[Intensity modulated radiotherapy with dynamic multileaf collimator. Technique and clinical experience]

Histoire de la prise en charge des cancers bronchopulmonaires non à petites cellules de stade précoce : de la chirurgie à la radiothérapie stéréotaxique

Avant le début du XXe siècle, le cancer bronchopulmonaire était une maladie rare. Aujourd’hui, c’est le quatrième cancer le plus fréquent en France et concerne, chaque année, près de 50 000 patients. Si à travers l’histoire, la pierre angulaire de la prise en charge thérapeutique du cancer bronchopulmonaire reste la chirurgie, la radiothérapie en est un des piliers, notamment chez les patients à haut risque chirurgical. La radiothérapie est apparue quelques mois après la découverte des rayons X en 1896 et, rapidement, des protocoles standardisés ont été mis au point par les premiers radiobiologistes. Ces protocoles sont ceux que nous connaissons encore aujourd’hui : 2 Gy par fraction et 5 fractions par semaine sur une durée totale de 5 à 8 semaines. Si les protocoles ont peu changé en un siècle, la technique et la balistique ont connu de grandes avancées. Ces améliorations ont mené à un bouleversement profond des protocoles. Les améliorations techniques de délivrance de dose, par l’optimisation de l’imagerie, de la précision du positionnement des patients et dans la modulation de la géométrie des faisceaux ont conduit au développement de la radiothérapie en conditions stéréotaxiques ou radiothérapie stéréotaxique. Aujourd’hui, la radiothérapie stéréotaxique est utilisée pour la prise en charge des tumeurs bronchopulmonaires de stade précoce comme alternative à la chirurgie.

A simple theoretical verification of monitor unit calculation for intensity modulated beams using dynamic mini-multileaf collimation

A spreadsheet based program is presented to perform an independent Monitor Unit (MU) calculation verification for the Quality Assurance (QA) of Intensity Modulated Radiation Therapy (IMRT) using Dynamic MultiLeaf Collimation (DMLC). The computed dose value is compared to the planned dose by calculating the percent dose difference per Intensity Modulated Beam (IMB) and absolute dose difference per IMB. The proposed acceptability levels are +/-5.0% or +/-2.0 cGy for the percent dose difference per IMB and the absolute dose difference per IMB, respectively. For percent dose difference per treatment, an acceptability level of +/-2.0% is proposed. The presented program is considered adequate for checking the treatment plans calculated for IMRT treatments using DMLC as a part of the QA procedure.

Intensity-modulated Stereotactic Radiotherapy of Paraspinal Tumors: A Preliminary Report

OBJECTIVE

Radioresistant paraspinal tumors may benefit from conformal treatment techniques such as intensity-modulated radiotherapy (IMRT). Local tumor control and long-term palliation for both primary and metastatic tumors may be achieved with IMRT while reducing the risk of spinal cord toxicity associated with conventional radiotherapy techniques. In this article, we report our initial clinical experience in treating 16 paraspinal tumors with IMRT in which the planning target volume was 2 mm or greater from the spinal cord.

METHODS

IMRT was administered by using a linear accelerator mounted with a multileaf collimator. Two immobilization body frames developed at Memorial Sloan-Kettering Cancer Center were used for patients with and without spinal implants. During a 30-month period, 16 patients underwent IMRT for metastatic and primary tumors. Eleven patients were treated for symptomatic recurrences after undergoing surgery and prior external beam radiotherapy, and one patient was treated after undergoing radiotherapy for a metastatic pancreatic gastrinoma with overlapping ports to the spine. Four patients with primary tumors were treated after primary resection that resulted in positive histological margins. Twelve patients were symptomatic with pain, functional radiculopathy, or both. Tumoral doses were determined on the basis of the relative radiosensitivity of tumors. Patients with metastatic tumors were administered a median tumoral dose of 20 Gy in four to five fractions and a spinal cord maximum dose of 6.0 Gy in addition to the full tolerance dose administered in previous radiation treatments. The primary tumors were delivered a median dose of 70 Gy in 33 to 37 fractions and a spinal cord maximum dose of 16 Gy. The median tumoral volume was 7.8 cm3.

RESULTS

Of the 15 patients who underwent radiographic follow-up, 13 demonstrated either no interval growth or a reduction in tumor size in a median follow-up period of 12 months (range, 2–23 mo). Two patients, one with a thoracic chondrosarcoma and one with a chordoma, showed tumor progression 1 year after undergoing IMRT. Pain symptoms improved in 11 of 11 patients, and 4 of 4 patients had significant improvement in their functionally significant radiculopathy and/or plexopathy. Pain relief was durable in all patients except the two with tumor progression. No patient showed signs or symptoms of radiation-induced myelopathy, radiculopathy, or plexopathy, including 12 patients with a median follow-up of 18 months.

CONCLUSION

IMRT was effective for treating pain and improving functional radiculopathy in patients with metastatic and primary tumors. Although long-term tumor control is not established in this study, high-dose tumoral irradiation can be performed without causing radiation myelopathy in more than 1 year of follow-up.

Dose conformation in IMRT for head and neck tumors: which solution to apply?

At Ghent University Hospital, IMRT for head and neck cancer is routinely performed. The desired dose distribution is defined upfront as a range of acceptable doses assigned to each voxel of volumes of interest. It was found important to specify the range of acceptable doses separately to areas of the PTV either in or outside the buildup zone as well as to areas which do or do not intersect with PTV-dose limiting organs at risk (OAR). To avoid high doses at distance from the PTV, the creation of a "surrounding" OAR which is the whole scanned volume minus the PTV was found efficient, especially if inside this OAR, subvolumes were created at increasing distance from the PTV. By specifying inside these subvolumes maximum dose constraints which decreased with distance from the PTV, conformality is secured. The creation of these additional PTV and OAR subvolumes allows comprehensive and unambiguous definition of the range of acceptable doses and thereby avoids user-interactive assignment of weights to the terms of the objective function during optimization. The efficiency of inverse planning is highly improved. Its outcome is predictable, plan evaluation is objective as the plan either does or does not comply with the predefined range of acceptable doses. Accurate reporting of the planned dose distribution is facilitated by description of the dose range to all volumes. The expense of this procedure is modest and lays mostly 1) in the creation of the subvolumes, which can be done semi-automatically by modern image segmentation tools and 2) in the inclusion of constraints to all subvolumes into the objective function.

Intensity modulated radiation therapy for oropharyngeal and oral cavity tumors: clinical use and experience

Background and purpose. Intensity modulated radiation therapy (IMRT) offers an opportunity to generate dose distributions highly conformal to the target volume. Head and neck cancer patients, referred for radiotherapy, may be good candidates to benefit from IMRT. This paper discusses the clinical implementation of IMRT for oropharyngeal and oral cavity tumors, and reports the clinical results of the 14 patients treated with this technique at Ghent University Hospital (GUH). Patients and Methods. Between May 1999 and May 2001, 14 patients were treated with IMRT at GUH for oropharyngeal or oral cavity tumors. Two groups of patients can be distinguished. The first group consists of eight patients re-irradiated with IMRT for a locoregional relapse. The second group of six patients were treated with IMRT for a primary tumor. For the first group, IMRT was used to treat the relapse by generating a concave dose distribution, i.e. to combine a homogeneous target re-irradiation with a dose to the spinal cord as low as possible. For the second group, IMRT was applied in order to achieve a more homogeneous dose distribution inside the PTV and to preserve parotid gland function. Results. The majority of the patients of group 1 (6/8) relapsed in field within four months after the end of the re-irradiation, with a median overall survival of 7 months. For group 2, two patients died shortly after the end of the IMRT treatment, the other four patients are free of tumor relapse with a median follow-up of 5 months (1-13 months). The acute toxicity due to radiation was acceptable for both patient groups. Dysphagia and pain was more present in group 1. Regarding late complications for the group of re-irradiations (group 1), no myelitis, carotid rupture or cranial nerve palsy was observed. One patient of group 1 developed osteoradionecrosis of the mandible and feeding tube dependency was present for another patient. No fatal late complications were observed in this group. For the first two patients of group 2, sparing of the parotid function was not a treatment objective. For the other patients of group 2, the mean dose to the contralateral parotid gland ranged from 17 to 25 Gy, which resulted in a decrease of subjective symptoms of xerostomia compared to patients treated with conventional radiotherapy. Conclusions. The implementation of IMRT for oropharyngeal and oral cavity tumors results in a homogeneous target irradiation and allows to re-irradiate locoregional relapses with acceptable adverse effects. Sparing of the parotid gland by IMRT is feasible, although this may be significantly influenced by the delineation method of the elective lymph node regions.