Discussion topic:
For new students, contact the senior student/preceptor at your internship site.
Instruments: What dosimetry instruments are used in your department/clinical internship setting? What specifically are they used for?
For example, what tools are used for calibrating the linear accelerator, measuring patient dose, performing patient specific IMRT/VMAT quality control, etc.
Discussion post:
At my clinical sight an ionization chamber and ArcCheck diode array are the most commonly used dosimetry insruments. A cylindrical Farmer type ionization chamber with graphite shell is used by our physics staff for annual Linac QA. The standard TG-51 protocol is used for annual testing in a process usually done over the weekend. Annual QA compares data established at the Linac commissioning to new data and to ensure accuracy. Some items measured using the ionization chamber are percent depth dose, dose rate fluctuation, output vs change in dose rate, output vs gantry angle, off axis vs central axis factor. Additionally, mechanical isocenter parameters are verified along with imaging accuracy and quality.1
The ArcCheck Phantom QA device is a diode array used for IMRT and VMAT treatment plan verification. To run QA using ArcCheck, the phantom is placed on the treatment table, leveled, and plugged into a cat-5 cable that is run through a conduit to the QA computer at the treatment console. The phantom is setup similarly to a patient using the treatment room lasers and a QA plan is loaded and administered similar to a regular patient treatment. The QA treatment is recorded using an ArcCheck program and compared to QA plan created by the dosimetrist. What is unique about the ArccCheck device is that it is three dimensional and measures the entrance and exit dose of a plan for greater accuracy. In addition, VMAT treatment arcs can be measured and a plan can be administered as it would for an actual patient treatment. Previously IMRT QA was verified using the two dimensional Mapcheck QA device and a separate plan had to be created with all treatment field angles changed to zero. ArcCheck is the most frequently used physics and dosimetry instrument in our department as it is used nearly daily for QA on all IMRT plans.
References
1.Almond PR, Biggs PJ, Coursey BM, et al. AAPM’s TG-51 protocol for clinical reference dosimetry of high-e photon and electron beams. AAPM.org. https://www.aapm.org/pubs/reports/RPT_67.pdf. Accessed on September 27, 2016.
For new students, contact the senior student/preceptor at your internship site.
Instruments: What dosimetry instruments are used in your department/clinical internship setting? What specifically are they used for?
For example, what tools are used for calibrating the linear accelerator, measuring patient dose, performing patient specific IMRT/VMAT quality control, etc.
Discussion post:
At my clinical sight an ionization chamber and ArcCheck diode array are the most commonly used dosimetry insruments. A cylindrical Farmer type ionization chamber with graphite shell is used by our physics staff for annual Linac QA. The standard TG-51 protocol is used for annual testing in a process usually done over the weekend. Annual QA compares data established at the Linac commissioning to new data and to ensure accuracy. Some items measured using the ionization chamber are percent depth dose, dose rate fluctuation, output vs change in dose rate, output vs gantry angle, off axis vs central axis factor. Additionally, mechanical isocenter parameters are verified along with imaging accuracy and quality.1
The ArcCheck Phantom QA device is a diode array used for IMRT and VMAT treatment plan verification. To run QA using ArcCheck, the phantom is placed on the treatment table, leveled, and plugged into a cat-5 cable that is run through a conduit to the QA computer at the treatment console. The phantom is setup similarly to a patient using the treatment room lasers and a QA plan is loaded and administered similar to a regular patient treatment. The QA treatment is recorded using an ArcCheck program and compared to QA plan created by the dosimetrist. What is unique about the ArccCheck device is that it is three dimensional and measures the entrance and exit dose of a plan for greater accuracy. In addition, VMAT treatment arcs can be measured and a plan can be administered as it would for an actual patient treatment. Previously IMRT QA was verified using the two dimensional Mapcheck QA device and a separate plan had to be created with all treatment field angles changed to zero. ArcCheck is the most frequently used physics and dosimetry instrument in our department as it is used nearly daily for QA on all IMRT plans.
References
1.Almond PR, Biggs PJ, Coursey BM, et al. AAPM’s TG-51 protocol for clinical reference dosimetry of high-e photon and electron beams. AAPM.org. https://www.aapm.org/pubs/reports/RPT_67.pdf. Accessed on September 27, 2016.