Articole

 Introduction. Classical 2D and 3D techniques in cranio-spinal irradiation carry the problem of overdosing or underdosing at the junction between adjacent fields. At the same time doses recived by organs at risk can be significant and are difficult to control because of the limited special distribution of the radiation fields used. These inconveniences are virtually eliminated by using the RapidArc technique. To obtain a homogeneous dose distribution throughout the target volume ( whole brain and entire medullary canal) we used a 3 izocentre and 6 arc technique.

Materials and methods. Patients were scanned with a GE Optima CT580 16 sice CT , with 2.5mm distance between sections. Treatment planning was performed Eclipse 10 planning system , from Varian. Treatment plan verification was done with the device specially used form VMAT plans , Arc Check manufactured by Sun Nuclear. A second check of dose-volume distribution was performed with 3DVH software from Sun Nuclear. DVHs were recalculeted and verified with SNC 3DVH softwere using the original plan data and the delivered 3D dose distribution. Patient immobilization was obtained using thermoplastic head mask and set-up accuracy was verified with OBI device (Kv) of a Varian Trilogy iX Clinac.

Results. This RapidArc treatment technique was used for two patients with the diagnosis of medulloblastoma . In both cases PTV coverege was good ( 97%v95%PTV dose) according to DVH and gamma-map analysis showed tht 95% of the measured points wew within the tolerance level . Gamma-map analysis was carried out by comparing the exported and measured data at 3mm 3% tolerance level. The dose distributions was homogenius both in sagittal direction and transversal plans. Re-calculated DVHs differ from planned ones at a clinically irrelevant stage.Organs at risk doses were below those of the international protocols.

Conclusions. RapidArc compared to 3D conformal techniques offers a more conformal and homogeneous dose distribution in the target volumes and allowes more organ at risk sparing . This comes at the cost of more time spent with the treatment planning and verifications.

From the point of view of achieving treatment plan and especially the time required for treatment, RA techinique is time consuming and energy.

Centrul de Diagnostic și Tratament Oncologic Brașov

Brașov, str.Carierei, nr.65A

tel: 0268448000

fax: 0268448010

e-mail: [email protected]

web: www.oncocard.ro