Multi-institutional comparison of secondary check of treatment planning using computer-based independent dose calculation for non-C-arm linear accelerators.

PURPOSE: This report covers the first multi-institutional study of independent monitor unit (MU)/dose calculation verification for the CyberKnife, Vero4DRT, and TomoTherapy radiotherapy delivery systems. METHODS: A total of 973 clinical treatment plans were collected from 12 institutions. Commercial software employing the Clarkson algorithm was used for verification after a measurement validation study, and the doses from the treatment planning systems (TPSs) and verification programs were compared on the basis of the mean value ±â€¯two standard deviations. The impact of heterogeneous conditions was assessed in two types of sites: non-lung and lung. RESULTS: The dose difference for all locations was 0.5 ±â€¯7.2%. There was a statistically significant difference (P < 0.01) in dose difference between non-lung (-0.3 ±â€¯4.4%) and lung sites (3.5 ±â€¯6.7%). Inter-institutional comparisons showed that various systematic differences were associated with the proportion of different treatment sites and heterogeneity correction. CONCLUSIONS: This multi-institutional comparison should help to determine the departmental action levels for CyberKnife, Vero4DRT, and TomoTherapy, as patient populations and treatment sites may vary between the modalities. An action level of ±5% could be considered for intensity-modulated radiation therapy (IMRT), non-IMRT, and volumetric modulated arc radiotherapy using these modalities in homogenous and heterogeneous conditions with a large treatment field applied to a large region of homogeneous media. There were larger systematic differences in heterogeneous conditions with a small treatment field because of differences in heterogeneity correction with the different dose calculation algorithms of the primary TPS and verification program.

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.

Impact of Different Independent Dose Verification Software Programs for Secondary Check.

PURPOSE: A multi-institutional study was performed to identify the impact of different independent dose verification programs on independent dose verification software program. METHODS: Data for 1,543 treatment fields were collected in three institutions. RADCALC and Simple MU Analysis (Simple MU) using the Clarkson-based algorithm were used. RADCALC needs the input of radiological path length (RPL) from radiotherapy treatment planning systems (RTPSs) (Eclipse or Pinnacle3). The Simple MU computes the RPL using CT images independently from the RTPSs. Ion-chamber measurements were performed for commissioning the two programs and the RTPSs. Next, the results of the two programs were compared to the RTPSs obtained in the clinically-approved plans in all three institutions. RESULTS: The commissioning results showed ±1.5% variation in the ion-chamber measurements and there was slight difference between the institutions. The RADCALC (0.9±2.2%) and the Simple MU (1.7±2.1%) results showed a slight systematic difference. Pinnacle3 computed longer RPLs because it used CT-physical density tables. Thus, there was an impact on the accuracy in the treatment plans involving bone and other high-density materials. CONCLUSION: Dose calculation algorithms in different dose verification programs provided similar results. However, care must be taken because different RPL calculation methods in the RTPSs may affect dose difference between different independent dose verification programs by 1%.