Hypofractionated Radiotherapy in Localized, Low-Intermediate-Risk Prostate Cancer: Current and Future Prospectives

At the time of diagnosis, the vast majority of prostate carcinoma patients have a clinically localized form of the disease, with most of them presenting with low- or intermediate-risk prostate cancer. In this setting, various curative-intent alternatives are available, including surgery, external beam radiotherapy and brachytherapy. Randomized clinical trials have demonstrated that moderate hypofractionated radiotherapy can be considered as a valid alternative strategy for localized prostate cancer. High-dose-rate brachytherapy can be administered according to different schedules. Proton beam radiotherapy represents a promising strategy, but further studies are needed to make it more affordable and accessible. At the moment, new technologies such as MRI-guided radiotherapy remain in early stages, but their potential abilities are very promising.

In-line MRI-LINAC depth dose measurements using an in-house plastic scintillation dosimeter

Plastic scintillation dosimeters (PSDs) have many properties that make them desirable for relative dosimetry with MRI-LINACs. An in-house PSD, Farmer ionisation chamber and Gafchromic EBT3 film were used to measure central axis percentage depth dose distributions (PDDs) at the Australian MRI-LINAC Mean errors were calculated between each detector's responses, where the in-house PSD was on average within 0.7% of the Farmer chamber and 1.4% of film, while the Farmer chamber and film were on average within 1.1% of each other. However, the PSD systematically over-estimated the dose as depth increased, approaching a maximum overestimation of the order of 3.5% for the smallest field size measured. This trend was statistically insignificant for all other field sizes measured; further investigation is required to determine the source of this effect. The calculated values of mean absolute error are comparable to the those of trusted dosimeters reported in the literature. These mean absolute errors, and the ubiquity of desirable dosimetric qualities inherent to PSDs suggest that PSDs in general are accurate for relative dosimetry with the MRI-LINAC. Further investigation is required into the source of the reported systematic trends dependent on field-size and depth of measurement.

MRI-LINAC beam profile measurements using a plastic scintillation dosimeter

Plastic scintillation dosimeters (PSDs) possess many desirable qualities for dosimetry with LINACs. These qualities are expected to make PSDs effective for MRI-LINAC dosimetry, however little research has been conducted investigating their dosimetric performance with MRI-LINACs. In this work, an in-house PSD was used to measure 8 beam profiles with an in-line MRI-LINAC, compared with film measurements. One dimensional global gamma indices (γ) and corresponding γ pass rates were calculated to compare PSD and film profiles for the 1%/1 mm, 2%/2 mm and 3%/3 mm criterion. The mean global pass rates were 85.8%, 97.5% and 99.4% for the 1%/1 mm, 2%/2 mm and 3%/3 mm criteria, respectively. The majority of the γ failures occurred in the penumbral regions. Penumbra widths were measured to be slightly narrower with the PSD compared to film, however, the uncertainties in the measured penumbra widths brought the PSD and film penumbra widths into agreement. Differences in dose were calculated between the PSD and film, and remained within 2.2% global agreement for the central regions and 1.5% global agreement for out of field regions. These values for range of agreement were similar to the those reported in the literature for other dosimeters which are trusted for relative MRI-LINAC dosimetry.