Manindra Bhushan

Is volumetric modulated arc therapy (RapidArc) better than intensity modulated radiotherapy for gynecological malignancies? A dosimetric comparison

AIMS Evaluation of the dosimetric advantage, if any, of RapidArc (double arc and triple arc [DA and TA]) over standard fixed field intensity-modulated radiation therapy (IMRT) in gynecologic malignancies. MATERIALS AND METHODS A total of 20 cases of gynecologic malignancies were included. Static IMRT sliding window, single arc (SA), DA and TA plans were generated with eclipse planning system. The prescribed dose was 50.4 Gy/28# to the planning target volumes. RESULTS IMRT provided target coverage equivalent to DA and inferior to TA (D95% [in Gy]--49.94, 49.58, 49.96, 50.17 for IMRT, SA, DA and TA respectively--all observations in the same sequence). Conformity index 90 (CI 90 (0.964, 0.927, 0.918, 0.822) and homogeneity index (0.0683, 0.119, 0.098, 0.097) of IMRT were superior. TA was superior to other arcs in all parameters except CI 90 (P=0.805) and bladder dose (lower in DA). Rectal, bladder and bowel sparing was best achieved with IMRT followed by TA; bilateral femur dose was lower in arcs. The total monitor units and treatment time of arcs were significantly lower than IMRT, reduced by a factor of 2.41-2.59 and 3.2-3.5 respectively (All P values significant). CONCLUSION IMRT provided better overall plan for gynecologic malignancies with lower organs at risk dose and target coverage equivalent to DA and TA. Treatment delivery efficiency was higher with RapidArc. The TA plan is dosimetrically superior to DA, but the gain is small. The decision whether or not to add a third arc for a small gain should be individualized.

The dosimetric impact of different photon beam energy on RapidArc radiotherapy planning for cervix carcinoma.

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.

Randomized controlled study comparing simultaneous modulated accelerated radiotherapy versus simultaneous integrated boost intensity modulated radiotherapy in the treatment of locally advanced head and neck cancer

OBJECTIVES Comparison of two fractionation schedules of intensity modulated radiotherapy (IMRT) for locally advanced head and neck cancer - simultaneous integrated boost (SIB-IMRT) and simultaneous modulated accelerated radiotherapy (SMART) boost in terms of toxicity and survival end-point measures. PATIENTS AND METHODS Sixty patients with locally advanced head and neck cancer were randomized in two treatment arms (SIB-IMRT [control arm] and SMART boost arm [study arm]). In the control arm, patients received 70, 63 and 56 Gy in 35 fractions to clinical target volumes (CTV) 1, 2 and 3, respectively. In the study arm, patients received 60 and 50 Gy to CTV 1 and CTV 3, respectively. Toxicities, progression free survival (PFS) and overall survival (OS) were compared between both arms. RESULTS Baseline patient-related characteristics were comparable between the arms except for primary site of tumour. No significant differences were noted in acute toxicities between the arms except for fatigue which was statistically higher for control arm. No significant differences in 2-year late toxicities were observed. The median follow-up duration was 25.5 (range, 1.8-39.9) months. The 2-year PFS was 53.3% and 80.0% (p = 0.028) for control and study arm, respectively. The 2-year OS was 60.0% and 86.7% (p = 0.020) in control and study arms, respectively. Multivariate analysis showed clinical stage and site to be significant predictors for OS and PFS, respectively. CONCLUSIONS The SMART boost technique can be a feasible alternative fractionation schedule that reduces the overall treatment time, maintaining comparable toxicity and survival compared with SIB-IMRT.

Dosimetric Comparison of Pencil-Beam Scanning and Photon-Based Radiation Therapy as a Boost in Carcinoma of Cervix

Purpose Brachytherapy is essential for local treatment in cervical carcinoma, but some patients are not suitable for it. Presently, for these patients, the authors prefer a boost by using intensity-modulated radiation therapy (IMRT). The authors evaluated the dosimetric comparison of proton-modulated radiation therapy versus IMRT and volumetric-modulated arc therapy (VMAT) as a boost to know whether protons can replace photons. Patients and Methods Five patients who received external beam radiation therapy to the pelvis by IMRT were reviewed. Three different plans were made, including pencil beam scanning (PBS), IMRT, and VMAT. The prescribed planning target volume (PTV) was 20 Gy in 4 fractions. The dose to 95% PTV (D95%), the conformity index, and the homogeneity index were evaluated for PTV. The Dmax, D2cc, and Dmean were evaluated for organs at risk along with the integral dose of normal tissue and organs at risk. Results The PTV coverage was optimal and homogeneous with modulated protons and photons. For PBS, coverage D95% was 20.01 ± 0.02 Gy (IMRT, 20.08 ± 0.06 Gy; VMAT, 20.1 ± 0.04 Gy). For the organs at risk, Dmax of the bladder for PBS was 21.05 ± 0.05 Gy (IMRT, 20.8 ± 0.21 Gy; VMAT, 21.65 ± 0.41 Gy) while the Dmax for the rectum for PBS was 21.04 ± 0.03 Gy (IMRT, 20.81 ± 0.12 Gy; VMAT, 21.66 ± 0.38 Gy). Integral dose to normal tissues in PBS was 14.17 ± 2.65 Gy (IMRT, 25.29 ± 6.35 Gy; VMAT, 25.24 ± 6.24 Gy). Conclusions Compared with photons, modulated protons provide comparable conformal plans. However, PBS reduces the integral dose to critical structures significantly compared with IMRT and VMAT. Although PBS may be a better alternative for such cases, further research is required to substantiate such findings.

SU-F-T-431: Dosimetric Validation of Acuros XB Algorithm for Photon Dose Calculation in Water

PURPOSE To validate the Acuros XB algorithm implemented in Eclipse Treatment planning system version 11 (Varian Medical System, Inc., Palo Alto, CA, USA) for photon dose calculation. METHODS Acuros XB is a Linear Boltzmann transport equation (LBTE) solver that solves LBTE equation explicitly and gives result equivalent to Monte Carlo. 6MV photon beam from Varian Clinac-iX (2300CD) was used for dosimetric validation of Acuros XB. Percentage depth dose (PDD) and profiles (at dmax, 5, 10, 20 and 30 cm) measurements were performed in water for field size ranging from 2×2,4×4, 6×6, 10×10, 20×20, 30×30 and 40×40 cm2 . Acuros XB results were compared against measurements and anisotropic analytical algorithm (AAA) algorithm. RESULTS Acuros XB result shows good agreement with measurements, and were comparable to AAA algorithm. Result for PDD and profiles shows less than one percent difference from measurements, and from calculated PDD and profiles by AAA algorithm for all field size. TPS calculated Gamma error histogram values, average gamma errors in PDD curves before dmax and after dmax were 0.28, 0.15 for Acuros XB and 0.24, 0.17 for AAA respectively, average gamma error in profile curves in central region, penumbra region and outside field region were 0.17, 0.21, 0.42 for Acuros XB and 0.10, 0.22, 0.35 for AAA respectively. CONCLUSION The dosimetric validation of Acuros XB algorithms in water medium was satisfactory. Acuros XB algorithm has potential to perform photon dose calculation with high accuracy, which is more desirable for modern radiotherapy environment.

SU-F-T-522: Dosimetric Study of Junction Dose in Double Isocenter Flatten and Flatten Filter Free IMRT and VMAT Plan Delivery

PURPOSE To quantify the dosimetric accuracy of junction dose in double isocenter flattened and flatten filter free(FFF) intensity modulated radiation therapy(IMRT) and volumetric modulated arc therapy(VMAT) plan delivery using pelvis phantom. METHODS Five large field pelvis patients were selected for this study. Double isocenter IMRT and VMAT treatment plans were generated in Eclipse Treatment planning System (V.11.0) using 6MV FB and FFF beams. For all the plans same distance 17.0cm was kept between one isocenter to another isocenter. IMRT Plans were made with 7 coplanar fields and VMAT plans were made with full double arcs. Dose calculation was performed using AAA algorithms with dose grid size of 0.25 cm. Verification plans were calculated on Scanditronix Wellhofer pelvis slab phantom. Measurement point was selected and calculated, where two isocenter plan fields are overlapping, this measurement point was kept at distance 8.5cm from both isocenter. The plans were delivered using Varian TrueBeamTM machine on pelvis slab phantom. Point dose measurements was carried out using CC13 ion chamber volume of 0.13cm3. RESULTS The measured junction point dose are compared with TPS calculated dose. The mean difference observed was 4.5%, 6.0%, 4.0% and 7.0% for IMRT-FB,IMRT-FFF, VMAT-FB and VMAT-FFF respectively. The measured dose results shows closer agreement with calculated dose in Flatten beam planning in both IMRT and VMAT, whereas in FFF beam plan dose difference are more compared with flatten beam plan. CONCLUSION Dosimetry accuracy of Large Field junction dose difference was found less in Flatten beam compared with FFF beam plan delivery. Even though more dosimetric studies are required to analyse junction dose for FFF beam planning using multiple point dose measurements and fluence map verification in field junction area.

SU‐E‐T‐92: Comparison of the Depth Dose in the Build‐Up Region and Surface Dose for 6MV Flattened and 7MV Unflattened Photon Beams with Different Detectors

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.

SU‐E‐T‐93: A Comparison of Out‐Of‐Field Dose and Its Constituent Components for 6MV Flattened and 7MV Unflattened Photon Beam

PURPOSE A Comparison of out-of-field dose and its constituent components for 6MV Flattened and 7MV unflattened Photon BeamsMethods: The flattening filter and primary collimator are the major sources of producing the scattered radiation. The out-of-field photon dose, Sc,p, Sc and Sp were measured with CC 13 chamber for square open fields from 5 × 5 cm2 to 30 × 30 cm2 using IBA blue phantom and solid phantom as a function of distance from central axis and field size at depth of maximum for respective photon energies. Scatter radiation, which predominantly contributes to peripheral dose at larger distance from the field edge, was measured using a CC 13 ionization chamber. RESULTS All the values of Sc,p and Sc are normalized to 10 × 10 cm2 field size. The measured values of Sc,p for 6MV-FB and 7MV-UFB varies from 0.9437 to 1.0651 and 0.9690 to 1.0283 respectively. The Sc values for 6MV-FB maximum (max.) 2.1 percent lesser than 7MV-UFB for up to 10 ×10 cm2 field size and 6MV-FB max.1.7 percent higher than the 7MV-UFB for above 10 × 10cm2 field size. Out of field dose is max.42.0 percent higher for 6MV-FB compare to 7MV-UFB at 25 cm from the field edge for up to 10 × 10 cm2 field size and max.50.39 percent reduced dose for 7MV-UFB for above 10 × 10 cm2 . Out of field dose is max.70.0 percent reduced for 7MV-UFB compare to 6MV-FB above 50 cm away from the field edge for up to 10 × 10 cm2 field size and max.68 percent reduced dose for 7MV-UFB for above 10 × 10 cm2 . CONCLUSION 7MV-UFB may be advantageous by reduced out-of-field dose compare to 6MV-FB, but differences are small in absolute terms.