A multi-institutional study of secondary check of treatment planning using Clarkson-based dose calculation for three-dimensional radiotherapy.

PURPOSE: As there have been few reports on quantitative analysis of inter-institutional results for independent monitor unit (MU) verification, we performed a multi-institutional study of verification to show the feasibility of applying the 3-5% action levels used in the U.S. and Europe, and also to show the results of inter-institutional comparisons. METHODS: A total of 5936 fields were collected from 12 institutions. We used commercial software employing the Clarkson algorithm for verification after a validation study of measurement and software comparisons was performed. The doses generated by the treatment planning systems (TPSs) were retrospectively analyzed using the verification software. RESULTS: Mean ±â€¯two standard deviations of all locations were 1.0 ±â€¯3.6%. There were larger differences for breast (4.0 ±â€¯4.0%) and for lung (2.5 ±â€¯5.8%). A total of 80% of the fields with differences over 5% of the action level involved breast and lung targets, with 7.2 ±â€¯5.4%. Inter-institutional comparisons showed various systematic differences for field shape for breast and differences in the fields were attributable to differences in reference point placement for lung. The large differences for breast and lung are partially attributable to differences in the methods used to correct for heterogeneity. CONCLUSIONS: The 5% action level may be feasible for verification; however, an understanding of larger differences in breast and lung plans is important in clinical practice. Based on the inter-institutional comparisons, care must be taken when determining an institution-specific action level from plans with different field shape settings and incorrectly placed reference points.

Precision in Wedge Off-axis Using Independent Dose Verification.

It is essential for quality assurance to verify the safety of each individual patient's plan in radiation therapy. The tolerance level for independent verification of monitor unit calculations for non-IMRT clinical radiotherapy has been shown in the AAPM TG114. Thus, we investigated the precision of independent MU (dose) verification considering a wedge off-axis calculation and we conducted a study at twelve institutes for independent verification with the wedge off-axis calculation. The results obtained with the wedge off-axis calculation showed better agreement with the treatment planning system calculation results than those without the former calculation in a phantom study and in the patient retrospective study. The confidence limits with the wedge off-axis calculation were 2.2±3.4% and 2.0±4.3% for the plans with a physical wedge and a non-physical wedge in the patient study, respectively. However, the confidence limits were over 5% without the off-axis calculation. From our multi-institutional study, the results suggested that the tolerance level for the wedge off-axis plan would be 5% when considering the wedge off-axis calculation and the level was similar to that of the treatment planning system using other conventional irradiation techniques.