Margin Dose Distribution Based on A Breast Radiotherapy: A Case Report
Abstract:
Background: In radiotherapy, a known volume of disease should be covered by reachable dose distribution. Margin is usually added to cover different variations due to the clinical environment of the disease target. It is normal the inner target will attain more dose coverage than that of the outer margin. However, in some situation, the outer margin may have high coverage than that of inner volume. In this report, a special dose distribution situation was reported based on a tangent field left breast treatment setup, and this could be a variation in the intension of a target definition.
Methods: Following routine chart check procedure, a left breast radiotherapy case with special dose distribution was selected. The target definition is like the of Accelerated Partial Breast Irradiation approach to lower the possibility of ribs complication. And the gross target volume (GIV), clinical target volume (CTV), and prescription isodose volume (PIV) at the rib boundary were cutoff into one surface at abutment of the rib line. Then regular tangent fields were setup with photon energy at 10MV, and field In field technique was employed to teach the maximum dose requirement of 105% of the prescription dose of 520cGy per fraction and delivered 5 fractions to attain the clinical goal of 101% prescription dose volume covered 95% of the PTV. The volume coverage of the GTV, CTV, and PTV was analyzed.
Results: For the geometry setup of this plan with GTV at 7.75cc, with diameter of 2.5cm, and CTV at 50.11cc with diameter at 4.5cm, and PTV at 86.42cc with diameter at 5.5cm. The PTV coverage at prescription dose was 99.7%, and CTV coverage was at 99.5%, and GTV was at 98.5%, which meant that the GTV coverage was lower than CTV and PTV.
Conclusion: The analysis showed a special dose distribution of breast treatment where target was abutted to that of the chest wall ribs. The target definition and dose distribution were different with that of conventional understanding.
