Seiji Tachiiri MD, PhD, Presenter: Nothing to Disclose

Michihide Mitsumori, Abstract Co-Author: Nothing to Disclose

Chikako Yamauchi, Abstract Co-Author: Nothing to Disclose

Norio Araki, Abstract Co-Author: Nothing to Disclose

Natsuo Oya, Abstract Co-Author: Nothing to Disclose

Yasushi Nagata, Abstract Co-Author: Nothing to Disclose

Masahiro Hiraoka MD, PhD, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Purpose/Objective: Because of the current trend toward reduced axillary surgery, radiation therapy is expected to play a more important role in controlling the axilla. Although many authors have demonstrated that most of the axillary lymph node region can be geometrically covered by cranially extended tangential fields (CETF) for whole breast radiation therapy, the adequacy of the delivered dose, especially, in relation to the patient's physique, has not yet been studied. We investigated the relationship between the patient's physique and the dose distribution to Level I and II axillary lymph node regions treated with CETF for breast-conserving therapy (BCT). Materials/Methods: Fifty patients were randomly selected from 214 patients who underwent BCT between March 2001 and November 2001. These patients were clinically N0 and underwent axillary sampling. A metal clip was placed at the level of the intercosto-brachial nerve to mark the cranial extent of axillary surgery. Two experimental CETF treatment plans for WBRT, in which the upper border of the tangential field was extended cranially to cover the subclavian vein, were developed for each patient using Cadplan version 6.2.7 (Varian Medical Systems). One plan employed 4MV X-ray as a reference, whereas the other plan used either Co-60 gamma ray or 6MV X-ray so that a more homogenous dose distribution was obtained in the breast. We evaluated dose distributions to the Level I and II axillary lymph node regions in tangential irradiation using V95 and V80, indicating that the percent volumes of Level I and II lymph node areas received 95 % and 80 % of the prescribed dose, respectively. Nine distances in the chest and axilla were measured as parameters of the patient's physique: the separation of tangential irradiation, the height of the breast, the thickness of the thorax, the thickness of the chest wall at the anterior midline, the thickness of subcutaneous fatty tissue of the chest wall at the anterior midline, the separation of the axilla, the depth of the axilla from the skin, the depth of the lymph node area of the axilla and the thickness of subcutaneous fatty tissue of the axilla. The correlation between these parameters and the dose distribution in the axilla was investigated using Pearson correlation (StatView ver 5). Results: V95 of the Level I and II irradiated were 77.7 +- 22.5% (range 100.0-11.6) and 49.0 +- 35.9% (range 100.0-0.0), respectively, and V80 of the Level I and II irradiated were 91.5 +- 15.3% (range 100.0-31.1) and 85.3 +- 22.0% (range 100.0-1.6), respectively. There was no significant relation between the dose distribution and the patient's physique. When the dose distributions of all patients using 4MV X ray were compared, the mean percent volumes of Level I and II irradiated were 49.3 +- 31.6% (range 100.0-0.0) and 21.7 +- 32.0% (range 100.0-0.0) at a dose of 47.5Gy (95% of prescribed dose), and 93.3 +- 12.3% (range 100.0-34.4) and 87.1 +- 20.1% (range 100.0-0.5) at a dose of 40Gy (80% of prescribed dose), respectively. There was no significant relation between the dose distribution and the patient's physique for the treatment plan using 4MX. Conclusions: Adequate dose distribution of the axillary lymph node region was not accomplished even by CETF. Underdosing was more obvious in the Level II than in the Level I lymph node area. We were not able to predict the adequacy of the dose distribution from nine parameters of patient's physique. Individualized evaluation of dose distribution by 3D treatment planning using simulation-CT was indispensable to obtain optimal dose coverage of the axillary lymph node region as well as the breast.

Tachiiri, S, Mitsumori, M, Yamauchi, C, Araki, N, Oya, N, Nagata, Y, Hiraoka, M, et al, , The Relationship between the Patient's Physique and the Dose Distribution in the Axilla during Treatment with a Cranially Extended Tangential Radiation Field for Breast-conserving Therapy.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4420623.html