OBJECTIVE The end-to-end (E2E) testing method enables understanding the difficulties and uncertainties in treating any specific case type. This study was focused on bilateral metallic implant cases. METHODS The study was performed on a cylindrical phantom of Perspex with holes for implant inserts. Two stainless steel metal rods of 7.5-8.0 g/cc mass density were inserted in the phantom. The ionization chamber CC13 was kept at a 5 cm depth in the phantom. The phantom was scanned on a computed tomography simulator in pelvis protocol with a 1mm slice thickness. The scans were imported to the contouring station without applying artifacts correction. Chamber volume was contoured as gross tumor volume (GTV); margin to GTV, clinical target volume, and planning target volume were created. Four isocentric plans (Conventional, three-dimensional conformal radiotherapy[3D-CRT], intensity-modulated radiotherapy [IMRT], and volumetric-modulated radiotherapy [VMAT]) were generated for two LinacsTruebeam (TB)-sTx and 2300-CD. The conventional plan was a single anterior field, 3D-CRT was four field box techniques, IMRT was seven field plan, and VMAT was with two complete arc. Pre-treatment verification was done using CBCT. Four plans were created on helical tomotherapy with different prescriptions and delivered using MVCT guidance. RESULTS In conventional plans, variations were -1.40%, -1.57%, and for 3DCRT, variations were -5.08% and -4.93%, for IMRT, the differences between measured and TPS doses were 1.84 % and -1.55% for VMAT plans, and the variations were 0.68% and -0.88% for TB and 2300-CD, respectively. The tomotherapy plans with gradient showed deviations more significant than 3%. Similarly, the variations for single prescription plans were within 3%. CONCLUSION The phantom design used in the test provided a comprehensive understanding of simulation and delivery problems.

Purpose: To study the impact of different optimization methods in dealing with metallic hip implant using intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques. Materials and Methods: A cohort of 16 patients having metallic implants was selected for the study. Three sets of IMRT and VMAT plans were generated. Set 1 IMRT (IM_Base), VMAT (VM_Base) without any restrictions on beam entry and exit, set 2 (IM_ENT and VM_ENT) optimizer restricts the beam entry and set 3 (IM_EXT+ENT), neither entry nor exit doses were allowed toward the metallic implant. Results: There was no significant difference in target (D95%) and organ-at-risk doses between IM_Base and IM_ENT. There were significant (P = 0.002) improvements in planning target volume (PTV) V95% and homogeneity from IM_EXT+ENT to IM_ENT. There was no significant difference in plan quality between VM_Base and VM_ENT. There were significant (P = 0.005) improvements in PTV, V95%, homogeneity from VM_EXT+ENT to VM_ENT. V40Gy, V30Gy for bladder, rectum, bowel, and bowel maximum dose decreases significantly (P < 0.005) in IM_ENT compared to IM_EXT+ENT, but not significant for VMAT plans. Similarly, there was a significant decrease in dose spill outside target (P < 0.05) comparing 40%, 50%, 60%, and 70% dose spills for IM_ENT compared to IM_EXT+ENT, but variations among VMAT plans are insignificant. VMAT plans were always superior to IMRT plans for the same optimization methods. Conclusion: The best approach is to plan hip prosthesis cases with blocked entry of radiation beam for IMRT and VMAT. The VMAT plans had more volumetric coverage, fewer hotspots, and lesser heterogeneity.

Purpose/Objective(s) Hypofractionated EBRT is beneficial in localized prostate cancer in view of the low alpha by beta ratio of prostate cancer cells, however, the role of elective nodal irradiation with the hypofractionated regimen is not well established, as concern regarding toxicity with hypofractionated nodal irradiation remains. Materials/Methods Patients with Carcinoma prostate were prospectively selected for treatment with hypofractionated EBRT. Patients with high-risk prostate cancer (T3a-T3b, GS>/= 8, PSA>20ng/ml) with an estimated risk of nodal involvement > 30% were radically treated with 60Gy and 44 Gy in 20 fractions to the primary and elective nodal area, respectively. Similarly, postoperative patients with high-risk features (pT3a-T3b, GS>/=8, estimated risk of nodal involvement >30%) were treated with early salvage EBRT, upon two consecutive rises of serum PSA above 0.1ng/ml. The dose prescribed was 52.5Gy and 44Gy in 20 fractions to primary bed and elective nodal area, respectively. Contouring for radical and salvage EBRT was done as per CHHiP and RADICALS RT protocol, respectively. Nodal volume was contoured as per the RTOG contouring guideline. Acute toxicities were recorded during and 6 months after treatment, as per RTOG grading criteria. All patients were treated with IMRT or VMAT plan. All patients received concurrent & adjuvant hormonal therapy. Results Between 1st January 2020 to 30th June 2021, 26 patients were treated with the hypofractionated regimen and elective nodal irradiation, of which 14 patients (54%) received radical EBRT and 12 patients (46%) received early salvage EBRT. The median age of patients was 66 years. Patients were prospectively followed up with a median follow-up period of 12 months. For patients treated with radical EBRT, D95% to primary PTV was 60.06 Gy (Median, IQ range 59.8-60.2Gy) and D95% to nodal PTV was 44.1 Gy (Median, IQ range 43.7-44.3Gy). V48Gy of Bladder was 23.2% (Median, IQ range 21.5-26.6%). V40Gy for bowel bag was 112cc (Median, IQ range 90-145cc). Similarly in patients receiving early salvage EBRT, D95% to primary bed was 51.5Gy (Median, IQ range 51.2-51.7 Gy), D95% to the nodal area was 43.9Gy (Median, IQ range 43.1-44.5 Gy). V48Gy of bladder was 38% (Median, IQ range 28-47.6%) and V40Gy for bowel bag was 210cc (Median, IQ range 123-253cc). Overall, 5 patients (19%) had grade 2 genitourinary toxicities and 6 patients (23%) had grade 2 bowel toxicity. No patients experienced grade 3 or 4 bowel and bladder toxicity. Historical data for grade 2 or more acute bowel and bladder toxicities were 38% and 49% respectively in the CHHiP trial, which used IMRT plan for only 30% of patients. No patient in our study had a biochemical recurrence in the short follow-up period. Conclusion Hypofractionated elective nodal irradiation can be safely delivered in high-risk prostate cancer patients without any undue increase in acute bowel and bladder toxicities.

Purpose: This study was designed to investigate the dosimetric difference between intensitymodulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in head and neck cancer (HNC).The study primarily focuses on low-dose spillage evaluation between these two techniques.Methods: This retrospective study involved 45 patients with HNC.The treatment plans were generated using the IMRT and VMAT techniques for all patients.Dosimetric comparisons were performed in terms of target coverage, organ-at-risk (OAR) sparing, and various parameters, including conformity index, uniformity index, homogeneity index, conformation number, low-dose volumes, and normal tissue integral dose (NTID).Results: No significant (P>0.05)difference in planning target volume coverage (D 95% ) was observed between IMRT and VMAT plans for supraglottic larynx, hard palate, and tongue cancers.A decrease in dose volumes ranging from 1 Gy to 30 Gy was observed for VMAT plans compared with those for IMRT plans, except for V 1Gy and V 30Gy for supraglottic larynx cancer and V 1Gy for tongue cancer.Moreover, decreases (P<0.05) in NTID were observed for VMAT plans compared with that for IMRT plans in supraglottic larynx (4.50%), hard palate (12.80%), and tongue (7.76%) cancers.In contrast, a slight increase in monitor units for VMAT compared with those for IMRT in supraglottic larynx (0.46%), hard palate (2.54%), and tongue (7.56%) cancers. Conclusions:For advanced-stage HNC, both IMRT and VMAT offer satisfactory clinical plans.VMAT offers a conformal and homogeneous dose distribution with comparable OAR sparing and higher dose falloff outside the target volume than IMRT, which provides an edge to reduce the risk of secondary malignancies for HNC over IMRT.

AIM:To investigate the impact of Acuros XB (AXB) algorithm in the deep-inspiration breath-hold (DIBH) technique used for treatment of left sided breast cancer.BACKGROUND:AXB may estimate better lung toxicities and treatment outcome in DIBH.MATERIALS AND METHODS:Treatment plans were computed using the field-in-field technique for a 6 MV beam in two respiratory phases - free breathing (FB) and DIBH. The AXB-calculations were performed under identical beam setup and the same numbers of monitor units as used for AAA-calculation.RESULTS:Mean Hounsfield units (HU), mass density (g/cc) and relative electron density were -782.1 ± 24.8 and -883.5 ± 24.9; 0.196 ± 0.025 and 0.083 ± 0.032; 0.218 ± 0.025 and 0.117 ± 0.025 for the lung in the FB and DIBH respiratory phase, respectively. For a similar target coverage (p > 0.05) in the DIBH respiratory phase between the AXB and AAA algorithm, there was a slight increase in organ at risk (OAR) dose for AXB in comparison to AAA, except for mean dose to the ipsilateral lung. AAA predicts higher mean dose to the ipsilateral lung and lesser V20Gy for the ipsilateral and common lung in comparison to AXB. The differences in mean dose to the ipsilateral lung were 0.87 ± 2.66 % (p > 0.05) in FB, and 1.01 ± 1.07% (p < 0.05) in DIBH, in V20Gy the differences were 1.76 ± 0.83% and 1.71 ± 0.82% in FB (p < 0.05), 3.34 ± 1.15 % and 3.24 ± 1.17 % in DIBH (p < 0.05), for the ipsilateral and common lung, respectively.CONCLUSION:For a similar target volume coverage, there were important differences between the AXB and AAA algorithm for low-density inhomogeneity medium present in the DIBH respiratory phase for left sided breast cancer patients. DIBH treatment in conjunction with AXB may result in better estimation of lung toxicities and treatment outcome.

Management of Locally advanced cervical cancer (LACC) includes use of concurrent chemoradiation followed by high-dose-rate (HDR) brachytherapy boost. Aim is to deliver a cumulative EQD2 dose of 80-90Gy to primary tumor using brachytherapy after an external beam radiotherapy (EBRT) dose of 45Gy. However, dose to pelvic nodes is less certain with brachytherapy. This brings us to the question as to how much preceding EBRT dose should be considered adequate in order to eradicate gross nodal disease. Aim of the present study was to quantify the dosimetric contribution of image-based HDR intracavitary brachytherapy (ICRT) to pelvic lymphnodes. Between June 2018 and December 2018, thirty consecutive patients diagnosed with locally advanced squamous cell carcinoma cervix with pelvic nodes were enrolled in prospective observational study conducted at a tertiary cancer center in North India. All patients had previously received EBRT by intensity modulated radiotherapy (IMRT) to a dose of 45Gy/25# to planning target volume (PTV) whole pelvis with 55Gy/25# simultaneous integrated boost (SIB) to PTV gross nodal disease, followed by three fractions of Image guided brachytherapy to a dose of 7.5Gy/# to high risk CTV (HRCTV). CT-based brachytherapy planning was done and IV contrast administered for image acquisition. Pelvic nodal groups including right/left external iliac (EI), internal iliac (II), obturator and presacral lymph node groups in addition to HRCTV/IRCTV were delineated on each planning CT-scan for each session using Institutional contouring guidelines. Brachytherapy planning was done on treatment planning system (TPS) and dose volume histogram for HRCTV, nodal groups and organ at risk (OAR) was generated. Standard loading distribution was used with alterations made depending upon target volume coverage and OAR dose. Mean dose, D100%, D90%, D50%, D0.1cc, D1cc and D2cc were recorded for each pelvic nodal group and their equivalent dose in 2Gy/# (EQD2) were calculated. Contribution of ovoids and tandem to point B was noted and its value correlated with pelvic nodal dose. All patients had 3 sessions of brachytherapy (Total 90 sessions). HRCTV volume received a mean D90% dose of 7.24Gy±0.31Gy per fraction. Highest dose was received by obturator group of nodes from brachytherapy. Mean dose (Gy) per fraction to EI (Right 0.77+/-0.33, Left 0.86+/-0.33), II (Right 1.03+/- 0.30, Left 1.34+/-0.36), Obturator (Right 1.69+/-0.42, Left 1.74+/-0.59) and presacral nodes (1.10+/-0.50). Corresponding EQD2 value/# was EI (Right 0.69, Left, 0.78), II (Right 0.95, Left 1.27), Obturator (Right 1.65, Left 1.70) and presacral nodes (1.02) respectively. Significant difference existed between point B dose and DVH parameters of pelvic nodes. Pelvic lymph nodes tend to receive an appreciable dosimetric contribution from brachytherapy and this fact must be considered while planning EBRT boost to gross nodal disease.

Aim: Aim of the present study was to compare the dosimetric impact of different photon beam energies and number of arcs in the treatment of carcinoma cervix. Background: Carcinoma cervix is a common cancer in women worldwide with a high morbidity rate. Radiotherapy is used to treat such tumours. Volumetric Modulated Arc Therapy (VMAT) is considered superior to other techniques with multiple arcs and energies. Materials and methods: Twenty patients with carcinoma cervix underwent radiotherapy in a prospective observation study conducted at our institute. Volumetric modulated arc plans with 6 MV, 10 MV and 15 MV photon energies using single arc (SA) and dual arc (DA) were generated. Several physical indices for planning target volume (PTV) like V95%, V100%, V110%, D98%, D50%, D2 and total number of MUs were compared. Normal Tissue Integral Dose (NTID) and dose to a shell structure PHY2 5 and PHY50 were analyzed. Results: Comparable dose coverage to PTV was observed for all the energies and arcs. CI for DA6mv (1.095) was better than SA6mv (1.127), SAmmv (1.116) and SABmv (1.116). Evaluated parameters showed significant reduction in OAR doses. Mean bladder dose for DA6mv (41.90 Gy) was better than SA6mv (42.48 Gy), SAmmv (42.08 Gy) and SABmv (41.93 Gy). Similarly, p-value for the mean rectal dose calculated was 0.001 (SA6 vs 15), 0.013 (DA6,10) and 0.003 (DA6 vs is) and subsequently favoured DA6mv. Difference in NTID was very small. Conclusions: The study showed no greater advantage of higher energy, and DA VMAT plan with 6 MV photon energy was a good choice of treatment for carcinoma cervix as it delivered a highly homogeneous and conformal plan with superior target coverage and better OAR sparing. (C) 2016 Greater Poland Cancer Centre. Published by Elsevier Sp. z o.o. All rights reserved.

_____________________________________________________________________________________________________Gy in 28 fractions.Plans were evaluated based on the ability to meet the dose volume histogram.The homogeneity index (HI), conformity index (CI) of target volume, the dose of organs at risk, radiation delivery time and monitor units were also compared.Paired T-test model analysis was used to analyse the two sets of data. Results:The results showing that postoperative endometrial carcinoma can be implemented CDR-CAS-IMAT plans on conventional Varian 23EX Linac for smoothly and quickly at busy cancer center.Comparing with the IMRT techonology CDR-CAS-IMAT plans can meet the clinical demand(see Figure1), gives comparable OAR and improved CI of PTV (see.Table 1), can reduction treatment time ((84.6±7.8)sVs. (422.7±46.7)s),MU((787.5±78.5)MUVs.(927.4±79.1)MU)and high dose irradiated volume; while increase the low dose irradiated volume of healthy tissues and the volume of the bladder and bowel irradiated 40 Gy and 30Gy, respectively.This point needs to pay attention to implementation in clinical.There were no significant differences in other statistical index.Conclusion: Endometrial carcinoma patients with CDR-CAS-IMAT on Varian Clinical 23IX can get equivalent or superior dose distribution compared with the IMRT technology.CDR-CAS-IMAT have much less treatment time and MU can reduce the uncertainty factor and patient discomfort in treatment.

The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs.

Aim: To measure and compare the head scatter factor for 7 MV unflattened and 6 MV flattened photon beam using a home-made designed mini phantom.Background: The head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators.Materials and methods: A columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10 cm and d max dose water equivalent thickness.Results: The Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6-2.2% (Primus), 0.2-1.4% (Artiste) and 0.6-3.7% (Clinac iX (2300CD))) for field sizes ranging from 10 cm x 10 cm to 40 cm x 40 cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF.Conclusions: There were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10 cm x 10 cm to 40 cm x 04 cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms. (C) 2015 Greater Poland Cancer Centre. Published by Elsevier Sp. z o.o. All rights reserved.

Purpose:Aim of this study is to determine the dosimetric influence of Filtered and Flatting Filter Free Photon Beam of 10 MV energy on RA planning for Ca. Cervix.Methods:CT data sets of eleven patients reported with carcinoma cervix were used for RA planning for 10MV _FFB and 10MV_FFFB. RA plans were generated using two full arcs.All RA plans were generated to deliver a dose of 50.4Gy in 28 fractions for PTV and ALARA for OAR's. All plans were analysed for PTV Coverage, conformity Index, homogeneity index, dose to OAR's, integral dose to normal tissue and total monitor units were studied.Results:DVH was used to evaluate RA plans for both 10MV_FFB and 10MV_FFFB photon beam. Planning results show a comparable PTV coverage for both energies. Results shows volume of PTV receiving prescription dose were 95.10+ 0.09% and 95.09 +0.11%, and volume of PTV receiving a dose of 107% is 0.45+0.96% and 5.25+8.9%, homogeneity index (HI) were 1.051+0.007 and 1.066+0.008, Conformity Index(CI) were 1.003+0.019 and 1.012+0.013, Mean Integral dose were 2.65+0.34 and 2.60+0.33(*10−5Gy.cm3) for 10MV_FFB and 10MV_FFFB respectively. 10MV_FB shows statistically significant (p<0.05) improvement in mean doses to bladder, rectum, bowel and mean total number of MU's and also shows remarkable decrease in mean total no. of MU's by 43.7% in comparison to 10MV_FFFB. There is statistically significant (p<0.05) difference found in CI and HI for 10MV_FB in comparison to 10MV _FFF beam. 10MV_FFFB shows statistically significant (p<0.05) for mean NTID and delivers 1.65 % less NTID in comparison to 10 MV_ FB.Conclusion:10MV_FB is superior to 10MV_FFFB for rapid arc planning in case of Cervix carcinomas, it offers better target coverage and OAR's sparing, comparable mean Integral dose to normal tissues and 10 MV_ FB also produced highly conformal and homogeneous dose distribution in comparison to 10MV_FFFB.

The main purpose of this study is to know the effect of three different photon energies viz., 6, 10, and 15 mega voltage (MV) on RapidArc (RA) planning for deep-seated cervix tumor and to develop clinically acceptable RA plans with suitable photon energy. RA plans were generated for 6, 10, and 15 MV photon energies for twenty patients reported with cervix carcinoma. RA plans were evaluated in terms of planning target volume (PTV) coverage, dose to organs at risk (OARs), conformity index (CI), homogeneity index (HI), gradient measure, external volume index of dose distribution produced, total number of monitor units (MUs), nontumor integral dose (ID), and low dose volume of normal tissue. A two-sample paired t-test was performed to compare the dosimetric parameters of RA plans. Irrespective of photon energy used for RA planning, plans were dosimetrically similar in terms of PTV coverage, OARs sparing, CI and HI. The numbers of MUs were 13.4 ± 1.4% and 18.2 ± 1.5% higher and IDs were 2.7 ± 0.8% and 3.7 ± 0.9% higher in 6 MV plans in comparison to that in the 10 and 15 MV plans, respectively. V1Gy, V2Gy, V3Gy, and V4Gywere higher in 6 MV plans in comparison to that in 10 and 15 MV plans. Based on this study, 6 MV photon beam is a good choice for RA planning in case of cervix carcinoma, as it does not deliver additional exposure to patients caused by photoneutrons produced in high energy beams.

Purpose:The objective of this work is to evaluate and compare Large field IMRT and RapidArc planning for Carcinoma Cervix and Para‐aotic node irradiation.Methods:In this study, ten patients of Cervix with para‐aotic node have been selected with PTV length 35+2cm. All plans were generated in Eclipse TPS V10.0 with Dynamic IMRT and RapidArc technique using 6MV photon energy. In IMRT planning, 7 fields were chosen to get optimal plan and in RapidArc, double Full arc clockwise and counter clockwise were used for planning. All the plans were generated with single isocenter and calculated using AAA dose algorithm. For all the cases the prescribed dose to PTV was same and the plan acceptance criteria is; 95% of the PTV volume should receive 100% prescribed dose. The tolerance doses for the OAR's is also taken in to account. The evaluation criteria used for analysis are; 1) Homogeneity Index, 2) Conformity Index, 3) Mean Dose to OAR's, 4)Total monitor units delivered.Results:DVH analysis were performed for both IMRT and RapidArc planning. In both the plans, 95% of PTV volume receives prescribed dose and maximum dose are less than 107%. The conformity index are same in both the techniques. The mean Homogeneity index are 1.036 and 1.053 for IMRT and RapidArc plan. The mean (mean + SD) dose of bladder and rectum in IMRT is 44.2+1.55, 42.05+2.52 and RapidArc is 46.66+1.6, 44.2+2.75 respectively. There is no significant difference found in Right Femoral head, Left Femoral head and Kidney doses. It is found that total MU's are more in IMRT compared with RapidArc planning.Conclusion:In the case of cervix with Para‐arotic node single isocenter irradiation, IMRT planning in large‐field is better compared to RapidArc planning in terms of Homogeneity Index and mean dose of Bladder and Rectum.

Purpose:To quantify the dosimetric accuracy of respiratory gated stereotactic body radiation therapy delivery using dynamic thorax phantom.Methods:Three patients with mobile target (2 lung, 1liver) were chosen. Retrospective 4DCT image sets were acquired for using Varian RPM system. An in‐house MATLAB program was designed for MIP, MinIP and AvgIP generation. ITV was contoured on MIP image set for lung patients and on MinIP for liver patient. Dynamic IMRT plans were generated on selected phase bin image set in Eclipse (v10.0) planning system. CIRS dynamic thorax phantom was used to perform the dosimetric quality assurance. Patient breathing pattern file from RPM system was converted to phantom compatible file by an in‐house MATLAB program. This respiratory pattern fed to the CIRS dynamic thorax phantom. 4DCT image set was acquired for this phantom using patient breathing pattern. Verification plans were generated using patient gating window and delivered on the phantom. Measurements were carried out using with ion chamber and EBT2 film. Exposed films were analyzed and evaluated in FilmQA software.Results:The stability of gated output in comparison with un‐gated output was within 0.5%. The Ion chamber measured and TPS calculated dose compared for all the patients. The difference observed was 0.45%, −0.52% and −0.54 for Patient 1, Patient2 and Patient 3 respectively.Gamma value evaluated from EBT film shows pass rates from 92.41% to 99.93% for 3% dose difference and 3mm distance to agreement criteria.Conclusion:Dosimetric accuracy of respiratory gated SBRT delivery for lung and liver was dosimetrically acceptable. The Ion chamber measured dose was within 0.203±0.5659% of the expected dose. Gamma pass rates were within 96.63±3.84% of the expected dose.

Purpose: To compare the Collimator scatter factor (Sc), Phantom scatter factor (Sp) and Total scatter factors (Sc,p) of 6MV FFF and energy matched 6MV FFF (6MV eqFFF) Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation. In this study, the field sizes from 5 × 5 cm2 to 40 × 40 cm2 compared for 6MV FFF and 6MV eqFFF. We measured Sc,p with CC 13 chamber at the depth of 10 g/cm2 using IBA blue water phantom and Sc measured with CC 13 chamber at the depth of 10 g /cm2 using columnar phantom (TG 74) for 6MV FFF and 6MV eqFFF x‐ray beams from a Siemens — ARTISTE(6MV eqFFF ) and Varian True beam (6MV FFF) linear accelerator. The Sp values derived from the Sc,p and Sc Values. Results: All the values of Sc,p, Sc and Sp are normalized to 10 × 10 cm2 field size. The measured values of Sc,p for 6MV FFF and 6MV eqFFF varies from 0.9404 to 1.0760 and 0.9690 to 1.0283 respectively. The Sc values for 6MV FFF and 6MV eqFFF varies from 0.9880 to 1.133 and 0.9882 to 1.0075 respectively. The Sp values for 6MV FFF and 6MV eqFFF varies from 0.9518 to 1.0619 and 0.9806 to 1.0206 respectively. From the measured values, we found that Sc, Sc,p and Sp factors of 6MV FFF less than 10 × 10cm2 field is similar to the 6MV eqFFF. For greater than 10 × 10 cm2 field size Sc, Sc,p and Sp factors higher for 6MV FFF than 6MV eqFFF. Conclusion: The energy matched 6MV FFF (6MV eqFFF) photon beam producing lesser Scatter radiation compare to the conventional 6MV FFF photon beams for field size more than 10 × 10 cm2.

To measure and compare the head scatter factor for flattened (FB) and unflattened (FFF) of 6MV and 10MV photon beam using indigenously designed mini phantom. A columnar mini phantom was designed as recommended by AAPM Task Group 74 with low and high atomic number materials at 10 cm (mini phantom) and at approximately twice the depth of maximum dose water equivalent thickness (brass build-up cap). Scatter in the accelerator (Sc) values of 6MV-FFF photon beams are lesser than that of the 6MV-FB photon beams (0.66-2.8%; Clinac iX, 2300CD) and (0.47-1.74%; True beam) for field sizes ranging from 10 × 10 cm2 to 40 × 40 cm2. Sc values of 10MV-FFF photon beams are lesser (0.61-2.19%; True beam) than that of the 10MV-FB photons beams for field sizes ranging from 10 × 10 cm2 to 40 × 40 cm2. The SSD had no influence on head scatter for both flattened and unflattened beams and irrespective of head design of the different linear accelerators. The presence of field shaping device influences the Sc values. The collimator exchange effect reveals that the opening of the upper jaw increases Sc irrespective of FB or FFF photon beams and different linear accelerators, and it is less significant in FFF beams. Sc values of 6MV-FB square field were in good agreement with that of AAPM, TG-74 published data for Varian (Clinac iX, 2300CD) accelerator. Our results confirm that the removal of flattening filter decreases in the head scatter factor compared to flattened beam. This could reduce the out-of-field dose in advanced treatment delivery techniques.

Purpose: Comparison of the depth dose in the build-up region and Surface dose for 6MV flattened and 7MV unflattened photon beams with different detectorsMethods: The percentage depth dose in the build-up region and the surface dose for the 6MV-FB and 7MV-UFB photon beams from a Siemens Artiste medical linear accelerator were measured for square field sizes of 5×5, 10×10 and 15×15 cm 2 using Scanditronix NACP ion chamber, CC 13, and Stereotactic field Detectors (SFD) along the central axis of the beam at 100 cm source to surface distance with IBA blue phantom 2 and solid phantom. Results: The consistency between the measured percentage depth dose data from all four detector types were observed for depths beyond the depth of the maximum dose, but were all clearly different from each other data in the build-up region this is observed for both 6MV-FB and 7MV-UFB beams. The measured surface dose (16.2 Percent) applied with improved Velkley correction factors used for 10X10 cm2 of 6MV-FB using NACP parallel plate chamber values were all in good agreement with previously published data. The measured percentage surface doses obtained using the NACP parallel plate chamber, CC 13 and SFD without any correction factor values are 0.3885,0.4330 and 0.4751, 0.4485,0.4922 and 0.5323,0.3652,0.4076 and 0.4580 respectively for field sizes of 5X5,10X10 and 15×15 cm2 for the 6MV-FB photon beams and 0.3800,0.4117 and 0.4398, 0.4364, 0.4655 and 0.4965, 0.3611,0.4100 and 0.4349 for the 7MV-UFB photon beams. Conclusion: The measured surface dose clearly increases with increasing field size, regardless of the detector used in the measurement for both 6MV-FB and 7MV-UFB photon beams. Compare to NACP parallel plate chamber CC 13 chamber is showing over response and SFD is showing lesser surface dose.