Breast radiotherapy in women with pectus excavatum (funnel chest): is the lateral decubitus technique an answer? A dosimetric study.

Breast radiotherapy is a technical challenge in women with pectus excavatum. We aim to assess isocentric lateral decubitus (ILD) technique as a means to irradiate breasts for patients with pectus excavatum. Four women presenting with left-sided breast cancers and found to have pectus excavatum were offered breast-conserving treatments. Post-operative breast radiotherapy was indicated (50 Gy) in two patients, with an additional boost to the tumour bed (16 Gy). Both ILD and supine techniques were simulated. We report the dosimetric comparison of these techniques and the acute skin toxicity of ILD radiotherapy. ILD permitted the same breast dose-homogeneity as the supine technique while decreasing breast thickness by 4.5-6.8 cm. The width of lung and/or heart receiving > 20 Gy ranged between 2.1 cm and 4.3 cm with the supine technique and between 0.5 cm and 1.1 cm with ILD. The estimated percentage of ipsilateral lung receiving > 20 Gy ranged from 21% to 34% with the supine technique and from 0% to 5% with ILD. Acute skin toxicity was scored 1 for all patients at completion of ILD radiotherapy. ILD is an effective breast radiotherapy technique for patients with pectus excavatum that preserves the underlying heart and lung from unnecessary toxicity.

[Radiotherapy for breast cancer: respiratory and set-up uncertainties]. / Irradiation du cancer du sein: incertitudes liées aux mouvements respiratoires et au repositionnement.

Adjuvant Radiotherapy has been shown to significantly reduce locoregional recurrence but this advantage is associated with increased cardiovascular and pulmonary morbidities. All uncertainties inherent to conformal radiation therapy must be identified in order to increase the precision of treatment; misestimation of these uncertainties increases the potential risk of geometrical misses with, as a consequence, underdosage of the tumor and/or overdosage of healthy tissues. Geometric uncertainties due to respiratory movements or set-up errors are well known. Two strategies have been proposed to limit their effect: quantification of these uncertainties, which are then taken into account in the final calculation of safety margins and/or reduction of respiratory and set-up uncertainties by an efficient immobilization or gating systems. Measured on portal films with two tangential fields, CLD (central lung distance), defined as the distance between the deep field edge and the interior chest wall at the central axis, seems to be the best predictor of set-up uncertainties. Using CLD, estimated mean set-up errors from the literature are 3.8 and 3.2 mm for the systematic and random errors respectively. These depend partly on the type of immobilization device and could be reduced by the use of portal imaging systems. Furthermore, breast is mobile during respiration with motion amplitude as high as 0.8 to 10 mm in the anteroposterior direction. Respiratory gating techniques, currently on evaluation, have the potential to reduce effect of these movements. Each radiotherapy department should perform its own assessments and determine the geometric uncertainties with respect of the equipment used and its particular treatment practices. This paper is a review of the main geometric uncertainties in breast treatment, due to respiration and set-up, and solutions proposed to limit their impact.