Introduction: This study aimed to measure the neutron contamination of flattening filter (FF) and flattening filter-free (FFF) 10-MV photon beams delivered by the Elekta InfinityTM accelerator. Material and Methods: The photoneutron spectrum produced by the Linac head was evaluated using a Monte Carlo (MC) simulation. The geometry and composition of the head Linac material were modelled based on information obtained from the manufacturer. In this simulation, MC N-Particle Transport Code software (MCNP6) was utilized to model the Linac head and simulate the particle transport. Evaluation of neutron contamination was carried out for the Linac with FF and without it (i. e., FFF). In this regard, the FFF beam was built by removing the FF from the Linac components. The scoring plane, as the neutron spectra calculation area for FF and FFF beams, was placed 99 cm from the target. Results: The neutron type produced by the head Linac Elekta InfinityTM 10-MV photon mode was mostly thermal and fast. Although there were differences in the neutron intensity of FF and FFF beams, the type of neutrons produced by these two modes had the same energy. Based on the photoneutron reaction energy threshold, it can be concluded that the neutrons produced from the head Linac were the result of photoneutron interactions of high-energy photons with molybdenum-96 and tungsten-184 isotopes. Conclusion: The photoneutron quantity did not change for FF and FFF beams; however, a larger quantity of neutrons was produced in the FF beam.

Background: As compared to the flattened photon beam, removing the flattening filter (FF) from the head of a gantry decreases the average energy of the photon beam and increases the dose rate, leading to an impact on the quality of treatment plans. Objective: This study aimed to compare the quality of intensity-modulated radiation therapy (IMRT) treatment plans for esophageal cancer with and without a flattened filter photon beam. Material and Methods: In this analytical study, 12 patients, who had already been treated with a 6X FF photon beam, were treated based on new IMRT methods using a 6X the flattening filter-free (FFF) photon beam. Both 6X FF IMRT and 6X FFF IMRT plans used identical beam parameters and planning objectives. All plans were evaluated with planning indices and doses for organs at risk (OARs). Results: Insignificant dose variation was for HI, CI, D98%, and V95% between FF and FFF photon beam IMRT plans. FF-based IMRT plan delivered a 15. 51% and 11. 27% higher mean dose to both lungs and heart than the FFF plan, respectively. The integral dose (ID) for the heart and lungs was 11. 21% and 15. 51%, respectively, less in the IMRT plan with an FFF photon beam. Conclusion: In contrast to the FF photon beam, a filtered photon beam-oriented IMRT plan provides significant OAR sparing without losing the quality of the treatment plan. High monitor units (MUs), low ID, and Beam on Time (BOT) are major highlights of the IMRT plan with FFF beam.

Background: In the treatment of prostate cancer, radiotherapy is the potential to increase second primary cancers such as bladder and rectal cancers. The reasons for this potential are more monitor units (MUs), therefore a larger total body dose because of leakage radiation, a bigger volume of normal tissue is exposed to lower radiation doses. This study was designed to compare the integral dose of using Flattening Filter (FF) and Flattening Filter-Free (FFF) 6 and 10 MV photon beams via volumetric modulated arc therapy (VMAT) for prostate cancer patients. Materials and Methods: Twenty prostate cancer patients were selected retrospectively for this planning study. VMAT plans were developed using the Eclipse (Varian Medical System, Palo Alto, California, USA) Treatment Planning System (TPS) with 6 MV FF, 6 MV FFF, 10 MV FF and 10 MV FFF for each patient. Conformity index (CI), homogeneity index (HI), Integral dose (ID), the volume receiving 5 Gy (V5%) and monitor units (MUs) were compared. Results: The use of 10 MV FF had 206 liter*Gy integral dose to Body-CTV volume. Using 10 MV FFF had 204 liter*Gy integral dose to normal structures. When 10 MV FF or 10 MV FFF were used instead of 6 MV FF and 6 MV FFF integral dose decreased as-7% and-8%, respectively. The dosimetric difference were statistically significant (p<0. 05). The use of 10 MV FFF rather than 10 MV FF had limited influence on the integral dose for rectum, bladder, penile bulb and femoral heads. Conclusion: This study showed that high energy photons (10 MV FF, 10 MV FFF) have lower integral dose than low energy photons (6 MV FF, 6 MV FFF). The relationship between low energies, high energies and integral doses is significant, although there is no significant relationship between V5% doses of all energies. In comparison to different treatment plans, we showed that V5% alone did not provide enough information when possible secondary cancer risks were calculated.

Purpose: In the last years, some studies investigated dosimetric benefits of a free flattening filter for the photon mode in the radiotherapy field. This study aims to provide a theoretical study published and analysis of basic dosimetric properties for a Saturne 43 Linac head to implement free flattening filter beams clinically. Material and Methods: This is the first Monte Carlo study for the head of Saturne 43 with replacement flattening filter mode investigating beam dosimetric characteristics, including central axis absorbed doses, beam profiles and photon energy spectra. The later ones were analyzed for flattening filter and replacement flattening filter beams using BEAMnrc and DOSXYZnrc Monte Carlo codes for 10 × 10 cm2, 5 × 5 cm2 and 2 × 2 cm2 square field sizes. Results: A 3. 94-fold increase of dose rate and electron contaminating increased by 246. 4 % with the replacement flattening filter mode for field size of 10 × 10 cm2. Reduction was made by replacement flattening filter beam in the peripheral dose up to 30%, and the time was reduced more than 50 %. Conclusion: Results obtained from our study revealed that some characteristic dosimetries such as the maximum increase in depth dose rate, decrease in out-ofdepth dose, and reducing time can be beneficial for the unflattened beam to be used in the radiotherapy for the advanced techniques.