Analysis of fetal dose using Optically Simulated Luminescence Dosimeter and ion chamber in randophantom for various radiotherapy techniques.

To analyse the fetal dose in all three trimesters in patients treated for brain tumors during pregnancy, a modified rando phantom representing three different trimesters was used with provisions for insertion of ion-chamber and Optically Simulated Luminescence Dosimeter (OSLD). The measurement regions were chosen at the level of fundus, umbilicus and pubis. Seven different treatment plans with 6FF and 6FFF beam energies were generated. Treating pregnant patients with brain tumors is safe irrespective of planning modalities except 3DCRT plan where the dose is 10.24 cGy.

Dosimetric evaluation of hybrid and volumetric-modulated arc therapy plan for left-sided chest wall irradiation in MONACO treatment planning system.

Background and Objective: Radiation induced toxicities in heart and lungs are diminishes the survival rate of cancer patients. The purpose of this study is to evaluate the dosimetric parameters of hybrid plans for chest wall irradiation of left breast carcinoma patients using Monaco treatment planning system and compare with the volumetric-modulated arc therapy (VMAT) treatment plans. Materials and Methods: Fifteen carcinoma left breast patients were randomly selected to evaluate the advantage of hybrid plan over VMAT. Hybrid plans were generated with 70% and 30% dose contribution from forward intensity-modulated radiotherapy and VMAT, respectively, whereas VMAT had been done with full prescription. Conformity and homogeneity indices were evaluated for target coverage between hybrid and VMAT plans. Results: Hybrid plan has proved its superiority over VMAT in terms of better organ at risk sparing and lesser low dose spillage and at the same time providing comparable target coverage. In low-dose spectrum, VMAT showed higher dose-volume than the hybrid plan. The maximum variation was found to be 44.75% at 7 Gy and the minimum dose difference was observed at 1 Gy (6.02%). Conclusion: This study suggests that the hybrid plan could be a better option for left-sided chest wall irradiation in regular clinical practice.

Dose Estimation Using Optically Stimulated Luminescence Dosimeter and EBT3 Films for Various Treatment Techniques in Alderson Rando Phantom and Estimation of Secondary Cancer Incidence for Carcinoma of Left Breast.

Aim: The aim of this study was to measure the dose to planning target and organ at risk (OAR) using Alderson Rando phantom for various treatment techniques in left breast radiotherapy and to estimate the secondary cancer incidence. Materials and Methods: Eleven different combinations of plans containing four techniques (three dimensional conformal radiotherapy, intensity-modulated radiation therapy [IMRT], volumetric modulated arc therapy [VMAT], and combination of 3DCRT and VMAT plans (HYBRID)) were created with 6 MV FF and 6 MV FFF (flattening filter and flattening filter-free) photon energies in phantom. Planned target volume and OAR doses in 23 different locations were measured using optically stimulated luminescence dosimeter (OSLD) and EBT3 films. Assuming the age of exposure as 30 years, lifetime attributable risk (LAR) was estimated based on excess absolute risk (EAR) models outlined in the Biological Effects of Ionizing Radiation VII report. Results: Film showed maximum deviations of 6.15% with IMRT_C_FF plan when compared with treatment planning system (TPS). The maximum percentage difference of 1.7% was found with OSLD measurement when compared with TPS for VMAT_T_FFF plan. EAR estimation was done for all the OARs including target. The LARs for left lung, right lung, and right breast were evaluated. The maximum LAR values of 2.92 ± 0.14 were found for left lung with VMAT_C_FFF plans. Conclusion: This study shows that both OSLD and EBT3 films are suitable for dose measurements using Rando phantom. OSLD shows superior results when compared with films, especially with relatively larger distances. Maximum LAR values were found with VMAT_C_FFF plans. Considering the secondary cancer risk associated with the patients treated in the younger age group, it is suggested that in vivo dose estimation should be a part of treatment quality audit whenever possible.

Application of bi-nanoparticle on dose enhancement effect in two different polymer gel dosimeter using spectrophotometer.

PURPOSE: This study aimed at proving the ability of bismuth-nanoparticle (Bi-np) in dose enhancement effect (DEE) using the polymer gel dosimeter. Two different polymer gels, namely poly acrylamide gelatin tetrakis hydroxymethyl phosphonium chloride (PAGAT) and N-isopropylacrylamide (NIPAM) gels were chosen for this study. MATERIALS AND METHODS: The gels were doped with Bi-np particle with various concentrations of 0.5 mM, 1 mM, and 2.5 mM and were then irradiated with a CO-60 gamma radiation source of energy 1.25 MeV. Gel samples were analyzed by spectrophotometer. The dose enhancement factor (DEF) was calculated for both gels for all concentrations of Bi-np particle. RESULTS: The higher DEF for PAGAT and NIPAM was calculated as 1.3415 and 1.1823, respectively, for 0.5 mM concentration of Bi-np. CONCLUSION: From our results, we infer that 0.5 mM is the optimal concentration in polymer gel to obtain good DEEs in the energy range of 1.25 MeV.

Dose rate and energy dependence study of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride gel with flattened and unflattened photon beams.

AIMS: The aim of this study is to evaluate the dose rate and energy dependency of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride (MAGAT) gel in unflattened photon beam using X-ray computed tomography (CT) and ultraviolet (UV)-visible spectroscopy. MATERIALS AND METHODS: MAGAT gel was prepared and it was exposed to 6 MV flattened and unflattened beams. The dose selected for irradiation was ranging from 3 to 15 Gy with an increment of 3 Gy. The dose rate dependency of the gel was investigated by exposing the gel to three different dose rates of 250, 500, and 1500 cGy/min for flattening filter free (FFF). To verify the energy dependency of the gel, it was exposed by both FFF and flattening filter (FF) for constant dose rate (250 cGy/min) and different energy (6 and 10 MV X-ray photons). The exposed gels were scanned by X-ray CT and UV-visible spectrophotometer. RESULTS: The change in dose sensitivity observed over the dose rate from 250 cGy/min to 1500 cGy/min was 58.00% and 57.89% using a UV-visible spectrophotometer and X-ray CT analysis method. Energy dependency was evaluated with respect to dose sensitivity and the variation between 6 MV FF and FFF photon beams was found to be 2.20% and 2.21% using UV-visible spectrophotometer analysis and X-ray CT, respectively. Similarly, the variation noticed with 10 MV FF and FFF was 2.30% using UV-visible spectrophotometer analysis and 2.22% using X-ray CT analysis. CONCLUSIONS: The results clearly show that the MAGAT gel was highly dose rate-dependent and less dependent on energy. The beam quality variation between FF and FFF was less. The similar results obtained using X-ray CT scanner and UV-visible spectrophotometer indicate that this study can be recommended for polymer gel scanning procedure.