1. DETERMINATION OF PERIPHERAL DOSES FROM DYNAMIC MLC IMRT FOR 6 MV AND 18 MV BEAM ENERGIES
A. Sánchez-Reyes*, N. López Vilanova+, A. Vila*, M.A. Duch+, A. Rodríguez García*, S. Loscos*, L.M. Moya*, M. Ginjaume+, A. Pedro*
* Servei d’ Oncología Radioteràpica, Hospital Plató. Plató 21, Barcelona.
+INTE. Universitat Politècnica de Catalunya. Diagonal Barcelona.
Objectives:
Determination of peripheral doses (Fig. 1 and Fig. 2) from the delivery of 6 MV an 18 MV intensity modulated radiation therapy (IMR) and conventional radiotherapy (3DCRT) in some different real treatments (prostatae, breast, head and neck, brain cancer). Comparison between 6 MV and 18 MV IMRT treatments and 3DCRT treatments.
Material and Methods:
Peripheral doses (PD) from uniform dynamic multileaf collimation fields were measured for 6 MV and 18 MV on a Varian 2100 CD 120 Millenium MLC using TLD dosimeters inserted into a RANDO Anderson anthropomorphic phantom (Fig. 3). PD measurements were carried out under identical conditions for 4 prostatae patients (6 and 18 MV), 4 head and neck patients ( 6MV), 1 breast patient (6 MV), 1 hypophysis patient (6 and 18 MV) and 1 glioma patient (6 and 18 MV) (Fig. 4). The measured PD from these patients were compared with the corresponding data from uniform fields (3DCRT treatment) having similar jaws setting. Dosimetric planning was carried out using ECLIPSE Varian and HELIOS IMRT module. No effective doses of secondary neutron produced by 18 MV photon fields were taken into account in this communication.
Fig 1. IMRT Peripheral dose leakage
Fig 2. Peripheral doses in patient
Fig 3. Rando Anderson phantom
Fig 4. Posicioning at the LINAC
TABLES
Results:
The measured peripheral dose per monitor unit (PD/UM) decreases almost exponentially for both static field and IMRT field regardless of energy (6 or 18 MV). We also found that PD per UM are very similar regardless the type of field, IMRT or static, as well as the energy employed. However, the difference between UM delivered in a IMRT or 3DCRT treatment implies that PD in a 3DCRT treatment are four times lower than those corresponding to the equivalent IMRT treatment. a c b a
Conclusions:
The study shows that PD data generated by dynamic multileaf and uniform fields can be used to estimate the out of field dose in critical organs in real patients treated with different radiotherapy treatments.
This work was supported in part by a grant FIS PI06/0394