Dosimetric Correlation between Point Doses and Volumetric Doses in Gynecological Intracavitary HDR Brachytherapy:  A statistical analysis

Jyoti Bisht; Surendra Prasad Mishra; Raj kumar Tyagi; Ravi kant; Meenu gupta; Vipul Nautiyal

Volume : VI, Issue : III, March - 2016

Dosimetric Correlation between Point Doses and Volumetric Doses in Gynecological Intracavitary HDR Brachytherapy: A statistical analysis

Jyoti Bisht, Surendra Prasad Mishra, Raj Kumar Tyagi, Ravi Kant, Meenu Gupta, Vipul Nautiyal

Abstract :

Objective: Recent studies have reported that ICRU–38 point doses did not provide accurate estimations and clinical correlations. In this study the significance of the correlation between 2cc volumetric doses and point doses have been statistically analyzed. Methods: Sixty intracavitary gynecological applications has been selected. Patients were treated with EBRT dose of 46Gy/23# followed by 9Gy/2session of achytherapy. Each patient underwent for CT–simulation scan and 3D treatment planning for achytherapy session. Bladder and rectum were contoured and doses to the bladder and rectum were reported according to ICRU–38 and GEC–ESTRO recommendations. Result: The data was analyzed in SPSS 16.0 software. Q–Q plot test showed that data is normally distributed and unweighted for bladder and rectum. For bladder and rectum, the ratio test was found to be1.009 and 1.056 respectively for point dose to 2cc volume dose. The Pearson correlation coefficient is found to be 0.685, 0.639 and covariance is 67.51, 26.65 for bladder and rectum resp. Mean standardized residual came 0.000, 0.000 and standard deviation evaluated is 1.019 and 0.991 for bladder and rectum resp. The Kruskal Wallis test showed p value for bladder 2cc volumetric and point dosimetry is 0.018* and for rectum 0.004*. The regression analysis curve fit line equation has been modeled from intercept model. The regression equations shows that it is under estimating the dose to the bladder as well as it is over estimating the rectum doses. Conclusion: However, point dosimetry might not be the alternative for defining the doses to the OARs. Thus for precise and accurate dosimetry of OARs (bladder and rectum) three dimensional imaging and volumetric dosimetry is necessary.