Impact of brachytherapy applicators geometry on dose distribution in gynaecological cancer.

OBJECTIVE: To evaluate the efficacy of suitable applicators for intracavitary brachytherapy to treat cervical cancer. METHODS: This study was conducted at the Bahawalpur Institute of Nuclear Medicine and Oncology, Bahawalpur, Pakistan, in February 2014. Dose distributions for Fletcher and ring applicators were analysed at target points according to recommended protocols using Abacus software. The doses to the organs at risk, i.e. bladder and rectum, were also focused. SPSS 16 was used for data analysis. RESULTS: A total of 40 patients' plans were considered. The mean absorbed dose at target point A was 6.87±0.201Gy in case of Fletcher applicator (p=0.082) and 6.79±0.107Gy in case of ring applicator (p=0.001). Absorbed dose at the target point was significantly higher for the Fletcher type applicators as compared to the ring applicators. However, the amount of doses at bladder and rectum were smaller for the Fletcher applicators. CONCLUSIONS: Fletcher applicator was more effective in achieving a better dose distribution in gynaecological malignancies, resulting in better treatment outcome.

Dose of radiation enhancement, using silver nanoparticles in a human tissue equivalent gel dosimeter.

OBJECTIVE: To quantify the radiation dose enhancement in a human tissue-equivalent polymer gel impregnated with silver nanoparticles. METHODS: The case-control study was conducted at the Bahawalpur Institute of Nuclear Medicine and Oncology, Bahawalpur, Pakistan, in January 2014. Silver nanoparticles used in this study were prepared by wet chemical method. Polymer gel was prepared by known quantity of gelatine, methacrylic acid, ascorbic acid, copper sulphate pentahydrate, hydroquinone and water. Different concentrations of silver nanoparticles were added to the gel during its cooling process. The gel was cooled in six plastic vials of 50ml each. Two vials were used as a control sample while four vials were impregnated with silver nanoparticles. After 22 hours, the vials were irradiated with gamma rays by aCobalt-60 unit. Radiation enhancement was assessed by taking magnetic resonance images of the vials. The images were analysed using Image J software. RESULTS: The dose enhancement factor was 24.17% and 40.49% for 5Gy and 10Gy dose respectively. The dose enhancement factor for the gel impregnated with 0.10mM silver nanoparticles was 32.88% and 51.98% for 5Gy and 10Gy dose respectively. CONCLUSIONS: The impregnation of a tissue-equivalent gel with silver nanoparticles resulted in dose enhancement and this effect was magnified up to a certain level with the increase in concentration of silver nanoparticles.

Evaluation criteria for film based intensity modulated radiation therapy quality assurance.

The aim of this study was to use different gamma histogram criteria for the comparison of planned dose with irradiated dose distribution and find that what percent of pixels passing a certain criteria imitate a good quality plan. The dose was calculated for 156 patients by inverse planning optimization using the Corvus treatment planning system. Gafchromic films in combination with 2571 0.6 cm(3) Farmer type ionization chamber and Farmer 2570/1 electrometer from NE Technology were used to measure the delivered dose in solid water phantom. All the measurements were performed on Varian CL21EX linear accelerator (Varian Medical Systems, Palo Alto, CA) fitted with a Millennium 120 leaf collimator. In this study the mean value of the percent of passing pixels within the region of interest under the criterion of 3% DD and 3mm DTA is 90.2+/-7.1% for head and neck cases and 92.2+/-5.8% for non-head and neck cases. If we choose the criteria of 3% DD and 3mm DTA then 96.3% head and neck plans have the percent of passing pixels>or=75% and 95.1% non-head and neck plans have the percent of passing pixels>or=80%. It is evident from the results of this study that the criterion of 5% DD and 3mm DTA with the percent of passing pixels>or=90 for non-head and neck cases while the percent of passing pixels>or=85 for head and neck cases endorse that a plan is good. The results of this study may be useful for other institutions which use verification software and EBT films for patient specific IMRT QA.

IMRT quality assurance using a second treatment planning system.

We used a second treatment planning system (TPS) for independent verification of the dose calculated by our primary TPS in the context of patient-specific quality assurance (QA) for intensity-modulated radiation therapy (IMRT). QA plans for 24 patients treated with inverse planned dynamic IMRT were generated using the Nomos Corvus TPS. The plans were calculated on a computed tomography scan of our QA phantom that consists of three Solid Water slabs sandwiching radiochromic films, and an ion chamber that is inserted into the center slab of the phantom. For the independent verification, the dose was recalculated using the Varian Eclipse TPS using the multileaf collimator files and beam geometry from the original plan. The data was then compared in terms of absolute dose to the ion chamber volume as well as relative dose on isodoses calculated at the film plane. The calculation results were also compared with measurements performed for each case. When comparing ion chamber doses, the mean ratio was 0.999 (SD 0.010) for Eclipse vs. Corvus, 0.988 (SD 0.020) for the ionization chamber measurements vs. Corvus, and 0.989 (SD 0.017) for the ionization chamber measurements vs. Eclipse. For 2D doses with gamma histogram, the mean value of the percentage of pixels passing the criteria of 3%, 3 mm was 94.4 (SD 5.3) for Eclipse vs. Corvus, 85.1 (SD 10.6) for Corvus vs. film, and 93.7 (SD 4.1) for Eclipse vs. film; and for the criteria of 5%, 3 mm, 98.7 (SD 1.5) for Eclipse vs. Corvus, 93.0 (SD 7.8) for Corvus vs. film, and 98.0 (SD 1.9) for Eclipse vs. film. We feel that the use of the Eclipse TPS as an independent, accurate, robust, and time-efficient method for patient-specific IMRT QA is feasible in clinic.