A study on conventional IMRT and RapidArc treatment planning techniques for head and neck cancers

AimTo evaluate the performance of volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.BackgroundRapidArc is a novel technique that has recently been made available for clinical use. Planning study was done for volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.Materials and methodsTen patients with advanced tumors of the nasopharynx, oropharynx, and hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning was done by means of simultaneously integrated boost technique. A total dose of 70[[ce:hsp sp="0.25"/]]Gy was delivered to the boost volume (PTV boost) and 57.7[[ce:hsp sp="0.25"/]]Gy to the elective PTV (PTV elective) in 35 equal treatment fractions. PTV boost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes, whereas the PTV elective consisted of elective nodal regions. Planning was done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam was equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360° gantry rotation and double arc consists of 2 co-planar arcs of 360° in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45° to cover the entire tumor, which reduced the tongue and groove effect during gantry rotation. All plans were generated with 6[[ce:hsp sp="0.25"/]]MV X-rays for CLINAC 2100 Linear Accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm.ResultsDouble arc plans show superior dose homogeneity in PTV compared to a single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in the double arc technique by 4.5% when compared to the IMRT 9 field and single arc techniques. For healthy tissue, no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V15[[ce:hsp sp="0.25"/]]Gy (5.81% for single arc and 4.69% for double arc) and V20[[ce:hsp sp="0.25"/]]Gy (7.55% for single arc and 5.89% for double arc) dose levels when compared to the 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200[[ce:hsp sp="0.25"/]]cGy per fraction was 474[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]80[[ce:hsp sp="0.25"/]]MU and 447[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]45[[ce:hsp sp="0.25"/]]MU for double arc and single arc as against 948[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]162[[ce:hsp sp="0.25"/]]MU for the 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc shows a reduction in the parotid mean dose when compared with single arc and IMRT plans.ConclusionRapidArc using double arc provided a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The main disadvantage with IMRT observed was higher monitor units and longer treatment time

Treatment planning and dosimetric comparison study on two different volumetric modulated arc therapy delivery techniques

AimTo compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.BackgroundVolumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.Materials and methodsTen patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50[[ce:hsp sp="0.25"/]]Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6[[ce:hsp sp="0.25"/]]MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.ResultsRapidArc plans achieved the best conformity (CI95%[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]1.08[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.07) while Elekta VMAT plans were slightly inferior (CI95%[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]1.10[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.02[[ce:hsp sp="0.25"/]]Gy when compared to RapidArc with 0.08[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]2.90)[[ce:hsp sp="0.25"/]]Gy when compared to RapidArc (7.83[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.31)[[ce:hsp sp="0.25"/]]Gy. The integral dose is found to be inferior with Elekta VMAT (11.50[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]6.49)[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]104[[ce:hsp sp="0.25"/]]Gy[[ce:hsp sp="0.25"/]]cm3 when compared to RapidArc (13.11[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]7.52)[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]104[[ce:hsp sp="0.25"/]]Gy[[ce:hsp sp="0.25"/]]cm3. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3[[ce:hsp sp="0.25"/]]mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.ConclusionThe study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation