Dosimetric Study of Tissue Heterogeneity Correction for Breast Conformal Radiotherapy

Document Type : Original Paper

Authors

1 Specialist of Medical Physics (Radiotherapy Department)at Meet Ghammr Oncology Center,Ministry of Health.

2 Prof. of Medical physics ; Children’s Cancer Hospital&National Cancer Institute; Cairo University; Cairo Egypt.

3 Professor of Bio-Physics , Zagazig University, Egypt.

4 Consultant of Medical physics; children cancer Hospital, Egypt

5 Specialist of Medical Physics, National Cancer Institute (NCI),Cairo,Egypt.

6 Chief Executive Officer (CEO) of On-Medical Company.

Abstract

Introduction: Heterogeneity correction is an important parameter in dose calculation for cancer patients where it may be cause inaccuracy in dose calculation as a result of different densities of patients. This study studied the impact of dose calculation of breast cancer patients with and without heterogeneity correction. Material and Methods: Twenty breast cancer patients were treated with Three-Dimensional Conformal Radiotherapy(3DCRT). Dose calculations were performed using two modes: Fast Photon mode for homogeneity and Fast Photon Effective Path length for heterogeneity with two photon energies. Monitor Units(MU), Modulation Factor, Dose Volume Histograms(DVH) and quality indices were used to evaluate the effect of heterogeneity correction on dose calculation and investigate the mechanism of this effect in the low and high energies.
Results: Heterogeneity correction compared to without it showed significant reduction in MU and modulation factor at 6MVand 10MV (p <0.05). Dosimetric parameters derived from DVH were significantly lower for Planning Target Volume (PTV) with homogeneity versus heterogeneity (p <0.05) as D95% (95.1%vs93.7%) and V95%(95.3%vs89%) for 6MV while max Dose and D2 increased. Also the dose for organs at risk exhibited an increase with heterogeneity correction. Quality indices were be worst with heterogeneity correction with a significant difference (p <0.05). The differences between the dose with heterogeneity correction and without it in 6MV and 10MV were as follows: ΔD95% (4.4%vs3.4%;P=0.001) and ΔV95%(4.76%vs4.5%;P=0.001).
Conclusion: non-use of the heterogeneity correction can be cause to deliver under or overdose dose to the target volume. Tissue heterogeneity correction had an impact on dose calculation for breast cancer patients and this impact was more effective for the low energy. 

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References
 
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