In vivo dosimetry using radiochromic films(EBT-2) during Intraoperative electron beam radiation therapy (IORT) in early-stage breast cancer and comparison withMonte Carlo simulation results

In vivo dosimetry is nowadays quite a common practice in radiotherapy, as an overall check of the dose delivered to the patient and within a comprehensive quality assurance program. The aim of this work is to check the dose delivered to patients during Intraoperative Electron beam Radiation Therapy IOERT in the conservative treatment of early-stage breast cancer, by means of entrance dose using radiochromic films (EBT-2)Methods and materials: 10 patients affected by early-stage breast cancer underwent exclusive IOERT to the tumor bed using a LIAC (Sordina SPA, Italy) with nominal energy (6, 8, 10 and 12 MEV). In 10 cases, in vivo dosimetry was performed. The entrance dose was derived from the maximum dose in PTV measured by thin and calibrated EBT-2 radiochromic films, put on protection disk and wrapped in sterile envelopes. Films were analyzed 24–72 h after the irradiation using a calibrated Microtek scanner. EBT-2 films showing responses independent of dose per pulse. We want to measure mean deviation between measured and expected doses that derived by Sordina Monte Carlo simulation. So QA (Quality Assurance) of IORT system for breast cancers is achievable. For measurement of absolute dose, two or three films cut into 1.5 * 1.5 cm2 pieces. Then, the films were scanned before and after irradiation that for irradiation of films, put them on the disk with sterile envelope. Finally, using Matlab and ImageJ software, the pixel values of scanned images were obtained before and after irradiation. We use calibration curve for calculating net optical density (OD). Software were used to determine the parameters statistics of OD values in the region of interest (in approximately equal area 352 pixels), selected in the central part of each film to avoid the edge artefacts, caused by cutting the films.Results: When deviations are larger than 4%, there is evidence of serious malfunctioning or human mistake (wrong monitor unit calculation or setting) was found. For three cases there was a big deviation and errors. The reasons were include barometer that not calibrate, wrong monitor unite entered to LIAC, disposition of applicator or protection disk. For other cases results were logical and deviations were under 4%.Conclusion: In 10 cases, invivo dosimetry with radiochromic films were performed that for most cases the good agreement between measured and expected dose values were observed. But in 2-3 cases the results shows deviation more than 4% because of human mistakes. So for more reliable treatment, the QA of IOERT procedures is recommended.

Keywords:

Radiotherapy , IOERT , radiochromic film , invivo dosimertry