Small field correction factors determination for several active detectors using a Monte Carlo method in the Elekta Axesse linac equipped with circular cones.

A Monte Carlo (MC) method was used to determine small field output correction factors for several active detectors (Exradin A16, Exradin A26, PTW microLion, PTW microDiamond, Exradin W1 and IBA RAZOR) for an Elekta Axesse linac equipped with circular cones. MC model of the linac was built with the GamBet software, using the Penelope code system. The dose-to-water simulation for each cone, ranging from 5 to 30 mm of diameter size, was used to calculate field factors and the results were validated together with Gafchromic EBT3 film. Output factors (OFs) were measured with the active detectors and correction factors were determined using the MC results. The MC simulations agreed with films within 1.2%. OFs measured with Exradin W1 scintillator were in agreement within 0.8% with MC simulations. The Exradin A16 and A26 microchambers under-responded for small fields relative to the MC (-13.1% and -4.6%, respectively). PTW microLion, IBA RAZOR and PTW microDiamond overestimated the output factor for the smallest field (+3.9%, +5.4 and +7.1%, respectively). The present study pointed out that it is crucial to apply the appropriate correction factors in order to provide accurate measurements in small beams geometry. The results showed that the Exradin W1 can be used for very small field dosimetry without correction factors, which shall be contrariwise employed for other detectors.

Evaluation of a commercial automatic treatment planning system for liver stereotactic body radiation therapy treatments.

PURPOSE: Automated treatment planning is a new frontier in radiotherapy. The Auto-Planning module of the Pinnacle3 treatment planning system (TPS) was evaluated for liver stereotactic body radiation therapy treatments. METHODS: Ten cases were included in the study. Six plans were generated for each case by four medical physics experts. The first two planned with Pinnacle TPS, both with manual module (MP) and Auto-Planning one (AP). The other two physicists generated two plans with Monaco TPS (VM). Treatment plan comparisons were then carried on the various dosimetric parameters of target and organs at risk, monitor units, number of segments, plan complexity metrics and human resource planning time. The user dependency of Auto-Planning was also tested and the plans were evaluated by a trained physician. RESULTS: Statistically significant differences (Anova test) were observed for spinal cord doses, plan average beam irregularity, number of segments, monitor units and human planning time. The Fisher-Hayter test applied to these parameters showed significant statistical differences between AP e MP for spinal cord doses and human planning time; between MP and VM for monitor units, number of segments and plan irregularity; for all those between AP and VM. The two plans created by different planners with AP were similar to each other. CONCLUSIONS: The plans created with Auto-Planning were comparable to the manually generated plans. The time saved in planning enables the planner to commit more resources to more complex cases. The independence of the planner enables to standardize plan quality.

Is Karnofsky Performance Status Correlate with Better Overall Survival in Palliative Conformal Whole Brain Radiotherapy? Our Experience.

AIM: Brain metastases (BMs) are a common event in the progression of many human cancers. The aim of this study was to evaluate the potential prognostic factors for the clinical identification of a subgroup of patients that could benefit from whole brain conformal radiotherapy (WBRT). MATERIALS AND METHODS: From January 2010 to February 2014, 80 patients with a diagnosis of BMs underwent WBRT at our Radiation Oncology Department, San Luigi Hospital, Italy. Among them, 36 medical records were retrospective reviewed. Gender, age, Karnofsky performance status (KPS), number of BMs on computed tomography and/or magnetic resonance images, presence or absence of perilesional edema, presence or absence of necrosis pattern, and histology of primary tumor were analyzed. Univariate and multivariate analyses were performed. RESULTS: In our cohort of patients, significant prognostic factors for 20 months overall survival was KPS> 70, while a statistical trend (P = 0.098) was registered regarding primary breast. CONCLUSION: WBRT can be still considered a standard and effective treatment in patients with BMs. High KPS and breast cancer primary tumor seem to be useful parameters for characterize a subgroup of patients with more favorable prognosis.

Implementation of a program for quality assurance on leaf positioning accuracy using Gafchromic(®) RTQA2 films.

In radiotherapy treatments the correct dose delivery to the target volume and the consequent conservation of healthy tissues is affected by multileaf collimator (MLC) leaf positioning accuracy and reproducibility, mostly in intensity-modulated radiation therapy (IMRT): For this reason a quality assurance (QA) program is necessary to ensure the best treatment possible to each patient. The aim of this study is the implementation of a method using Gafchromic(®) RTQA 2 films to perform routine QA on the MLC, both for qualitative and quantitative analysis. A flatbed document scanner (Epson 10000XL) was used in conjunction with radiochromic detector; a scanning protocol was firstly defined to improve readout accuracy. RTQA2 films were irradiated with 6 MV X-rays at different dose levels to obtain calibration curve. To evaluate the leaf positioning accuracy in different conditions, a rhomboidal shape and a field consisting in three rectangular segments were selected. The images quantitative analysis was handled with a program developed in MATLAB to evaluate the differences between expected and measured leaves positions. The reproducibility and global uncertainty of the method were estimated to be equal to 0.5% and 0.6 mm, respectively. Moreover, a qualitative test was performed: A garden picket fence field, consisting in multiple segments 2 × 22 cm(2), was realized setting known leaves shifts to test the method sensitivity. The picket fence test shows that the method is able to detect displacements equal to 1 mm. The results suggest that Gafchromic(®) RTQA2 films represent a reliable tool to perform MLC routine QA.