The agreement between Monte Carlo simulations and experimental data proved that the evaluated Varian phase-space files for FFF beams from TrueBeam can be used as radiation sources for accurate Monte Carlo dose estimation, especially for field sizes up to 10 × 10 cm(2), that is the range of field sizes mostly used in combination to the FFF, high dose rate beams.

Objective: Quality assurance data from five centres were analysed to assess the reliability of RapidArc radiotherapy delivery in terms of machine and dosimetric performance. Methods: A large group of patients was treated with RapidArc radiotherapy and treatment data recorded. Machine quality assurance was performed according to Ling et al (Int J Radiat Oncol Biol Phys 2008;72:575-81). In addition, treatment to a typical clinical case was delivered biweekly as a constancy check. Pre-treatment dosimetric validation of plan delivery was performed for each patient. All measurements and computations were performed at the depth of the maximum dose in water according to the GLAaS method using electronic portal imaging device measurements. Evaluation was carried out according to a gamma agreement index (GAI, the percentage of field area passing the test); the threshold dose difference was 3% and the threshold distance to agreement was 3 mm. Results: A total of 275 patients (395 arcs) were included in the study. Mean delivery parameters were 31.0¡20.0 u (collimator angle), 4.7¡0.5 u s -1 (gantry speed), 343¡134 MU min -1 (dose rate) and 1.6¡1.4 min (beam-on time) for prescription doses ranging from 1.8 to 16.7 Gy/fraction. Mean deviations from the baseline dose rate and gantry speed ranged from 20.61% to 1.75%. Mean deviations from the baseline for leaf speed variation ranged from 20.73% to 0.41%. The mean GAI of repeated clinical fields was 99.2¡0.2%. GAI varied from 84.7% to 100%; the mean across all patients was 97.1¡2.4%. Conclusion: RapidArc can provide a reliable and accurate delivery of radiotherapy for a variety of clinical conditions.

Background: The management of breath-induced tumor motion is a major challenge for lung stereotactic body radiation therapy (SBRT). Three techniques are currently available for these treatments: tracking (T), gating (G) and free-breathing (FB). Aim: To evaluate the dosimetric differences between these three treatment techniques for lung SBRT. Materials and methods: Pretreatment 4DCT data were acquired for 10 patients and sorted into 10 phases of a breathing cycle, such as 0% and 50% phases defined respectively as the inhalation and exhalation maximum. GTV ph , PTV ph (=GTV ph + 3 mm) and the ipsilateral lung were contoured on each phase. For the tracking technique, 9 fixed fields were adjusted to each PTV ph for the 10 phases. The gating technique was studied with 3 exhalation phases (40%, 50% and 60%). For the free-breathing technique, ITV FB was created from a sum of all GTV ph and a 3 mm margin was added to define a PTV FB. Fields were adjusted to PTV FB and dose distributions were calculated on the average intensity projection (AIP) CT. Then, the beam arrangement with the same monitor units was planned on each CT phase. The 3 modalities were evaluated using DVHs of each GTV ph , the homogeneity index and the volume of the ipsilateral lung receiving 20 Gy (V 20Gy). Results: The FB system improved the target coverage by increasing D mean (75.87 (T)-76.08 (G)-77.49 (FB) Gy). Target coverage was slightly more homogeneous, too (HI: 0.17 (T and G)-0.15 (FB)). But the lung was better protected with the tracking system (V 20Gy : 3.82 (T)-4.96 (G)-6.34 (FB) %). Conclusions: Every technique provides plans with a good target coverage and lung protection. While irradiation with free-breathing increases doses to GTV, irradiation with the tracking technique spares better the lung but can dramatically increase the treatment complexity.

No abstract

BackgroundTo present the results of quality assurance (QA) in IMRT of film dosimetry and ionization chambers measurements with an eight year follow-up.MethodsAll treatment plans were validated under the linear accelerator by absolute and relative measures obtained with ionization chambers (IC) and with XomatV and EDR2 films (Kodak).ResultsThe average difference between IC measured and computed dose at isocenter with the gantry angle of 0° was 0.07 ± 1.22% (average ± 1 SD) for 2316 prostate, 1.33 ± 3.22% for 808 head and neck (h&n), and 0.37 ± 0.62% for 108 measurements of prostate bed fields. Pelvic treatment showed differences of 0.49 ± 1.86% in 26 fields for prostate cases and 2.07 ± 2.83% in 109 fields of anal canal.Composite measurement at isocenter for each patient showed an average difference with computed dose of 0.05 ± 0.87% for 386 prostate, 1.49 ± 1.86% for 158 h&n, 0.37 ± 0.34% for 23 prostate bed, 0.80 ± 0.28% for 4 pelvis, and 2.31 ± 0.56% for 17 anal canal cases. On the first 250 h&n analyzed by film in absolute dose, the average of the points crossing a gamma index 3% and 3 mm was 93%. This value reached 99% for the prostate fields.ConclusionMore than 3500 beams were found to be within the limits defined as validated for treatment between 2001 and 2008.