This study presents the basic dosimetric properties of photon beams of a Versa HD linear accelerator (linac), which is capable of delivering flattening filter‐free (FFF) beams with a beam quality equivalent to the corresponding flattened beams based on comprehensive beam data measurement. The analyzed data included the PDDs, profiles, penumbra, out‐of‐field doses, surface doses, output factors, head and phantom scatter factors, and MLC transmissions for both FFF and flattened beams of 6 MV and 10 MV energy from an Elekta Versa HD linac. The 6MVFFF and 10MVFFF beams had an equivalent mean energy to the flattened beams and showed less PDD variations with the field sizes. Compared with their corresponding flattened beams, Dmax was deeper for FFF beams for all field sizes; the ionization ratio variations with the field size were lower for FFF beams; the out‐of‐field doses were lower and the penumbras were sharper for the FFF beams; the off‐axis profile variations with the depths were lesser for the FFF beams. Further, the 6MVFFF and 10MVFFF beams had 35.7% and 40.9% less variations in output factor with the field size, respectively. The collimator exchange effect was reduced in the FFF mode. The head scatter factor showed 59.1% and 73.6% less variations, on average, for the 6MVFFF and 10MVFFF beams, respectively; the variations in the phantom scatter factor were also smaller. The surface doses for all beams increased linearly with the field size. The 6MVFFF and 10MVFFF beams had higher surface doses than the corresponding flattened beams for field sizes of up to 10×10cm2 but had lower surface doses for larger fields. Both FFF beams had lower average MLC transmissions than the flattened beams. The finding that the FFF beams were of equivalent quality to the corresponding flattened beams indicates a significant difference from the data on unmatched FFF beams.PACS number(s): 87.56.bd, 87.55.Qr

No abstract

A complex neutron spectrum generated along with a useful photon beam imposes an additional radiation protection risk around medical linear accelerators (linac). The thermal neutron component of this complex neutron spectrum formed during different photon modes of operation of Elekta Versa HD linac has been quantified using Indium foil activation technique. The thermal neutron fluence (Φ th ) at isocenter for 15 MV, 10 MV and 10 MV FFF beams was found to be 2.45 × 105, 4.35 × 104 and 3.2 × 104 neutrons cm−2 Gy−1, respectively. The analysis shows a reduction in the Φ th as the flattening filter is being taken out from the beam path. A negative correlation in Φ th with respect to field size has been observed with an average 18% reduction in Φ th per monitor units as field size changes from 10 cm × 10 cm to 40 cm × 40 cm. For particular field size and photon energy, Φ th was found to be uniform across the patient plane. From the measured gamma ray spectrum inside the treatment room six major isotopes have been identified which were 122Sb, 187W, 82Br, 56Mn, 24Na and 28Al.

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The use of high-energy charged particles in radiotherapy has evolved into an advanced cancer treatment. Even though proton beams and carbon ions are currently the popular particles used for radiotherapy in cancer, ions such as pions, helium, argon, and neon were previously used. To prepare this article, reviewed the literature relevant to the history, current status, and clinical outcomes of particle therapy for specific types of tumors by searching in PubMed and Google Scholar using specific search terms. This article reviews the history, current status, physics, and radiobiological advantages of particle therapy. Outcomes of particle therapy for sites such as the head-and-neck, central nervous system, lung, and prostate have been discussed. The physical and biological properties of particle therapy have been shown to be effective in reducing radiation-induced acute toxicities to a large extent as well as reducing the integral dose, i.e., the sum of dose delivered at every point in a patient’s body, multiplied by the volume of tissue at each point and then added up over the entire treated volume. It is used to assess the potential risks associated with radiation therapy. The advantages of particle therapy over conventional photon therapy in terms of overall survival and local control rates have been described. Advances in image guidance and newer particle acceleration technologies have improved the efficiency of particle therapy treatment.