Discussion topic:
Protocols: Discuss the role of AAPM TG-51. Why did AAPM TG-51 replace TG-21 protocol, and what calibration protocol came before TG-21? What protocol do other countries use to calibrate their linear accelerators. Be specific in your answer. This may take some additional research. Which protocol does your facility follow? Why?
Discussion post:
The TG-21 protocol was replaced by the TG-51 protocol because the TG-51 method is less complex and has less margin for error. The older TG-21 method measures exposure in air-kerma which can be affected by external factors. TG-21 also requires the physicist to perform more calculations to obtain the required correction factors for absorbed dose. The more current TG-51 protocol measures absorbed dose to water using a given calibration factor for absorbed dose in water (Dw).1 Additionally, studies have shown that there is a 1-2% discrepancy when comparing TG-21 measurements to TG-51 measurements. Due to this discrepancy it has been recommended that clinics switching from the older TG-21 method to the TG-51 method perform both types of measurements. If a discrepancy of larger than 3% is discovered an investigation should be done to ensure no errors have been made.2 Prior to the TG-21 protocol the SCRAD protocol was used. The SCRAD protocol also used dose measured in air-kerma but it presented issues based on the numerous calibration factors needed to be calculated by the physicist.3
At UF Cancer Center the TG-51 protocol is used to calibrate linacs. The TG-51 protocol is used because is removes the necessity for the physicist to perform complex calculations. The TG-51 protocol ensured the right dose is administered by calibrating the linac to deliver 1cGy per MU. The TG-51 protocol is also important because it creates a constant method of calibration which ensured dose delivered at clinic is comparable to dose delivered at another clinic. Accurate delivered dose is very important for research facilities and data must be reliable. By using the TG-51 protocol our clinic can ensure any data gathered is accurate and admissible to academis studies.
References
1) Nes EM. Comparison between AAPM's TG-21 and TG-51 clinical reference protocols for high-energy photon and electron beams.Oregonstate.edu. https://ir.library.oregonstate.edu/xmlui/handle/1957/30243.Accessed on October 5, 2016.
2)Cho SH, Lowenstein B, Balter C, et al. Comparison between TG-51 and TG-21: Calibration of photon and electron beams in water using cylindrical chambers. Journal of Applied Clinical Medical Physics. 2000;1(3). http://www.jacmp.org/pages/files/backfiles/jacmpv1i3a4.pdf Accessed on October 5, 2016
3)Ibot G, Ma CM, Rogers DW, et al. Anniversary Paper: Fifty years of AAPM involvement in radiation dosimetry. Medical Physics 2008;35(4). http://scitation.aip.org/upload/AAPM/MPH/open_access/MPH001418.pdf. Accessed on October 4, 2016.
Protocols: Discuss the role of AAPM TG-51. Why did AAPM TG-51 replace TG-21 protocol, and what calibration protocol came before TG-21? What protocol do other countries use to calibrate their linear accelerators. Be specific in your answer. This may take some additional research. Which protocol does your facility follow? Why?
Discussion post:
The TG-21 protocol was replaced by the TG-51 protocol because the TG-51 method is less complex and has less margin for error. The older TG-21 method measures exposure in air-kerma which can be affected by external factors. TG-21 also requires the physicist to perform more calculations to obtain the required correction factors for absorbed dose. The more current TG-51 protocol measures absorbed dose to water using a given calibration factor for absorbed dose in water (Dw).1 Additionally, studies have shown that there is a 1-2% discrepancy when comparing TG-21 measurements to TG-51 measurements. Due to this discrepancy it has been recommended that clinics switching from the older TG-21 method to the TG-51 method perform both types of measurements. If a discrepancy of larger than 3% is discovered an investigation should be done to ensure no errors have been made.2 Prior to the TG-21 protocol the SCRAD protocol was used. The SCRAD protocol also used dose measured in air-kerma but it presented issues based on the numerous calibration factors needed to be calculated by the physicist.3
At UF Cancer Center the TG-51 protocol is used to calibrate linacs. The TG-51 protocol is used because is removes the necessity for the physicist to perform complex calculations. The TG-51 protocol ensured the right dose is administered by calibrating the linac to deliver 1cGy per MU. The TG-51 protocol is also important because it creates a constant method of calibration which ensured dose delivered at clinic is comparable to dose delivered at another clinic. Accurate delivered dose is very important for research facilities and data must be reliable. By using the TG-51 protocol our clinic can ensure any data gathered is accurate and admissible to academis studies.
References
1) Nes EM. Comparison between AAPM's TG-21 and TG-51 clinical reference protocols for high-energy photon and electron beams.Oregonstate.edu. https://ir.library.oregonstate.edu/xmlui/handle/1957/30243.Accessed on October 5, 2016.
2)Cho SH, Lowenstein B, Balter C, et al. Comparison between TG-51 and TG-21: Calibration of photon and electron beams in water using cylindrical chambers. Journal of Applied Clinical Medical Physics. 2000;1(3). http://www.jacmp.org/pages/files/backfiles/jacmpv1i3a4.pdf Accessed on October 5, 2016
3)Ibot G, Ma CM, Rogers DW, et al. Anniversary Paper: Fifty years of AAPM involvement in radiation dosimetry. Medical Physics 2008;35(4). http://scitation.aip.org/upload/AAPM/MPH/open_access/MPH001418.pdf. Accessed on October 4, 2016.