Purpose: To perform a systematic and thorough assessment, using the Uncomplicated and Cancer-Free Control Probability (UCFCP) function, of a broad range of photon prostate cancer RT treatments, on the same scenario (a unique pelvic CT set). UCFCP considers, together with the probabilities of local tumour control (TCP) and deterministic (late) sequelae (NTCP), the second primary cancer risk (SPCR) due to photon and neutron peripheral doses. Methods and materials: Thirty-six radiotherapy plans were produced for the same CT. 6, 10, 15 and 18 MV 3DCRT, IMRT and VMAT (77.4 Gy in 43 fractions) and 6 and 10 MV SBRT (36.25 Gy in 5 fractions with flattened and FFF beams) for Elekta, Siemens and Varian Linacs plans were included. DVH and peripheral organ dosimetry were used to compute TCP, NTCP, and SPCR (the competition and LNT models) for further plan ranking. Results: Biological models (and parameters) used predicted an outcome which is in agreement with epidemiological findings. SBRT plans showed the lowest SPCR and a below average NTCPrectal. High energy plans did not rank worse than the low energy ones. Intensity modulated plans were ranked above the 3D conformal techniques. Conclusions: According to UCFCP, the best plans were the 10 MV SBRTs. SPCR rates were low and did not show a substantial impact on plan ranking. High energy intensity-modulated plans did not increase in excess the average of SPCR. Even more, they ranked among the best, provided that MU were efficiently managed.

Total skin electron irradiation (TSEI) is a radiotherapy technique which consists of an homogeneous body surface irradiation by electrons. This treatment requires very strict technical and dosimetric conditions, requiring the implementation of multiple controls. Recently, the Task Group 100 report of the AAPM has recommended adapting the quality assurance program of the facility to the risks of their processes.

There is a growing interest in the combined use of Stereotactic Body Radiation Therapy (SBRT) with Flattening Filter Free (FFF) due to the high local control rates and reduced treatment times, compared to conventionally fractionated treatments. It has been suggested that they may also provide a better radiation protection to radiotherapy patients as a consequence of the expected decrease in peripheral doses. This work aims to determine this reduction in unattended out-of-field regions, where no CT information is available but an important percentage of second primary cancers occur. For that purpose, ten different cases suitable for SBRT were chosen. Thus, 142 different treatment plans including SBRT, as well as 3D-CRT, IMRT and VMAT (with standard fractionation) in low and high energies for Varian (FF and FFF), Siemens and Elekta machines were created. Then, photon and neutron peripheral dose in 14 organs were assessed and compared using two analytical models. For the prostate case, uncomplicated and cancer free control probability estimation was also carried out. As a general behavior, SBRT plans led to the lowest peripheral doses followed by 3D-CRT, VMAT and IMRT, in this order. Unflattened beams proved to be the most effective in reducing peripheral doses, especially for 10 MV. The obtained results suggest that FFF beams for SBRT with 10 MV represent the best compromise between dose delivery efficiency and peripheral dose reduction.

Total Skin Electron Irradiation (TSEI) is a radiotherapy treatment which involves irradiating the entire body surface as homogeneously as possible. It is composed of an extensive multi-step technique in which quality management requires high consumption of resources. The TG-100 proposes a new perspective of quality management in radiotherapy, presenting a systematic method of risk analysis throughout the global flow of the stages through the patient. With the intention of applying this method, a multidisciplinary team of people was involved in the procedure that produced the process map (PM). This PM can be useful for those centers that intend to implement the TSEI technique. This is the first stage of a full risk analysis performed in a reference center in this treatment technique.

PURPOSE:The high mass density and low mobilities of charge carriers can cause important recombination in liquid-filled ionization chambers (LICs). Saturation correction methods have been proposed for LICs. Correction methods for pulsed irradiation are based on Boag equation. However, Boag equation assumes that the charge ionized by one pulse is fully collected before the arrival of the next pulse. This condition does not hold in many clinical beams where the pulse repetition period may be shorter than the charge collection time, causing overlapping between charge carriers ionized by different pulses, and Boag equation is not applicable there. In this work, the authors present an experimental and numerical characterization of collection efficiencies in LICs beyond the Boag limit, with overlapping between charge carriers ionized by different pulses. METHODS:The authors have studied recombination in a LIC array for different dose-per-pulse, pulse repetition frequency, and polarization voltage values. Measurements were performed in a Truebeam Linac using FF and FFF modalities. Dose-per-pulse and pulse repetition frequency have been obtained by monitoring the target current with an oscilloscope. Experimental collection efficiencies have been obtained by using a combination of the two-dose-rate method and ratios to the readout of a reference chamber (CC13, IBA). The authors have also used numerical simulation to complement the experimental data. RESULTS:The authors have found that overlap significantly increases recombination in LICs, as expected. However, the functional dependence of collection efficiencies on the dose-per-pulse does not change (a linear dependence has been observed in the near-saturation region for different degrees of overlapping, the same dependence observed in the nonoverlapping scenario). On the other hand, the dependence of collection efficiencies on the polarization voltage changes in the overlapping scenario and does not follow that of Boag equation, the reason being that changing the polarization voltage also affects the charge collection time, thus changing the amount of overlapping. CONCLUSIONS:These results have important consequences for saturation correction methods for LICs. On one hand, the two-dose-rate method, which relies on the functional dependence of the collection efficiencies on dose-per-pulse, can also be used in the overlapping situation, provided that the two measurements needed to feed the method are performed at the same pulse repetition frequency (monitor unit rate). This result opens the door to computing collection efficiencies in LICs in many clinical setups where charge overlap in the LIC exists. On the other hand, correction methods based on the voltage-dependence of Boag equation like the three-voltage method or the modified two-voltage method will not work in the overlapping scenario due to the different functional dependence of collection efficiencies on the polarization voltage.

Purpose: Total Skin Electron Irradiation (TSEI) is a radiotherapy treatment which involves irradiating the entire body surface as homogeneously as possible. It is composed of an extensive multi‐step technique in which quality management requires high consumption of resources and a fluid communication between the involved staff, necessary to improve the safety of treatment. The TG‐100 proposes a new perspective of quality management in radiotherapy, presenting a systematic method of risk analysis throughout the global flow of the stages through the patient. The purpose of this work has been to apply TG‐100 approach to the TSEI procedure in our institution. Methods: A multidisciplinary team specifically targeting TSEI procedure was formed, that met regularly and jointly developed the process map (PM), following TG‐100 guidelines of the AAPM. This PM is a visual representation of the temporal flow of steps through the patient since start until the end of his stay in the radiotherapy service. Results: This is the first stage of the full risk analysis, which is being carried out in the center. The PM provides an overview of the process and facilitates the understanding of the team members who will participate in the subsequent analysis. Currently, the team is implementing the analysis of failure modes and effects (FMEA). The failure modes of each of the steps have been identified and assessors are assigning a value of severity (S), frequency of occurrence (O) and lack of detection (D) individually. To our knowledge, this is the first PM made for the TSEI. The developed PM can be useful for those centers that intend to implement the TSEI technique. Conclusion: The PM of TSEI technique has been established, as the first stage of full risk analysis, performed in a reference center in this treatment.

Material and Methods: We modeled the CBCT system which built-in Varian Clinac iX with full-fan and half-fan filter by using the Monte Carlo code (MCNPX 2.7.0).By acquiring the measured data with EBT3 films for PDD(percent-depth dose) and beam profile for open, full-fan and half-fan filter in static mode, we verified that simulated data was coincided with measured data for spectrum.The assessment of absorbed dose of each organ during the CBCT scanning was performed with ORNL(Oak Ridge National Laboratory)-male-MIRD(Medical Internal Radiation Dose) phantom.In this study, we set the scan range adapted for the CBCT scan conditions and then the absorbed dose of each organ was evaluated applying a half-fan filter.In that time, the CBCT scan range was changed by modulating the Y jaw from 16 cm to 8 cm at intervals of 2 cm and we verified the difference of absorbed dose of each organ according to CBCT scan range.Results: For CBCT scan in thorax, the absorbed dose of heart and lung were reduced for 46.6~32.1 mGy and 75~47.4mGy, respectively, and the other side lung was reduced for 31.7~19.1 mGy.As the scan range was decreased at intervals of 2 cm, the absorbed dose in lung was reduced up to 10 %.In the case of heart, the absorbed dose was reduced drastically.For prostate, absorbed dose of bladder, sigmoid colon and testes showed dose reduction for 61.4~41.7 mGy, 50.4~38.8mGy and 81.1~45.4mGy, respectively.In the case of penis, the absorbed dose was reduced from 81.1 to 45.4 mGy. Conclusion:We evaluated the change of organ dose according to CBCT scan range with Monte Carlo code MCNPX and male-MIRD phantom.In the result, we verified the organ dose can be different about 30~40% according to changes of CBCT scan range.We thought this study can be used in optimization for radiation exposure to patients, usefully.

Purpose:The purpose of this work is the characterization of a new Varian TrueBeam™ facility in terms of neutron production, in order to estimate neutron equivalent dose in organs during radiotherapy treatments.Methods:The existing methodology [1] was used with the reference SRAMnd detector, calibrated in terms of thermal neutron fluence at the reference field operated by PTB (Physikalisch‐Technische‐Bundesanstalt) at the GeNF (Geesthacht‐Neutron‐Facility) with the GKSS reactor FRG‐1 [2]. Thermal neutron fluence for the 5 available possibilities was evaluated: 15 MV and 10&6 MV with and without Flattening Filter (FF and FFF, respectively). Irradiation conditions are as described in [3]. In addition, three different collimator‐MLC configurations were studied for 15 MV: (a) collimator of 10×10 cm2 and MLC fully retracted (reference), (b) field sizes of 20×20 cm2 and 10×10 cm2 for collimator and MLC respectively, and (c) collimator and MLC aperture of 10×10 cm2.Results:Thermal fluence rate at the “reference point” [3], as a consequence of the neutron production, obtained for (a) conformation in 15 MV is (1.45±0.11) x10⁴ n•cm2/MU. Configurations (b) and (c) gave fluences of 96.6% and 97.8% of the reference (a). Neutron production decreases up to 8.6% and 5.7% for the 10 MV FF and FFF beams, respectively. Finally, it decreases up to 2.8% and 0.1% for the 6 MV FF and FFF modes, respectively.Conclusion:This work evaluates thermal neutron production of Varian TrueBeam™ system for organ equivalent dose estimation. The small difference in collimator‐MLC configuration shows the universality of the methodology [3]. A decrease in this production is shown when decreasing energy from 15 to 10 MV and an almost negligible production was found for 6 MV. Moreover, a lower neutron contribution is observed for the FFF modes.[1]Phys Med Biol,2012;57:6167–6191.[2]Radiat Meas,2010;45:1513–1517.[3]Med Phys,2015;42:276–281.

Finding out the best treatment plan that could be designed for a specific patient could be a difficult task. Benefits on terms of better tumor coverage have to be balanced against the drawbacks of poorer organ at risk sparing in order to make the decision on the optimum treatment technique. A large variety of photon beam radiotherapy (RT) techniques are currently available. The relative merits of different 34 treatment modalities for a prostate cancer, using the same CT data set and contours, have been analyzed in terms of the area under the Uncomplicated Control Probability curve. IMRT forward techniques have resulted to be the best ranked treatment modalities.

Nowadays, neutron contamination in high energy photon beams normally used in radiotherapy treatments is an issue of interest from the radioprotection point of view. However, neutron production when using electron beams to treat superficial tumors has usually been ignored. The aim of this paper was to study such contamination and its effect on patients. In order to do that, experimental measurements in a radiotherapy environment were carried out using a digital device sensitive to thermal neutrons. Besides, Monte Carlo simulations were performed to estimate the difference in number of particles between photon and electron operational modes, required to deposit the same dose at a certain depth. Results show that neutron production is lower for electron beams than photon ones but not as low as previously expected.