Quality assurance in IMRT: Importance of the transmission through the jaws for an accurate calculation of absolute doses and relative distributions

Azcona, Juan Diego; Siochi, R; Azinovic, I.

doi:10.1118/1.1446110

Cited by 22 publications

(18 citation statements)

References 9 publications

(13 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The variation in the contribution of transmission to dose throughout the patient makes it difficult to summarize the clinical impact of errors in transmission modeling. However, there are a number of studies which have presented results on the clinical impact of changes to MLC transmission 2 , 23 , 24 , 25 . Errors in MLC offset equate to systematically opening or closing the gaps between MLCs by a set distance.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Determination of MLC model parameters for Monaco using commercial diode arrays

Kinsella

Shields

McCavana

et al. 2016

J Applied Clin Med Phys

View full text Add to dashboard Cite

Multileaf collimators (MLCs) need to be characterized accurately in treatment planning systems to facilitate accurate intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT). The aim of this study was to examine the use of MapCHECK 2 and ArcCHECK diode arrays for optimizing MLC parameters in Monaco X‐ray voxel Monte Carlo (XVMC) dose calculation algorithm. A series of radiation test beams designed to evaluate MLC model parameters were delivered to MapCHECK 2, ArcCHECK, and EBT3 Gafchromic film for comparison. Initial comparison of the calculated and ArcCHECK‐measured dose distributions revealed it was unclear how to change the MLC parameters to gain agreement. This ambiguity arose due to an insufficient sampling of the test field dose distributions and unexpected discrepancies in the open parts of some test fields. Consequently, the XVMC MLC parameters were optimized based on MapCHECK 2 measurements. Gafchromic EBT3 film was used to verify the accuracy of MapCHECK 2 measured dose distributions. It was found that adjustment of the MLC parameters from their default values resulted in improved global gamma analysis pass rates for MapCHECK 2 measurements versus calculated dose. The lowest pass rate of any MLC‐modulated test beam improved from 68.5% to 93.5% with 3% and 2 mm gamma criteria. Given the close agreement of the optimized model to both MapCHECK 2 and film, the optimized model was used as a benchmark to highlight the relatively large discrepancies in some of the test field dose distributions found with ArcCHECK. Comparison between the optimized model‐calculated dose and ArcCHECK‐measured dose resulted in global gamma pass rates which ranged from 70.0%–97.9% for gamma criteria of 3% and 2 mm. The simple square fields yielded high pass rates. The lower gamma pass rates were attributed to the ArcCHECK overestimating the dose in‐field for the rectangular test fields whose long axis was parallel to the long axis of the ArcCHECK. Considering ArcCHECK measurement issues and the lower gamma pass rates for the MLC‐modulated test beams, it was concluded that MapCHECK 2 was a more suitable detector than ArcCHECK for the optimization process.PACS number(s): 87.55.Qr

show abstract

Section: Discussionmentioning

confidence: 99%

“…fraction of the delivered monitor units (MU) 1 , 2 . Consequently, MLCs need to be characterized accurately in treatment planning systems (TPSs) to facilitate accurate IMRT and VMAT.…”

Section: Introductionmentioning

confidence: 99%

Determination of MLC model parameters for Monaco using commercial diode arrays

Kinsella

Shields

McCavana

et al. 2016

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

“…Azcona et al 23 has pointed out that any set of step-andshoot or sliding window segments may underestimate the value of leaf, interleaf and end leaf transmission of the MLC 24 . Ensuring these effects remain small is a sufficient reason to maintain routine use of dosimetry films until such time as we have enough data to be more confident these effects are unlikely to significantly affect the dose delivered to the patient.…”

Section: Comparison Of Film Measurement With the Rtp Computer For An mentioning

confidence: 99%

Intensity modulated radiation therapy: Film verification of planar dose maps

Tangboonduangjit

Butson³

et al. 2003

Australas. Phys. Eng. Sci. Med.

View full text Add to dashboard Cite

A new slow response radiographic film (Kodak EDR) is compared with a more traditional faster responding dosimetry film (Kodak XV) in an intensity modulated radiation therapy x-ray field. Dose profiles derived from the two films are compared with doses obtained using a radiotherapy dose planning system (Philips-Pinnacle) which calculates planar dose using a collapsed cone convolution algorithm. Comparisons of the dose maps delivered from film with the Pinnacle dose maps are useful to ensure accurate dose delivery. The Pinnacle dose maps agreed with measurement using both film types to within +/- 3% (in the umbral region) at depths ranging from d(max) to 15 cm. Both XV and EDR films can be used to verify IMRT. EDR film is better suited for dosimetry for combined field dose maps due to its useful dose range of 1-5 Gy. We found XV to be more suitable for individual field dose maps (dose range 0-1 Gy) as no scaling of monitor units were required to achieve acceptable optical density response.

show abstract

“…However, transmission corrections are crucial for relative dose calculations. 9 In the case of compensators, dose modulation is achieved by attenuating the energy fluence so that the dose contribution is effectively weighted. Compensators would introduce spectral changes in the heterogeneous photon beam that will alter its in-phantom scatter and beam penetration properties.…”

Section: Introductionmentioning

confidence: 99%

Inclusion of compensator-induced scatter and beam filtration in pencil beam dose calculations

Plessis¹,

Willemse²

2006

Med. Phys.

View full text Add to dashboard Cite

Compensators can be used as beam intensity modulation devices for intensity-modulated radiation therapy applications. In contrast with multileaf collimators, compensators introduce scatter and beam hardening into the therapeutic x-ray beam. The degree of scatter and beam filtering depends on the compensator material and beam energy. Pencil beam dose calculation models can be used to derive the shape of the compensator. In this study a novel way of incorporating the effect of compensator-induced scatter and beam filtration is presented. The study was conducted using 6, 8, and 15 MV polyenergetic pencil beams (PBs). The compensator materials that were studied included wax, brass, copper, and lead. The perturbation effects of the compensators on the PB dose profiles were built in the PB dose profiles and tested for regular fields containing a step compensator and benchmarked against DOSXYZnrc Monte Carlo calculated dose profiles. These effects include compensator beam filtration and Compton-scattered photons generated in the compensator materials that influence the resulting PB dose profiles. These data were obtained from DOSXYZnrc simulations. A Gaussian function was used to model off-axis scatter and an exponential function was used to model beam hardening at any radius, r. Dose profiles were calculated under a step compensator using the method that can model beam hardening and off-axis scatter, as well as a conventional method where the PB profiles are not adjusted, but a single effective attenuation coefficient is used instead to best match the dose profiles. Both sets of data were compared to the DOSXYZnrc data. Depth and profile dose data for 10 x 10 cm2 and 20 x 20 cm2 fields indicated that at 2 cm depth in water the method that takes compensator scatter into account agrees more closely with the DOSXYZnrc data compared to the data using only an effective attenuation coefficient. Further, it was found that the effective attenuation method can only replicate the DOSXYZnrc data at 10 cm depth where it was chosen to do so. At shallower depths the effective attenuation method overestimates the dose and beyond 10 cm depth it causes an underestimation in the dose. The scatter and beam hardening inclusion method does not exhibit such properties. The exclusion of scatter can lead to dose errors of up to 4 percent with a copper compensator at 5 cm depth for a 10 X 10 cm2 field under a thickness of 5 cm at 6 MV. For materials such as lead this discrepancy could be as high as 7 to 8 percent at 6 MV. For larger fields (20 X 20 cm2) the effect of in-phantom scatter reduces the differences between the dose profiles calculated with the mentioned methods.

show abstract

Quality assurance in IMRT: Importance of the transmission through the jaws for an accurate calculation of absolute doses and relative distributions

Cited by 22 publications

References 9 publications

Determination of MLC model parameters for Monaco using commercial diode arrays

Determination of MLC model parameters for Monaco using commercial diode arrays

Intensity modulated radiation therapy: Film verification of planar dose maps

Inclusion of compensator-induced scatter and beam filtration in pencil beam dose calculations

Contact Info

Product

Resources

About