeneous dose calculation algorithm is used, users should be aware of the possibility of small treatment planning dose errors for this device and make modifications to the treatment delivery, if necessary.

Improve definition of titanium tandems in MR-guided high dose rate brachytherapy for cervical cancer using proton density weighted MRI

BackgroundFor cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid. Standard T2-weighted (T2W) MRI has good tumor-tissue contrast. However, it suffers from poor uterus-tandem contrast, which makes the tandem delineation very challenging. In this study, we evaluated the possibility of using proton density weighted (PDW) MRI to improve the definition of titanium tandems.MethodsBoth T2W and PDW MRI images were obtained from each cervical cancer patient. Imaging parameters were kept the same between the T2W and PDW sequences for each patient except the echo time (90 ms for T2W and 5.5 ms for PDW) and the slice thickness (0.5 cm for T2W and 0.25 cm for PDW). Uterus-tandem contrast was calculated by the equation C = (Su-St)/Su, where Su and St represented the average signal in the uterus and the tandem, respectively. The diameter of the tandem was measured 1.5 cm away from the tip of the tandem. The tandem was segmented by the histogram thresholding technique.ResultsPDW MRI could significantly improve the uterus-tandem contrast compared to T2W MRI (0.42±0.24 for T2W MRI, 0.77±0.14 for PDW MRI, p=0.0002). The average difference between the measured and physical diameters of the tandem was reduced from 0.20±0.15 cm by using T2W MRI to 0.10±0.11 cm by using PDW MRI (p=0.0003). The tandem segmented from the PDW image looked more uniform and complete compared to that from the T2W image.ConclusionsCompared to the standard T2W MRI, PDW MRI has better uterus-tandem contrast. The information provided by PDW MRI is complementary to those provided by T2W MRI. Therefore, we recommend adding PDW MRI to the simulation protocol to assist tandem delineation process for cervical cancer patients.

Split-Field Helical Tomotherapy With or Without Chemotherapy for Definitive Treatment of Cervical Cancer

OBJECTIVE The objective of this study was to investigate the chronic toxicity, response to therapy, and survival outcomes of patients with cervical cancer treated with definitive pelvic irradiation delivered by helical tomotherapy (HT), with or without concurrent chemotherapy. METHODS AND MATERIALS There were 15 patients with a new diagnosis of cervical cancer evaluated in this study from April 2006 to February 2007. The clinical stages of their disease were Stage Ib1 in 3 patients, Ib2 in 3, IIa in 2, IIb in 4, IIIb in 2, and IVa in 1 patient. Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) simulation was performed in all patients. All patients received pelvic irradiation delivered by HT and high-dose-rate (HDR) brachytherapy. Four patients also received para-aortic irradiation delivered by HT. Thirteen patients received concurrent chemotherapy. Patients were monitored for chronic toxicity using the Common Terminology Criteria for Adverse Events version 3.0 criteria. RESULTS The median age of the cohort was 51 years (range, 29-87 years), and the median follow-up for all patients alive at time of last follow-up was 35 months. The median overall radiation treatment time was 54 days. One patient developed a chronic Grade 3 GI complication. No other Grade 3 or 4 complications were observed. At last follow-up, 3 patients had developed a recurrence, with 1 patient dying of disease progression. The 3-year progression-free and cause-specific survival estimates for all patients were 80% and 93%, respectively. CONCLUSION Intensity-modulated radiation therapy delivered with HT and HDR brachytherapy with or without chemotherapy for definitive treatment of cervical cancer is feasible, with acceptable levels of chronic toxicity.

Design and dosimetric characteristics of a new endocavitary contact radiotherapy system using an electronic brachytherapy source

PURPOSE To present design aspects and acceptance tests performed for clinical implementation of electronic brachytherapy treatment of early stage rectal adenocarcinoma. A dosimetric comparison is made between the historically used Philips RT-50 unit and the newly developed Axxent(®) Model S700 electronic brachytherapy source manufactured by Xoft (iCad, Inc.). METHODS Two proctoscope cones were manufactured by ElectroSurgical Instruments (ESI). Two custom surface applicators were manufactured by Xoft and were designed to fit and interlock with the proctoscope cones from ESI. Dose rates, half value layers (HVL), and percentage depth dose (PDD) measurements were made with the Xoft system and compared to historical RT-50 data. A description of the patient treatment approach and exposure rates during the procedure is also provided. RESULTS The electronic brachytherapy system has a lower surface dose rate than the RT-50. The dose rate to water on the surface from the Xoft system is approximately 2.1 Gy∕min while the RT-50 is 10-12 Gy∕min. However, treatment times with Xoft are still reasonable. The HVLs and PDDs between the two systems were comparable resulting in similar doses to the target and to regions beyond the target. The exposure rate levels around a patient treatment were acceptable. The standard uncertainty in the dose rate to water on the surface is approximately ±5.2%. CONCLUSIONS The Philips RT-50 unit is an out-of-date radiotherapy machine that is no longer manufactured with limited replacement parts. The use of a custom-designed proctoscope and Xoft surface applicators allows delivery of a well-established treatment with the ease of a modern radiotherapy device. While the dose rate is lower with the use of Xoft, the treatment times are still reasonable. Additionally, personnel may stand farther away from the Xoft radiation source, thus potentially reducing radiation exposure to the operator and other personnel.

American Association of Physicists in Medicine Task Group 263: Standardizing Nomenclatures in Radiation Oncology

A substantial barrier to the single- and multi-institutional aggregation of data to supporting clinical trials, practice quality improvement efforts, and development of big data analytics resource systems is the lack of standardized nomenclatures for expressing dosimetric data. To address this issue, the American Association of Physicists in Medicine (AAPM) Task Group 263 was charged with providing nomenclature guidelines and values in radiation oncology for use in clinical trials, data-pooling initiatives, population-based studies, and routine clinical care by standardizing: (1) structure names across image processing and treatment planning system platforms; (2) nomenclature for dosimetric data (eg, dose–volume histogram [DVH]-based metrics); (3) templates for clinical trial groups and users of an initial subset of software platforms to facilitate adoption of the standards; (4) formalism for nomenclature schema, which can accommodate the addition of other structures defined in the future. A multisociety, multidisciplinary, multinational group of 57 members representing stake holders ranging from large academic centers to community clinics and vendors was assembled, including physicists, physicians, dosimetrists, and vendors. The stakeholder groups represented in the membership included the AAPM, American Society for Radiation Oncology (ASTRO), NRG Oncology, European Society for Radiation Oncology (ESTRO), Radiation Therapy Oncology Group (RTOG), Children’s Oncology Group (COG), Integrating Healthcare Enterprise in Radiation Oncology (IHE-RO), and Digital Imaging and Communications in Medicine working group (DICOM WG); A nomenclature system for target and organ at risk volumes and DVH nomenclature was developed and piloted to demonstrate viability across a range of clinics and within the framework of clinical trials. The final report was approved by AAPM in October 2017. The approval process included review by 8 AAPM committees, with additional review by ASTRO, European Society for Radiation Oncology (ESTRO), and American Association of Medical Dosimetrists (AAMD). This Executive Summary of the report highlights the key recommendations for clinical practice, research, and trials.

SU‐E‐J‐79: Proton Density Weighted MRI for MR‐Guided Radiotherapy for Cervical Cancer

Purpose: For cervical cancer patients treated by MR‐guided HDR brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the “tandem and ovoid” applicator. Although T2‐weighted (T2W) MRI has a good tumorcontrast, it is not a good choice for defining the applicator because of signal dropout and geometric distortion around the titanium applicator. In this study, we evaluated the possibility of using proton density weighted (PDW) MRI to improve the definition of the applicator. Methods: Both T2W and PDW images in the para‐sagittal plane were obtained from a 1.5T MRI scanner. For both images sets, in‐plane resolution was 1mm*1mm, spacing between slices was 0mm, TR was set to be between 3000ms and 6000ms, and FOV and the number of slices was adjusted based on the anatomy of individual patients. TE was 90ms and 5.5ms; slice thickness was 5mm and 2.5mm for T2W and PDW MRI respectively. PDW MRI had a smaller coverage in R/L direction. Images were sent to a workstation for treatment planning and another workstation after de‐identification for further image analysis. Results: Images from 10 patients were retrospectively reviewed. PDW MRI had a better definition of the applicator for all cases. A smaller ROI was placed around the tip of the tandem, which only included two structures: the tandem and the uterus. Histograms of signal intensity within the ROI showed that two peaks corresponding to the two structures were clearly separated in PDW MRI but not in T2W MRI. Conclusions: We showed that PDW MRI could provide a good visualization of the applicator. Therefore, we recommend adding PDW MRI to the imaging protocol for MR‐guided radiotherapy for cervical cancer. This will enable us to precisely localize both tumors and the applicator, which is essential for ensuring dose delivery accuracy.

SU‐E‐T‐305: Limitations of Using DICOM Data for BrachyVision Treatment Plan Evaluation

PURPOSE To evaluate the accuracy of a real-time automated method of performing dosimetric quality assurance using Eclipse DICOM files for patients receiving HDR-brachytherapy and IMRT. METHODS GYN patients are treated with concurrent high-dose rate brachtherapy and IMRT. The dosimetric parameters were obtained through an in-house QA program developed using Matlab. The DICOM files containing DVH data for organsat-risk (OAR) were analyzed Dosimetric data for 7 patients (total 42 fractions) were collected for bladder, rectum and sigmoid. The accuracy of the dosimetric parameters was estimated by comparing the parameters obtained from the DICOM based QA program and those in BrachyVision. RESULTS The maximal dose values (Dmax) for the OARs obtained using the DICOM-based program are significantly smaller than those valued reported in BrachyVision by 36.2%-48.3%. The mean dose has a deviation from 1% - 2.4%. The dose for the volume of 2cc (D2cc) has a difference up to 7.6% for structures with the volume larger than 200 cc. The average difference of D2cc is 0.5% for structures less than 200 cc. We found that Eclipse BrachyVision only exports DVH data down to a volume equivalent to 1% of the maximum volume for a given structure. Therefore, the reported maximal dose values obtained from DICOM RT dose file do not accurately reflect the maximum dose in a treatment plan. This will also slightly affect the mean dose calculation and D2cc when the structure volume is larger than 200cc. CONCLUSIONS The automatic QA tool based on DICOM files provides a quick retrieval of dose to organs-at-risk and coverage of targets. However, maximal dose to structures is not accurate due to the truncationof the DVH information contained in DICOM files.