IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119

This study on patients with localized prostate cancer was set up to investigate valuable differences using flattened beam (FB) and flattening filter free (FFF) mode in the application of intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc therapy (VMAT). For ten patients, four different plans were calculated with Oncentra planning system of Elekta, using Synergy machines: IMRT and VMAT, with and without flattening filter. Homogeneity and conformity indexes, dose to the organs at risk, and measurements of peripheral dose and dosimetric plan verification including record of the delivery times were analyzed and statistically evaluated. The indexes for homogeneity and conformity (CTV and PTV) are either advantageous or not significantly different for FFF compared to FB with one minor exception. Regarding the doses to the organs at risk and the measured peripheral dose, equivalent or lower doses were delivered for FFF than with FB. Furthermore, the delivery times were significantly shorter for FFF. VMAT compared to IMRT reveals benefits or at least equivalent values. VMAT‐FFF combines the most advantageous plan quality parameters with the shortest delivery times and reduced peripheral dose and is therefore recommended for the given equipment and cancer localization.

Section: Methodsmentioning

confidence: 99%

Volumetric‐modulated arc therapy and intensity‐modulated radiation therapy treatment planning for prostate cancer with flattened beam and flattening filter free linear accelerators

Treutwein¹,

Hipp

Koelbl³

et al. 2017

“…Calibration formula was applied to convert adjusted counts to measured dose. Percent difference was calculated using TG‐119 formalism (10)

[(measured dose - planned dose) / prescribed dose] \times 100

.…”

Section: Resultsmentioning

confidence: 99%

“…While dose difference analysis breaks down in high‐dose gradient regions, distance‐to‐agreement is not meaningful in low‐dose gradient regions (9) . OSLD and ion chamber measurements were compared to point doses from treatment planning system using the dose comparison methodology from AAPM Task Group Report 119 (10) in order to utilize a widely accepted comparison technique.…”

Section: Methodsmentioning

confidence: 99%

Development and evaluation of an end‐to‐end test for head and neck IMRT with a novel multiple‐dosimetric modality phantom

Zakjevskii

Knill

Rakowski

et al. 2016

A comprehensive end‐to‐end test for head and neck IMRT treatments was developed using a custom phantom designed to utilize multiple dosimetry devices. Initial end‐to‐end test and custom H&N phantom were designed to yield maximum information in anatomical regions significant to H&N plans with respect to: (i) geometric accuracy, (ii) dosimetric accuracy, and (iii) treatment reproducibility. The phantom was designed in collaboration with Integrated Medical Technologies. The phantom was imaged on a CT simulator and the CT was reconstructed with 1 mm slice thickness and imported into Varian's Eclipse treatment planning system. OARs and the PTV were contoured with the aid of Smart Segmentation. A clinical template was used to create an eight‐field IMRT plan and dose was calculated with heterogeneity correction on. Plans were delivered with a TrueBeam equipped with a high definition MLC. Preliminary end‐to‐end results were measured using film, ion chambers, and optically stimulated luminescent dosimeters (OSLDs). Ion chamber dose measurements were compared to the treatment planning system. Films were analyzed with FilmQA Pro using composite gamma index. OSLDs were read with a MicroStar reader using a custom calibration curve. Final phantom design incorporated two axial and one coronal film planes with 18 OSLD locations adjacent to those planes as well as four locations for IMRT ionization chambers below inferior film plane. The end‐to‐end test was consistently reproducible, resulting in average gamma pass rate greater than 99% using 3normal%/3 mm analysis criteria, and average OSLD and ion chamber measurements within 1% of planned dose. After initial calibration of OSLD and film systems, the end‐to‐end test provides next‐day results, allowing for integration in routine clinical QA. Preliminary trials have demonstrated that our end‐to‐end is a reproducible QA tool that enables the ongoing evaluation of dosimetric and geometric accuracy of clinical head and neck treatments.PACS number(s): 87.55.Qr

“…Nevertheless, the gamma‐index passing rate exceeded 90% in each case that was investigated in this study, even in the MLC cases. According to a report by Ezzell et al,28 the action level in DQA of IMRT for composite irradiation analyzed using radiographic film was 88%–90% of the gamma‐index passing rate with a criterion of 3% LPDD/3 mm DTA. In addition, Zeidan et al stated that the percentage of dose pixels passing in GafChromic dosimetry for 10 IMRT cases, including five prostate cases, was 87% ± 8% with the 3% LPDD/3 mm DTA criterion 29.…”

Section: Discussionmentioning

confidence: 99%

Clinical usefulness of MLCs in robotic radiosurgery systems for prostate SBRT

Tomida

Kamomae

Suzuki

et al. 2017

Stereotactic body radiation therapy (SBRT) using recently introduced multileaf collimators (MLC) is preferred over circular collimators in the treatment of localized prostate cancer. The objective of this study was to assess the clinical usefulness of MLCs in prostate SBRT by comparing the effectiveness of treatment plans using fixed collimators, variable collimators, and MLCs and by ensuring delivery quality assurance (DQA) for each. For each patient who underwent conventional radiation therapy for localized prostate cancer, mock SBRT plans were created using a fixed collimator, a variable collimator, and an MLC. The total MUs, treatment times, and dose–volume histograms of the planning target volumes and organs at risk for each treatment plan were compared. For DQA, a phantom with a radiochromic film or an ionization chamber was irradiated in each plan. We performed gamma‐index analysis to evaluate the consistency between the measured and calculated doses. The MLC‐based plans had an ~27% lower average total MU than the plans involving other collimators. Moreover, the average estimated treatment time for the MLC plan was 31% and 20% shorter than that for the fixed and variable collimator plans respectively. The gamma‐index passing rate in the DQA using film measurements was slightly lower for the MLC than for the other collimators. The DQA results acquired using the ionization chamber showed that the discrepancies between the measured and calculated doses were within 3% in all cases. The results reinforce the usefulness of MLCs in robotic radiosurgery for prostrate SBRT treatment planning; most notably, the total MU and treatment time were both reduced compared to the cases using other types of collimators. Moreover, although the DQA results based on film dosimetry yielded a slightly lower gamma‐index passing rate for the MLC than for the other collimators, the MLC accuracy was determined to be sufficient for clinical use.