ESTRO meets Asia 2024 - Abstract Book

S69

Interdisciplinary – Brachytherapy

ESTRO meets Asia 2024

The predictability of point doses to rectal volumetric doses in HDR brachytherapy of cervical cancer

Nor Hayati Hashim 1 , Wan Zamaniah Wan Ishak 2 , Zulaikha Jamaluddin 2

1 Oncology, Hospital Sultan Ismail, Johor, Malaysia. 2 Oncology, University Malaya Medical Centre, KL, Malaysia

Purpose/Objective:

The introduction of 3D planning into gynecologic brachytherapy in UMMC began in March 2011. However, the use is interchangeable with the traditional 2D planning method due to unforeseen circumstances such as CT machine breakdown which resulted in uncertainties during the planning evaluation. Several studies have shown a good correlation between the ICRU point doses and the volumetric doses to both target volumes and organs at risk. This study aims to investigate the correlation between rectal point doses and rectal volumetric doses, subsequently derive a clinically relevant predictive relationship between point and volumetric doses, and provide a quantitative assessment of the error in such an equation.

Material/Methods:

A total of 150 planning data sets from 50 patients who underwent at least 3 sessions of full HDR ICBT in UMMC between 2017 to 2019 were retrospectively analysed and were divided into two groups. Group A (n=100) was used to derive the correlation between the point dose and volumetric doses using linear regression analysis. The formula obtained was tested in Group B (n=50) insertions and subsequently validated using studentised residuals and Intraclass Correlation Coefficients.

Results:

Significant correlations were obtained for all rectal volumetric doses and ICRU point doses for rectum in Group A insertions. The strongest correlation was found for the D5cc volumes (correlation coefficient = 0.74), followed by D2cc, D1cc and D0.1cc, with values of 0.73, 0.72 and 0.64, respectively (p<0.001). Statistical validation of equations generated in Group B showed mean studentised residual values of 0.000 (SD±0.61-1.00). However, Intraclass Correlation Coefficients analysis for all rectal subvolumes ranged between 0.16 to 0.44, which indicates a poor to moderate significance.

Conclusion:

Our study showed a strong correlation between rectal point dose and rectal volumetric doses. However, the equation obtained is considered unreliable for daily clinical use owing to its tenuous correlation. Therefore, more robust data is needed to derive a clinically relevant predictive relationship between point dose and volumetric doses and developed an equation to quantitatively measure the error.

Keywords: Rectal dose, intracavitary brachytherapy, HDR

References: