Philippe Giraud

A dosimetric comparison was made of Helical Tomotherapy (HT) and Rapid'Arc® (RA) in 115 patients with head and neck carcinoma included in a prospective and multicentric study. HT and RA provided highly conformal plans that easily complied with dose volume constraints for organs at risk. HT reduced high doses to the planning target volumes (PTVs) compared to RA and provided a more homogeneous dose distribution but with an increased Non Tumoral Integral Dose (NTID) than RA. However, the clinical consequences of these dosimetric advantages and disadvantages need further investigation.

The objective of this study was to evaluate set-up uncertainties using a portal imaging system in a population of inoperable non-small cell lung cancer. Twenty-one patients were treated by a conformal radiotherapy technique with a personalized immobilization cast. The beam was verified by comparison with a corresponding digitally reconstructed radiograph by superimposition of anatomical structures. One thousand eight hundred eighty three images were analyzed. The mean intrafraction and interfraction errors (+/-SD) were 2.17 mm and 0.9 +/- 3.7 mm, 2.3 mm and 0.9 +/- 3.1 mm, 3 mm and 0.7 +/- 3 mm on the lateral (x), cranio-caudal (y) and anterior-posterior (z) axes, respectively. The mean systematic error was small, less than 1 mm, in all directions. The random errors were 2.5 mm, 2.4 mm, and 1.8 mm on the x, y, and z axes, respectively. No correlation between errors and the patient's height, weight, age, or sex was found. Set-up errors accuracy depending on practices, each institution should review their own treatments to quantify and reduce set-up errors in clinical practice.

A dynamic lung tumor phantom was used to investigate the geometric reconstruction accuracy of a commercial four‐dimensional computed tomography (4D‐CT) system. A ball filled with resin, embedded in a cork cube, was placed on a moving platform. Various realistic antero‐posterior (AP) motions were programmed to reproduce the respiratory motion of a lung tumor. Several three‐dimensional (3D) CT and 4D‐CT images of this moving object were acquired and compared using different acquisition parameters. Apparent volume and diameter of the ball were measured and compared to the real values. The position of two points (the AP limits of the ball) during the motion in the coordinate system of the CT scanner were also compared with the expected values. Volume error was shown to increase with object speed. However, although the volume error was associated with intraslice artifacts, it did not reflect large interslice inconstancies in object position and should not be used as an indicator of image accuracy. The 3D‐CT gave a random position of the tumor along the phantom excursion; accuracy in the assessment of position by 4D‐CT ranged from 0.4 mm to 2.6 mm during extreme phases of breathing. We used average projection (AVE) and maximum intensity projection (MIP) algorithms available on the commercial software to create internal target volumes (ITVs) by merging gross tumor volume (GTV) images at various respiratory phases. The ITVs were compared to a theoretical value computed from the programmed ball excursion. The ITVs created from the MIP algorithm were closer to the theoretical value (within 12%) than were those created from the AVE algorithm (within 40%).PACS numbers: 87.53.Xd, 87.56.Mp, 87.57.Ce, 87.59.Fm

Respiration-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast and liver tumors. An increased conformality of irradiation fields leading to decreased complications rates of organs at risk (lung, heart...) is expected. Respiratory gating is in line with the need for improved precision required by radiotherapy techniques such as 3D conformal radiotherapy or intensity modulated radiotherapy. Reduction of respiratory motion can be achieved by using either breath hold techniques or respiration synchronized gating techniques. Breath hold techniques can be achieved with active, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-hold. Synchronized gating techniques use external devices (CCD camera for the GEMS/Varian system tested at Curie Institute) to predict the phase of the respiration cycle while the patient breaths freely. A new strategy is currently developed: the 4D Respiration correlated CT. It consists of retrospectively reconstruct CT slices at different phases of the breathing cycle allowing to measure residual movements and to choose the optimal patient's breathing phase where tumor movements are lower. These techniques presently investigated in several medical centers worldwide. The first results are very promising.

Irradiation of the heart begets different complications in which pericardial disease is the most common manifestation. Thoracic irradiation of lymphoma, Hodgkin's disease, lung and breast cancer could be complicated by adverse effects to every structure of the heart. Potential injury of mediastinal irradiation can include acute and late pericarditis, cardiomyopathy, valvular disease and conduction abnormalities. The pathophysiology of these various syndromes is probably similar, starting by prior microvascular injury that leads to subsequent myocardium ischemia, all of which cause late fibrous scars. Acute pericarditis is often asymptomatic and clear spontaneously. Late pericarditis affects approximately 5% of the patients when the irradiation dose exceeds 40 Gy. At this dose, the mortality rate is below than 1%. Cardiomyopathy is rare and often asymptomatic. A long time unrecognized, coronary artery disease, diagnosed in 5 to 10% of the patients, begets multifarious sequelae like myocardial infarction, valvular abnormalities and cardiac rhythm changes. This coronary artery disease is more likely to occur if the patient was young at the time of the irradiation (< or = 21 years) and/or if other cardiovascular risk factors are associated. Incidence and mortality rates of valvular defects are about 20 and 0.5%, respectively. Conduction dysfunctions can also be seen in 5% of the patients. Radiation-induced heart complications seem to be related to total dose (> 30 Gy), irradiated tissue volume and fraction size. Since cardiac complications appear months to years following incidental irradiation of the heart, appropriate screening and long-term cardiac follow-up of these patients is essential.