Per-Fraction Positional and Dosimetric Performance of Prone Breast Tangential Radiotherapy on Halcyon™ Linear Accelerator Assessed with Daily Rapid Kilo-voltage Cone Beam Computed Tomography: A Single-Institution Pilot Study

Abstract Background: This study investigates daily breast geometry and delivered dose to prone-positioned patients undergoing tangential whole breast radiation therapy (WBRT) on an O-ring linear accelerator with 6X flattening filter free mode (6X-FFF), planned with electronic compensation (ECOMP) method. Most practices rely on skin marks or daily planar image matching for prone breast WBRT. This system provides low dose daily CBCT, which was used to study daily robustness of delivered dose parameters for prone-positioned WBRT.Methods: Eight patients treated with 16-fraction prone-breast WBRT were retrospectively studied. Planning CTs were deformed to daily CBCT to generate daily synthetic CTs, on which delivered dose distributions were calculated. A total of 8x16=128 synthetic CTs were generated. Consensus ASTRO definition was used to contour Breast PTV Eval for each daily deformed CT. Breast PTV Eval coverage (V90%) and hotspot (V105% and Dmax) were monitored daily to compare prescription dose with daily delivered dose. Various predictors including patient weight, breast width diameter (BWD), and Dice similarity coefficient (DSC) were fit into an analysis of covariance model predicting V90% and V105% deviation from prescribed (ΔV90%, ΔV105%). Statistical significance is indicated with asterisks (* for p<0.05; ** for p<0.001).Results: Daily delivered Breast PTV Eval V90% was moderately smaller than prescribed (median ΔV90%=-0.1%*), while V105% was much larger (median ΔV105%=+10.1%** or +92.4cc**). Patient’s weight loss correlated with significantly increased ΔV105% (+4.6% / -1% weight., R2=0.4**) and moderately decreased ΔV90% (-0.071%/-1% wt., R2=0.2**). Comprehensive ANCOVA models indicated three factors affect ΔV90% and ΔV105% the most: (1) BWD decrease (-0.09%* and +10%**/-1cm respectively), (2) PTV Eval volume decrease (-0.4%** and +9%**/-100cc), and for ΔV105% only, (3) the extent of breast deformation (+10%**/-0.01 DSC). Breast PTV Eval volume also decreased with time (-2.21*cc/fx), possibly indicating seroma resolution and increase in V105% over time.Conclusions: Daily CBCT revealed key delivered dose parameters vary significantly for patients undergoing tangential prone breast WBRT planned with ECOMP using 6X-FFF. Patient weight, BWD, and breast shape deformation could be used to predict dosimetric variations from prescribed. Preliminary findings suggest an adaptive plan based on daily CBCT could reduce excessive dose to the breast.

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Per-fraction positional and dosimetric performance of prone breast tangential radiotherapy on Halcyon™ linear accelerator assessed with daily rapid kilo-voltage cone beam computed tomography: a single-institution pilot study

Radiation Oncology ◽

10.1186/s13014-020-01700-6 ◽

2020 ◽

Vol 15 (1) ◽

Author(s):

Suk W. Yoon ◽

Neil K. Taunk ◽

Gary M. Freedman ◽

Emily Hubley ◽

Shannon O’Reilly ◽

...

Keyword(s):

Linear Accelerator ◽

Statistical Significance ◽

Analysis Of Covariance ◽

Dice Similarity Coefficient ◽

Flattening Filter Free ◽

Flattening Filter ◽

Prescription Dose ◽

Patient Weight ◽

Electronic Compensation ◽

Delivered Dose

Abstract Background This study investigates daily breast geometry and delivered dose to prone-positioned patients undergoing tangential whole breast radiation therapy (WBRT) on an O-ring linear accelerator with 6X flattening filter free mode (6X-FFF), planned with electronic compensation (ECOMP) method. Most practices rely on skin marks or daily planar image matching for prone breast WBRT. This system provides low dose daily CBCT, which was used to study daily robustness of delivered dose parameters for prone-positioned WBRT. Methods Eight patients treated with 16-fraction prone-breast WBRT were retrospectively studied. Planning CTs were deformed to daily CBCT to generate daily synthetic CTs, on which delivered dose distributions were calculated. A total of 8 × 16 = 128 synthetic CTs were generated. Consensus ASTRO definition was used to contour Breast PTV Eval for each daily deformed CT. Breast PTV Eval coverage (V90%) and hotspot (V105% and Dmax) were monitored daily to compare prescription dose with daily delivered dose. Various predictors including patient weight, breast width diameter (BWD), and Dice similarity coefficient (DSC) were fit into an analysis of covariance model predicting V90% and V105% deviation from prescribed (ΔV90%, ΔV105%). Statistical significance is indicated with asterisks (* for p < 0.05; ** for p < 0.001). Results Daily delivered Breast PTV Eval V90% was moderately smaller than prescribed (median ΔV90% = − 0.1%*), while V105% was much larger (median ΔV105% = + 10.1%** or + 92.4 cc**). Patient’s weight loss correlated with significantly increased ΔV105% (+ 4.6%/ − 1% weight, R2 = 0.4**) and moderately decreased ΔV90% (− 0.071%/ − 1% wt., R2 = 0.2**). Comprehensive ANCOVA models indicated three factors affect ΔV90% and ΔV105% the most: (1) BWD decrease (− 0.09%* and + 10%**/ − 1 cm respectively), (2) PTV Eval volume decrease (− 0.4%** and + 9%**/ − 100 cc), and for ΔV105% only, (3) the extent of breast deformation (+ 10%**/ − 0.01 DSC). Breast PTV Eval volume also decreased with time (− 2.21*cc/fx), possibly indicating seroma resolution and increase in V105% over time. Conclusions Daily CBCT revealed key delivered dose parameters vary significantly for patients undergoing tangential prone breast WBRT planned with ECOMP using 6X-FFF. Patient weight, BWD, and breast shape deformation could be used to predict dosimetric variations from prescribed. Preliminary findings suggest an adaptive plan based on daily CBCT could reduce excessive dose to the breast.

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Per-Fraction Positional and Dosimetric Performance of Prone Breast Tangential Radiotherapy Assessed with Daily Rapid Kilo-voltage Cone Beam Computed Tomography: Key Statistics, Predictors, and Recommendations

10.21203/rs.3.rs-38928/v1 ◽

2020 ◽

Author(s):

Suk Whan Yoon ◽

Neil K Taunk ◽

Gary M Freedman ◽

Emily Hubley ◽

Shannon O'Reilly ◽

...

Keyword(s):

Statistical Significance ◽

Analysis Of Covariance ◽

Dice Similarity Coefficient ◽

Flattening Filter Free ◽

Flattening Filter ◽

Prescription Dose ◽

Free Mode ◽

Patient Weight ◽

Electronic Compensation ◽

Delivered Dose

Abstract Background This study investigates daily breast geometry and delivered dose to prone-positioned patients undergoing tangential whole breast radiation therapy (WBRT) on an O-ring linear accelerator with 6X flattening filter free mode (6X-FFF), planned with electronic compensation (ECOMP) method. Most practices rely on skin marks or daily planar image matching for prone breast WBRT. This system provides low dose daily CBCT, which was used to study daily robustness of delivered dose parameters for prone-positioned WBRT. Methods Eight patients treated with 16-fraction prone-breast WBRT were retrospectively studied. Planning CTs were deformed to daily CBCT to generate daily synthetic CTs, on which delivered dose distributions were calculated. A total of 8 × 16 = 128 synthetic CTs were generated. Consensus ASTRO definition was used to contour Breast PTV Eval for each daily deformed CT. Breast PTV Eval coverage (V90%) and hotspot (V105% and Dmax) were monitored daily to compare prescription dose with daily delivered dose. Various predictors including patient weight, breast width diameter (BWD), and Dice similarity coefficient (DSC) were fit into an analysis of covariance model predicting V90% and V105% deviation from prescribed (ΔV90%, ΔV105%). Statistical significance is indicated with asterisks (* for p < 0.05; ** for p < 0.001). Results Daily delivered Breast PTV Eval V90% was moderately smaller than prescribed (median ΔV90%=-0.1%*), while V105% was much larger (median ΔV105%=+10.1%** or + 92.4cc**). Patient’s weight loss correlated with significantly increased ΔV105% (+ 4.6% / -1% weight., R2 = 0.4**) and moderately decreased ΔV90% (-0.071%/-1% wt., R2 = 0.2**). Comprehensive ANCOVA models indicated three factors affect ΔV90% and ΔV105% the most: (1) BWD decrease (-0.09%* and + 10%**/-1cm respectively), (2) PTV Eval volume decrease (-0.4%** and + 9%**/-100 cc), and for ΔV105% only, (3) the extent of breast deformation (+ 10%**/-0.01 DSC). Breast PTV Eval volume also decreased with time (-2.21*cc/fx), possibly indicating seroma resolution and increase in V105% over time. Conclusions Daily CBCT revealed key delivered dose parameters vary significantly for patients undergoing tangential prone breast WBRT planned with ECOMP using 6X-FFF. Patient weight, BWD, and breast shape deformation could be used to predict dosimetric variations from prescribed. Preliminary findings suggest an adaptive plan based on daily CBCT could reduce excessive dose to the breast.

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Initial Clinical Experience Treating Patients with Breast Cancer on a 6-MV Flattening-Filter-Free O-Ring Linear Accelerator

Advances in Radiation Oncology ◽

10.1016/j.adro.2019.05.006 ◽

2019 ◽

Vol 4 (4) ◽

pp. 571-578 ◽

Cited By ~ 4

Author(s):

Andrew R. Barsky ◽

Fionnbarr O'Grady ◽

Christopher Kennedy ◽

Neil K. Taunk ◽

Lei Dong ◽

...

Keyword(s):

Breast Cancer ◽

Clinical Experience ◽

Linear Accelerator ◽

Flattening Filter Free ◽

Flattening Filter ◽

Initial Clinical Experience

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Interplay effect on a 6-MV flattening-filter-free linear accelerator with high dose rate and fast multi-leaf collimator motion treating breast and lung phantoms

Medical Physics ◽

10.1002/mp.12899 ◽

2018 ◽

Vol 45 (6) ◽

pp. 2369-2376 ◽

Cited By ~ 8

Author(s):

Tucker Netherton ◽

Yuting Li ◽

Paige Nitsch ◽

Simona Shaitelman ◽

Peter Balter ◽

...

Keyword(s):

Dose Rate ◽

Linear Accelerator ◽

High Dose Rate ◽

High Dose ◽

Flattening Filter Free ◽

Multi Leaf Collimator ◽

Flattening Filter ◽

Interplay Effect

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Comparative investigation of beam quality index Q on flattening filter and flattening filter free 6 and 15 MV photon beams of an medical linear accelerator

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2017-0059 ◽

2017 ◽

Vol 3 (2) ◽

pp. 287-290

Author(s):

Michael Schaks ◽

Johannes Zähle ◽

Martin Janich ◽

Patrick Hübsch ◽

Nico Homonnay ◽

...

Keyword(s):

Linear Accelerator ◽

Quality Index ◽

Beam Quality ◽

Comparative Investigation ◽

Central Axis ◽

Photon Beams ◽

Medical Linear Accelerator ◽

Flattening Filter Free ◽

Flattening Filter ◽

Beam Quality Correction Factor

AbstractAn Elekta Synergy LINAC was used to investigate the beam quality index Q and the beam quality correction factor kQ, which is used for absolute dosimetry, in off-axis photon fields. It was found that the beam quality index Q of the photon energies with flattening filter decreases with increasing distance to the central axis, at 6 MV by 4.27% and at 15 MV by 3.98% inside a range of 15 cm off-axis. The beam quality index for flattening filter free photon fields also decreases with increasing distance to the central axis. In this case Q changed only by 1.01% inside the above range.

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