Consensus and recommendations on vaginal-cuff Brachytherapy of the Spanish Brachytherapy Groups of SEOR and SEFM.

PURPOSE/OBJECTIVE(S): On October 5, 2018, a meeting of the Spanish Society of Radiation Oncology (SEOR) Brachytherapy Group was held, in collaboration with the Spanish Society of Medical Physics (SEFM), with the aim of preparing a consensus document on postoperative vaginal-cuff brachytherapy (VCBT). MATERIALS/METHODS: A survey including 42 questions was sent to Spanish Radiation Oncology Centres before the meeting. The survey items included: experience in VCBT, technique indications, previous patient preparation, applicator type, implant procedure, computerized tomography (CT) simulation, definition of target volumes and organs at risk (OAR), dose prescription, fractionation, treatment planning, dosimetric parameters and constraints to OAR. Thirty-three centres answered the survey. Statistical analysis of the survey considered that there was consensus when there was ≥ 85% of agreement related to a survey item, otherwise an item with < 85% of agreement would be discussed during the meeting to reach consensus. RESULTS: The results of the survey are reported here. The mean number of patients treated per centre in 2017 was 52 ± 41 (range 7-175), and the mean number of procedures per centre was 175 ± 150 (range 24-701).There was consensus on: the indications, applicator type, the OAR to be considered, the prescription point, standardisation and dosimetric quality parameters. There was no consensus on: patient preparation for the implant, the need for performing CT simulation and the frequency, the length of the vagina to be treated, if CTV should be delimited, the definition of the clinical target volume, fractionation, overall EQD2, active source length, separation between dwelling stepping source positions, if considering the uniformity/maximum values for dwelling stepping sources, the optimization mode, and the limiting doses to the OAR. After presenting the results of the survey, the consensus meeting discussion focused on the issues for which there was no consensus. CONCLUSION: A consensus document on postoperative VCBT of the Spanish Brachytherapy Groups of SEOR-SEFM was elaborated.

D-IMRT verification with a 2D pixel ionization chamber: dosimetric and clinical results in head and neck cancer.

Dynamic intensity-modulated radiotherapy (D-IMRT) using the sliding-window technique is currently applied for selected treatments of head and neck cancer at Institute for Cancer Research and Treatment of Candiolo (Turin, Italy). In the present work, a PiXel-segmented ionization Chamber (PXC) has been used for the verification of 19 fields used for four different head and neck cancers. The device consists of a 32x32 matrix of 1024 parallel-plate ionization chambers arranged in a square of 24x24 cm2 area. Each chamber has 0.4 cm diameter and 0.55 cm height; a distance of 0.75 cm separates the centre of adjacent chambers. The sensitive volume of each single ionization chamber is 0.07 cm3. Each of the 1024 independent ionization chambers is read out with a custom microelectronics chip.The output factors in water obtained with the PXC at a depth of 10 cm were compared to other detectors and the maximum difference was 1.9% for field sizes down to 3x3 cm2. Beam profiles for different field dimensions were measured with the PXC and two other types of ionization chambers; the maximum distance to agreement (DTA) in the 20-80% penumbra region of a 3x3 cm2 field was 0.09 cm. The leaf speed of the multileaf collimator was varied between 0.07 and 2 cm s-1 and the detector response was constant to better than 0.6%. The behaviour of the PXC was measured while varying the dose rate between 0.21 and 1.21 Gy min-1; the mean difference was 0.50% and the maximum difference was 0.96%. Using fields obtained with an enhanced dynamic wedge and a staircase-like (step) IMRT field, the PXC has been tested for simple 1D modulated beams; comparison with film gave a maximum DTA of 0.12 cm. The PXC was then used to check four different IMRT plans for head and neck cancer treatment: cervical chordoma, parotid, ethmoid and skull base. In the comparison of the PXC versus film and PXC versus treatment planning system, the number of pixels with gamma parameter

Dosimetric characterization of a large area pixel-segmented ionization chamber.

A pixel-segmented ionization chamber has been designed and built by Torino University and INFN. The detector features a 24 x 24 cm2 active area divided in 1024 independent cylindrical ionization chambers and can be read out in 500 micros without introducing dead time; the digital charge quantum can be adjusted between 100 fC and 800 fC. The sensitive volume of each single ionization chamber is 0.07 cm3. The purpose of the detector is to ease the two-dimensional (2D) verifications of fields with complex shapes and large gradients. The detector was characterized in a PMMA phantom using 60Co and 6 MV x-ray photon beams. It has shown good signal linearity with respect to dose and dose rate to water. The average sensitivity of a single ionization chamber was 2.1 nC/Gy, constant within 0.5% over one month of daily measurements. Charge collection efficiency was 0.985 at the operating polarization voltage of 400 V and 3.5 Gy/min dose rate. Tissue maximum ratio and output factor have been compared with a Farmer ionization chamber and were found in good agreement. The dose profiles have been compared with the ones obtained with an ionization chamber in water phantom for the field sizes supplied by a 3D-Line dynamic multileaf collimator. These results show that this detector can be used for 2D dosimetry of x-ray photon beams, supplying a good spatial resolution and sensibly reducing the time spent in dosimetric verification of complex radiation fields.