La délimitation des volumes cibles en radiothérapie : application des techniques d’imagerie

The development of three-dimensional conformal radiotherapy (3DCRT) and intensity modulated therapy (IMRT) has enabled high dose radiation to be directed to tumors, this however subject to a perfect demarcation of the tumoral volume and the anatomical structures to be saved. At the same time, imaging modalities have improved their ability to demonstrate the location and the extension of tumors. The precise location of the target volume and the prediction of the dose absorbed by the tumor thus become an essential stage of the planning of the treatment. This planning is mostly determined on CT pictures. The technique usually used is a non enhanced CT allowing a location of the tumor by its mass effect mass or by its spontaneous difference of density from the adjacent structures. However, the clear visualization of the tumoral volume remains sometimes difficult for small-sized tumors or those with limited contrast with regard to surrounding tissues. This lack of contrast represents a source of variability for the demarcation of the target volume which has been highlighted in numerous papers. Tumors must be then localized by correlation with pictures made at the diagnosis time by other imaging modalities, essentially the MRI and the PET. This approach answers the concept of multimodality diagnosis which resumes the principle of complementarity of the various techniques. Every technique indeed brings, according to its physical principle, one or several specific information. It is advisable from then to clarify the contribution of every used imaging modality, this according to the pathologies and their localizations.     

Apport de l’échographie Doppler avec injection de contraste pour la prise en charge des cancers du col de l’utérus de stades IB et II par chimioradiothérapie concomitante

The aim of the present study was to evaluate whether angiogenic parameters as assessed by transvaginal color Doppler ultrasound and by enhanced cervix ultrasound may predict prognostic factors of stage IB greater than 4 cm and II cervical cancer treated by radiochemotherapy. A total of 40 patients with histologically proven advanced stage invasive cervical cancer will be evaluated by color Doppler, contrast ultrasound, and MRI before radiotherapy, after the second chemotherapy cycle and prior to surgery. Subjective assessment of the amount of vessels within the tumor (scanty-moderate or abundant) and resistance index (RI) will be recorded for Doppler, enhancement and washout period will be studied after injection of SonoVue^® for contrast ultrasound. All patients will have radical hysterectomy and pelvic lymph node dissection. Comparison with MRI results will be done. The main parameter studied will be persistence of tumor cells in the analysis of the radical hysterectomy. We expected to correlate contrast parameters with persistent disease in order to confirm ultrasound parameters that will be useful to monitor radiochemotherapy and to predict therapeutic answer of such treatment.     

Haute dose dans la prostate par radiothérapie guidée par l’image : apport de l’arcthérapie avec modulation d’intensité du faisceau

PurposeTo compare two Intensity Modulated Radiation Therapy (IMRT) techniques for prostate cancer: the Volumetric Modulated Arc Therapy (VMAT) and the “Step and Shoot” technique (S&;S).Materials and methodsVMAT and S&;S plans (RX 18 MV) were created and compared (Wilcoxon test) for 10 patients. The dosimetric goal of both treatments was to deliver 46 Gy to the seminal vesicles and 80 Gy to the prostate, while respecting the dose constrains in the organs at risk of toxicity. For one patient, the two techniques were compared for dose painting and escalation in target volumes defined on MRI and registered thanks to intraprostatic fiducials.ResultsVMAT, compared to S&;S, offered: an increase of the PTV2s (prostate) volume receiving 77 to 80 Gy and a decrease of V₈₂ and V₈₃; a decrease of V₄ to V₆, V₁₆ to V₂₃, and V₆₉ to V₇₃ for the rectal wall; a decrease of V₂₅ for the bladder wall; a decrease of V₂₁ to V₄₃ for the femoral heads; a decrease of V₂₆ to V₄₄ and V₇₂ to V₈₀ but an increase of V₁ to V₂₁ and V₄₉ to V₆₀ for the healthy tissues. The Conformal Index “COIN” was better with VMAT than S&;S (0.60 to 0.66). The delivered MU were significantly reduced with VMAT (8% mean) as well as the delivery time (4 min to 1.5 min). VMAT allowed delivering theorically 90 Gy in the peripheral zone and 100 Gy in the tumor.ConclusionIn case of prostate irradiation, VMAT shows improvement compared with S&;S. In particular, organs at risk are better spared, the delivery time is shortened and the number of delivered UM is decreased.     

Délais et retards à la radiothérapie : réflexion à propos de trois types de tumeurs

In the following review of the literature, the reasons and consequences of a tendency to the increase of the delay between the diagnosis and the first irradiation session will be studied. The duration of the delay varies according to the protocol of treatment, which itself depends on the tumour. Moreover, all types of radiotherapy are concerned by the increase in delay. A retrospective study enables to determine for a given series of similar tumours and treatments the mean duration of delay and find the excessive duration. The increase of delay phenomenon exists in different countries. We know that before irradiation the tumour grows according to its biological characteristics and the TNM initial determination will no longer be true. On the other hand, effective treatments such as chemotherapy and hormone therapy are increasingly used alone, before or in combination with radiotherapy. Consequently, the classical timing of radiation therapy could be modified often delayed. It is difficult to consider that successive treatments are a real increase of delay and compare its results with previous data from radiotherapy alone. We will study its impact in three types of tumours, including tumours of head and neck, of the breast and prostate, which are the most widely reported. The consequences of prolonged delay are not easily evaluated: one of the more important parameters is the possible modification of the stage of tumour. This phenomenon is not restricted to the studied types of tumours. We will try to find possible ways of reducing abnormal delays before irradiation.     

Bénéfice volumétrique de la radiothérapie guidée par l’image dans les cancers prostatiques : marges et cartographies de probabilité de présence

PurposeTo quantify the prostate and seminal vesicles (SV) anatomic variations in order to choose appropriate margins including intrapelvic anatomic variations. To quantify volumetric benefit of image-guided radiotherapy (IGRT).Patients and methodsTwenty patients, receiving a total dose of 70 Gy in the prostate, had a planning CT scan and eight weekly CT scans during treatment. Prostate and SV were manually contoured. Each weekly CT scan was registered to the planning CT scan according to three modalities: radiopaque skin marks, pelvis bone or prostate. For each patient, prostate and SV displacements were quantified. 3D maps of prostate and SV presence probability were established. Volumes including minimal presence probabilities were compared between the three modalities of registration.ResultsFor the prostate intrapelvic displacements, systematic and random variations and maximal displacements for the entire population were: 5 mm, 2.7 mm and 16.5 mm in anteroposterior axis; 2.7 mm, 2.4 mm and 11.4 mm in superoinferior axis and 0.5 mm, 0.8 mm and 3.3 mm laterally. Margins according to van Herk recipe (to cover the prostate for 90% of the patients with the 95% isodose) were: 8 mm, 8.3 mm and 1.9 mm, respectively. The 100% prostate presence probability volumes correspond to 37%, 50% and 61% according to the registration modality. For the SV, these volumes correspond to 8%, 14% and 18% of the SV volume.ConclusionsWithout IGRT, 5 mm prostate posterior margins are insufficient and should be at least 8 mm, to account for intrapelvic anatomic variations. Prostate registration almost doubles the 100% presence probability volume compared to skin registration. Deformation of SV will require either to increase dramatically margins (simple) or new planning (not realistic).     

Intérêt de la tomographie par émission de positons au [18F]-fluoro-2-désoxyglucose dans la détermination des volumes cibles de radiothérapie. Application à l''irradiation conformationnelle des cancers bronchiques non à petites cellules

Traditional radiation treatment planning relies on density imaging such as Computed Tomography for anatomic information of various structures of interest including target and normal tissues. However, the difficulties to distinguish malignant from normal tissue on CT slides often leads to inaccurate outlining of the GTV and/or to geographic misses. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) has shown an increase in both sensitivity and specificity over CT in locoregional staging of patients with non-small cell lung cancer (NSCLC). The co registration of FDG-PET images to the data of the CT planning offers the radiation oncologist the possibility to include functional information into the target outlining. For the treatment of patients with NSCLC, it has been shown that the use of FDG-PET images: 1) modified the shape and volume of radiation fields in 22-62% of cases, mainly due to a better nodal staging and distinction of atelectasis from tumor and; 2) significatively reduced the interobserver and intraobserver variability. This paper reviews the results reported in the literature. Challenges and proposed solutions are discussed.     

Inhibiteurs de l’angiogenèse et radiothérapie : du concept à la clinique

Angiogenesis is central to cancer research. Recent progresses in understanding its mechanisms have enabled the development of therapies that inhibit this process. Many molecules have shown a synergistic effect in combination with irradiation in preclinical studies, and several are being tested in phase I or II. This effect could be explained by a transient normalization of tumor vasculature, leading to improve tumor oxygenation and thus greater radiosensitivity. Although promising, many questions remain about the dose, optimal sequences of the association.