Study of dosimetric and spatial variations due to applicator positioning during inter-fraction high dose rate brachytherapy in the treatment of carcinoma of the cervix; A three dimensional dosimetric analysis

Background: This study evaluates dosimetric and spatial variations in inter-fraction applicator positioning in high dose rate [HDR] brachytherapy

Materials and Methods: This study includes 25 retrospective patients of carcinoma of the cervix. Each patient received 5 fractions of HDR intracavitary brachytherapy. High Risk-Clinical Target Volume [HR-CTV] were drawn on CT images. First implant was considered as a reference, and all subsequent CT data sets were rigidly registered on first implant's CT data set. Another point A, called point Aabs, was defined on first plan and all subsequent plans. Registration properties were recorded for all 125 plans that include X, Y, Z DICOM offset, rotational, translational values and normalized D90 [ND90] doses were also recorded

Results: The mean angle of rotation on X, Y and Z axis are 0.63 +/- 1.85 deg, -0.86 +/- 1.30 deg, -1.14 +/- 2.44 deg, respectively. While mean translational motion on X, Y and Z axes are -2.77 +/- 10.32 mm, -6.12 +/- 9.71 mm and 14.62 +/-23.83 mm, respectively. Mean ND90, and mean HR-CTV were found to be 1.18 +/- 0.26 and 26.91 +/- 17.70 cc, respectively

Conclusion: Results of the study reveals that translational motion is higher than the rotational motions, and inter - fraction applicator variation does not produce any significant change in Point A doses. The change in volume coverage is observed only due to applicator motion. HR-CTV coverage decreases with increasing HR-CTV volume. Hence, dose prescription should be based on 3D HR-CTV volume?

Accelerated proliferation correction factors in linear-quadratic and multiple-component models

Study in design to incorporate accelerated proliferation correction factors into linearquadratic and multiple-component models. Accelerated proliferation rate correction factor has been incorporated into the linearquadratic and the multiple component models by applying accelerated exponential cell growth to explain the tumor cell kinetics and estimates proper treatment results. Biological effectiveness and tumor control probability, in terms of BED [LQ model], BRD [MC model], TCP[LQ model] and TCP[MC model], were computed for three conventional and two accelerated hyperfractionated radiation therapy treatment schedules with using a range of accelerated proliferation rate constants to demonstrate the effect of the proliferation process. The results of the study show that the accelerated proliferation rate reduces the effectiveness of a treatment schedule delivered in a prolonged period of time. Care should be taken in the selection of a treatment protocol for a patient of head and neck cancer with an account of the cell kinetics of the tumor

3-Dimensional conformal radiotherapy versus intensity modulated radiotherapy for localized prostate cancer: dosimetric and radiobiologic analysis

To analyze the dosimetric and radio biologic advantages between intensity modulated radiotherapy [IMRT] and 3 dimensional conformal radiotherapy [3DCRT] and selection of optimal photon energy for IMRT treatments. 24 patients with localized prostate carcinoma were planned for 3DCRT and IMRT techniques. Radiation dose of 54 Gy with 2 Gy/fraction, was planned to Planning target volume [PTV1] [prostate + seminal vesicle + 1 cm margin] and 72 Gy to PTV2 [prostate + 1 cm margin] respectively. 3DCRT planning was done using 15 MV photon beam while IMRT plans were created using 6 MV and 15MV photons. Treatment plans were analyzed using mean, median, dose maximum and cumulative dose volume histogram for PTV1, PTV2, bladder, and rectum. Tumor control probability [TCP] was calculated for prostate. Normal tissue complication probability [NTCP] was calculated for bladder, rectum, and head of femur. Mean dose to prostate was 72.79 +/- 0.18 Gy for IMRT 15 MV, 72.16 +/- 0.27 Gy for 3DCRT and 72.48 +/- 0.19 Gy for IMRT 6 MV. TCP was greater for IMRT 15 MV followed by IMRT 6 MV. The mean value of NTCP was significantly lower [p = 0.0015] for IMRT 6 MV compared to 3DCRT for rectum while for bladder all were comparable. IMRT techniques shows superiority in sparing surrounding critical organs, thus reducing normal tissue complication rates while maintaining the same or higher tumor control probability. No significant difference was observed between IMRT 6 MV and IMRT 15 MV techniques.