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ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
In vivo dosimetry with XR-RV3 radiochromic films in intraoperative radiotherapy of the breast
Sergio Lozares, Spain
PO-1350

Abstract

In vivo dosimetry with XR-RV3 radiochromic films in intraoperative radiotherapy of the breast
Authors: Verónica Alba.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), José Antonio Font.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), Almudena Gandía.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), Mónica Hernández.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), Sara Jiménez.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), Sergio Lozares.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain), David Villa.(Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain)
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Purpose or Objective

To carry out treatment verification and in vivo dose measurements in intraoperative breast radiotherapy patients, treated with the Axxent (Xoft Inc.) equipment with 50 kVp of energy with XR-RV3 radiochromic films model, specific for low energies and high doses.
With this work we will get to know the in vivo dose in skin, the main risk organ in IORT treatments.

Material and Methods

480 patients were treated with IORT with the Axxent device in our hospital from May 2015 to October 2019.
Dosimetric measurements were performed in vivo with XR-RV3 radiochromic films in 10 patients to determine the skin dose in IORT with Axxent.Gafchromic XR-RV3 radiochromic films are specific for measurements in the low energy and high dose range, the films were calibrated following the 3-channel method (Radiochromic.com) to measure dose in vivo in patients with breast IORT. The tratment prescription is 20 Gy on the balloon surface following the TARGIT study.
Four pieces of properly oriented films were placed on each patient to obtain skin doses at different points on each patient. The pieces were placed progressively from the area closest to the applicator (point 1) to the furthest (point 4) following the example in the image (Fig 1).
In addition to obtaining the doses on the skin, a piece was placed on the balloon applicator to monitor the prescribed dose for each treatment and verify the correct administration of the treatment.
The process of converting the result into dose was carried out with an Epson Expression 12000XL scanner. The films were scanned before and after irradiation with five consecutive scans in both cases, in the case of those irradiated, 24 hours after irradiation.
The calibration process was carried out with known doses calculated after measurements with the Exradin A20 ionization chamber and using the TG-61 protocol, the calibration curve extends from 0 to 25 Gy ,and another calibration curve from 0 to 10 Gy was performed more suitable for skin doses.

Results

The skin doses obtained for all patients are shown in Fig 2, these doses are lower than those estimated by the TPS (Eclipse, Varian Inc.) calculated with the Axxent specific parameters of TG-43.
The doses of the film pieces placed on the balloon surface match the expected, i.e. 20 Gy, the prescribed dose.

Conclusion

The skin doses are sufficiently low, which explains why in the 480 patients treated, less than 1% of the cases presented early toxicity of acute grade 3 dermatitis and no case of a higher grade.
The in vivo dosimetry procedure initiated will be performed with all patients measuring doses in other areas of interest from now on.