Les contraintes aux organes à risque en radiothérapie par modulation d'intensité des cancers ORL

Organs at risk radiation dose constraints

Dose constraints are essential for performing dosimetry, especially for intensity modulation and for radiotherapy under stereotaxic conditions. We present the update of the recommendations of the French society of oncological radiotherapy for the use of these doses in classical current practice but also for reirradiation.

Development of a contouring guide for three different types of optic chiasm: A practical approach

INTRODUCTION

Sparing of the organs at risk (OARs) is a crucial task in daily radiotherapy practice. Irradiation of the optic chiasm (OC) results in radiation-induced optic neuropathy (RION). The structure of the OC is complex, and OC morphology can vary in axial images. Therefore, a standard atlas can result in inaccurate descriptions of OC morphology in different patients. The aim of our study was to provide a guide based on computed tomography (CT) for the delineation of different types of OC.

METHODS

Thirty-six patients were selected to participate in our study. These patients underwent CT analysis of the brain, head and neck regions in a supine position. Axial images 3 mm in thickness were obtained at 3-mm intervals. A magnetic resonance imaging (MRI) study was also performed using the same set-up. The OC was then delineated. The contours were revised by three neuroradiologists and nine radiation oncologists with > 5 years of expertise.

RESULTS

Three types of OC were distinguished by magnetic resonance (MR). The location and boundaries of normal, prefixed and postfixed chiasms were developed with a CT-based atlas. Discrepancies were observed in the delineation of the prefixed and postfixed OC.

CONCLUSIONS

Our guide allows improved definitions of the anatomical boundaries for different types of OC. Our experience could provide useful information for radiation oncologists in daily practice.

[Normal tissue tolerance to external beam radiation therapy: Bone marrow and cortical bone structures]

In patients undergoing external radiation therapy, bone marrow and cortical bone structures are all often neglected as organs at risk. Still, from increased febrile neutropenia risk in patients undergoing chemoradiation for a pelvic tumour to increased risk of vertebral fracture when undergoing hypofractioned stereotactic radiotherapy of a spinal metastasis, adverse effects are frequent and sometimes serious. This literature review first defines the rules for contouring these structures, then the dose constraints currently recommended. This article focuses first on conventional irradiation or intensity modulation radiotherapy considering classical fractionation. Secondly, it focuses on stereotactic radiotherapy. The considered organs will be haematopoietic structures, and bone cortical structures. Current recommendations are summarised in a table.

[Radiotherapy for nasopharyngeal carcinoma]

Nasapharyngeal carcinoma is a rare disease. Oftenly, the diagnostic is made for advanced disease. Localized tumors, T1 or T2 NO observed a good prognosis and are locally controlled in more than 90 % of the cases by radiotherapy alone. The standard treatment of locally advanced disease is combined chemoradiation. A special vigilance of fast decrease of the volume of the pathological lymph nodes, sometimes associated to loss of weight might indicate an adaptive dosimetric revision. The treatment of recurrent disease is of great importance. Surgical indications are limited but should be discussed in multidisciplinary tumor board when possible. Surgical nodal sampling has to be proposed for nodal recurrence as well as reirradiation, which could be indicated according to the technical issues.

Stereotactic radiotherapy of intracranial tumors: a comparison of intensity-modulated radiotherapy and dynamic conformal arc

PURPOSE

Intensity-modulated radiotherapy (IMRT) and dynamic conformal arc (DCA) are two state-of-the-art techniques for linac-based stereotactic radiotherapy (SRT) using the micromultileaf collimator. The purpose of this planning study is to examine the relative merits of these techniques in the treatment of intracranial tumors.

MATERIALS AND METHODS

SRT treatment plans were made for 25 patients with a glioma or meningioma. For all patients, we made an IMRT and a DCA plan. Plans were evaluated using: target coverage, conformity index (CI), homogeneity index (HI), doses in critical structures, number of monitor units needed, and equivalent uniform dose (EUD) in planning target volume (PTV) and critical structures.

RESULTS

In the overall comparison of both techniques, we found adequate target coverage in all cases; a better mean CI with IMRT in concave tumors (p = 0.027); a better mean HI with DCA in meningiomas, complex tumors, and small (< 92 mL) tumors (p = 0.000, p = 0.005, and p = 0.005, respectively); and a higher EUD in the PTV with DCA in convex tumors (gliomas) and large tumors (p = 0.000 and p = 0.003, respectively). In all patients, significantly more monitor units were needed with IMRT. The results of the overall comparison did not enable us to predict the preference for one of the techniques in individual patients. The DCA plan was acceptable in 23 patients and the IMRT plan in 19 patients. DCA was preferred in 18 of 25 patients.

CONCLUSIONS

DCA is our preferred SRT technique for most intracranial tumors. Tumor type, size, or shape do not predict a preference for DCA or IMRT.

Cancers ORL: les grands principes thérapeutiques

Cancers of the upper aerodigestive tract cover the solid tumors of the oral cavity, pharynx and larynx. The principal risk factors identified are smoking and alcohol. Moreover, the combination of alcohol and smoking increases the relative risk by more than simple multiplication. The pretreatment work-up represents the starting point in the natural history of the patient's disease and conditions recovery and time course; it must be both specific and exhaustive. It leads to a TNM classification or staging that is a major prognostic factor and essential to determination of the appropriate therapy. Patients with cancer of the upper aerodigestive tract must receive cooperative multidisciplinary treatment. Conservative treatment strategies must be favored. Treatment is essentially surgical and radiological. Prognosis for survival is poor. For all stages and sites together, 5-year survival remains between 30 and 40%.

Radiothérapie postopératoire des cancers laryngés classés N0

PURPOSE

A retrospective study to re-assess the indications for postoperative radiation therapy in squamous cell carcinoma of the larynx staged N0 after gross resection.

PATIENTS AND METHODS

Between January 1975 and December 2000, 166 patients with squamous cell carcinoma of the larynx were treated by total laryngectomy with or without neck dissection. Surgery was completed by external radiotherapy delivering 45 to 65 Gy to the tumour bed and 45 to 50 Gy to cervical lymphatic chains. Minimal follow-up was 36 months and median follow-up was 98 months.

RESULTS

The rate of nodal recurrence was 6% (median time for relapse was 9 months). The survival rates at 1, 2, 3 and 5 years were 93.5, 84, 80 and 69% respectively, with a 8 year 3 month median survival. The univariate analysis showed 4 parameters, which significantly increased the risk of local recurrence: the medical necessity for immediate tracheotomy, the subglottic involvement, the involvement of the whole larynx and the presence of lymphatic embols in the neck dissection. There was no statistically significant difference between the patients with or without a neck dissection. Fifty-nine secondary cancers were observed, 15 of them occurring in the head and neck area. The late complications consisted of cervical subcutaneous fibrosis (7%), oesophageal stricture (4%), oeso-tracheal fistula (l%), hypothyroidism (3%), bone necrosis (1%).

CONCLUSION

Prophylactic cervical radiotherapy in laryngeal cancers resulted in 6% cervical node recurrence rate. This value may represent the maximal rate to accept if one would favour new therapeutic strategies based on restricted indications for radiotherapy.