Eli Sapir MD, Presenter: Nothing to Disclose

Nir Sharon, Abstract Co-Author: Nothing to Disclose

Marc Wygoda, Abstract Co-Author: Nothing to Disclose

Amichay Meirovitz, Abstract Co-Author: Nothing to Disclose

Purpose/Objective(s): Breast irradiation is a key component of breast conservation therapy. Dose to the underlying lung predicts toxicity after irradiation. The volume of irradiated lung receiving more than 20 Gy (V20) has been shown to accurately predict the incidence of pneumonitis. In the absence of CT based simulation and treatment planning chest wall geometry, particularly central lung distance (CLD), has been used to assess the volume of lung at risk. When CLD ò 2cm clinicians tend to add an anterior electron field or use other treatment techniques. In this scenario CLD does not perform well as a predictor of irradiated lung volume. This pilot study presents a method to accurately predict V20 using 2D parameters that can easily be measured even when 3D treatment planning is not available. Materials/Methods: 82 consecutive early breast cancer patients who underwent CT simulation and received conventional tangential radiation treatment were analyzed for lung volume, chest wall and lung dimensions and Central Lung Distance (CLD). 44 had left, 36 right, and 2 patients had bilateral breast cancer, the parameters were calculated for each lung separately. Patients were stratified according to CLD and percentage of lung volume at the radiation field was calculated. The data was normalized to a dose of 50Gy and the V120 of ipsilateral lung was calculated. Linear regression models were used. Results: The mean irradiated lung volume was 1294cc(S.D. +/- 305cc), mean CLD- 1.77 cm (S.D. +/- 0.47 cm), mean separation- 21 cm (S.D. +/- 3.7 cm), anterior-posterior chest wall distance (APCWD) 21.32 cm (S.D. +/- 2.42 cm), chest wall width (CWW) 32.91 cm (S.D. +/- 3.96 cm). As expected correlation between irradiated lung volume V120 and CLD was statistically significant (R =0.676 , p<0.0001). However, when only patients with CLD ò2 were analyzed there was no significant correlation (R=0.270 ,p=0.1652). Based on our data set, a linear model was developed to accurately predict the V20 based on the geometric parameters of the chest wall. The formula (V120 = 32.7 + Separation - 0.7X(APCWD + CWW) with r2=0.3543 and p<0.0001 improves the accuracy of the predicted V120 value approximately fourfold compared with CLD. Conclusions: For CLDò2 cm, CLD is not a reliable surrogate for lung at risk. However, a simple formula using parameters easily measured using a conventional simulator can accurately predict the volume of lung at risk. Centers with limited access to CT simulation women can offer safer breast irradiation, thus increasing the acceptability of breast conservation therapy to women who would otherwise be forced to resort to a disfiguring mastectomy.

Sapir, E, Sharon, N, Wygoda, M, Meirovitz, A, Factors Contributing to Lung Volume Exposure in Breast Cancer Patients during Treatment by Tangential Irradiation Technique.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8501280.html