Dose homogeneity in accelerated partial breast irradiation

Autor: Birgitte Vrou Offersen
Rok vydání: 2010
Předmět:
Zdroj: Radiotherapy and Oncology. 94:390
ISSN: 0167-8140
Popis: Dear Editor, Firstly, we would like to thank Dr. Nairz and Sedlmayer for their valuable comments. In our review entitled ‘‘Accelerated partial breast irradiation as part of breast conserving therapy of early breast carcinoma: A systematic review’’ [1] different aspects of this new treatment were discussed, e.g. background/rationale, patient inclusioncriteria, technical aspects of the various methods, and radiobiological issues. Essentially five different techniques are used in accelerated partial breast irradiation (APBI), two of them intraoperative radiotherapy (IORT) (an orthovolt system, Intrabeam, and intraoperative use of electrons) and three post-operative (3D-conformal radiotherapy, MammoSite and interstitial brachytherapy using either LDR or HDR). The total doses and dose per fraction varies greatly among these techniques from moderately hypofractionated therapy using 2.67 Gy per fraction to the much higher dose of 21 Gy given in one fraction. In our reviewa comparison of the different techniqueswas listed, andwe stated that the dose homogeneitywas best for 3D-conformal radiotherapy, whilst fair for the remaining four methods. In their letter, Dr. Nairz and Sedlmayer argue that the method of IORT using electrons has a favourable dose homogeneity compared to MammoSite, Intrabeam and interstitial brachytherapy, in fact they report aDmax of 110% inside the target volume using IORTwith electrons whilst 200%, 276% and 635–969% for the MammoSite, Intrabeam and interstitial brachytherapy methods, respectively. We acknowledge this point, and in principle it is correct that the technique using IORT with electrons has a better dose homogeneity than the MammoSite, Intrabeam and interstitial brachytherapy techniques. On the other hand, the dose homogeneity index in our opinion should be considered in the context of dose and fractionation, thus in the context of 21 Gy in one fraction.Nobiologicalmodels candescribewhathappenswhenusing suchhighdoses, although 0167-8140/$ see front matter 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2010.03.001 others have previously applied the LQ-model to this dose [2]. Based on the LQ-model and a a/b 3 Gy, 21 Gy/one fraction corresponds to 100 Gy (BED2 Gy), and an overdose of 110% translates into 120 Gy. The ICRU dose recommendations for therapy of 2 Gy per fraction prescribe 107% as max dose. However, for moderately hypofractionated therapy we recommend a lower acceptable Dmax, e.g. for therapy with for example 2.67 Gy per fraction the Dmax of 107% should be adjusted to 105% based on the LQ-model. Given these figures we advocate that the most homogenous dose is provided by the 3D CRT method, and that the dose homogeneity in the context of 20–21 Gy in 1 fraction using the IORT electron method is fair.
Databáze: OpenAIRE
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