The influence of the dwell time deviation constraint (DTDC) parameter on dosimetry with IPSA optimisation for HDR prostate brachytherapy.

Purpose:Dose inhomogeneity is inherent to high dose rate (HDR) brachytherapy treatment technique. The use of the generalized equivalent uniform dose (gEUD) in the objective function used for the optimization process is suggested as more effective in addressing inhomogeneity, compared to dose‐ or dose‐volume‐ based objectives. The purpose of the current work is to introduce and study a gEUD‐based objective function in HDR brachytherapytreatment planningoptimization.Method and Materials: A gEUD‐based objective function was used to optimize HDR prostate brachytherapy treatment plans for 12 patients. The quality of these plans has been compared to alternative, dose‐based optimized plans, generated by HIPO, a commercially available optimizer, as implemented in Oncentra Prostate v3.1. The comparison was based on dose‐volume‐histograms (DVHs) and biological indices for each plan. Results: DVH comparisons between the two optimization methods indicate that the gEUD‐based optimization model can lead to equivalent or better target coverage while better sparing the normal tissue structures than the dose‐based optimized plans. Comparisons of the resulting gEUD values for each structure and plan showed a statistically significant improvement in normal tissue sparing (6.9% decrease in gEUD values for the bladder and 2.2% for the rectum on average) for the same or better target coverage (1.1% average increase in the gEUD values). Conclusion: The results of this study indicate that biologically‐based optimization can significantly improve the quality of the treatment plan in HDR brachytherapy. Considering the very high doses per fraction delivered by this treatment method, better sparing of the normal tissue structures obtained by gEUD‐based optimization may be of high importance for the patient's clinical outcome.

To obtain dose distributions more physically representative to the patient anatomy in brachytherapy, calculation algorithms that can account for heterogeneity are required. The current standard AAPM Task Group No 43 (TG-43) dose calculation formalism has some clinically relevant dosimetric limitations. Lack of tissue heterogeneity and scattered dose corrections are the major weaknesses of the TG-43 formalism and could lead to systematic dose errors in target volumes and organs at risk. Over the last decade, model-based dose calculation algorithms (MBDCAs) have been clinically offered as complementary algorithms beyond the TG43 formalism for high dose rate (HDR) brachytherapy treatment planning. These algorithms provide enhanced dose calculation accuracy by using the information in the patient's computed tomography images, which allows modeling the patient's geometry, material compositions, and the treatment applicator. Several researchers have investigated the implementation of MBDCAs in HDR brachytherapy for dose optimization, but moving toward using them as primary algorithms for dose calculations is still lagging. Therefore, an overview of up-to-date research is needed to familiarize clinicians with the current status of the MBDCAs for different cancers in HDR brachytherapy. In this paper, we review the MBDCAs for HDR brachytherapy from a dosimetric perspective. Treatment sites covered include breast, gynecological, lung, head and neck, esophagus, liver, prostate, and skin cancers. Moreover, we discuss the current status of implementation of MBDCAs and the challenges.

A method has been developed to permit the calculation of dwell times for endobronchial high dose rate (HDR) brachytherapy treatment using two catheters, without using a dedicated treatment planning system. Worksheets were developed to guide a user through manual calculations, and a computer program was written to automate the process. This empirical algorithm produces dose distributions that are clinically safe and reasonable. The total dwell times match those predicted by individually optimized distributions to within a few percent. The method has been used most frequently as a quality assurance check on optimized plans produced by a commercial treatment planning system, but it can serve as a back-up method should the commercial system fail. [Worksheets with example calculations may be retrieved using anonymous ftp from the American Institute of Physics, Electronic Physics Auxillary Publication Service (EPAPS).]

To develop and validate a class solution for inverse planning simulated annealing (IPSA) with CT based prostate high dose rate brachytherapy (HDR). Between November 2008 and November 2011, our institution treated 40 prostate cancer patients with HDR in 7 Gy fractions followed by external beam radiotherapy. The HDR treatments were planned with Nucletron Oncentra using manual graphical optimization (GO). Plans were optimized to the following clinical goals: = 95% of prostate volume received 7 Gy, < 1 cc of rectum received 5.6 Gy, < 0.1 cc of rectum received 6.3 Gy, and < 0.01 cc of urethra received 8.75 Gy. New plans were manually customized using IPSA (MC-IPSA) for each patient to match prostate coverage by the prescription dose to within ± 1% of the GO plans while meeting the rectal and urethral dose constraints. An IPSA class solution (CS-IPSA) was created from the mean MC-IPSA parameters. New plans were developed for each of these 40 patients using only CS-IPSA with no further optimization. Additionally, plans were created on an independent dataset of 30 different patients using only CS-IPSA with no further optimization. Plans were optimized in about 30 minutes using GO, MC-IPSA took an average of 14.1 ± 6.5 minutes, and CS-IPSA optimizationwas < 1 minute. There was no significant difference (p > 0.05) among the optimization methods for all clinical goals over the 40 CS-IPSA source patients. There was no significant difference (p > 0.05) between the source and the independent datasets for all clinical goals when using CS-IPSA with no further optimization. A prostate HDR IPSA class solution was developed and validated on a source and an independent dataset. The IPSA class solution yields plans comparable to custom manual IPSA and graphical optimization while saving considerable time.

Brachytherapy (BT) deals with high gradient internal dose irradiation made up of a complex system where the source is placed nearby the tumor to destroy cancerous cells. A primary concern of clinical safety in BT is quality assurance to ensure the best matches between the delivered and prescribed doses targeting small volume tumors and sparing surrounding healthy tissues. Hence, the purpose of this study is to evaluate the performance of a point size inorganic scintillator detector (ISD) in terms of high dose rate brachytherapy (HDR-BT) treatment. A prototype of the dose verification system has been developed based on scintillating dosimetry to measure a high dose rate while using an 192 Ir BT source. The associated dose rate is measured in photons/s employing a highly sensitive photon counter (design data: 20 photons/s). Dose measurement was performed as a function of source-to-detector distance according to TG43U1 recommendations. Overall measurements were carried out inside water phantoms keeping the ISD along the BT needle; a minimum of 0.1cm distance was maintained between each measurement point. The planned dwell times were measured accurately from the difference of two adjacent times of transit. The ISD system performances were also evaluated in terms of dose linearity, energy dependency, scintillation stability, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR). Finally, a comparison was presented between the ISD measurements and results obtained from TG43 reference dataset. The detection efficiency of the ISD was verified by measuring the planned dwell times at different dwell positions. Measurements demonstrated that the ISD has a perfectly linear behavior with dose rate (R2 =1) and shows high SNR (>35) and SBR (>36) values even at the lowest dose rate investigated at around 10cm from the source. Standard deviation (1σ) remains within 0.03% of signal magnitude, and less than 0.01% STEM signal was monitored at 0.1cm source-to-detector distance. Stability of 0.54% is achieved, and afterglow stays less than 1% of the total signal in all the irradiations. Excellent symmetrical behavior of the dose rate regarding source position was observed at different radiation planes. Finally, a comparison with TG-43 reference dataset shows that corrected measurements agreed with simulation data within 1.2% and 1.3%, and valid for the source-to-detector distance greater than 0.25cm. The proposed ISD in this study anticipated that the system could be promoted to validate with further clinical investigations. It allows an appropriate dose verification with dwell time estimation during source tracking and suitable dose measurement with a high spatial resolution both nearby (high dose gradient) and far (low dose gradient) from the source position.

An Analysis of Learning Curve Effect on the Speed and Quality of High Dose Rate Prostate Brachytherapy Procedures

High dose rate afterloading intraluminal brachytherapy in malignant airway obstruction of lung cancer

Automated Plan Checks in High Dose Rate Prostate Brachytherapy Using Custom Scripts in a Commercially Available Spreadsheet Application

In this study, a method was developed for delivering high dose rate (HDR) brachytherapy treatments to basal cell carcinomas (BCCs) as well as squamous cell carcinomas (SCCs) of the lower eyelid via superficial catheters. Clinically-realistic BCC/SCC treatment areas were marked in the lower-eyelid region on a head phantom and several arrangements of catheters and bolus were trialled for treating those areas. The use of one or two catheters of different types was evaluated, and sources of dosimetric uncertainty (including air gaps) were evaluated and mitigated. Test treatments were planned for delivery with an iridium-192 source, using the Oncentra Brachy treatment planning system (Elekta AB, Stockholm, Sweden). Dose distributions were evaluated using radiochromic film. The proposed method was shown to be clinically viable, for using superficial HDR brachytherapy to overcome anatomical difficulties and create non-surgical treatments for BCC and SCC of the lower eyelid.

Purpose: To statistically find out the achievable and practical simulation tolerance for HDR cylinder treatment using scout AP/LAT images and the corresponding organ at risks dosimetry effects. Methods: Five previously treated vaginal cuff cancer patients were randomly selected. All of the patients had prescription of 5 mm above the cylinder surface with 500 cGy per fraction for 5 fractions. The treatment plans were developed using the Oncentra treatment planning system with graphical local optimization method. Two scouts (AP/LAT) were taken during CT scan day and each fraction treatment day. The dummy source was placed in the cylinder and the tip of the dummy source to the top of the pubic bone vertical distance on the AP scout was recorded. The cylinder diameter was also measured. The LAT dummy source angle relative to the horizontal line was also recorded. The treatment for each fraction was then reconstructed using AP/LAT scout images. The source position was registered back to the planning CT. A dummy cumulative plan was then created with a prescription of 2500 cGy for 1 fraction. Results: The AP shifts were ranging from −5 mm to 10 mm and the LAT shifts were ranging from −13 deg to 9 deg. The percentage dose difference can be ranging up 0.3%–14% for the rectum and −17.8%–8.0% for the bladder. Based on the statistics results, we propose the pre‐treatment simulation tolerance: trying to maintain the cylinder in AP direction shift under 5 mm, a warning zone is 5 mm‐10 mm. For the lateral angle, the tolerance is trying to maintain the angle difference under 5 degree with 5–10 degree as warning zone. Conclusion: We have done pre‐treatment simulation quality assurance study using AP/LAT scout images. The tolerance for this pre‐treatment simulation was proposed. The relative dosimetry effects for the rectum and bladder were reported.

Dosimetric verification of a high dose rate brachytherapy treatment planning system in homogeneous and heterogeneous media

PP03 Presentation Time: 9:20 AM: Patterns of Failure for Salvage HDR Prostate Brachytherapy in the Prostate PET Imaging Era

Purpose:The purpose of this work was to develop a quality assurance (QA) system for high dose rate (HDR) brachytherapy to verify the absolute position of an 192Ir source in real time and to measure dwell time and position of the source simultaneously with a movie recorded by a web camera.Methods:A web camera was fixed 15 cm above a source position check ruler to monitor and record 30 samples of the source position per second over a range of 8.0 cm, from 1425 mm to 1505 mm. Each frame had a matrix size of 480×640 in the movie. The source position was automatically quantified from the movie using in‐house software (built with LabVIEW) that applied a template‐matching technique. The source edge detected by the software on each frame was corrected to reduce position errors induced by incident light from an oblique direction. The dwell time was calculated by differential processing to displacement of the source. The performance of this QA system was illustrated by recording simple plans and comparing the measured dwell positions and time with the planned parameters.Results:This QA system allowed verification of the absolute position of the source in real time. The mean difference between automatic and manual detection of the source edge was 0.04 ± 0.04 mm. Absolute position error can be determined within an accuracy of 1.0 mm at dwell points of 1430, 1440, 1450, 1460, 1470, 1480, 1490, and 1500 mm, in three step sizes and dwell time errors, with an accuracy of 0.1% in more than 10.0 sec of planned time. The mean step size error was 0.1 ± 0.1 mm for a step size of 10.0 mm.Conclusion:This QA system provides quick verifications of the dwell position and time, with high accuracy, for HDR brachytherapy.This work was supported by the Japan Society for the Promotion of Science Core‐to‐Core program (No. 23003).

Genitourinary Toxicity In Prostate Cancer Patients With History Of Transurethral Resection Of The Prostate Undergoing High Dose Rate Brachytherapy With A Novel Urethral-Sparing Technique

Updated results of MR-assisted focal salvage HDR prostate brachytherapy: a prospective study.