A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques.

Objective: The aim of this study is to implement a new treatment technique in total body irradiation (TBI) using the manual field-in-field-TBI (MFIF-TBI) technique and dosimetrically verifying its results with respect to compensator-based TBI (CB-TBI) and open field TBI technique. Materials and Methods: A rice flour phantom (RFP) was placed on TBI couch with knee bent position at 385 cm source to surface distance. Midplane depth (MPD) was calculated for skull, umbilicus, and calf regions by measuring separations. Three subfields were opened manually for different regions using the multi-leaf collimator and jaws. The treatment Monitor unit (MU) was calculated based on each subfield size. In the CB-TBI technique, Perspex was used as a compensator. Treatment MU was calculated using MPD of umbilicus region and the required compensator thickness was calculated. For open field TBI, treatment MU was calculated using MPD of umbilicus region, and the treatment was executed without placing compensator. The diodes were placed on the surface of RFP to measure the delivered dose and the results were compared. Results: The MFIF-TBI results showed that the deviation was within ± 3.0% for the different regions, except for the neck for which the deviation was 8.72%. In the CB-TBI delivery, the dose deviation was ± 3.0% for different regions in the RFP. The open field TBI results showed that the dose deviation was not within the limit ± 10.0%. Conclusion: The MFIF-TBI technique can be implemented for TBI treatment as no TPS is required, and laborious process of making a compensator can be avoided while ensuring that the dose uniformity in all the regions within the tolerance limit.

Quality assurance of dynamic parameters in volumetric modulated arc therapy.

OBJECTIVES: The purpose of this study was to demonstrate quality assurance checks for accuracy of gantry speed and position, dose rate and multileaf collimator (MLC) speed and position for a volumetric modulated arc treatment (VMAT) modality (Synergy S; Elekta, Stockholm, Sweden), and to check that all the necessary variables and parameters were synchronous. METHODS: Three tests (for gantry position-dose delivery synchronisation, gantry speed-dose delivery synchronisation and MLC leaf speed and positions) were performed. RESULTS: The average error in gantry position was 0.5° and the average difference was 3 MU for a linear and a parabolic relationship between gantry position and delivered dose. In the third part of this test (sawtooth variation), the maximum difference was 9.3 MU, with a gantry position difference of 1.2°. In the sweeping field method test, a linear relationship was observed between recorded doses and distance from the central axis, as expected. In the open field method, errors were encountered at the beginning and at the end of the delivery arc, termed the "beginning" and "end" errors. For MLC position verification, the maximum error was -2.46 mm and the mean error was 0.0153 ±0.4668 mm, and 3.4% of leaves analysed showed errors of >±1 mm. CONCLUSION: This experiment demonstrates that the variables and parameters of the Synergy S are synchronous and that the system is suitable for delivering VMAT using a dynamic MLC.

Relative dosimetrical verification in high dose rate brachytherapy using two-dimensional detector array IMatriXX.

For high dose rate (HDR) brachytherapy, independent treatment verification is needed to ensure that the treatment is performed as per prescription. This study demonstrates dosimetric quality assurance of the HDR brachytherapy using a commercially available two-dimensional ion chamber array called IMatriXX, which has a detector separation of 0.7619 cm. The reference isodose length, step size, and source dwell positional accuracy were verified. A total of 24 dwell positions, which were verified for positional accuracy gave a total error (systematic and random) of -0.45 mm, with a standard deviation of 1.01 mm and maximum error of 1.8 mm. Using a step size of 5 mm, reference isodose length (the length of 100% isodose line) was verified for single and multiple catheters of same and different source loadings. An error ≤1 mm was measured in 57% of tests analyzed. Step size verification for 2, 3, 4, and 5 cm was performed and 70% of the step size errors were below 1 mm, with maximum of 1.2 mm. The step size ≤1 cm could not be verified by the IMatriXX as it could not resolve the peaks in dose profile.

Dosimetric verification of brain and head and neck intensity-modulated radiation therapy treatment using EDR2 films and 2D ion chamber array matrix.

BACKGROUND: The evaluation of the agreement between measured and calculated dose plays an essential role in the quality assurance (QA) procedures of intensity-modulated radiation therapy (IMRT). AIM: The purpose of this study is to compare performances of the two dosimetric systems (EDR2 and I'matriXX) in the verification of the dose distributions calculated by the TPS for brain and head and neck dynamic IMRT cases. MATERIALS AND METHODS: The comparison of cumulative fluence by using Kodak extended dose rate (EDR2) and I'matriXX detectors has been done for the evaluation of 10 brain, 10 head and neck IMRT cases treated with 6 MV beams. The parameter used to assess the quality of dose calculation is the gamma-index (g -index) method. The acceptance limits for g calculation we have used are 3% and 3 mm respectively for dose agreement and distance to agreement parameters. Statistical analyses were performed by using the paired, two-tailed Student t-test, and P< 0.01 is kept as a threshold for the significance level. RESULTS: The qualitative dose distribution comparison was performed using composite dose distribution in the measurement plane and profiles along various axes for TPS vs. EDR2 film and TPS Vs I'matriXX. The quantitative analysis between the calculated and measured dose distribution was evaluated using DTA and g-index. The percentage of pixels matching with the set DTA and g values are comparable for both with EDR2 film and I'matriXX array detectors. Statistically there was no significant variation observed between EDR2 film and I'matriXX in terms of the mean percentage of pixel passing g for brain cases (98.77 +/- 1.03 vs 97.62 +/- 1.66, P = 0.0218) and for head and neck cases (97.39 +/- 2.13 vs 97.17 +/- 1.52%, P = 0.7404). CONCLUSION: Due to simplicity and fast evaluation process of array detectors, it can be routinely used in busy departments without compromising the measurement accuracy.