Volume 35, Issue 6, June 2008
Index of content:
- Therepy Scientific Session: Auditorium B
TH‐D‐AUD B‐01: Comparison of Single‐Arc and Multiple‐Arc Approaches for Delivering of Volumetric Modulated Arc Therapy35(2008); http://dx.doi.org/10.1118/1.2962903View Description Hide Description
Purpose:Linear accelerator vendors have recently introduced deliverycontrol systems with the ability to deliver Volumetric Modulated Arc Therapy (VMAT). These systems can deliver VMAT using either a single‐arc or a multi‐arc approach. The goal of this study is to compare single‐arc and multi‐arc delivery techniques in terms of both plan quality and delivery efficiency. Method and Materials: Two prostate cases and three head‐and‐neck cases were included in this study. For each case, single‐arc and three‐arc VMAT plans were generated using our home‐grown arc sequencing algorithm that converts optimized fluence maps into deliverable arcs. Each VMAT plan was evaluated using Pinnacle's superposition dose calculation, and DVH comparisons were made between the two sets of VMAT plans. VMAT deliveries using Elekta's PreciseBeam Infinity™ control system were performed for each patient to compare the delivery efficiency. Results: For the two prostate cases, the single‐arc and three‐arc VMAT plans resulted in similar target dose coverage and organ at risk (OAR) sparing. For the three head‐and‐neck cases, the three‐arc plans provided improved target dose coverage as compared with the single‐arc plans with the average standard deviation in the target dose reduced from 7.06 to 5.82 cGy. The target volume covered by 95% of the prescribed dose also increased from 97.5% to 98.5% for the three‐arc VMAT plans. For single‐arc VMAT delivery, the average delivery time was approximately 3.2 minutes for prostate cases and 5 minutes for head‐&‐neck cases. While for three‐arc VMAT delivery, these values increased to 4.5 and 5.6 minutes. Conclusion: For simple cases such as prostate, single arc delivery provides comparable plan quality and improved delivery efficiency. However, for more complex cases, multi‐arc VMAT plans are preferable due to the ability to achieve improved dose conformity while maintaining acceptable treatment times.
This work was sponsored in part through a grant from Elekta.
35(2008); http://dx.doi.org/10.1118/1.2962904View Description Hide Description
Purpose: The objective of this study was to develop a technique for single rotation volume modulated arc therapy (VMAT) treatment plans using the current clinical version of the Pinnacle Treatment Planning system. The goal was to create treatment plans using only tools currently available in Pinnacle. Method and Materials:Treatment planning for VMAT was performed using the Direct Machine Parameter Optimization (DMPO) algorithm. With DMPO, inverse planning is performed by optimizing MLC leaf positions and segment weights. The treatment delivery was modeled and optimized as 51 equally spaced fixed beams. This beam geometry was selected to generate comparable plans to helical tomotherapy. Upon completion of optimization, the MLC delivery files were exported and converted into a single arc. Fixed‐gantry IMRT plans were also created for comparison by analyzing dose statistics, volume histograms, and differences. Calculated doses and MLC controller files were extracted from Pinnacle and imported into MATLAB for analysis. Gamma analyses were performed between the fixed‐gantry and VMAT plans. In addition, the modulation factor was calculated for the VMAT plans. Results: A total of 11 treatment plans were created for VMAT and fixed‐gantry IMRT. In all cases, the DMPO algorithm was able to optimize a plan resulting in one beam aperture. For prostate and H&N cases, the modulation factors ranged from 1.25–1.87 and 1.86–4.26. The VMAT delivery had less sparing of the parotids than the fixed‐gantry IMRT. For one patient, the volume of the parotids receiving over 20 Gy was 20% for the fixed‐gantry and 25–30% for VMAT. In addition, the dose uniformity through both the prostate and H&N PTVs were less with VMAT. Conclusion: Two conclusions can be drawn from the study: 1.) It is possible to create VMAT plans using DMPO in Pinnacle; and 2.) The VMAT plans have dose distributions similar to fixed‐gantry IMRT.
35(2008); http://dx.doi.org/10.1118/1.2962905View Description Hide Description
Purpose: Recently, there has been a renewed interest in the delivery of arcbased IMRT using conventional linear accelerators. Elekta and Varian have developed linear acceleratorcontrol systems that are capable of delivering rotational IMRT by combining gantry rotation, dynamic MLC leaf motion, and a variable dose rate. Elekta's new Precise Beam Infinity™ control system has been installed in our clinic and acceptance testing and plan verifications have been performed. In this study, we will report on our initial experiences with volumetric modulated arc therapy (VMAT) delivered using an Elekta Precise linear accelerator.Method and Materials: VMAT is a radiotherapydelivery technique that combines the dosimetric advantages of rotational delivery with the dose painting capabilities of IMRT. We have developed an arc sequencing algorithm that translates optimized fluence maps into deliverable VMAT treatment plans. In this investigation, one head‐and‐neck and five prostate plans have been delivered in an effort to quantify the efficiency and accuracy of the VMAT delivery system. Results: A complex head‐and‐neck plan involving two targets and a simultaneous boost was delivered in 5 minutes 29 seconds. For this three‐arc head‐and‐neck plan, the point dose agreed within 1.9%. Additional measurements for 5 prostate cases demonstrated an average delivery time of 3 minutes 28 seconds with all ion chamber measurements agreeing within 3%. Film measurements demonstrated close agreement between the predicted and measured isodose curves. Measurements have also been performed to quantify efficiency of single‐arc versus multi‐arc VMAT deliveries.Conclusion: Elekta's Precise Beam Infinity control system can safely and efficiently delivery highly complex VMAT treatment plans. In our initial investigation, all plans delivered in less than 5.5 minutes. Numerous additional plan verifications will be performed as we move towards an anticipated clinical implementation of VMAT in May 2008.
Research sponsored in part through a grant from Elekta.