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Dosimetric Evaluation of 3 and 4 Field Radiation Therapy of Breast Cancer

S Dang*, E Osei, J Darko, Grand River Hospital, Kitchener, ON, CA.

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: In external beam radiotherapy planning, three or four field mono-isocentric techniques are used to treat breast cancer patients with nodal invasion. However, there is a lack of consistency between institutions and individuals as to what is deemed an acceptable treatment plan with regards to target coverage and dose to organs at risk. Therefore, there is a growing need for the development of institutional specific treatment plan acceptability criteria in order to minimize significant variations in patient treatment plans.


Methods: We evaluated the treatment plans of 368 breast cancer patients with nodal involvement who were previously treated at our Cancer Center. All patients underwent a computerized tomography simulation for treatment planning and were positioned in the supine position with both arms raised above the head. The deep inspiration breath-hold (DIBH) technique was used for all left sided breast cancer patients. Treatment planning was either a three or four field mono-isocentric plan using 6, 10 and/or 15 MV depending on breast size and using a hybrid technique consisting of open and optimized fields. All patients’ plans were prescribed to 50Gy/25.


Results: Dose volume histograms were extracted from all 368 patient plans for the PTV-eval target volume, the organs at risk including the lungs and heart. The mean DVH for each structure was also derived. We observed that the dose to the heart was relatively lower as expected using the DIBH technique when compared to patients with free breathing but with relatively increased dose to the ipsilateral lung.


Conclusion: Mean DVHs obtained from this study can be used as guideline for treatment plan acceptability. Implementation of such criteria would establish an evaluation process to define a consistent and transparent treatment path for all patients that reduces significant variations in the acceptability of treatment plans and potentially improve patient standard of care.

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Keywords

Breast, Dose Volume Histograms, Radiation Dosimetry

Taxonomy

TH- External Beam- Photons: IMRT/VMAT dose optimization algorithms

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