Plan quality score to evaluate the dwell time deviation restricted inverse planning by simulated annealing and graphically optimized treatment plans for template based interstitial brachytherapy.

PURPOSE: To evaluate the impact of dwell time deviation constraint (DTDC) on the quality of IPSA-optimized treatment plans in comparison with graphical plans using plan quality scores (PQS). MATERIAL AND METHODS: Seventy optimized plans (graphical & IPSA with different DTDC values) of ten cervical cancer patients were generated. Various DVH parameters like D90, V100, V150, V200, V300 were compared to evaluate the impact of DTDC on target coverage and high dose regions inside target for different plans. Similarly, for the OAR dose, values of D2cc were compared. Various planning parameters like CI, COIN, DHI, DNR, ODI, EI and gain factor (GF) for different OARs were calculated. Based on these indices a plan quality score (PQS) was formulated and calculated. PQS values were used to see the impact of DTDC on plan quality of IPSA in comparison with dosimetric quality of graphical plan. RESULTS: We have found that target coverage is similar for IPSA and graphically optimized treatment plans. However, dose homogeneity was improved in IPSA compared to graphical optimization whereas conformality was better in graphically optimized plans. OAR dose was less in IPSA plans. High-dose regions inside the target were also reduced in IPSA comparatively. However, IPSA plans optimized with various values of DTDC did not necessarily reduce high-dose regions beyond 0.6. Plan quality scores (PQS) were 6.31, 6.31, 6.34, and 6.17 for the graphically optimized plan, IPSA with DTDC values of 0.0, 0.4, and 1.0 respectively. CONCLUSION: We found that IPSA is dosimetrically advantageous over graphical optimization. IPSA with a DTDC value of 0.4 improved overall plan quality. However, DTDC value beyond 0.6 produces dosimetrically sub-optimal plans hence the use of DTDC should be very selective and limited.

Monte Carlo Study of Unflattened Photon Beams Shaped by Multileaf Collimator.

INTRODUCTION: This study investigates basic dosimetric properties of unflattened 6 MV photon beam shaped by multileaf collimator and compares them with those of flattened beams. MATERIALS AND METHODS: Monte Carlo simulation model using BEAM code was developed for a 6MV photon beam based on Varian Clinic 600 unique performance linac operated with and without a flattening filter in beam line. Dosimetric features including lateral profiles, central axis depth dose, photon and electron spectra were calculated for flattened and unflattened cases, separately. RESULTS: An increase in absolute depth dose with a factor of more than 2.4 was observed for unflattened beam which was dependent on depth. PDDs values were found to be lower for unflattened beam for all field sizes. Significant decrease in calculated mlc leakage was observed when the flattening filter was removed from the beam line. The total scatter factor, SCP was found to show less variation with field sizes for unflattened beam indicating a decrease in head scatter. The beam profiles for unflattened case are found to have lower relative dose value in comparison with flattened beam near the field edge, and it falls off faster with distance. CONCLUSION: Our study showed that increase in the dose rate and lower peripheral dose could be considered as realistic advantages for unflattened 6MV photon beams.

Age-related changes in the elemental constituents and molecular behaviour of bone.

Age-related changes in bone composition within the age groups of 30, 60, 120 and 180 days in rats have been studied using thermogravimetery, elemental analysis and energy dispersive Xray (ED X-ray). The structural changes in rats the bone samples were monitored by IR spectroscopy. The main constituents of hydroxyapatite, namely Ca, P and their oxides were analyzed. Organic changes, such as C and N contents in the matrix were found to have a predominant role in the initial development of the bone. An incremental increase in the mineral content of bone with advancing age was also observed. Elemental composition (C and N contents) was observed to be independent of age at the initial stages. The amount of Ca and its oxide content was found to increase, and the P and its oxides showed a decreasing trend, with the advancing age. IR spectra revealed that the mineral phase comprised both amorphous and crystalline hydroxyapatite, even at maturity; the amorphous content being higher at the earlier stages (14.09%, at 30 days), but was gradually replaced by crystalline component with advancing age (63.09% at 180 days). The present data may be useful in explaining the ageing phenomenon and helpful in understanding the bone growth and remodeling.