Do all the linear accelerators comply with the ICRU 91's constraints for stereotactic body radiation therapy treatments?

Recent technological developments in linear accelerators (linacs) and their imaging systems have made it possible to routinely perform stereotactic radiotherapy (SRT) treatments. To ensure the security and quality of the treatments, national and international recommendations have been written. This review focuses on the recommendations of the report 91 of the International Commission on Radiation Units (ICRU) on stereotactic treatments with small photon beams and proposes to answer the question of the eligibility of the commercially available accelerators for the treatment of extra-cranial SRT (SBRT). The ICRU 91 report outlines important features needed to respect the constraints, which are high intensity photon beam, integrated image-guidance, high mechanical accuracy of the linac, multileaf collimator with reduced leaf width, bundled motion management and bundled 6 Dimensional "robotic" couch tabletop. Most of the contemporary linacs meet these recommendations, in particular, stereotactic dedicated linacs, or modern gantry-based linacs equipped with 3 dimensional cone-beam CT imaging and 2D-stereoscopic planar imaging. Commercially available ring-based linacs have some limitations: they offer only coplanar treatments, and couch movements are limited to translations and, some have limited imaging equipment and no ability to manage intrafraction motion. However, for performing SBRT, non-coplanar irradiations are not mandatory, contrarily to intracranial stereotactic irradiations. Furthermore, patients' rotations can be corrected, thanks to real-time adaptive radiotherapy available on MRI-linacs. Finally, significant improvements are expected in the short term to compensate the weaknesses of the current devices.

[Localized Ewing sarcoma of the spine: a preliminary dose-escalation study comparing innovative radiation techniques in a single patient]. / Sarcomes d'Ewing localisés du rachis chez l'enfant : étude préliminaire d'escalade de dose comparant les techniques innovantes.

PURPOSE: Although radiosensitive, spinal locations of Ewing's sarcomas are challenging for the radiation oncologist due to poor radiation tolerance of the spinal cord. However, some favorable anatomical compartments - that may represent more than 20% - were associated with a better outcome and could benefit from a radiation dose escalation using the most recent radiation therapy techniques. MATERIALS AND METHODS: We performed a dose escalation study on one patient, declined in two scenarios: (1) a tumour located within a single vertebral body and (2) a locally advanced disease involving the vertebral foramen and paraspinal soft tissues. Five dose-levels are proposed: 44.8Gy, 54.4Gy, 59.2Gy, 65.6Gy and 70.4Gy (1.6Gy per session, 8Gy per week). The 3D-conformational technique is compared with static intensity modulated radiation therapy (IMRT), helical tomotherapy, volumetric modulated arc therapy (VMAT), stereotactic body robotic radiation therapy (SBRT) and protontherapy (passive scattering). Two constraints had to be respected in order to skip to the next level: the planned target volume (PTV) coverage must exceed 95% and the D(2%) on the spinal cord shall not exceed a given constraint set at 50Gy in case 1 and 44Gy in case 2 due to initial neurological sufferance. RESULTS: Only protontherapy, SBRT, helical tomotherapy and VMAT appear able to reach the last dose level while respecting the constraints in case 1. On the other hand, only helical tomotherapy seems capable of reaching 59.2Gy on the PTV in case 2. CONCLUSION: With the most recent radiation therapy techniques, it becomes possible to deliver up to 70.4Gy in a favorable compartment in this sham patient. Unfavorable compartments can receive up to 59.2Gy. Definitive radiation therapy may be an interesting local treatment option to be validated in an early phase trial.

[Linac-based stereotactic radiosurgery and radiotherapy]. / Radiothérapie stéréotaxique par accélérateurs adaptés ou dédiés.

Stereotactic radiation therapy, consisting in irradiating the tumor with a high dose per fraction, has a therapeutic potential because of excellent local control. This technique requires a high accuracy level in order to minimize the risk of normal tissue toxicity. Initially used for cerebral localization, the stereotactic radiation therapy can be used for lung and liver tumors thanks to personalized immobilization devices, time resolved tomodensitometry for tumor deformation, collimators with small size leaves, advanced dose distribution calculation algorithms and 3D imaging for patient set-up. This article will review the different clinical applications and the different aspects (mechanical, dosimetric and biological) to evaluate before implementing this complex irradiation technique using adapted or dedicated linear accelerators.

[Image guided radiotherapy with the Cone Beam CT kV (Elekta): experience of the Léon Bérard centre]. / Radiothérapie guidée par l'image avec le Cone Beam CT kV (Elekta) : expérience du centre Léon-Bérard.

Image guide radiotherapy with the Cone Beam CT kV (CBCT-kV) developed by Elekta has been implemented at the centre Léon Bérard in November 2006. The treatment procedure is presented and detailed for prostate cancer IGRT and non small cell lung cancer (NSCLC) stereotactic radiotherapy (SRT). CBCT-kV is routinely used for SRT, selected paediatric cancers, all prostate carcinomas, primitive brain tumours and head and neck cancers that do not require nodes irradiation. Thirty-five to 40 patients are treated within a daily 11-hours period. The general procedure for 3D images acquisition and their analysis is described. The CBCT-kV permitted to identify about 10% of prostate cancer patients for whom a positioning with bone-based 2D images only would have led to an unacceptable dose distribution for at least one session. SRT is now used routinely for inoperable NSCLC. The easiness of implementing CBCT-kV imaging and its expected medical benefit should lead to a rapid diffusion of this technology that is also submitted to prospective and multicentric medico-economical evaluations.

[The French preliminary experience of the use of a seed-projector for exclusive iodine 125 prostate brachytherapy: feasibility and acute toxicity]. / L'expérience française de l'utilisation d'un projecteur de source pour la curiethérapie prostatique exclusive par implants permanents d'iode radioactif: faisabilité et données de toxicité aiguë.

PURPOSE: To analyse a new technique for prostate brachytherapy with permanent Iodine implants characterized by the use of a seed projector after a 3D dosimetric peroperative treatment planning (FIRST technique). PATIENTS AND METHOD: 395 patients have been treated in France with this technique in six radiotherapy centres between November 2002 and December 2005 for a localized prostate cancer. RESULTS: Thirteen patients (3.3%) developped a urinary retention, and respectively 7.8 and 26.5% an acute RTOG grade 3 and 2 toxicity. The 6-weeks IPSS score was equal or lower to 15 in 73% with a 11 median IPSS value. A failure of the loading with the seed-projector, leading to a manual loading of the seeds, occurred in 9 patients (2.3%) in two centres, directly related to the loading procedure with the seed-projector in 5 cases. The median duration of the procedure was reduced by 30 minutes for the patients treated in 2005. CONCLUSIONS: This multicenter study establishes the feasibility of the routine use of a seed projector for permanent iodine 125 prostate implants with an initial tolerance similar to the best results published for other implants techniques.

[The stereotactic body radiation therapy: initiation and clinical program]. / Principe et mise en oeuvre de la radiothérapie en conditions stéréotaxiques extracrânienne.

We fully describe an innovative radiotherapy technique called Stereotactic Body Radiation Therapy (SBRT), and explain how this technique is commonly used for clinical purpose at the anticancer center Léon-Bérard (Lyon, France). In this technique, a non-invasive stereotactic body frame is used to locate the tumor site with a great precision. This frame is combined with a system, which enables to track the respiratory motions (Active Breathing Control (ABC) or diaphragmatic compression (DC)) in order to reduce the treatment margins for organ motion due to breathing. Thus, the volume of normal tissues that will be irradiated is considerably reduced. The dosimetry is realized with 3 CT exams performed in treatment conditions. The 3D patient "repositioning" is done with a volume CT acquisition (kV) combined with orthogonal images (kV and MV). The SBRT requires a system to limit the organ motions. Although the ABC seems to be more fastidious for patient, it would enable to use smaller margins than with DC technique. Nevertheless, the ABC is not compatible with volume CT acquisitions, which considerably improve the patient repositioning. In conclusion, the quality of repositioning and the high level of conformation enable to deliver high equivalent doses (>100 Gy) in hypofractionated mode, without increasing the treatment toxicity. The SBRT employs the last technologic innovations in radiotherapy and is therefore considered as a new efficient tool for solid tumors treatment.