Herbert W. Mower

Quality assurance methodology for Varian RapidArc treatment plans

With the commercial introduction of the Varian RapidArc, a new modality for treatment planning and delivery, the need has arisen for consistent and efficient techniques for performing patient‐specific quality assurance (QA) tests. In this paper we present our methodology for a RapidArc treatment plan QA procedure. For our measurements we used a 2D diode array (MapCHECK) embedded at 5 cm water equivalent depth in MapPHAN 5 phantom and an Exradin A16 ion chamber placed in six different positions in a cylindrical homogeneous phantom (QUASAR). We also checked the MUs for the RapidArc plans by using independent software (RadCalc). The agreement between Eclipse calculations and MapCHECK/MapPHAN 5 measurements was evaluated using both absolute distance‐to‐agreement (DTA) and gamma index with 10% dose threshold (TH), 3% dose difference (DD), and 3 mm DTA. The average agreement was 94.4% for the DTA approach and 96.3% for the gamma index approach. In high‐dose areas, the discrepancy between calculations and ion chamber measurements using the QUASAR phantom was within 4.5% for prostate cases. For the RadCalc calculations, we used the average SSD along the arc; however, for some patients the agreement for the MUs obtained with RadCalc versus Eclipse was inadequate (discrepancy>5%). In these cases, the plan was divided into partial arc plans so that RadCalc could perform a better estimation of the MUs. The discrepancy was further reduced to within ~4% using this approach. Regardless of the variation in prescribed dose and location of the treated areas, we obtained very good results for all patients studied in this paper. PACS number: 87.55.Qr

Code of Ethics for the American Association of Physicists in Medicine: report of Task Group 109.

A comprehensive Code of Ethics for the members of the American Association of Physicists in Medicine (AAPM) is presented as the report of Task Group 109 which consolidates previous AAPM ethics policies into a unified document. The membership of the AAPM is increasingly diverse. Prior existing AAPM ethics polices were applicable specifically to medical physicists, and did not encompass other types of members such as health physicists, regulators, corporate affiliates, physicians, scientists, engineers, those in training, or other health care professionals. Prior AAPM ethics policies did not specifically address research, education, or business ethics. The Ethics Guidelines of this new Code of Ethics have four major sections: professional conduct, research ethics, education ethics, and business ethics. Some elements of each major section may be duplicated in other sections, so that readers interested in a particular aspect of the code do not need to read the entire document for all relevant information. The prior Complaint Procedure has also been incorporated into this Code of Ethics. This Code of Ethics (PP 24-A) replaces the following AAPM policies: Ethical Guidelines for Vacating a Position (PP 4-B); Ethical Guidelines for Reviewing the Work of Another Physicist (PP 5-C); Guidelines for Ethical Practice for Medical Physicists (PP 8-D); and Ethics Complaint Procedure (PP 21-A). The AAPM Board of Directors approved this Code or Ethics on July 31, 2008.

Treatment planning methodology for the Miami Multichannel Applicator following the American Brachytherapy Society recently published guidelines: the Lahey Clinic experience

The objective of this study was to develop a standardized procedure from simulation to treatment delivery for the multichannel Miami applicator, in order to increase planning consistency and reduce errors. A plan is generated prior to the 1st treatment using the CT images acquired with the applicator in place, and used for all 3 fractions. To confirm the application placement before each treatment fraction, an AP image is acquired and compared with the AP baseline image taken at simulation. A preplanning table is generated using the EBRT doses and is used to compute the maximum allowable D2cc for bladder, rectum, and sigmoid, and the mean allowable dose for the upper vaginal wall per HDR brachytherapy fraction. These data are used to establish the criteria for treatment planning dose optimization. A step‐by‐step treatment planning approach was developed to ensure appropriate coverage for the tumor (D90>100% prescribed dose of 700 cGy/fraction) and the uninvolved vaginal surface (dose for the entire treatment length > 600 cGy/fraction), while keeping the organs at risk below the tolerance doses. The equivalent dose 2 Gy (EQD2) tolerances for the critical structures are based on the American Brachytherapy Society (ABS) recently published guidelines. An independent second check is performed before the 1st treatment using an in‐house Excel spreadsheet. This methodology was successfully applied for our first few cases. For these patients: the cumulative tumor dose was 74–79 EQD2 Gy10 (ABS recommended range 70–85); tumor D90 was >100% of prescribed dose (range 101%–105%); cumulative D2cc for bladder, rectum, and sigmoid were lower than the tolerances of 90, 75, and 75 EQD2 Gy3, respectively; cumulative upper vaginal wall mean dose was below the tolerance of 120 EQD2 Gy3; the second check agreement was within 5%. By using a standardized procedure the planning consistency was increased and all dosimetric criteria were met. PACS numbers: 87.55‐x, 87.56 bg

Anniversary Paper: AAPM Education Council: Looking back or looking forward

As we celebrate the 50th year of the American Association of Physicists in Medicine (AAPM), what better time to look back at our development as well as to look forward to the opportunities that lie ahead. Here the authors will review some of the achievements of the Education Council and show how the activities are helping to shape the future educational goals and opportunities of the AAPM and the medical physics profession. Much of the work of the Education Council is carried out by the various committees and subcommittees that make up the Council or have a liaison relationship with the Council.

Retrospective review of Contura HDR breast cases to improve our standardized procedure

To retrospectively review our first 20 Contura high dose rate breast cases to improve and refine our standardized procedure and checklists. We prepared in advance checklists for all steps, developed an in-house Excel spreadsheet for second checking the plan, and generated a procedure for efficient contouring and a set of optimization constraints to meet the dose volume histogram criteria. Templates were created in our treatment planning system for structures, isodose levels, optimization constraints, and plan report. This study reviews our first 20 high dose rate Contura breast treatment plans. We followed our standardized procedure for contouring, planning, and second checking. The established dose volume histogram criteria were successfully met for all plans. For the cases studied here, the balloon-skin and balloon-ribs distances ranged between 5 and 43 mm and 1 and 33 mm, respectively; air_seroma volume/PTV_Eval volume≤5.5% (allowed≤10%); asymmetry<1.2mm (goal≤2 mm); PTV_Eval V90%≥97.6%; PTV_Eval V95%≥94.9%; skin max dose≤98%Rx; ribs max dose≤137%Rx; V150%≤29.8 cc; V200%≤7.8 cc; the total dwell time range was 225.4 to 401.9 seconds; and the second check agreement was within 3%. Based on this analysis, more appropriate ranges for the total dwell time and balloon diameter tolerance were found. Three major problems were encountered: balloon migration toward the skin for small balloon-to-skin distances, lumen obstruction, and length change for the flexible balloon. Solutions were found for these issues and our standardized procedure and checklists were updated accordingly. Based on our review of these cases, the use of checklists resulted in consistent results, indicating good coverage for the target without sacrificing the critical structures. This review helped us to refine our standardized procedure and update our checklists.

SU‐E‐T‐138: Quantification of Dwell Position Inaccuracy in Varian GammaMed HDR Titanium Ring Applicators

PURPOSE To quantify the dwell position inaccuracy in Titanium ring applicators and develop a test to be performed quarterly, after source exchange. METHODS All three rings from our Titanium kit (30, 45, 60 deg.) were used for this study. EDR2 film was placed on the Simulator table and a ring was taped to the film, with a solid water slab as buildup. A 1-cm spacing dummy wire was inserted into the ring. The film was exposed using 135 kV, 80 mA, 400 mAs. An HDR treatment was then delivered using the even source dwell positions from 2 to 16, with a 5 mm step size, nominal dwell time 0.4 sec/position. The procedure was repeated three times for each ring. The films were scanned and analyzed with the RIT software. The distance between the center of each source position to the adjacent dummy dots was measured for each ring on all three films. An average shift (AS) was obtained for each ring.New films were exposed with a treatment offset equal and in the opposite direction relative to the AS for the ring used. The films were visually inspected to assess if the source positions are centered in between two adjacent dummy dots, and also scanned and analyzed with the RIT software. This test will be performed quarterly to verify if the shifts remain stable. RESULTS The average shift was 2.5, 2.4, and 2.4 mm distally for the 30, 45, and 60 deg. rings, respectively. The offset for the quarterly test was set to 2 mm proximally, to take into account the 1 mm tolerance for the source position. CONCLUSIONS The dwell position inaccuracy in Titanium ring applicators was quantified and the quarterly test was successfully performed for two quarters. Work is started to assess the dosimetric implications of this shift.

SU‐E‐T‐418: Characteristics of MLC Leaf Positioning Errors in VMAT Delivery for SBRT Plans

Purpose: Volumetric modulated arc therapy (VMAT) is a favored modality for SRS/SBRT treatment due to the efficiency in delivery and high conformality to targets achievable by this technique. Due to the dynamic characteristics of the MLC movement throughout the delivery process, tolerance is necessary in the system configuration for the deviation of MLC leaf position from the planned position. This work examines the characteristics of the MLC positioning errors in VMAT delivery. Methods: Five RapidArc fields with a mean MU=892 planned for SBRTlung cases were selected for this study. Each field was delivered 8 times using a Varian Trilogy machine. The MLC leaf positions were recorded at 50ms intervals by the MLC controller into the system dynalog files. The analysis of the dynalog files yields the statistics of the MLC position error and leaf bank gap error. The cumulative distribution functions(CDF) for the errors were calculated. These distribution functions were compared with the configured limit of 2 mm at the isocenter for dynamic leaf tolerance. Results: The distribution function of the leaf positioning error peaked at 0.5mm for each delivery. No violation on the system limitation was observed. The standard deviation from repeated delivery of the same field is very small. For all the fields, 90%, 95%, and 99% of the leaf positioning errors (E90, E95, E98) are within 0.50, 0.69, and 0.94 mm. The leaf gap error has similar overall characteristics as the leaf positioning error. E90, E95, E98 for the gap errors are respectively 0.69, 0.87 and 1.3 mm. Conclusions: The MLC leaf positioning errors are within the system tolerance throughout VMAT delivery.Cumulative distribution function is a useful method for analyzing these errors. The statistical characteristics and some key statistical parameters for the MLC positioning error and the leaf gap errors were obtained.

SU-E-T-597: Starting an HDR Breast Implant Program Using the Contura Multilumen Balloon

Purpose: To prepare all forms, establish criteria for dose volume histogram (DVH) for automatic plan optimization, and analyze various treatment planning approaches for the HDR ‐ Contura multilumen balloon breast implant modality. Methods: We established a strategy to increase our efficiency in planning and treating partial breast implants. We prepared in advance the checklist for the day of simulation, the list for second checking the plan, and the treatment delivery checklist. Also, we developed in‐house software for plan second check. We generated a procedure for proficient contouring, and a set of optimization constraints to meet the DVH criteria. Templates were created in our TPS (Brachyvision 8.6) for structures, isodose levels, optimization constraints, and plan report. The vendor provided images for four anonimized patients with various levels of planning difficulty. For these cases we generated treatment plans using: a) central lumen only; b) the four peripheral lumens; and c) all five lumens. Although using either the central lumen alone or the four peripheral lumens could result in a good plan for cases of low and intermediate level of difficulty, we decided to load all five lumens for all future patients to increase plan flexibility.Results: We knowledgeably used the approach and forms described above for our first five patients. For each case we checked for any balloon asymmetry, measured the balloon to skin and ribs distances, and contoured air and seroma to evaluate patient eligibility. We did all the contours following the guidelines we formulated. The established DVH criteria were successfully met for all plans. Second check was performed using our in‐house software (discrepancy within 5%) Conclusions: The work presented here helped us to gain experience and increased our efficiency in HDR breast planning and treatment. It may also help other groups to start such a program in their clinic.

SU‐E‐T‐894: Rapid Arc for Stereotactic Body Radiotherapy

Purpose: To compare Rapid Arc treatment planning with current standard 3D/IMRT technique in stereotactic body radiotherapy(SBRT) and to evaluate the difference in total treatment delivery time.Methods: Ten SBRT patient plans were selected, 5 treated with IMRT or 3D conformal and 5 treated with Rapid Arc. Repeat plans were performed to provide a data set of ten plans with IMRT or 3D conformal and ten plans with Rapid Arc for review. The cases studied were delivered at a standard 6MV dose rate of 600MU/min with a 999 monitor unit limit. The plans were analyzed for total monitor units, number of beams, dose conformity, dose fall off, PTV D95, PTV D5, PTV dose heterogeneity and OAR dose including mean dose, D1% and D5%. Treatments including imaging were observed to estimate treatment times. General estimations of time per Rapid Arc (coplanar/noncoplanr), IMRT/3D (coplanar/noncoplanar) and cone beam Results: In all cases we were able to achieve dosimetrically comparable plans for PTV and OAR. The Rapid Arc plans required 2 to 5 arcs and the IMRT/3D conformal plans required 6 to 10 beams. Four of the IMRT/3D conformal plans were noncoplanar. One RapidArc plan was noncoplanar. Monitor units were on average 50% higher for the Rapid Arc plans. Treatment time was on average 6 minutes less for the Rapid Arc plans. Conclusions: High quality Rapid Arc plans can be achieved for stereotactic cases. Based on time to deliver treatments in the standard dose rate mode, Rapid Arc shows potential for reducing treatment time. Future work to commission Rapid Arc in the stereotactic mode with an increased dose rate and an increased monitor unit limit per beam has potential for even greater treatment time efficiency.

TU‐D‐304A‐09: Evaluation of Localization Accuracy of Motion in 4DCT

Purpose: To develop a method and corresponding analysis tool to accurately evaluate the performance of 4DCT in localizing moving objects and to verify the correlation between motion characterization and the respiratory curve. Methods: Several radio opaque markers were affixed to the surface of a Varian Real‐time Positioning Management (RPM) infrared reflective block which was mounted on a moving platform. One of the markers was located right between the two infrared reflective markers of the RPM block. The CTimages of the moving system were acquired with a GE Discovery STEscanner in cine mode. GE Advantage4D was applied to create phased images by dividing the motion cycle into 10 bins. A software tool was developed to process the phased image sets and an algorithm was developed to find the number of markers and to analyze the most probable location of each marker. The motion amplitude was compared with the respiratory curve as recorded by the RPM system during imaging.Results: The multiple markers were identified from the 4DCT image sets simultaneously by the model algorithm. Their phase motion matches the recording of the RPM infrared sensor in both pattern and magnitude. The positioning error of the procedure is <0.5 mm along lateral directions, and 2.5mm along sup‐inf direction, which is within the scope of the image acquisition setup. Conclusion: Tracking multiple point‐like fiducials provides an accurate and efficient means of evaluating the localization performance in 4DCT images. Phantom studies have validated the 4DCT performance in imaging moving object. The method and tool developed in this work can be useful for radiation therapy target margin study and imaging QA alike.