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Determination of geometrical margins in external beam radiotherapy for prostate cancer

  • Mohamed Bencheikh (a1), Abdelmajid Maghnouj (a1), Jaouad Tajmouati (a1), Ahmed Dadouch (a1) and Zakariae Benjelloun (a1)...
  • Please note a correction has been issued for this article.



The focus of this study is to find the optimal clinical tumour volume (CTV) to planning tumour volume (PTV) margins for precise radiotherapy treatment of prostate cancer. The geometrical shape of the target volume posses challenges in accurately identifying the CTV to PTV margins, especially when the organ affected by cancer demonstrates anatomical variations and the surrounding organs have high radio-sensitivity, in comparison to the organ of origin of the cancer.

Materials and methods

The geometrical margins of CTV to PTV are investigated using portal imaging, in three directions. This study is carried out on 20 patients treated by the external photon beam radiotherapy of prostate cancer using standard accelerator without stereotaxic and without prostate markers.

Results and discussion

Based on previous studies and the findings of our work, we propose CTV to PTV margin of 5·84 mm in the lateral direction, of 5·1 mm in the cranio-spinal direction and of 7·3 mm in the antero-posterior direction for external photon beam radiotherapy of prostate cancer.


The proposed CTV to PTV margins ensure high radiotherapy treatment precision of prostate cancer.


Corresponding author

Author for correspondence: Mohamed Bencheikh, Physics Department, Faculty of Sciences Dhar El-Mahraz, University of Sidi Mohamed Ben Abdellah, Fez, 30000, Morocco. E-mail:


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Cite this article: Bencheikh M, Maghnouj A, Tajmouati J, Dadouch A, Benjelloun Z. (2019) Determination of geometrical margins in external beam radiotherapy for prostate cancer. Journal of Radiotherapy in Practice18: 186–189. doi: 10.1017/S1460396918000699



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