3DVH Software Research Articles

Impact of multi-leaf collimator positioning accuracy on quality control of volumetric modulation arc therapy plan for cervical cancer treated with Elekta linear accelerator

To investigate the influence of positioning accuracy of the multi-leaf collimators (MLC) on the passing rate of the plan dose verification for volumetric modulation arc therapy (VMAT) of cervical cancer using an Elekta linear accelerator. The dose distributions were measured using Sun Nuclear's Mapcheck and Arccheck semiconductors matrix before and after MLC calibration in30 cervical cancer patients undergoing VMAT. Dosimetric comparisons were performed with 2D and 3D gamma passing rates of 3%, 3 mm and 2%, and 2 mm. The 3D gamma distribution was reconstructed with respect to the patient's anatomy using 3DVH software to evaluate the possible influence of MLC positioning accuracy. Before and after MLC calibration, the gamma passing rates of Mapcheck were (88.80±1.81)% and (99.25 ± 0.53)% under 3% and 3 mm standard, respectively, with an average increase of 10.45%. The corresponding gamma passing rates of Arccheck were (87.61±1.98)% and (98.13±0.99)%, respectively, with an average increase of 10.52%. The gamma passing rates of 3DVH were (89.87±2.28)% and (98.3±1.15)%, respectively, with an average increase of 8.43%. The MLC positioning accuracy is one of the main factors influencing dosimetric accuracy of VMAT for cervical cancer. The application of Autocal software facilitates MLC calibration and improves the accuracy and safety of VMAT delivery for cervical cancer.

Implementation of TG-218 for patient-specific quality assurance tolerance and action limits determination: Gamma passing rate evaluation using 3DVH software.

To determine the tolerance limit (TL) and action limit (AL) of gamma passing rates (%GP) for volumetric-modulated arc therapy (VMAT) patient-specific quality assurance (PSQA) according to the American Association of Physicists in Medicine (AAPM) Task Group (TG)-218 recommendations, and to comparatively evaluate the clinical relevance of 2D %GP and 3D %GP. PSQA was performed for 100 head and neck (H&N) and 73 prostate cancer VMAT treatment plans. Measurements were acquired using a cylindrical water equivalent phantom, hollow in the center, allowing measurements with homogeneous or heterogeneous inserts. The LINAC-delivered dose distributions were compared to those calculated from the treatment planning system through the gamma index. TL and AL were determined through the computation of two-dimensional (2D) %GP using the recommended acceptance criteria. Dose-volume histograms were reconstructed from the measurements using a commercially available software to detect the dosimetric errors (%DE) between the compared dose distributions. Utilizing the estimated dose on the patient anatomy, structure-specific %GP (3D %GP) were calculated. The 3D %GP were compared to the 2D %GP ones based on their correlation with the %DE. Each metric's sensitivity was determined through receiver operator characteristic analysis. TL and AL were in concordance with the universal ones, regarding the prostate cancer cases, but were lower for the H&N cases. Evaluation of %DE did not deem the plans unacceptable. The 2D %GP and the 3D %GP did not differ significantly regarding their correlation with %DE. For prostate plans, %GP sensitivity was higher than for H&N cases. Determination of institutional-specific TL and AL allows the monitoring of the PSQA procedure, yet for plans close to the limits, clinically relevant metrics should be used before they are deemed unacceptable for the process to be of higher sensitivity and efficiency.

АНАЛИЗ ФИЗИЧЕСКОЙ И РАДИОБИОЛОГИЧЕСКОЙ ЭКВИВАЛЕНТНОСТИ РАССЧИТАННЫХ И ИЗМЕРЕННЫХ ДОЗОВЫХ РАСПРЕДЕЛЕНИЙ ДЛЯ СТЕРЕОТАКСИЧЕСКОЙ ТЕРАПИИ ПРЕДСТАТЕЛЬНОЙ ЖЕЛЕЗЫ

Purpose: Carrying out the analysis of the physical and radiobiological equivalence of dose distributions obtained during the planning of hypofractionated stereotactic radiation therapy of the prostate cancer and verification using a three-dimensional cylindrical dosimeter.
 Material and Methods: Based on the anatomical data of twelve patients diagnosed with prostate carcinoma, stage T2N0M0 with low risk, plans were developed for stereotactic radiation therapy with volumetric modulates arc therapy (VMAT). The dose per fraction was 7,25 Gy for 5 fractions (total dose 36,25 Gy) with a normal photon energy of 10 MV. The developed plans were verified using a three-dimensional cylindrical ArcCHECK phantom. During the verification process, the three-dimensional dose distribution in the phantom was measured, based on which the values of the three-dimensional gamma index and the dose–volume histogram within each contoured anatomical structures were calculated with 3DVH software.
 The gamma index value γ (3 %, 2 mm, GN) at a threshold equal to 20 % of the dose maximum of the plan and the percentage of coincidence of points at least 95 % was chosen as a criterion of physical convergence of the calculated and measured dose distribution according to the recommendations of AAPM TG-218. To analyze the radiobiological equivalence of the calculated and measured dose distribution, the local control probability (TCP) and normal tissue complication probability (NTCP) criteria were used based on the calculated and measured dose–volume histograms. Contours of the target (PTV) and the anterior wall of the rectum were used for the analysis. The approach based on the concept of equivalent uniform dose (EUD) by A. Niemierko was used to calculate the values of TCP/NTCP criteria.
 Results: The results of physical convergence of plans for all patients on the contour of the whole body were higher than 95 % for the criteria γ (3 %, 2 mm, GN). The convergence along the PTV contour is in the range (75.5–95.2)%. The TCP and NTCP values obtained from the measured dose-volume histograms were higher than the planned values for all patients. It was found that the accelerator delivered a slightly higher dose to the PTV and the anterior wall of the rectum than originally planned.
 Conclusion: The capabilities of modern dosimetric equipment allow us move to the verification of treatment plans based on the analysis of TCP / NTCP radiobiological equivalence, taking into account the individual characteristics of the patient and the capabilities of radiation therapy equipment.

Dosimetric verification of stereotactic body radiotherapy treatment plan via ArcCHECK-3DVH system.

To study the feasibility of ArcCHECK-3DVH system in dosimetric verification for stereotactic body radiaotherapy (SBRT) with flattening filter free (FFF) model. SBRT treatment plans for 57 patients were introduced into ArcCHECK phantom and recalculated. The calculated dose distribution of treatment planning system and the measured dose distribution of ArcCHECK phantom were compared by γ analysis. Then the 3 dimensional dose distribution of target and organs at risk was reconstructed by 3DVH software. The reconstructed dose and calculated dose with treatment planning system (TPS) were compared, and the dose volume γ pass rate and deviation of dose volume parameters to the target and organs at risk were quantitatively valuated. Based on the threshold criteria (3%, 3 mm, 10%), namely the deviation of measuring points between the planned value and the measured value was less than 3%, and the proportion of points with similar values in the plane or sphere with the center of the point and the radius of 3 mm was 10%, the relative and absolute dose pass rates of SBRT treatment plans in ArcCHECK system via γ analysis were greater than 95%. Based on the stricter threshold criteria (2%, 2 mm, 10%), the relative and absolute dose pass rates of SBRT treatment plan in ArcCHECK system via γ analysis were about 93%. In 3DVH dose verification, the γ pass rate of target and organs at risk was exceed 97%, and the deviations in 3DVH of the target and organs at risk were less than ±5%. The ArcCHECK-3DVH system in dose verification can provide more comprehensive dose distribution information to reasonably evaluate the SBRT plan, with more significance for guiding clinical treatment.

Impact of different optimization strategies on the compatibility between planned and delivered doses during radiation therapy of cervical cancer.

To analyse the impact of different optimization strategies on the compatibility between planned and delivered doses during radiotherapy of cervical cancer. Four treatment plans differing in optimisation strategies were prepared for ten cervical cancer cases. These were: volumetric modulated arc therapy with (_OPT) and without optimization of the doses in the bone marrow and for two sets of margins applied to the clinical target volume that arose from image guidance based on the bones (IG(B)) and soft tissues (IG(ST)). The plans were subjected to dosimetric verification by using the ArcCHECK system and 3DVH software. The planned dose distributions were compared with the corresponding measured dose distributions in the light of complexity of the plans and its deliverability. The clinically significant impact of the plans complexity on their deliverability is visible only for the gamma passing rates analysis performed in a local mode and directly in the organs. While more general analyses show statistically significant differences, the clinical relevance of them has not been confirmed. The analysis showed that IG(ST)_OPT and IG(B)_OPT significantly differ from IG(ST) and IG(B). The clinical acceptance of IG(ST)_OPT obtained for hard combinations of gamma acceptance criteria (2%/2 mm) confirm its satisfactory deliverability. In turn, for IG(B)_OPT in the case of the rectum, the combination of 2%/2 mm did not meet the criteria of acceptance. Despite the complexity of the IG(ST)_OPT, the results of analysis confirm the acceptance of its deliverability when 2%/2 mm gamma acceptance criteria are used during the analysis.

A correlation study between clinical dose distribution and gamma passing rates in pre-treatment Tomotherapy quality assurance

Introduction: we focused on Tomotherapy patient-specific Quality Assurance (QA) in prostate cancer cases. Conventionally it is possible to accomplish QA with the calculation of in-phantom gamma passing rate (GPR). However, GPR, although widely used, is not a good predictor of the agreement between calculated and delivered dose to the patient and recent studies suggest the use of clinical metrics. To our best knowledge, there are no similar studies in Tomotherapy. In this work, we used 3DVH software and ArcCheck matrix (SunNuclear Corporation, Melbourne, FL) and we looked for the correlation between clinical metrics results and phantom GPRs. 3DVH applies perturbations to the in-patient TPS planned dose to account for discrepancies in dose delivery. Materials and methods: we retrospectively selected patients between those treated in our centre for prostatic cancer with Tomotherapy between April 2017 and August 2018. We submitted all plans to a specific QA; for data acquisition, we used the ArcCheck matrix and SNC patient software. We compared delivered and calculated volumetric dose distributions via the GPR and evaluated the clinical metrics using the 3DVH software. Unlike what previous authors have done, we did not investigate DVH clinical endpoints (e.g. rectum v70) agreement, but the complete dose distributions agreement applying gamma metric to the comparison of in-patient calculated and delivered dose distribution. For statistical analysis, we made both two tails Pearson’s correlation coefficient calculation and a linear regression evaluation. Results: from our results do not emerge any significant correlation between GPR and 3DVH results for every DTA and %D values used in gamma analysis. Conclusions: from this study, the need for employing clinical patient metrics instead of the simple gamma analysis, already suggested for conventional Linacs treatments, is extended to Tomotherapy treatments. Further studies are necessary to extend this result to Tomotherapy pre-treatment QA to other anatomical districts.

P148] Evaluation of delta4 phantom’s spatial sensitivity

Purpose The aim of this study is to evaluate the spatial sensitivity of the Delta4 diode array phantom (Scandidos, Uppsala, Sweden) investigating how set up errors affect the measurement’s results during head and neck treatment plan verification. Method The Delta4 phantom is used to verify ten IMRT head and neck plans, created on Oncentra v4.5.2 (Nucletron, Elekta) treatment planning system. Patient plans were transferred to the Delta4 geometry and were delivered on a 6MV photon beam SIEMENS Oncor Impression linac. Each reference (no-shift) plan was then delivered on the linac with a ± 3 mm shift of the phantom at lateral, longitudinal and vertical direction. The measurements’ results for all delivered plans were evaluated using the gamma index criteria (3%/3 mm). The application of the treatment plan is considered successful with an over 90% gamma index passing rate. Results The gamma index passing rate was measured at no-shift position (96.1 ± 0.7) %. Mean gamma index for each direction (lateral, longitudinal, vertical) was measured as 85.5% (SD = 2.6), 85.7% (SD = 4.5) and 85.2% (SD = 4.5) respectively. For all shifts, in all directions, the mean gamma index passing rate was found enough below the passing rate limit of 90% and more specifically 10.6% less than the no-shift measured gamma index. Conclusion Delta4 is an efficient QA tool for individual patient treatment plan verification exhibiting high reproducibility of results for γ -index. Shifts of 3 mm reveal significant deviation of measured 3%/3 mm gamma index passing rates, indicating high spatial sensitivity and efficiency of this QA tool. Future work with 3DVH software analysis is needed to report more statistics apart from γ -index values.

Retrospective dosimetry study of intensity-modulated radiation therapy for nasopharyngeal carcinoma: measurement-guided dose reconstruction and analysis

BackgroundConventional phantom-based planar dosimetry (2D-PBD) quality assurance (QA) using gamma pass rate (GP (%)) is inadequate to reflect clinically relevant dose error in intensity-modulated radiation therapy (IMRT), owing to a lack of information regarding patient anatomy and volumetric dose distribution. This study aimed to evaluate the dose distribution accuracy of IMRT delivery for nasopharyngeal carcinoma (NPC), which passed the 2D-PBD verification, using a measurement-guided 3D dose reconstruction (3D-MGR) method.MethodsRadiation treatment plans of 30 NPC cases and their pre-treatment 2D-PBD data were analyzed. 3D dose distribution was reconstructed on patient computed tomography (CT) images using the 3DVH software and compared to the treatment plans. Global and organ-specific dose GP (%), and dose-volume histogram (DVH) deviation of each structure was evaluated. Interdependency between GP (%) and the deviation of the volumetric dose was studied through correlation analysis.ResultsThe 3D-MGR achieved global GP (%) similar to conventional 2D-PBD in the same criteria. However, structure-specific GP (%) significantly decreased under stricter criteria, including the planning target volume (PTV). The average deviation of all inspected dose volumes (DV) and volumetric dose (VD) parameters ranged from − 2.93% to 1.17%, with the largest negative deviation in V100% of the PTVnx of − 15.66% and positive deviation in D1cc of the spinal cord of 6.66%. There was no significant correlation between global GP (%) of 2D-PBD or 3D-MGR and the deviation of the most volumetric dosimetry parameters (DV or VD), when the Pearson’s coefficient value of 0.8 was used for correlation evaluation.ConclusionEven upon passing the pre-treatment phantom based dosimetric QA, there could still be risk of dose error like under-dose in PTVnx and overdose in critical structures. Measurement-guided 3D volumetric dosimetry QA is recommended as the more clinically efficient verification for the complicated NPC IMRT.

Patient-Specific Quality Assurance Protocol for Volumetric Modulated Arc Therapy using Dose Volume Histogram.

A retrospective study was performed to explore the use of dose volume histogram (DVH) metrics in a patient-specific quality assurance protocol for volumetric modulated arc therapy (VMAT). Fourteen head and neck (HN) and ten brain patients treated with VMAT at the Launceston General Hospital were retrospectively analyzed using the new protocol to identify cases where patient dose errors exceed the established action levels that were not originally detected by either point dose and/or gamma index methods. The Sun Nuclear 3DVH software was used to estimate the dose delivered to the patient volume in terms of DVH dose errors. Thus, three different pretreatment verification methods were used to assess if a plan was considered acceptable. In two particular cases, the dose difference determined with point dose was above the established threshold, although it was found that this was due to the placement of the chamber in the phantom. In all cases, 3DVH confirmed that the dose delivered to target volumes (planning target volume – D50%) and to relevant organs at risk was within prescribed dose tolerances. This study has demonstrated the integration of DVH metrics into a VMAT PSQA protocol to provide clinically meaningful results that complement point dose and gamma index measurements. 3DVH should be regarded as an investigative tool that may be useful in diagnosing the cause of failed plans since it allows dose errors to be related to the patient anatomy.

Can clinically relevant dose errors in patient anatomy be detected by gamma passing rate or modulation complexity score in volumetric-modulated arc therapy for intracranial tumors?

We investigated whether methods conventionally used to evaluate patient-specific QA in volumetric-modulated arc therapy (VMAT) for intracranial tumors detect clinically relevant dosimetric errors. VMAT plans with coplanar arcs were designed for 37 intracranial tumors. Dosimetric accuracy was validated by using a 3D array detector. Dose deviations between the measured and planned doses were evaluated by gamma analysis. In addition, modulation complexity score for VMAT (MCSv) for each plan was calculated. Three-dimensional dose distributions in patient anatomy were reconstructed using 3DVH software, and clinical deviations in dosimetric parameters between the 3DVH doses and planned doses were calculated. The gamma passing rate (GPR)/MCSv and the clinical dose deviation were evaluated using Pearson's correlation coefficient. Significant correlation (P < 0.05) between the clinical dose deviation and GPR was observed with both the 3%/3 mm and 2%/2 mm criteria in clinical target volume (D99), brain (D2), brainstem (D2) and chiasm (D2), albeit that the correlations were not ‘strong’ (0.38 < |r| < 0.54). The maximum dose deviations of brainstem were up to 4.9 Gy and 2.9 Gy for Dmax and D%, respectively in the case of high GPR (98.2% with 3%/3 mm criteria). Regarding MCSv, none of the evaluated organs showed a significant correlation with clinical dose deviation, and correlations were ‘weak’ or absent (0.01 < |r| < 0.21). The use of high GPR and MCSv values does not always detect dosimetric errors in a patient. Therefore, in-depth analysis with the DVH for patient-specific QA is considered to be preferable for guaranteeing safe dose delivery.

Gamma index variation in the verification of step & shoot IMRT

Introduction IMRT plan verification is one of the most important parameters in the modern radiotherapy chain in order to achieve high quality and reproducible treatment delivery. Purpose The purpose of this study is to present a detailed analysis of the variation of gamma index (γ-index), which is used as a primary quantitative parameter in IMRT plan verification. Materials and methods We retrospectively considered 60 Prostate and 30 Head and Neck (H&N) step and shoot IMRT cases treated in our department. All plans were created on the Oncentra v4.5 TPS (Elekta, Sweden), using 5–7–9 beams, maximum 10 segments/beam and minimum 4 cm2 segments. Plan verification was implemented using the ArcCheck phantom (SunNuclear, FL, USA). γ-index was calculated at 3%–3 mm and at 2%–2 mm using a 10% threshold value with and without global correction. Results γ-Index (3%/3 mm, global) for Prostate and H&N was 97.1 ± 1.7 and 97 ± 2.1 respectively, γ-index was 9% less when not using global corection factor. 1 mm y-shift variation occurred in 70% of verification plans, while x-shift was negligible. Correcting for y-shift, γ-index was 0.4% and 0.9% higher for prostate and H&N respectively. γ-index variation showed no dependance upon the number of beams used. Conclusion Arccheck is an efficient QA tool for individual patient verification, exhibiting γ-index >97% and high reproducibility of results. Further work is done to correlate γ-index values with ROI specific passing rates, as estimated by the 3DVH software analysis.

SU‐F‐T‐300: Impact of Electron Density Modeling of ArcCHECK Cylindricaldiode Array On 3DVH Patient Specific QA Software Tool Analysis

Purpose:3DVH software is a patient specific quality assurance tool which estimates the 3D dose to the patient specific geometry with the help of Planned Dose Perturbation algorithm. The purpose of this study is to evaluate the impact of HU value of ArcCHECK phantom entered in Eclipse TPS on 3D dose &amp; DVH QA analysis.Methods:Manufacturer of ArcCHECK phantom provides CT data set of phantom &amp; recommends considering it as a homogeneous phantom with electron density (1.19 gm/cc or 282 HU) close to PMMA. We performed this study on Eclipse TPS (V13, VMS) &amp; trueBEAM STx VMS Linac &amp; ArcCHECK phantom (SNC). Plans were generated for 6MV photon beam, 20cm×20cm field size at isocentre &amp; SPD (Source to phantom distance) of 86.7 cm to deliver 100cGy at isocentre. 3DVH software requires patients DICOM data generated by TPS &amp; plan delivered on ArcCHECK phantom. Plans were generated in TPS by assigning different HU values to phantom. We analyzed gamma index &amp; the dose profile for all plans along vertical down direction of beam's central axis for Entry, Exit &amp; Isocentre dose.Results:The global gamma passing rate (2% &amp; 2mm) for manufacturer recommended HU value 282 was 96.3%. Detector entry, Isocentre &amp; detector exit Doses were 1.9048 (1.9270), 1.00(1.0199) &amp; 0.5078(0.527) Gy for TPS (Measured) respectively.The global gamma passing rate for electron density 1.1302 gm/cc was 98.6%. Detector entry, Isocentre &amp; detector exit Doses were 1.8714 (1.8873), 1.00(0.9988) &amp; 0.5211(0.516) Gy for TPS (Measured) respectively.Conclusion:Electron density value assigned by manufacturer does not hold true for every user. Proper modeling of electron density of ArcCHECK in TPS is essential to avoid systematic error in dose calculation of patient specific QA.

SU‐G‐TeP3‐11: Radiobiological‐Cum‐Dosimetric Quality Assurance of Complex Radiotherapy Plans

Purpose:Dosimetric gamma‐analysis used for QA of complex radiotherapy plans tests the dosimetric equivalence of a delivered plan with the treatment planning system (TPS) optimized plan. It does not examine whether a dosimetric difference results in any radiobiological difference. This study introduces a method to test the radiobiological and dosimetric equivalence between a delivered and the TPS optimized plan.Methods:Six head and neck and seven lung cancer VMAT or IMRT plans optimized for patient treatment were calculated and delivered to an ArcCheck phantom. ArcCheck measured dose distributions were compared with the TPS calculated dose distributions using a 2‐D gamma‐analysis. Dose volume histograms (DVHs) for various patient structures were obtained by using measured data in 3DVH software and compared against the TPS calculated DVHs using 3‐D gamma analysis. DVH data were used in the Poisson model to calculate tumor control probability (TCP) for the treatment targets and in the sigmoid dose response model to calculate normal tissue complication probability (NTCP) for the normal structures.Results:Two‐D and three‐D gamma passing rates among six H&amp;N patient plans differed by 0 to 2.7% and among seven lung plans by 0.1 to 4.5%. Average ± SD TCPs based on measurement and TPS were 0.665±0.018 and 0.674±0.044 for H&amp;N, and 0.791±0.027 and 0.733±0.031 for lung plans, respectively. Differences in NTCPs were usually negligible. The differences in dosimetric results, TCPs and NTCPs were insignificant.Conclusion:The 2‐D and 3‐D gamma‐analysis based agreement between measured and planned dose distributions may indicate their dosimetric equivalence. Small and insignificant differences in TCPs and NTCPs based on measured and planned dose distributions indicate the radiobiological equivalence between the measured and optimized plans. However, patient plans showing larger differences between 2‐D and 3‐D gamma‐analysis can help us make a more definite conclusion through our ongoing research with a larger number of patients.

Accuracy of one algorithm used to modify a planned DVH with data from actual dose delivery.

Detection and accurate quantification of treatment delivery errors is important in radiation therapy. This study aims to evaluate the accuracy of DVH based QA in quantifying delivery errors. Eighteen previously treated VMAT plans (prostate, H&N, and brain) were randomly chosen for this study. Conventional IMRT delivery QA was done with the ArcCHECK diode detector for error‐free plans and plans with the following modifications: 1) induced monitor unit differences up to ±3.0%,2) control point deletion (3, 5, and 8 control points were deleted for each arc), and 3) gantry angle shift (2° uniform shift clockwise and counterclockwise). 2D and 3D distance‐to‐agreement (DTA) analyses were performed for all plans with SNC Patient software and 3DVH software, respectively. Subsequently, accuracy of the reconstructed DVH curves and DVH parameters in 3DVH software were analyzed for all selected cases using the plans in the Eclipse treatment planning system as standard. 3D DTA analysis for error‐induced plans generally gave high pass rates, whereas the 2D evaluation seemed to be more sensitive to detecting delivery errors. The average differences for DVH parameters between each pair of Eclipse recalculation and 3DVH prediction were within 2% for all three types of error‐induced treatment plans. This illustrates that 3DVH accurately quantifies delivery errors in terms of actual dose delivered to the patients. 2D DTA analysis should be routinely used for clinical evaluation. Any concerns or dose discrepancies should be further analyzed through DVH‐based QA for clinically relevant results and confirmation of a conventional passing‐rate‐based QA.PACS number(s): 87.56.Fc, 87.55.Qr, 87.55.dk, 87.55.km

Evaluation of 3D pre-treatment verification for volumetric modulated arc therapy plan in head region

The development of pre-treatment QA tools contributes to the three dimension (3D) dose verification using the calculation software with the measured planar dose distribution. This research is aimed to evaluate the Sun Nuclear 3DVH software with Thermo luminescence dosimeter (TLD) measurement. The two VMAT patient plans (2.5 arcs) of 6 MV photons with different PTV locations were transferred to the Rando phantom images. The PTV of the first plan located in homogeneous area and vice versa in the second plan. For treatment planning process, the Rando phantom images were employed in optimization and calculation with the PTV, brain stem, lens and TLD position contouring. The verification plans were created, transferred to the ArcCHECK for measurement and calculated the 3D dose using 3DVH software. The range of the percent dose differences in both PTV and organ at risk (OAR) between TLD and 3DVH software of the first and the second plans were -2.09 to 3.87% and -1.39 to 6.88%, respectively. The mean percent dose differences for the PTV were 1.62% and 3.93% for the first and the second plans, respectively. In conclusion, the 3DVH software results show good agreement with TLD when the tumor located in the homogeneous area.

Comparison of 3-dimensional dose reconstruction system between fluence-based system and dose measurement-guided system

COMPASS system (IBA Dosimetry, Schwarzenbruck, Germany) and ArcCHECK with 3DVH software (Sun Nuclear Corp., Melbourne, FL) are commercial quasi-3-dimensional (3D) dosimetry arrays. Cross-validation to compare them under the same conditions, such as a treatment plan, allows for clear evaluation of such measurement devices. In this study, we evaluated the accuracy of reconstructed dose distributions from the COMPASS system and ArcCHECK with 3DVH software using Monte Carlo simulation (MC) for multi-leaf collimator (MLC) test patterns and clinical VMAT plans. In a phantom study, ArcCHECK 3DVH showed clear differences from COMPASS, measurement and MC due to the detector resolution and the dose reconstruction method. Especially, ArcCHECK 3DVH showed 7% difference from MC for the heterogeneous phantom. ArcCHECK 3DVH only corrects the 3D dose distribution of treatment planning system (TPS) using ArcCHECK measurement, and therefore the accuracy of ArcCHECK 3DVH depends on TPS. In contrast, COMPASS showed good agreement with MC for all cases. However, the COMPASS system requires many complicated installation procedures such as beam modeling, and appropriate commissioning is needed. In terms of clinical cases, there were no large differences for each QA device. The accuracy of the compass and ArcCHECK 3DVH systems for phantoms and clinical cases was compared. Both systems have advantages and disadvantages for clinical use, and consideration of the operating environment is important. The QA system selection is depending on the purpose and workflow in each hospital.

Comparison of 3DVH Software with Two-dimensional Array Systems on Pretreatment Verification for Volumetric-modulated Arc Therapy

Abstract Objectives: The purpose of this study is to investigate the comparison of 3DVH software and two-dimensional array systems (MatriXX, ArcCHECK, and portal dosimetry system) on pretreatment verification for volumetricmodulated arc therapy. Methods: Dosimetric measurements were performed using the verification for 20 treatment plans. Measured dosimetric differences were evaluated by gamma pass rate and percentage dose difference. Dose-volume histograms (DVHs) calculated by the treatment planning system were also compared with those predicted by the 3DVH software. Results: The mean gamma pass rates were more than 95% for the 3%/3 mm criterion, except for 3D evaluation using the 3DVH (3DVH (3D)) software in prostate cancer cases. In the cases of head-and-neck (HN) cancer, the mean gamma pass rates by ArcCHECK and 3DVH 2D evaluation (3DVH (2D)) were estimated to be lower than those of MatriXX, EPID, and 3DVH (3D) for the 2%/2 mm and 1%/1 mm criteria. The percentage dose differences were within 4% for all structures, and correlated with the mean gamma pass rate for the planning target volume (PTV) and the Dmean of the spinal cord (p < 0.05). On the other hand, the mean gamma pass rates of prostate cases presented similar results for all criteria. The percentage dose differences for structure volumes in the cases of prostate cancer (from 2.76% to 12.58%) were larger than those in the cases of HN cancer, and there was no statistical significance except for the Dmax of the bladder. Conclusion: Judging from our results, the three dosimetric devices showed similar results for pretreatment verification and portal dosimetry can be replaced as the verification system. However, the use of 3DVH software remains to be a matter for further discussion.

TU‐G‐BRD‐09: Evaluation of Patient DVH‐Based QA Metrics for Prostate VMAT: Correlation Between Accuracy of Estimated 3D Patient Dose and MLC Position Error

Purpose:The purpose of this study was to evaluate the accuracy of patient DVH‐based QA metrics and test the hypothesis: measurement‐guided 3D dose reconstruction (MGDR) captures the induced dose error.Methods:We used 3DVH software with an ArcCHECK to estimate 3D patient dose by MGDR. Two different calculating modes of MGDR were used: “Normal Sensitivity” and “High Sensitivity”. Ten prostate cancer patients treated with hypo‐fractionated VMAT (67.6 Gy/26 Fr) were studied. For the baseline plan, we induced MLC errors (−0.75, −0.5, −0.25, 0.25, 0.5 and 0.75 mm for each single bank), generated by in‐house software. We compared the 3D patient dose estimated by 3DVH and that calculated by the treatment planning system. We evaluated the correlation between dose estimation error and MLC position error.Results:Slopes of linear fit to dose estimation error versus MLC position error for mean dose and D95 to the PTV were 1.76 and 1.40% mm‐1, respectively, for “Normal Sensitivity” and −0.53 and −0.88% mm‐1, respectively, for “High Sensitivity”, showing better accuracy for “High Sensitivity” than “Normal Sensitivity”. On the other hand, the slopes for mean dose to the rectum and bladder and V55 to the rectum and bladder were −1.00, −0.55, −3.53 and −1.85% mm‐1, respectively, for “Normal Sensitivity” and −2.89, −2.39, −6.24 and −4.11% mm‐1, respectively, for “High Sensitivity”, showing significant better accuracy for “Normal Sensitivity” than “High Sensitivity”.Conclusion:Our results showed that 3DVH had some residual error for both sensitivities, indicating the MGDR could capture a part of the induced error but not all of the induced error.Furthermore, we found that “Normal Sensitivity” might have better accuracy for the DVH metric for PTV and that “High Sensitivity” might have better accuracy for DVH metrics for the rectum and bladder. We must be willing to tolerate this residual error in clinical care.

SU‐E‐T‐789: Validation of 3DVH Accuracy On Quantifying Delivery Errors Based On Clinical Relevant DVH Metrics

Purpose:Detection of treatment delivery errors is important in radiation therapy. However, accurate quantification of delivery errors is also of great importance. This study aims to evaluate the 3DVH software's ability to accurately quantify delivery errors.Methods:Three VMAT plans (prostate, H&amp;N and brain) were randomly chosen for this study. First, we evaluated whether delivery errors could be detected by gamma evaluation. Conventional per‐beam IMRT QA was performed with the ArcCHECK diode detector for the original plans and for the following modified plans: (1) induced dose difference error up to ±4.0% and (2) control point (CP) deletion (3 to 10 CPs were deleted) (3) gantry angle shift error (3 degree uniformly shift). 2D and 3D gamma evaluation were performed for all plans through SNC Patient and 3DVH, respectively. Subsequently, we investigated the accuracy of 3DVH analysis for all cases. This part evaluated, using the Eclipse TPS plans as standard, whether 3DVH accurately can model the changes in clinically relevant metrics caused by the delivery errors.Results:2D evaluation seemed to be more sensitive to delivery errors. The average differences between ECLIPSE predicted and 3DVH results for each pair of specific DVH constraints were within 2% for all three types of error‐induced treatment plans, illustrating the fact that 3DVH is fairly accurate in quantifying the delivery errors. Another interesting observation was that even though the gamma pass rates for the error plans are high, the DVHs showed significant differences between original plan and error‐induced plans in both Eclipse and 3DVH analysis.Conclusion:The 3DVH software is shown to accurately quantify the error in delivered dose based on clinically relevant DVH metrics, where a conventional gamma based pre‐treatment QA might not necessarily detect.

SU‐E‐T‐34: A Feasible Action Level System for DVH‐Based IMRT QA

Purpose:Gamma‐based IMRT QA metrics have been shown to inadequately predict clinically relevant patient dose errors. In this study, we develop and evaluate an intuitive and feasible DVH‐based IMRT QA action level system, which incorporates both physical and clinical considerations.Methods:VMAT plans from previously treated prostate (n=11) and brain (n=13) patients are analyzed. Treatment plans were created using Eclipse TPS and delivered using Varian's Trilogy linac. Initial IMRT QA was performed using the ArcCHECK phantom. All plans passed gamma‐based criteria (3%/3mm) with at least a 97% passing rate. To design and test the feasibility of the DVH‐based IMRT QA metric, 3DVH software is used to process the QA data from the ArcCHECK measurement and predict the 3D distribution of dose delivered to the patient. This enables comparison of a standard set of clinically important DVH values between TPS calculations and that predicted by the QA process. A two‐level system is implemented to determine the IMRT QA Result. Level 1 requires that QA predicted DVH values for the PTV and OARs fall within a physical tolerance generated by scaling the original planned dose uniformly by ±5%. If level 1 tolerance is exceeded, level 2 requires that the QA‐predicted DVH values are within institutional normal tissue tolerances. OARs for prostate cases include bladder and rectum. OARs for brain cases include the lens, optic nerve, optic chiasm, and brainstem.Results:All analyzed QAs passed the proposed action levels, with prostate cases all satisfying physical tolerances. Ten brain cases had DVH values failing physical tolerances, but satisfying clinical tolerances. All DVHs failing physical tolerances are in low dose region.Conclusion:The proposed IMRT QA metrics represents a straightforward alternative to the gamma‐based metric. It has the potential to better address both physical and clinical concerns that are specific to individual patients.