Dose de tolérance à l’irradiation des tissus sains : encéphale et hypophyse

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.

Radiotherapy of benign intracranial tumours

We present the updated recommendations of the French Society for Radiation Oncology on benign intracranial tumours. Most of them are meningiomas, vestibular schwannomas, pituitary adenomas, craniopharyngiomas, and glomus tumours. Some grow very slowly, and can be observed without specific treatment, especially if they are asymptomatic. Symptomatic or growing tumours are treated by surgery, which is the reference treatment. When surgery is not possible, due to the location of the lesion, or general conditions, radiotherapy can be applied, as it is if there is a postoperative growing residual tumour, or a local relapse. Indications have to be discussed at a multidisciplinary panel, with precise evaluation of the benefit and risks of the treatments. The techniques to be used are the most modern ones, as multimodal imaging and image-guided radiation therapy. Stereotactic treatments, using fractionated or single doses depending on the size or the location of the tumours, are commonly realized, to avoid as much a possible the occurrence of late side effects.

[Radiotherapy of benign intracranial tumors]

Most of the benign intracranial tumors are meningiomas, vestibular schwannomas, pituitary adenomas, craniopharyngiomas, and glomus tumors. Some of them grow very slowly, and can be observed without specific treatment, especially if they are asymptomatic. Symptomatic or growing tumors are treated by surgery, which is the reference treatment. When surgery is not possible, due to the location of the lesion, or general conditions, radiotherapy can be applied, as it is if there is a postoperative growing residual tumor, or a local relapse. Indications have to be discussed in polydisciplinary meetings, with precise evaluation of the benefit and risks of the treatments. The techniques to be used are the most modern ones, as multimodal imaging and image-guided radiation therapy. Stereotactic treatments, using fractionated or single doses depending on the size or the location of the tumors, are commonly realized, to avoid as much a possible the occurrence of late side effects.

The role of radiotherapy in adult medulloblastoma: long-term single-institution experience and a review of the literature

Medulloblastoma (MB) occurs infrequently in adult patients and standard treatment is still controversial. We report our long-term, single-institution experience of adult MB and a review of the literature. We analysed adult patients with histologically proved MB treated by postoperative radiotherapy. Primary endpoints were local control (LC), disease-free survival (DFS), and overall survival (OS). Acute toxicity was reported according to CTC-NCI score vers. 3.0 and specific neuropsychological assessment analysis was performed to define late brain toxicity. From 1990-2008, 13 patients were treated by craniospinal (CSI, 12/13) or cranial irradiation (1/13, because of bad clinical conditions). Median follow up was 101 months (64-218). Complete radiological response was observed in 12/13 patients and a partial response in 1/13. Ten-year LC, OS, and DFS were 91, 76, and 84%, respectively. Two patients died because of local and spinal progression after 13 and 62 months. Acute G3 haematological toxicity (RTOG score) was observed for one patient only. The neuropsychological analysis did not reveal late toxicity related to brain radiotherapy. This experience confirms the efficacy and safety of radiotherapy in adult MB patients, resulting in very interesting 10-year LC and OS.

[Dosimetry comparison of irradiation with conformal radiotherapy, intensity modulated radiotherapy, conformal radiotherapy in stereotactic conditions and robotic stereotactic radiotherapy for benign brain tumours]

PURPOSE

To compare several techniques in order to determine the best treatment for benign brain tumours.

METHODS AND PATIENTS

A retrospective study was performed for five patients who received 3D-conformal radiotherapy, intensity modulated radiotherapy or CyberKnife(®). These patients had a meningioma, a pituitary tumour, a craniopharyngioma or a neurinoma. In each case, these treatment plans were optimised and compared with the three other dosimetries. Radiobiological or positioning parameters were evaluated, as well as dosimetric parameters, in order to compare treatments with different characteristics.

RESULTS

The dosimetric parameters showed that the choice of treatment seemed to be determined mostly by tumour size, shape and proximity with organs at risk (not tumour localisation). Whereas the results showed no significant deviations with regards to the radiobiological parameters. Therefore, with these parameters, it was difficult to give priority to a treatment.

CONCLUSIONS

With regards to benign brain tumours of medium or large size, intensity modulated radiotherapy seemed the recommended treatment. It enabled to obtain a good ratio between efficacy and toxicity for tumours that are really close to organs at risk. Concerning small benign brain tumours, the CyberKnife(®) was probably the best treatment.

[Benefit of a prolonged adjuvant treatment with temozolomide for the management of patients with glioblastoma]

PURPOSE

Temozolomide has significantly improved the outcome of patients with glioblastoma. However, the optimal duration of continuation treatment after chemoradiation remains uncertain. This retrospective analysis aims at assessing the feasibility, the tolerance, and the potential benefit of prolonging adjuvant temozolomide more than six months, which is the reference protocol.

PATIENTS AND METHODS

Forty-six patients were included in the analysis. Median age at diagnosis was 61 years old (range 40 to 77). Forty-five patients received a conformal external beam radiation with concurrent temozolomide-based chemotherapy. Then, 37 patients received adjuvant chemotherapy with temozolomide. The treatment was continued until progression or toxicity.

RESULTS

During the adjuvant phase, no treatment discontinuation for toxicity was necessary. Eight patients required dose adaptation because of toxicity. Thirty-two patients presented tumor progression during the adjuvant phase. Overall median survival was 12.3 months (range 11-13.2 months) and progression-free survival (PFS) was 7.6 months (range 5.6-9.6 months).

CONCLUSION

These results suggest feasibility of delivering temozolomide beyond the six months of the standard protocol, with mild toxicity and survival data at least comparable to those from literature. Prospective assessments are ongoing.

[Post-radiation mucocele in two patients treated for nasopharyngeal cancer]

A 30-year-old woman, with a history of nasopharyngeal carcinoma, which was treated by radiotherapy nine years previously, presented with occasional diplopia and recent headaches. A nasopharyngeal biopsy showed no recurrence. The imaging revealed a sphenoidal sinus mucocele. Endoscopic marsupialization of the mucocele allowed clinical improvement. A 56-year-old woman presented, five years after radiotherapy for nasopharyngeal carcinoma, with a fronto-orbital mass. CT-scan revealed a fronto-ethmoidal mucocele. Nasopharyngeal biopsy showed tumour recurrence. Marsupialization of mucocele was performed. Recurrence of the carcinoma was treated by radiotherapy and chemotherapy. Sphenoidal sinus mucocele developing after radiotherapy for nasopharyngeal carcinoma has rarely been reported. CT scan and MRI are useful tools in making the diagnosis. Biopsy is required to diagnose recurrence or associated radio-induced tumor. Endoscopic approach gives good results.

[Malignant gliomas]

Glial tumors represent 2000 to 3000 new cases per year in France and 75% of them are of high grade. Recent understanding of the molecular biology of these tumors revealed the importance of 1p19q codeletion and mgMT promotor methylation. Radiotherapy also recently evolved with the progress in medical imaging which allows a better definition of the target volumes. Even modest, therapeutic progress is based on chemoradiotherapy with temozolomide and on the development of non-coplanar conformational radiotherapy. Knowledge and precise evaluation of potential late effects of our treatments is necessary due to actual improvement of survival with chemoradiotherapy in glioblastoma.