Impact de la modulation d’intensité dans l’irradiation des aires ganglionnaires du cancer du sein

[Modalities and advantages of image guided radiation therapy of breast cancer in adjuvant setting]

In adjuvant setting, breast cancer radiotherapy volumes include whole mammary gland or chest wall, and when indicated, nodal area such as axilla, supraclavicular, and internal mammary chain. An accurate patients positioning is required due to some geometric complexity of target volumes closed to organs at risk as heart and lung. Image guided radiation therapy allows such accuracy. Here we propose a review on image guided radiotherapy for breast cancer.

[Technique of complex mammary irradiation: Mono-isocentric 3D conformational radiotherapy and helical tomotherapy]

PURPOSE

To evaluate the dosimetric contribution of helical tomotherapy for breast cancers compared with conformal radiotherapy in mono-isocentric technique.

PATIENTS AND METHOD

For 23 patients, the dosimetric results in mono-isocentric 3D conformational radiotherapy did not satisfy the constraints either of target volumes nor organs at risk. A prospective dosimetric comparison between mono-isocentric 3D conformational radiotherapy and helical tomotherapy was therefore carried out.

RESULTS

The use of helical tomotherapy showed a benefit in these 23 patients, with either an improvement in the conformity index or homogeneity, but with an increase in low doses. Of the 23 patients, two had pectus excavatum, five had past thoracic irradiation and two required bilateral irradiation. The other 14 patients had a combination of morphology and/or indication of lymph node irradiation. For these patients, helical tomotherapy was therefore preferred to mono-isocentric 3D conformational radiotherapy.

CONCLUSIONS

Tomotherapy appears to provide better homogeneity and tumour coverage. This technique of irradiation may be justified in the case of morphological situations such as pectus exavatum and in complex clinical situations. In other cases, conformal radiotherapy in mono-isocentric technique remains to be favoured.

Early Changes of Volume and Spatial Location in Target and Normal Tissues Caused by IMRT for Cervical Cancer

Aims

To investigate the early changes of volume and spatial location in target and normal tissues caused by intensity-modulated radiotherapy (IMRT) for cervical cancer.

Methods

Forty patients with cervical cancer were included in this study and treated by IMRT. Computed tomography (CT) was performed before radiotherapy and when the patient had received 27 Gy in 15 fractions. After image registration, the volume of interest (VOI) for the targets and organs at risk was delineated by clinicians on the CT images. Changes of volume, spatial location and Dice similarity were calculated for all VOIs.

Results

There were significant changes in gross tumor volume (GTV) in the primary tumor (GTV-T) with t = 8.304 (p<0.01) and visible pelvic lymph nodes (GTV-N) with t = 4.996 (p<0.01) caused by IMRT. The mean volume differences for GTV-T and GTV-N were 38.64% ± 19.50% (range 3.16%–86.49%) and 42.49% ± 25.68% (range 2.79%–87.42%), respectively. Among the organs at risk, the bladder had the greatest volume change with 55.13% ± 33.40% (range 3.25%–116.01%). The Dice similarity for GTV-T and GTV-N was 0.50 ± 0.18 (range 0.10–0.85) and 0.31 ± 0.20 (range 0.00–0.71), respectively. The rectum had the least Dice similarity among the normal tissues, with a mean value of 0.57 ± 0.14 (range 0.18–0.76).

Conclusions

There were significant changes in volume and spatial location of the target and normal tissues after 27 Gy IMRT. In order to maintain the radiation dose to the targets and minimize the radiation to normal tissues, it is necessary to modify the radiotherapy planning.