AAPM Medical Physics Practice Guideline 5.a.: Commissioning and QA of Treatment Planning Dose Calculations — Megavoltage Photon and Electron Beams

The purpose of this study is to perform dosimetric validation of Monaco treatment planning system version 5.1. The Elekta VersaHD linear accelerator with high dose rate flattening filter‐free photon modes and electron energies was used in this study. The dosimetric output of the new Agility head combined with the FFF photon modes warranted this investigation into the dosimetric accuracy prior to clinical usage. A model of the VersaHD linac was created in Monaco TPS by Elekta using commissioned beam data including percent depth dose curves, beam profiles, and output factors. A variety of 3D conformal fields were created in Monaco TPS on a combined Plastic water/Styrofoam phantom and validated against measurements with a calibrated ion chamber. Some of the parameters varied including source to surface distance, field size, wedges, gantry angle, and depth for all photon and electron energies. In addition, a series of step and shoot IMRT, VMAT test plans, and patient plans on various anatomical sites were verified against measurements on a Delta4 diode array. The agreement in point dose measurements was within 2% for all photon and electron energies in the homogeneous phantom and within 3% for photon energies in the heterogeneous phantom. The mean ± SD gamma passing rates of IMRT test fields yielded 93.8 ± 4.7% based on 2% dose difference and 2 mm distance‐to‐agreement criteria. Eight previously treated IMRT patient plans were replanned in Monaco TPS and five measurements on each yielded an average gamma passing rate of 95% with 6.7% confidence limit based on 3%, 3 mm gamma criteria. This investigation on dosimetric validation ensures accuracy of modeling VersaHD linac in Monaco TPS thereby improving patient safety.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Dosimetric validation of Monaco treatment planning system on an Elekta VersaHD linear accelerator

Narayanasamy

Saenz²,

Defoor³

et al. 2017

“…These QA tests include checks of x‐ray output, energy, and beam profile constancy as well as image‐guided radiation therapy (IGRT) functionality as recommended by the American Association of Physicist in Medicine (AAPM) Task Group (TG) 142,1 MPPG5a,2 and TG‐179 3. In general, several devices are used each morning to perform this QA.…”

Section: Introductionmentioning

confidence: 99%

Independent validation of machine performance check for the Halcyon and TrueBeam linacs for daily quality assurance

Netherton

Nitsch

et al. 2018

PurposeTo evaluate the ability of the machine performance check (MPC) on the Halcyon to detect errors, with comparison with the TrueBeam.Methods MPC is an automated set of quality assurance (QA) tests that use a phantom placed on the couch and the linac's imaging system(s) to verify the beam constancy and mechanical performance of the Halcyon and TrueBeam linacs. In order to evaluate the beam constancy tests, we inserted solid water slabs between the beam source and the megavoltage imager to simulate changes in beam output, flatness, and symmetry. The MPC results were compared with measurements, using two‐dimensional array under the same conditions. We then studied the accuracy of MPC geometric tests. The accuracies of the relative gantry offset and couch shift tests were evaluated by intentionally inserting phantom shifts, using a rotating or linear motion stage. The MLC offset and absolute gantry offset tests were assessed by miscalibrating these motions on a Halcyon linac.ResultsFor the Halcyon system, the average difference in the measured beam output between the IC Profiler and MPC, after intentional changes, was 1.3 ± 0.5% (for changes ≤5%). For Halcyon, the MPC test failed (i.e., prevented treatment) when the beam symmetry change was over 1.9%. The accuracy of the MLC offset test was within 0.05 mm. The absolute gantry offset test was able to detect an offset as small as 0.02°. The accuracy of the absolute couch shift test was 0.03 mm. The accuracy of relative couch shift test of Halcyon was measured as 0.16 mm.ConclusionWe intentionally inserted errors to evaluate the ability of the MPC to identify errors in dosimetric and geometric parameters. These results showed that the MPC is sufficiently accurate to be effectively used for daily QA of the Halcyon and TrueBeam treatment devices.

“…Second, in departure from the previous school of thought, (20) the AAPM TG‐244 Report on medical physics practice guidelines for commissioning of dose calculations (21) allows the use of electronic dosimetry arrays as a primary commissioning tool for evaluating IMRT/VMAT dose distributions, provided that dose measurement or reconstruction is performed with adequate spatial resolution. Furthermore, TG‐244 makes challenging, patient‐based cases (image sets, structure sets, and detailed lists of dosimetric objectives) available for download to be used for commissioning of the IMRT/VMAT systems.…”

Section: Introductionmentioning

confidence: 99%

Validation of an improved helical diode array and dose reconstruction software using TG‐244 datasets and stringent dose comparison criteria

Ahmed

Nelms²,

Kozelka

et al. 2016

Self Cite

The original helical ArcCHECK (AC) diode array and associated software for 3D measurement‐guided dose reconstruction were characterized and validated; however, recent design changes to the AC required that the subject be revisited. The most important AC change starting in 2014 was a significant reduction in the overresponse of diodes to scattered radiation outside of the direct beam, accomplished by reducing the amount of high‐Z materials adjacent to the diodes. This change improved the diode measurement accuracy, but in the process invalidated the dose reconstruction models that were assembled based on measured data acquired with the older version of the AC. A correction mechanism was introduced in the reconstruction software (3DVH) to accommodate this and potential future design changes without requiring updating model parameters. For each permutation of AC serial number and beam model, the user can define in 3DVH a single correction factor which will be used to compensate for the difference in the out‐of‐field response between the new and original AC designs. The exact value can be determined by minimizing the dose‐difference with an ionization chamber or another independent dosimeter. A single value of 1.17, corresponding to the maximum measured out‐of‐field response difference between the new and old AC, provided satisfactory results for all studied energies (6X, 15X, and flattening filter‐free 10XFFF). A library of standard cases recommended by the AAPM TG‐244 Report was used for reconstructed dose verification. The overall difference between reconstructed dose and an ion chamber in a water‐equivalent phantom in the targets was 0.0% ± 1.4% (1 SD). The reconstructed dose on a homogeneous phantom was also compared to a biplanar diode dosimeter (Delta4) using gamma analysis with 2% (local dose‐error normalization)/2 mm/10% cutoff criteria. The mean agreement rate was 96.7% ± 3.7%. For the plans common with the previous comparison, the mean agreement rate was 98.3% ± 0.8%, essentially unchanged. We conclude that the proposed software modification adequately addresses the change in the dosimeter response.PACS number(s): 87.55Qr