Dosimetric comparison of dynamic conformal arc integrated with segment shape optimization and variable dose rate versus volumetric modulated arc therapy for liver SBRT

AimThe aim is a dosimetric comparison of dynamic conformal arc integrated with the segment shape optimization and variable dose rate (DCA_SSO_VDR) versus VMAT for liver SBRT and interaction of various treatment plan quality indices with PTV and degree of modulation (DoM) for both techniques.BackgroundThe DCA is the state-of-the-art technique but overall inferior to VMAT, and the DCA_SSO_VDR technique was not studied for liver SBRT.Materials and methodsTwenty-five patients of liver SBRT treated using the VMAT technique were selected. DCA_SSO_VDR treatment plans were also generated for all patients in Monaco TPS using the same objective constraint template and treatment planning parameters as used for the VMAT technique. For comparison purpose, organs at risk (OARs) doses and treatment plans quality indices, such as maximum dose of PTV (D_max%), mean dose of PTV (D_mean%), maximum dose at 2 cm in any direction from the PTV (D_2cm%), total monitor units (MU’s), gradient index R_50%, degree of modulation (DoM), conformity index (CI), homogeneity index (HI), and healthy tissue mean dose (HTMD) were compared.ResultsSignificant dosimetric differences were observed in several OARs doses and lowered in VMAT plans. The D_2cm%, R_50%, CI, HI and HTMD are dosimetrically inferior in DCA_SSO_VDR plans. The higher DoM results in poor dose gradient and better dose gradient for DCA_SSO_VDR and VMAT treatment plans, respectively.ConclusionsFor liver SBRT, DCA_SSO_VDR treatment plans are neither dosimetrically superior nor better alternative to the VMAT delivery technique. A reduction of 69.75% MU was observed in DCA_SSO_VDR treatment plans. For the large size of PTV and high DoM, DCA_SSO_VDR treatment plans result in poorer quality.     

Comparison between two treatment planning systems for volumetric modulated arc therapy optimization for prostate cancer

PurposeTo investigate the performances of two commercial treatment planning systems (TPS) for Volumetric Modulated Arc Therapy (VMAT) optimization regarding prostate cancer. The TPS were compared in terms of dose distributions, treatment delivery parameters and quality control results.Materials and methodsFor ten patients, two VMAT plans were generated: one with Monaco TPS (Elekta) and one with Pinnacle TPS (Philips Medical Systems). The total prescribed dose was 78 Gy delivered in one 360° arc with a Synergy^® linear accelerator equipped with a MLCi2^®.ResultsVMAT with Monaco provided better homogeneity and conformity indexes but lower mean dose to PTVs than Pinnacle. For the bladder wall (p = 0.019), the femoral heads (p = 0.017), and healthy tissues (p = 0.005), significantly lower mean doses were found using Monaco. For the rectal wall, VMAT with Pinnacle provided a significantly (p = 0.047) lower mean dose, and lower dose into 50% of the volume (p = 0.047) compared to Monaco. Despite a greater number of monitor units (factor 1.5) for Monaco TPS, the total treatment time was equivalent to that of Pinnacle. The treatment delivery parameter analysis showed larger mean MLC area for Pinnacle and lower mean dose rate compared to Monaco. The quality control results gave a high passing rate (>97.4%) for the gamma index for both TPS but Monaco provided slightly better results.ConclusionFor prostate cancer patients, VMAT treatment plans obtained with Monaco and Pinnacle offered clinically acceptable dose distributions. Further investigations are in progress to confirm the performances of the two TPS for irradiating more complex volumes.     

Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost

PurposeTo evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization.MethodsFive patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9–10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12 Gy prescribed to the PTV, with or without an additional 4 Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV D_mean < 110% of the prescribed dose, a PTV V_110% < 50%, and OAR D_mean ≤ 50–60%.ResultsPTV D_mean < 110% was accomplished for most plans (n = 18/20), while all achieved V_110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM D_mean = 16.3 Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR D_mean = 40–54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found.ConclusionsAdding a 4 Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.     

Efficacy of tangential irradiation with volumetric modulated arc therapy on scalp angiosarcoma using medical linac

PurposeTo increase the superficial dose and reduce the brain dose for radiotherapy of scalp angiosarcoma, we propose a novel irradiation technique of tangential irradiation volumetric modulated arc therapy (TI-VMAT).MethodsTI-VMAT and the conventional VMAT treatment plans for thirteen scalp angiosarcoma patients were created with a prescribed dose of 70 Gy. Each treatment was normalized to cover 95% of the planning target volume (PTV) with its prescribed dose. To realize TI-VMAT, an avoidance structure (AS) function was applied. AS was defined as a contour subtracted PTV by a certain space from the brain contour. TI-VMAT treatment plans for six different spaces between PTV and AS were developed and compared with the conventional VMAT treatment plan with respect to the following dosimetric parameters: homogeneity index (HI) and conformity index (CI) of the PTV, mean brain dose, and brain volume irradiated with 20% (V_20% [cc]), 40% (V_40% [cc]), 60% (V_60% [cc]), 80% (V_80% [cc]), and 100% (V_100% [cc]) of the prescribed dose.ResultsHI and CI were comparable between TI-VMAT and the conventional VMAT, the mean brain dose for TI-VMAT with AS defined by a space of 2.0 cm and jaw tracking was 14.27 Gy, which was significantly lower than that for the conventional VMAT (21.20 Gy). In addition, dosimetric parameters such as V_20% [cc] were significantly suppressed compared to those for high doses.ConclusionOur proposed irradiation technique TI-VMAT shows the potential to reduce radiation doses in the brain with maintaining higher dose coverage on the PTV.     

Monte Carlo investigation on the effect of air gap under bolus in post-mastectomy radiotherapy

ObjectivesTo investigate the dosimetric effect of air gaps under bolus on skin dose for left-sided post-mastectomy radiotherapy with loco regional involvement.MethodsEight patients were planned retrospectively with volume modulated arc therapy (VMAT) and conventional static Field-in-Field (FinF) methods. Three different setups were applied for the 5-mm bolus over the chest wall having 0, 5 or 10 mm air gap under the bolus. The dose calculation was performed using Monte Carlo (MC) simulation. In addition, Analytic Anisotropic Algorithm (AAA) was used to demonstrate the differences observed in clinical setting.ResultsThe investigated air gaps under the bolus had minimal effect on surface dose for FinF plans (relative difference ≤ 2.6%), whereas for VMAT plans the surface dose decreased 13.6% when compared to the case with no air gap. In both FinF and VMAT, the largest differences between AAA and MC were seen at the surface where AAA underestimated the dose by 1.5 Gy (p < 0.05) on average; while the dose in the target volume excluding the surface was relatively similar being on average 0.3 Gy (p > 0.05) larger with AAA than with MC calculations.ConclusionsThe surface dose was significantly lower with VMAT technique than with FinF technique. Possible air gaps under the bolus reduced the surface dose significantly further for VMAT but not for FinF treatments, which may have clinical impact on recurrence rate. AAA was shown to underestimate the surface dose when compared to MC calculation.     

Monte Carlo as quality control tool of stereotactic body radiation therapy treatment plans

Purpose/objectiveThe objective of this study was to verify the accuracy of treatment plans of stereotactic body radiation therapy (SBRT) and to verify the feasibility of the use of Monte Carlo (MC) as quality control (QC) on a daily basis.Material/methodsUsing EGSnrc, a MC model of Agility™ linear accelerator was created. Various measurements (Percentage depth dose (PDD), Profiles and Output factors) were done for different fields sizes from 1x1 up to 40x40 (cm²). An iterative model optimization was performed to achieve adequate parameters of MC simulation. 40 SBRT patient’s dosimetry plans were calculated by Monaco™ 3.1.1. CT images, RT-STRUCT and RT-PLAN files from Monaco™ being used as input for Moderato MC code. Finally, dose volume histogram (DVH) and paired t-tests for each contour were used for dosimetry comparison of the Monaco™ and MC.ResultsValidation of MC model was successful, as <2% difference comparing to measurements for all field’s sizes. The main energy of electron source incident on the target was 5.8 MeV, and the full width at half maximum (FWHM) of Gaussian electron source were 0.09 and 0.2 (cm) in X and Y directions, respectively. For 40 treatment plan comparisons, the minimum absolute difference of mean dose of planning treatment planning (PTV) was 0.1% while the maximum was 6.3%. The minimum absolute difference of Max dose of PTV was 0.2% while the maximum was 8.1%.ConclusionSBRT treatment plans of Monaco agreed with MC results. It possible to use MC for treatment plans verifications as independent QC tool.     

Static and rotational intensity modulated techniques for head-neck cancer radiotherapy: A planning comparison

PurposeTo compare helical Tomotherapy (HT), two volumetric-modulated arc techniques and conventional fixed-field intensity modulated techniques (S-IMRT) for head-neck (HN) cancers.Methods and materialsEighteen HN patients were considered. Four treatment plans were generated for each patient: HT, S-IMRT optimised with Eclipse treatment planning system and two volumetric techniques using Elekta–Oncentra approach (VMAT) and Varian-RapidArc (RA), using two full arcs. All techniques were optimised to simultaneously deliver 66Gy to PTV1 (GTV and enlarged nodes) and 54Gy to PTV2 (subclinical and electively treated nodes). Comparisons were assessed on several dosimetric parameters and, secondarily, on planned MUs and delivery time.ResultsConcerning PTV coverage, significantly better results were found for HT and RA. HT significantly improved the target coverage both compared to S-IMRT and VMAT. No significant differences were found between S-IMRT and volumetric techniques in terms of dose homogeneity. For OARs, all the techniques were able to satisfy all hard constraints; significantly better results were found for HT, especially in the intermediate dose range (15–30 Gy). S-IMRT reached a significantly better OARs sparing with respect to VMAT and RA. No significant differences were found for body mean dose, excepting higher values of V5–V10 for HT. A reduction of planned MUs and delivery treatment time was found with volumetric techniques.ConclusionsThe objectives of satisfying target coverage and sparing of critical structures were reached with all techniques. S-IMRT techniques were found more advantageous compared to RA and VMAT for OARs sparing. HT reached the best overall treatment plan quality.     

CyberKnife MLC-based treatment planning for abdominal and pelvic SBRT: Analysis of multiple dosimetric parameters,overall scoring index and clinical scoring

PurposeThis study evaluated the plan quality of CyberKnife MLC-based treatment planning in comparison to the Iris collimator for abdominal and pelvic SBRT. Multiple dosimetric parameters were considered together with a global scoring index validated by clinical scoring.Methods and materialsIris and MLC plans were created for 28 liver, 15 pancreas and 13 prostate cases including a wide range of PTV sizes (24–643 cm³). Plans were compared in terms of coverage, conformity (nCI), dose gradient (R50%), homogeneity (HI), OAR doses, PTV gEUD, MU, treatment time both estimated by TPS (t_TPS) and measured. A global plan quality score index was calculated for IRIS and MLC solutions and validated by a clinical score given independently by two observers.ResultsCompared to Iris, MLC achieved equivalent coverage and conformity without compromising OAR sparing and improving R50% (p < 0.001). MLC gEUD was slightly lower than Iris (p < 0.05) for abdominal cases. MLC reduced significantly MU (−15%) and t_TPS (−22%). Time reduction was partially lost when measured. The global score index was significantly higher for MLC solutions which were selected in 73% and 64% of cases respectively by the first and second observer.ConclusionIris and MLC comparison was not straightforward when based on multiple dosimetric parameters. The use of a mathematical overall score index integrated with a clinical scoring was essential to confirm MLC plans advantages over Iris solutions.     

Advanced optimization methods for whole pelvic and local prostate external beam therapy

PurposeRadiation treatment planning inherently involves multiple conflicting planning goals, which makes it a suitable application for multicriteria optimization (MCO). This study investigates a MCO algorithm for VMAT planning (VMAT–MCO) for prostate cancer treatments including pelvic lymph nodes and uses standard inverse VMAT optimization (sVMAT) and Tomotherapy planning as benchmarks.MethodsFor each of ten prostate cancer patients, a two stage plan was generated, consisting of a stage 1 plan delivering 22 Gy to the prostate, and a stage 2 plan delivering 50.4 Gy to the lymph nodes and 56 Gy to the prostate with a simultaneous integrated boost. The single plans were generated by three planning techniques (VMAT–MCO, sVMAT, Tomotherapy) and subsequently compared with respect to plan quality and planning time efficiency.ResultsPlan quality was similar for all techniques, but sVMAT showed slightly better rectum (on average D_mean −7%) and bowel sparing (D_mean −17%) compared to VMAT–MCO in the whole pelvic treatments. Tomotherapy plans exhibited higher bladder dose (D_mean +42%) in stage 1 and lower rectum dose (D_mean −6%) in stage 2 than VMAT–MCO. Compared to manual planning, the planning time with MCO was reduced up to 12 and 38 min for stage 1 and 2 plans, respectively.ConclusionMCO can generate highly conformal prostate VMAT plans with minimal workload in the settings of prostate-only treatments and prostate plus lymph nodes irradiation. In the whole pelvic plan manual VMAT optimization led to slightly improved OAR sparing over VMAT–MCO, whereas for the primary prostate treatment plan quality was equal.     

An automated Monte Carlo QC system for volumetric modulated arc therapy: Possibilities and challenges

PurposeTo develop and implement an automated Monte Carlo (MC) system for patient specific VMAT quality control in a patient geometry that generates treatment planning system (TPS) compliant DICOM objects and includes a module for 3D analysis of dose deviations. Also, the aims were to recommend diagnose specific tolerance criteria and an evaluation procedure.MethodsThe EGSnrc code package formed the basis for development of the MC system. The workflow consists of a number of modules connected to a TPS by means of manual DICOM exports and imports which were executed sequentially without user interaction. DVH comparison was performed in the TPS. In addition, MC- and TPS dose distributions were analysed by applying the normalized dose difference (NDD) formalism. NDD failure maps and a pass rate for a certain threshold were obtained. 170 clinical plans (prostate, thorax, head-and-neck and gynecological) were selected for analysis.ResultsAgreement within 1.5% was found between clinical- and MC data for the mean dose to the target volumes and within 3% for parameters more sensitive to the shape of the DVH e.g. D_98% PTV. Regarding the NDD analysis, tolerance criteria 2%/3 mm were established for prostate plans and 3%/3 mm for the rest of the cases.ConclusionsAn automated MC system was developed and implemented. Evaluation procedure is recommended with NDD-analysis as a first step. For pass rate < 95%, the evaluation continues with comparison of DVH parameters. For deviations larger than 2%, a visual inspection of the clinical- and MC dose distributions is performed.     

Critical Structure Sparing in Stereotactic Ablative Radiotherapy for Central Lung Lesions: Helical Tomotherapy vs. Volumetric Modulated Arc Therapy

Background

Helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are both advanced techniques of delivering intensity-modulated radiotherapy (IMRT). Here, we conduct a study to compare HT and partial-arc VMAT in their ability to spare organs at risk (OARs) when stereotactic ablative radiotherapy (SABR) is delivered to treat centrally located early stage non-small-cell lung cancer or lung metastases.

Methods

12 patients with centrally located lung lesions were randomly chosen. HT, 2 & 8 arc (Smart Arc, Pinnacle v9.0) plans were generated to deliver 70 Gy in 10 fractions to the planning target volume (PTV). Target and OAR dose parameters were compared. Each technique’s ability to meet dose constraints was further investigated.

Results

HT and VMAT plans generated essentially equivalent PTV coverage and dose conformality indices, while a trend for improved dose homogeneity by increasing from 2 to 8 arcs was observed with VMAT. Increasing the number of arcs with VMAT also led to some improvement in OAR sparing. After normalizing to OAR dose constraints, HT was found to be superior to 2 or 8-arc VMAT for optimal OAR sparing (meeting all the dose constraints) (p = 0.0004). All dose constraints were met in HT plans. Increasing from 2 to 8 arcs could not help achieve optimal OAR sparing for 4 patients. 2/4 of them had 3 immediately adjacent structures.

Conclusion

HT appears to be superior to VMAT in OAR sparing mainly in cases which require conformal dose avoidance of multiple immediately adjacent OARs. For such cases, increasing the number of arcs in VMAT cannot significantly improve OAR sparing.     

Radiotherapy for the treatment of pituitary adenomas: A dosimetric comparison of three planning techniques

AimOur goal was to compare conformal 3D (C3D) radiotherapy (RT), modulated intensity RT (IMRT), and volumetric modulated arc therapy (VMAT) planning techniques in treating pituitary adenomas.BackgroundRT is important for managing pituitary adenomas. Treatment planning advances allow for higher radiation dosing with less risk of affecting organs at risk (OAR).Materials and methodsWe conducted a 5-year retrospective review of patients with pituitary adenoma treated with external beam radiation therapy (C3D with flattening filter, flattening filter-free [FFF], IMRT, and VMAT). We compared dose-volume histogram data. For OARs, we recorded D2%, maximum, and mean doses. For planning target volume (PTV), we registered V95%, V107%, D95%, D98%, D50%, D2%, minimum dose, conformity index (CI), and homogeneity index (HI).ResultsFifty-eight patients with pituitary adenoma were included. Target-volume coverage was acceptable for all techniques. The HI values were 0.06, IMRT; 0.07, VMAT; 0.08, C3D; and 0.09, C3D FFF (p < 0.0001). VMAT and IMRT provided the best target volume conformity (CI, 0.64 and 0.74, respectively; p < 0.0001). VMAT yielded the lowest doses to the optic pathway, lens, and cochlea. The position of the neck in extreme flexion showed that it helps in planning mainly with VMAT by allowing only one arc to be used and achieving the desired conformity, decreasing the treatment time, while allowing greater protection to the organs of risk using C3D, C3DFFF.ConclusionsOur results confirmed that EBRT in pituitary adenomas using IMRT, VMAT, C3D, C3FFF provide adequate coverage to the target. VMAT with a single arc or incomplete arc had a better compliance with desired dosimetric goals, such as target coverage and normal structures dose constraints, as well as shorter treatment time. Neck extreme flexion may have benefits in treatment planning for better preservation of organs at risk. C3D with extreme neck flexion is an appropriate treatment option when other treatment techniques are not available.     

A comparative analysis of Acuros XB and the analytical anisotropic algorithm for volumetric modulation arc therapy

BackgroundThis study aimed to verify the dosimetric impact of Acuros XB (AXB) (AXB, Varian Medical Systems Palo Alto CA, USA), a two model-based algorithm, in comparison with Anisotropic Analytical Algorithm (AAA ) calculations for prostate, head and neck and lung cancer treatment by volumetric modulated arc therapy (VMAT ), without primary modification to AA. At present, the well-known and validated AA algorithm is clinically used in our department for VMAT treatments of different pathologies. AXB could replace it without extra measurements. The treatment result and accuracy of the dose delivered depend on the dose calculation algorithm.Materials and methodNinety-five complex VMAT plans for different pathologies were generated using the Eclipse version 15.0.4 treatment planning system (TPS). The dose distributions were calculated using AA and AXB (dose-to-water, AXB_w and dose-to-medium, AXB_m), with the same plan parameters for all VMAT plans. The dosimetric parameters were calculated for each planning target volume (PTV) and involved organs at risk (OA R). The patient specific quality assurance of all VMAT plans has been verified by Octavius^®-4D phantom for different algorithms.ResultsThe relative differences among AA, AXB_w and AXB_m, with respect to prostate, head and neck were less than 1% for PTV D_95%. However, PTV D_95% calculated by AA tended to be overestimated, with a relative dose difference of 3.23% in the case of lung treatment. The absolute mean values of the relative differences were 1.1 ± 1.2% and 2.0 ± 1.2%, when comparing between AXB_w and AA, AXB_m and AA, respectively. The gamma pass rate was observed to exceed 97.4% and 99.4% for the measured and calculated doses in most cases of the volumetric 3D analysis for AA and AXB_m, respectively.ConclusionThis study suggests that the dose calculated to medium using AXB_m algorithm is better than AAA and it could be used clinically. Switching the dose calculation algorithm from AA to AXB does not require extra measurements.     

Patient-specific quality assurance and plan dose errors on breast intensity-modulated proton therapy

PurposeTo investigate, in proton therapy, whether the Gamma passing rate (GPR) is related to the patient dose error and whether MU scaling can improve dose accuracy.MethodsAmong 20 consecutively treated breast patients selected for analysis, two IMPT plans were retrospectively generated: (1) the pencil-beam (PB) plan and (2) the Monte Carlo (MC) plan. Patient-specific QA was performed. A 3%/3-mm Gamma analysis was conducted to compare the TPS-calculated PB algorithm dose distribution with the measured 2D dose. Dose errors were compared between the plans that passed the Gamma testing and those that failed. The MU was then scaled to obtain a better GPR. MU-scaled PB plan dose errors were compared to the original PB plan.ResultsOf the 20 PB plans, 8 were passed Gamma testing (G_pass_group) and 12 failed (G_fail_group). Surprisingly, the G_pass_group had a greater dose error than the G_fail_group. The median (range) of the PTV DVH RMSE and PTV ΔDmean were 1.36 (1.00–1.91) Gy vs 1.18 (1.02–1.80) Gy and 1.23 (0.92–1.71) Gy vs 1.10 (0.87–1.49) Gy for the G_pass_group and the G_fail_group, respectively. MU scaling reduced overall dose error. However, for PTV D99 and D95, MU scaling worsened some cases.ConclusionFor breast IMPT, the PB plans that passed the Gamma testing did not show smaller dose errors compared to the plans that failed. For individual plans, the MU scaling technique leads to overall smaller dose errors. However, we do not suggest use of the MU scaling technique to replace the MC plans when the MC algorithm is available.     

Dose distribution comparison in volumetric-modulated arc therapy plans for head and neck cancers with and without an external body contour extended technique

AimThis study compared volumetric-modulated arc therapy (VMAT) plans for head and neck cancers with and without an external body contour extended technique (EBCT).BackgroundDose calculation algorisms for VMAT have limitations in the buildup region.Materials and methodsThree VMAT plans were enrolled, with one case having a metal artifact from an artificial tooth. The proper dose was calculated using Eclipse version 11.0. The body contours were extended 2 cm outward from the skin surface in three-dimensional space, and the dose was recalculated with an anisotropic analytical algorithm (AAA) and Acuros XB (AXB). Monitor units (MUs) were set, and the dose distributions in the planning target volume (PTV), clinical target volume, and organ at risk (OAR) and conformity index (CI) with and without an EBCT were compared. The influence of a metal artifact outside of the thermoplastic head mask was also compared.ResultsThe coverage of PTV by the 95% dose line near the patient’s skin was increased drastically by using an EBCT. Plan renormalization had a negligible impact on MUs and doses delivered to OARs. CI of PTV with a 6-MV photon beam was closer to 1 than that with a 10-MV photon beam when both AAA and AXB were used in all cases. Metal artifacts outside the head mask had no effect on dose distribution.ConclusionsAn EBCT is needed to estimate the proper dose at object volumes near the patient’s skin and can improve the accuracy of the calculated dose at target volumes.     

Adaptive volumetric modulated arc treatment planning for esophageal cancers using cone beam computed tomography

PurposeTo assess the potential of cone beam CT (CBCT) derived adaptive RapidArc treatment for esophageal cancers in reducing the dose to organs at risk (OAR).Methods and materialsTen patients with esophageal cancer were CT scanned in free breathing pattern. The PTV is generated by adding a 3D margin of 1 cm to the CTV as per ICRU 62 recommendations. The double arc RapidArc plan (Clin_RA) was generated for the PTV. Patients were setup using kV orthogonal images and kV-CBCT scan was acquired daily during first week of therapy, then weekly. These images were exported to the Eclipse TPS. The adaptive CTV which includes tumor and involved nodes was delineated in each CBCT image set for the length of the PTV. The composite CTV from first week CBCT was generated using Boolean union operator and 5 mm margin was added circumferentially to generate adaptive PTV (PTV1). Adaptive RapidArc plan (Adap_RA) was generated. NTCP and DVH of the OARs of the two plans were compared. Similarly, PTV2 was generated from weekly CBCT. PTV2 was evaluated for the coverage of 95% isodose of Adap_RA plan.ResultsThe PTV1 and PTV2 volumes covered by 95% isodose in adaptive plans were 93.51 ± 1.17% and 94.59 ± 1.43% respectively. The lung V_10Gy, V_20Gy and mean dose in Adap_RA plan was reduced by 17.43% (p = 0.0012), 34.64% (p = 0.0019) and 16.50% (p = 0.0002) respectively compared to Clin_RA. The Adap_RA plan reduces the heart D_35% and mean dose by 17.35% (p = 0.0011) and 17.16% (p = 0.0012). No significant reduction in spinal cord and liver doses were observed. NTCP for the lung (0.42% vs. 0.08%) and heart (1.39% vs. 0.090%) was reduced significantly in adaptive plans.ConclusionThe adaptive re-planning strategy based on the first week CBCT dataset significantly reduces the doses and NTCP to OARs.