A mathematical approach to beam matching

Sarkar, Biplab; Manikandan, A.; Nandy, Maitreyee; Gossman, Michael S.; Sureka, C.S.; Ray, Alok K.; Sujatha, N. V.

doi:10.1259/bjr.20130238

Cited by 19 publications

(21 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, the linacs in this study were matched at commissioning with PDD 20,10 matching <0.5% and all points in the PDD within 0.5% of the reference curve. All open profile points within 80% of the field size were within 1% of reference Comprehensive VMAT benchmarking should be performed for a variety of treatment sites, verifying a base level of beam matching traceable to the TPS model . Level 3 testing should also be performed in anatomical phantoms. kV‐MV isocentre coincidence should be within specification for SBRT delivery for all linacs concerned.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study

Rijken

Schachenmayr²,

Crowe

et al. 2019

J Applied Clin Med Phys

View full text Add to dashboard Cite

Purpose Beam matching occurs on all linacs to some degree and when two are more are matched to each other, patients are able to be transferred between machines. Quality assurance of plans can also be performed “distributively” on any of the matched linacs. The degree to which machines are matched and how this translates to like delivery of plans has been the focus of a number of studies. This concept has not yet been explored for stereotactic techniques which require a higher degree of accuracy. This study proposes beam matching criteria which allows for the distributive delivery and quality assurance of stereotactic body radiotherapy (SBRT) plans. Method Two clinically relevant and complex volumetric modulated arc therapy (VMAT) SBRT spine and lung plans were chosen as benchmarking cases. These were delivered on nine previously beam matched linacs with quality assurance performed through ArcCheck and film exposure in the sagittal plane. Measured doses were compared to their treatment planning system predictions through gamma analysis at a range of criteria. Results Despite differences in beam match parameters and variations in small fields, all nine linacs produced accurate deliveries with a tight deviation in the population sample. Pass rates were well above suggested tolerances at the recommended gamma criterion. Film was able to detect dose errors to a greater degree than ArcCheck. Conclusion Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linacs is certainly feasible provided the linacs are matched to a strict protocol like that suggested in this study and regular quality assurance is performed on the matched fleet. Distributive quality assurance and delivery of SBRT provides the possibility of efficiency gains for physicists as well as treatment staff.

show abstract

Section: Discussionmentioning

confidence: 99%

“…Sarkar et al. improved upon this criteria by developing a test package to aid in beam match testing which involved matching profiles and depth dose curves to within 1%/1 mm as well as their first and second derivatives, as they were found to be “ideally suited to discern any variance between the new beam and existing beam.”…”

Section: Introductionmentioning

confidence: 99%

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study

Rijken

Schachenmayr²,

Crowe

et al. 2019

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

“…Then, for beam profiles of 10 × 10 cm 2 and 30 × 30 cm 2 field sizes at 10 cm depth, any averaged point dose (average of the measurements over 1 cm range from that point) within the region covering 80% of full width at half maximum (FWHM) shall be within a 2% difference when compared to the same points from profiles of other beam-matched linacs. 4,5 Beammatched linacs have almost the same dosimetric characteristics and can be represented as one set of beam parameters in the treatment planning system (TPS). Having beam-matched linacs can not only increase the flexibility in patient treatment but also reduce the social and economic effects caused by machine down time.…”

Section: Introductionmentioning

confidence: 99%

Assessment of beam‐matched linacs quality/accuracy for interchanging SBRT or SRT patient using VMAT without replanning

Warrell

Lee

et al. 2018

J Applied Clin Med Phys

View full text Add to dashboard Cite

PurposeDosimetric accuracy is critical when switching a patient treated with stereotactic body radiation therapy (SBRT) or stereotactic fractionated radiotherapy (SRT) among beam‐matched linacs. In this study, the dose delivery accuracy of volumetric modulated arc therapy (VMAT) plans for SBRT/SRT patients were evaluated on three beam‐matched linacs.MethodBeam data measurements such as percentage depth dose (PDD 10), beam profiles, output factors, and multi‐leaf collimator (MLC) leaf transmission factor for 6 MV photon beam were performed on three beam‐matched linacs. The Edge™ diode detector was used for measurements of beams of field size less than 5 × 5 cm2. Ten lung and 15 brain plans were generated using VMAT with the same beam model. Modulation complexity score of the VMAT plan (MCSv) was used as a plan complexity indicator. Doses were measured using ArcCHECK™ and GafChromic™ EBT3 films. The measurements were compared with calculated doses through absolute dose gamma comparison using 3%/2 mm and 2%/2 mm criteria. Correlation between difference in passing rates among beam‐matched linacs and MCSv was evaluated using the Pearson coefficient. Point doses were measured with the A1SL micro ion chamber.ResultsDifference in beam outputs, beam profiles, and MLC leaf transmission factors of beam‐matched linacs were all within ±1%, except the difference in output factor for 1 × 1 cm2 field between linac 1 and 3 (1.3%). For all 25 cases, passing rates of measured doses on three linacs were all higher than 90% when using 2%/2 mm gamma criteria. The average difference in point dose measurements among three beam‐matched linacs was 0.1 ± 0.2% (P > 0.05, one‐way ANOVA).ConclusionMinimal differences in beam parameters, point doses, and passing rates among three linacs proved the viability of swapping SBRT/SRT using VMAT among beam‐matched linacs. The effect of plan complexity on passing rate difference among beam‐matched linacs is not statistically significant.

show abstract

“…Similarly, dose gradient concept is used in beam matching between two or more linear accelerators. [ 11 ] In general, any gradient can be recognized and quantified using different order derivatives. Therefore, different order derivatives are useful tools to handle the short comings of the gamma index in terms of dose gradient.…”

Section: Introductionmentioning

confidence: 99%

“…In a flat beam geometry, derivative up to second order is sufficient for the evaluation of dose distribution. [ 11 ]…”

Section: Introductionmentioning

confidence: 99%

Derivative based sensitivity analysis of gamma index

2015

View full text Add to dashboard Cite

Originally developed as a tool for patient-specific quality assurance in advanced treatment delivery methods to compare between measured and calculated dose distributions, the gamma index (γ) concept was later extended to compare between any two dose distributions. It takes into effect both the dose difference (DD) and distance-to-agreement (DTA) measurements in the comparison. Its strength lies in its capability to give a quantitative value for the analysis, unlike other methods. For every point on the reference curve, if there is at least one point in the evaluated curve that satisfies the pass criteria (e.g., δDD = 1%, δDTA = 1 mm), the point is included in the quantitative score as “pass.” Gamma analysis does not account for the gradient of the evaluated curve - it looks at only the minimum gamma value, and if it is <1, then the point passes, no matter what the gradient of evaluated curve is. In this work, an attempt has been made to present a derivative-based method for the identification of dose gradient. A mathematically derived reference profile (RP) representing the penumbral region of 6 MV 10 cm × 10 cm field was generated from an error function. A general test profile (GTP) was created from this RP by introducing 1 mm distance error and 1% dose error at each point. This was considered as the first of the two evaluated curves. By its nature, this curve is a smooth curve and would satisfy the pass criteria for all points in it. The second evaluated profile was generated as a sawtooth test profile (STTP) which again would satisfy the pass criteria for every point on the RP. However, being a sawtooth curve, it is not a smooth one and would be obviously poor when compared with the smooth profile. Considering the smooth GTP as an acceptable profile when it passed the gamma pass criteria (1% DD and 1 mm DTA) against the RP, the first and second order derivatives of the DDs (δD’, δD”) between these two curves were derived and used as the boundary values for evaluating the STTP against the RP. Even though the STTP passed the simple gamma pass criteria, it was found failing at many locations when the derivatives were used as the boundary values. The proposed derivative-based method can identify a noisy curve and can prove to be a useful tool for improving the sensitivity of the gamma index.

show abstract

A mathematical approach to beam matching

Abstract: We report a mathematically rigorous formulation for the qualitative evaluation of beam matching between linear accelerators.

Cited by 19 publications

References 14 publications

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study

Assessment of beam‐matched linacs quality/accuracy for interchanging SBRT or SRT patient using VMAT without replanning

Derivative based sensitivity analysis of gamma index

Contact Info

Product

Resources

About