Code of practice for brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task Group No. 56

As part of quality assurance (QA) in high dose rate brachytherapy, it is necessary to verify that the source dwell positions correspond to the radiographic markers used in simulation and treatment planning. The procedure is well established for linear tandem applicators. However, with the advent of ring applicators, this has become more critical and challenging. This work describes a new approach to determine positional inaccuracies for ring applicators in which the dummy markers are imaged just once and their dwell positions characterized with respect to an applicator‐defined axis. The radiograph serves as a reference for dummy markers for comparison with all subsequent measurements in which the active sources are autoradiographed at different offsets – thus obviating the back‐and‐forth transferring of setup between afterloader and simulator. The method has been used specifically to characterize the Varian GammaMed 60° ring applicator, but it may be adapted to any other applicator. The results show that an offset of 1–2 mm minimizes the overall inaccuracy to within ±2 mm.PACS numbers: 87.53.Jw, 87.56.Fc, 87.56.B, 87.56.bg, 87.56.‐v

“…This is in compliance with TG56 recommendation ( 2 ) that the correspondence between the planned and the actual dwell positions be within

\pm 2 mm

with reference to the applicator system.…”

Section: Discussionsupporting

confidence: 83%

“…This work shows that the TG56 ( 2 ) recommended tolerance of

\pm 2 mm

Section: Discussionmentioning

confidence: 91%

See 1 more Smart Citation

A new approach to measure dwell position inaccuracy in HDR ring applicators – quantification and corrective QA

Jangda

Hussein

Rehman

2010

“…Large dwell position displacements were observed at the curved portion of the ovoid applicator (Fig. 5), which is larger than the required 1 mm source position accuracy 16. The cause of that the pathways are different between the x‐ray marker and wire (radioactive source and check cable) 17.…”

Section: Discussionmentioning

confidence: 91%

High‐dose rate intracavitary brachytherapy pretreatment dwell position verification using a transparent applicator

Otani

Sumida

Nose

et al. 2018

PurposeThe major errors in HDR brachytherapy are related to treatment distance, almost all of which are caused by incorrect applicator information. The aim of this study is to propose a quick pretreatment verification method to evaluate channel length and dwell position with a transparent applicator, which, in addition, is suitable as an education tool to assist in the understanding of the applicator structure.MethodsA transparent applicator model was fabricated using a three‐dimensional printer and transparent resin. Its aim is to be a replica of a real gynecological applicator. The pretreatment verification is performed by observing the planned dwell positions of a check cable inside a transparent applicator. A digital camera acquired images and the dwell positions of the radioactive source and check cable were evaluated by comparing them with respect to the theoretical dwell positions marked by the proper x‐ray marker. The potential effectiveness of verification using a transparent applicator was also evaluated using brachytherapy events reported in the literature.ResultsThe transparent applicator closely resembles the real applicator in shape and had an error of less than 0.2 mm. The average dwell position displacement between the radioactive source and check cable was 0.4 mm. The analysis of brachytherapy events showed that channel‐length, dwell‐position, and step‐size errors made up 50% of all events, but affected 64% of all patients.ConclusionsThe transparent applicator model enables a noninvasive, repeatable verification of the channel length and dwell positions to be performed before treatment. This verification has the potential to help prevent common errors in treatment delivery. In addition, the transparent applicator model can be used as a teaching tool to help clinicians understand the operation of the applicator, lowering the risk of events.

“…There have been many recommendations by American Association of Physicists in Medicine (AAPM) task groups on the accuracy of seed calibration. The AAPM TG‐40,2 TG‐56,3 and TG‐644 all recommend that at least 10% of the I‐125 seeds have their activity verified against the manufacturers measurements, and if there is a discrepancy above 5% then it needs to be reported to the manufacturer. The task groups do not explicitly specify who should perform the assay of 10% of the seeds.…”

Section: Introductionmentioning

confidence: 99%

A method for confirming a third‐party assay of I‐125 seeds used for prostate implants

Muryn

Wilkinson

2016

The purpose of this work is to describe a method and apparatus that can be used to confirm the source strength of a large number of I‐125 seeds while maintaining sterility, accuracy, reproducibility, and time efficiency. Source strengths ranging from 0.395 to 0.504 U/seed were available for this study. Three different seed configurations were measured: loose, linked, and loaded needles. A third‐party 10% assay (NIST traceable) was provided. A custom stand was built out of aluminum to hold an exposure meter [Inovision (Fluke) 451P pressurized ion chamber] at 25 cm above the I‐125 sources to measure the exposure rate. The measurements were made in an operating room, and a sterile sheet was placed under the nonsterile aluminum stand on a sterile loading table. Seeds and needles were placed in a sterile tray for these measurements. Two hundred and six loose seeds in six batches (0.395, 0.395, 0.409, 0.444, 0.444, and 0.444 U/seed) and 1434 seeds in 10 batches containing various strands (0.444, 0.444, 0.444, 0.444, .0444, 0.466, 0.466, 0.504, and 0.504 U/seed) were measured. For the loose and stranded seeds, the average exposure rate per unit activity was measured to be 0.589 mR/h·U with a standard deviation of 0.017. Loaded needles were measured with an average exposure rate per unit activity to be 0.269 mR/h·U with a standard deviation of 0.014. We conclude that the method described here is capable of confirming a third‐party assay when performed on a large number of loose or stranded seeds in bulk. It is less reliable for preloaded needles.