Analysis of patient specific dosimetry quality assurance measurements in intensity modulated radiotherapy: a multi centre study.

Aim Of The Study: Statistical analysis of pre-treatment dose verification of intensity-modulated radiotherapy (IMRT) fields to assess the quality of the IMRT practice at different radiotherapy centers.

Materials And Methods: The dose verification data acquired by the institutional physicist of 10 different hospitals for various types of patients were collected and analyzed for mean, median, standard deviation (SD), range, minimum and maximum % deviation. The percentage of cases having positive and negative dose differences as well dose differences within ± 3% were also determined.

Results: The mean values of percentage variation in difference between treatment planning systems calculated dose and difference between measured dose (D(TPS) and D(Meas)) are found to be from -1.79 to 1.48 and median from -1.79 to 1.51. The SDs are found to be from 0.76 to 3.70. The range of variation at these centers varies from 3.99 to 16.45 while minimum and maximum values of percentage variation in difference between D(TPS) and D(Meas) ranges from -10.33 to 13.38. The percentage of cases having positive dose difference ranges from 8 to 94 and cases having negative dose difference ranges from 6 to 92. The percentage of cases having dose difference within ± 3% varies from 57 to 100.

Conclusion: IMRT centers are having random and biased (skewed towards over or under dose) distribution of the percentage variation in difference between measured and planned doses. The analysis of results of the IMRT pre-treatment dose verification reveals that there are systematic errors in the chain of IMRT treatment process at a few centers. The dosimetry quality audit prior to commissioning of IMRT may play an important role in avoiding such discrepancies.