The purpose of this procedure is to evaluate the constancy of isodose distributions and monitor unit calculations performed on a standardized water phantom and clinical CT scans for all photon energy beam models in clinical use. The calculations are performed over a range of field sizes, SSD’s, and depths that are clinically relevant and also test the edge of acceptable performance of the model.
II. GENERAL REQUIREMENTS
The requirements for this procedure are derived from the following sources:
AAPM TG-40 “Comprehensive QA for Radiation Oncology: Report of AAPM Radiation Therapy Committee Task Group 40”
AAPM TG-53 “Quality Assurance for Clinical Radiotherapy Treatment Planning”
QA for Treatment Planning Dose Delivery by 3DRTP and IMRT; Boyer, et al.; General Practice of Radiation Oncology Physics in the 21st Century: Med Phys Publishing 2000.
III. RESPONSIBILITIES
The dosimetry staff is responsible for the performance of this procedure.
IV. INSTRUCTIONS
A. Monitor Unit Check – Open and Wedge Fields
1) Principle. The integrity of monitor unit accuracy and constancy is a factor which affects all patient treatments. Data corruption, software bugs, and hardware failure can effect the calculation of monitor units for a given treatment plan. Performing periodic testing of the constancy, after acceptable accuracy has been established by acceptance testing of the beam model, is an established requirement of any treatment planning quality assurance program.
2) Method
a) In the clinical planning workspace go to the patient : QA.
b) There exists a list of plans. All of the plans must be re-computed under the current clinical version of the TPS software. If a new version has been recently installed ensure the plan is edited to such that it will be evaluated utilizing this new version.
c) Open the plan and re-compute each beam.
d) When the computation is complete, print only a summary of the plan. Compare the resulting monitor units to the expected monitor units on the appropriate Form 1.1.2.5A Monitor Unit Check.
B. Isodose Checks
1) Principle. The integrity of isodose accuracy and constancy is a factor which can effect all patient treatments. Data corruption, software bugs, and hardware failure can effect the calculation and/or display of isodose values or positioning. Performing periodic testing of the constancy, after acceptable accuracy has been established by acceptance testing of the beam model, is required for a comprehensive treatment planning quality assurance program.
3) 2) Method
a) In the clinical planning workspace go to the patient : QA Isodoses.
b) There exists a list of plans. All of the plans must be re-computed under the current clinical version of the TPS software. If a new version has been recently installed ensure the plan is edited to such that it will be evaluated utilizing this new version.
c) Open the plan and re-compute each beam.
d) When the computation is complete, print a color plot of the isodose distribution only. Compare the resulting distribution with the baseline distribution transparency. Document all discrepancies on the appropriate Form 1.1.2.5B Isodose Checks. Any deviation of 1mm or greater should be reported to the physicist immediately.
C. Clinical Isodose/Monitor Unit Check
4) Principle. The integrity of isodose, dose calculation, and monitor unit accuracy and constancy is a factor which affects all patient treatments. Data corruption, software bugs, and hardware failure can effect the calculation of monitor units for a given treatment plan. Performing periodic testing of the constancy, after acceptable accuracy has been established by acceptance testing of the beam model, is an established requirement of any treatment planning quality assurance program.
5) Method
a) In the clinical planning workspace go to the patients: QA Lung, QA Prostate, and QA H&N.
b) There exists a list of plans. All of the plans must be re-computed under the current clinical version of the TPS software. If a new version has been recently installed ensure the plan is edited to such that it will be evaluated utilizing this new version.
c) Open the plan and re-compute each beam.
d) When the computation is complete, print the complete plan. Compare the resulting monitor units to the expected monitor units on the appropriate Form 1.1.2.5C, D, & E.
V. ATTACHED FORMS
FORM 1.1.2.5A – MONITOR UNIT CHECK OPEN AND WEDGE FIELDS
FORM 1.1.2.5B – ISODOSE CHECKS
FORM 1.1.2.5C – BREAST PLAN EVALUATION
FORM 1.1.2.5D – PROSTATE PLAN EVALUATION
FORM 1.1.2.5E – IRREG FIELD EVALUATION