RTT
Investigating the Feasibility of Radiation Therapists Performing Portal Dose Verifications for Volumetric Modulated Arc Therapy (VMAT) Plans Using Electronic Portal Imaging Devices (EPIDs) and the Practical Implications in a Clinical Setting Kenny Zhan, Dr. Krista Chytyk-Praznik, Carol-Anne Davis 1.01
1000
RTT vs Graduate Students Measured γ-values
RTT vs Graduate Students Measured Verification Times
900 1 800
700
0.99
Introduction
Material and Methods EPID Study In our study there were two experimental groups: physics graduate students and RTT. Over the course of two months, physics graduate students were observed performing dose verifications for a number of different treatment sites (e.g.: prostate, head and neck, breast, rectum) over a number of different linacs. The raw data and analysis from the Portal Dosimetry program from these verifications were then recorded. The students were also timed to determine how efficiently they could perform the verification, beginning when the first arc is beamed on and ending when the data has been analyzed. At a later date the same plans were provided to the RTT. The RTT then performed the same verifications. The RTT was timed in the same way and the same data was collected after the verifications. National Survey For the national survey a simple voluntary questionnaire will be sent out to all of the cancer centres in Canada, using SelectSurvey, which is an online service hosted at the NSCC.
Time (s)
0.98
γ-Values
Accuracy is critical when delivering a therapeutic course of radiation. Institutions such as the International Atomic Energy Agency (IAEA) recommend that all plans undergo an independent check prior to treatment, which may include a secondary dose calculation or a dose measurement (IAEA, 2000). Therefore to ensure that treatments are delivered as planned it is imperative that complex treatments such as VMAT treatments are measured before they are delivered. In the past, there have been well documented cases where failure to measure the dose prior to treatment have resulted in a fatality (IAEA, 2008). Currently, physics graduate students dose verify VMAT treatment plans using the EPID on the treatment units at the Nova Scotia Cancer Centre (NSCC). In our current study we are interested in seeing if radiation therapists (RTTs) are able to perform the dose verification of VMAT treatment plans as accurately as physics graduate students. We are also interested in finding out what other cancer centres in Canada are doing in terms of VMAT / IMRT QA and will be sending out a questionnaire surveying all centres in Canada in late March.
600
RTT 0.97
500 RTT Physics Graduate Student
400 Physics Graduate Student 300
0.96 200 0.95
100
0 1
0.94 1
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7
8
9
10
11
12
2
3
13
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VMAT Plan
VMAT Plan
Chart 1: RTT vs Physics Graduate students r-values
Chart 2.: RTT vs Physics Graduate Students Verification Time (s)
Results EPID Study Figure one shows the data captured by the Portal Dosimetry (v. 10, Varian Medical Systems) program during the verification process. The images represent the dose distribution of the treatment plan. The leftmost image represents the predicted dose distribution, while the rightmost image is the measured dose distribution. The image in the middle is a comparison between the two images. An algorithm compares each pixel to ensure that the value of the pixel is within 3% and 3 mm of the predicted pixel. A overall γ-value is then reported, which represents the percentage of pixels meeting the 3% and 3 mm threshold. Chart 1 shows the γ-value tabulated by the RTT vs the γ-value tabulated by the graduate student. Overall they align closely with each other. A two one sided t-test (TOST) was performed on this data to determine equivalence. Chart 2, provides a graphical comparison on the amount of time it took an graduate student and the RTT to perform the verification on each plan. National Survey The survey is still currently under review by the REB. The results are pending.
Analysis EPID Study A T-OST test was performed to prove the equivalence on the γ-value collected from the RTT and graduate student groups. A range of equivalence of +/- 3% was set and the following hypotheses used. H01 = μphysics - μRTT >3% H1 = μphysics - μRTT ≤ 3%
H02 = μphysics - μRTT tcrit95% and reject H02 because t< -tcrit95%. Therefore we must accept our alternate hypotheses H1 and H2, which state that μphysics - μRTT ≤ 3% and ≥ -3% which means that | μphysics - μRTT |< 3% and therefore within our range of equivalence.
Figure 1. Sample data collected by the Portal Dosimetry program.
Discussion and Future Directions EPID Study During the verifications of plans by the RTT, the RTT made the observation that it would be possible to reorder the beams to improve efficiency between plans with an odd number of arcs or non-standard arcs. It was observed that the RTT was familiar with machine interlocks and troubleshooting them. The RTT was able to quickly clear interlocks and proceed with the verification. It is believed that due to the familiarity of the RTT with the treatment units, RTTs would be better able to troubleshoot and find new ways of performing verifications more efficiently over time. These observations and comments are not reflected in the measured verification times as it did not fall within the period of time measured. However, this may be something to consider in the methodology of future studies. Our current research is designed as a feasibility study. As such we only have one RTT participating. Currently all graduate students performing verifications are participating in the study for n = 4. Therefore we cannot extrapolate this to the entire RTT population at the NSCC. A further study involving more RTTs will need to be done.
Conclusions In conclusion, from our current study, we have determined that it is possible for an RTT to perform VMAT dose verifications as effectively as a physics graduate student.
Acknowledgements and References I would like to thank Danny McAloney RTT, who volunteered to stay after hours to run the verifications for this study, the graduate students of the Dalhousie Medical Physics program, Dr. Waseem Sharif for his help with the statistical analysis, and the staff at the NSCC for their support of this research project. International Atomic Energy Agency. (2000). Lessons learned from accidental exposures in radiotherapy. Vienna: International Atomic Energy Agency. International Atomic Energy Agency. (2008) Module 2.10: Accident update – some new events (UK, USA, France)[Powerpoint Slides]. Retrieved December 21, 2015 from https:// rpop.iaea.org/RPOP/RPoP/Content/Documents/ TrainingAccidentPrevention/Lectures/AccPr_2.10_Accident_update1_WEB.ppt (Dec 21, 2015)
1000
RTT vs Graduate Students Measured γ-values
RTT vs Graduate Students Measured Verification Times
900 1 800
700
0.99
Introduction
Material and Methods EPID Study In our study there were two experimental groups: physics graduate students and RTT. Over the course of two months, physics graduate students were observed performing dose verifications for a number of different treatment sites (e.g.: prostate, head and neck, breast, rectum) over a number of different linacs. The raw data and analysis from the Portal Dosimetry program from these verifications were then recorded. The students were also timed to determine how efficiently they could perform the verification, beginning when the first arc is beamed on and ending when the data has been analyzed. At a later date the same plans were provided to the RTT. The RTT then performed the same verifications. The RTT was timed in the same way and the same data was collected after the verifications. National Survey For the national survey a simple voluntary questionnaire will be sent out to all of the cancer centres in Canada, using SelectSurvey, which is an online service hosted at the NSCC.
Time (s)
0.98
γ-Values
Accuracy is critical when delivering a therapeutic course of radiation. Institutions such as the International Atomic Energy Agency (IAEA) recommend that all plans undergo an independent check prior to treatment, which may include a secondary dose calculation or a dose measurement (IAEA, 2000). Therefore to ensure that treatments are delivered as planned it is imperative that complex treatments such as VMAT treatments are measured before they are delivered. In the past, there have been well documented cases where failure to measure the dose prior to treatment have resulted in a fatality (IAEA, 2008). Currently, physics graduate students dose verify VMAT treatment plans using the EPID on the treatment units at the Nova Scotia Cancer Centre (NSCC). In our current study we are interested in seeing if radiation therapists (RTTs) are able to perform the dose verification of VMAT treatment plans as accurately as physics graduate students. We are also interested in finding out what other cancer centres in Canada are doing in terms of VMAT / IMRT QA and will be sending out a questionnaire surveying all centres in Canada in late March.
600
RTT 0.97
500 RTT Physics Graduate Student
400 Physics Graduate Student 300
0.96 200 0.95
100
0 1
0.94 1
2
3
4
5
6
7
8
9
10
11
12
2
3
13
4
5
6
7
8
9
10
11
12
13
VMAT Plan
VMAT Plan
Chart 1: RTT vs Physics Graduate students r-values
Chart 2.: RTT vs Physics Graduate Students Verification Time (s)
Results EPID Study Figure one shows the data captured by the Portal Dosimetry (v. 10, Varian Medical Systems) program during the verification process. The images represent the dose distribution of the treatment plan. The leftmost image represents the predicted dose distribution, while the rightmost image is the measured dose distribution. The image in the middle is a comparison between the two images. An algorithm compares each pixel to ensure that the value of the pixel is within 3% and 3 mm of the predicted pixel. A overall γ-value is then reported, which represents the percentage of pixels meeting the 3% and 3 mm threshold. Chart 1 shows the γ-value tabulated by the RTT vs the γ-value tabulated by the graduate student. Overall they align closely with each other. A two one sided t-test (TOST) was performed on this data to determine equivalence. Chart 2, provides a graphical comparison on the amount of time it took an graduate student and the RTT to perform the verification on each plan. National Survey The survey is still currently under review by the REB. The results are pending.
Analysis EPID Study A T-OST test was performed to prove the equivalence on the γ-value collected from the RTT and graduate student groups. A range of equivalence of +/- 3% was set and the following hypotheses used. H01 = μphysics - μRTT >3% H1 = μphysics - μRTT ≤ 3%
H02 = μphysics - μRTT tcrit95% and reject H02 because t< -tcrit95%. Therefore we must accept our alternate hypotheses H1 and H2, which state that μphysics - μRTT ≤ 3% and ≥ -3% which means that | μphysics - μRTT |< 3% and therefore within our range of equivalence.
Figure 1. Sample data collected by the Portal Dosimetry program.
Discussion and Future Directions EPID Study During the verifications of plans by the RTT, the RTT made the observation that it would be possible to reorder the beams to improve efficiency between plans with an odd number of arcs or non-standard arcs. It was observed that the RTT was familiar with machine interlocks and troubleshooting them. The RTT was able to quickly clear interlocks and proceed with the verification. It is believed that due to the familiarity of the RTT with the treatment units, RTTs would be better able to troubleshoot and find new ways of performing verifications more efficiently over time. These observations and comments are not reflected in the measured verification times as it did not fall within the period of time measured. However, this may be something to consider in the methodology of future studies. Our current research is designed as a feasibility study. As such we only have one RTT participating. Currently all graduate students performing verifications are participating in the study for n = 4. Therefore we cannot extrapolate this to the entire RTT population at the NSCC. A further study involving more RTTs will need to be done.
Conclusions In conclusion, from our current study, we have determined that it is possible for an RTT to perform VMAT dose verifications as effectively as a physics graduate student.
Acknowledgements and References I would like to thank Danny McAloney RTT, who volunteered to stay after hours to run the verifications for this study, the graduate students of the Dalhousie Medical Physics program, Dr. Waseem Sharif for his help with the statistical analysis, and the staff at the NSCC for their support of this research project. International Atomic Energy Agency. (2000). Lessons learned from accidental exposures in radiotherapy. Vienna: International Atomic Energy Agency. International Atomic Energy Agency. (2008) Module 2.10: Accident update – some new events (UK, USA, France)[Powerpoint Slides]. Retrieved December 21, 2015 from https:// rpop.iaea.org/RPOP/RPoP/Content/Documents/ TrainingAccidentPrevention/Lectures/AccPr_2.10_Accident_update1_WEB.ppt (Dec 21, 2015)
