Dosimetric evaluation of the compass program for patient dose analysis in IMRT delivery quality assurance
Dosimetric evaluation of the compass program for patient dose analysis in IMRT delivery quality assurance
Ju-Young Song 0 1
Sung-Ja AhnID 0 1
0 Department of Radiation Oncology, Chonnam National University Medical School , Gwangju , Korea
1 Editor: Qinghui Zhang, North Shore Long Island Jewish Health System, UNITED STATES
A practical method was designed to verify the accuracy of dose distributions calculated using Compass, which can reconstruct the dose distribution inside a patient's body during intensity-modulated radiation therapy (IMRT). Twelve virtual IMRT treatment plans were developed using an ArcCHECK diode detector array, and then the recalculated and reconstructed doses in Compass were compared with the actual measurements to assess the dosimetric accuracy. Based on the results of gamma evaluation for the 12 plans, Compass achieved average pass rates higher than 98%, which confirmed proper dosimetric accuracy in the IMRT quality assurance process. The validity of Compass for clinical applications was also confirmed through an additional comparison with the results calculated using 3DVH, another dose reconstruction program. It is necessary to verify the accuracy of the dose calculated using the program in advance before the commercialized dose reconstruction program is applied in clinical practice. This study has limitations in that it did not provide a real scientific contribution such as an introduction of new algorithm for dose calculation and the development of new measurement tools. However, the method based on the comparative analysis with the actual measured dose values as devised in this study seems to be useful in that it can be applied effectively to verify the dosimetric accuracy of the dose reconstruction program before first using it in the clinical cases.
Delivery quality assurance (DQA) has been investigated in various studies for the verification
of the dosimetric accuracy of intensity-modulated radiation therapy (IMRT) and volumetric
modulated arc therapy (VMAT) [1–5]. A conventional procedure used for IMRT DQA is
measurement of a dose distribution in a phantom structure. The dosimetric errors are thereafter
analyzed by comparing the measured data with the calculated dose in a treatment planning
The conventional DQA process has some limitations because it measures and analyzes
the dose in a phantom material and not within the body of the patient [6–8]. In order to
overcome this limitation, special tools were developed for calculating the dose distribution
in a patient’s body using the measured data in the DQA process [9,10]. Typical tools that
employ this method include Compass (IBA, Schwarzenbruck, Germany), 3DVH
(SunNuclear, Melbourne, FL, USA), and Delta4DVH (ScandiDos, Uppsala, Sweden) [11–15].
Compass calculates the dose inside a patient’s body using two different methods. One method
is the calculation-based TPS check, which recalculates the dose using a TPS class collapsed
cone algorithm without the phantom measurement. The other method is the dose
reconstruction based on the measured data using a two-dimensional (2D) detector array such as
MatriXX (IBA, Schwarzenbruck, Germany) or Dolphin (IBA, Schwarzenbruck,
Although the dosimetric accuracy of Compass was analyzed in various studies and
appropriate accuracy was demonstrated for IMRT and VMAT, most of the studies were limited to
verifying the accuracy of the calculated dose by comparing it with the dose distribution
calculated using other reference dose calculation tools such as a Monte Carlo simulation [16–18]. In
addition, few studies have been conducted for the analysis of dose accuracy calculated using
Compass through the actual measurement of dose distribution for various clinical cases. In
order to apply a dose recalculation tool such as Compass to clinical cases, the confirmation of
tool accuracy and characteristics of the calculated dose should be performed by comparing the
actual measured dose distribution for various cases with the dose distribution calculated using
In this study, a practical method was developed to verify the accuracy and characteristics of
dose distributions calculated using Compass through a comparative analysis with the actual
measured dose values before applying Compass to clinical practice.
After acquiring computed tomography (CT) images of ArcCHECK (SunNuclear,
Melbourne, FL, USA) for IMRT DQA, IMRT plans were made based on the virtual tumor targets
and organs at risk (OARs), which were contoured on the CT images, for typical clinical cases.
The dosimetric accuracy of Compass was evaluated by analyzing the degree of similarity
between the dose distribution by the actual beam delivery measured at the detector array of
ArcCHECK, the recalculated dose distribution in Compass, and the reconstructed dose
distribution based on the data measured using MatriXX.
In addition, we evaluated the dosimetric characteristics of Compass by comparing the
calculated dosimetric results in the typical cancer cases with the results calculated using another
dose reconstruction program, 3DVH.
Materials and methods
Verification of the calculated dose accuracy in compass
Preparation of the virtual treatment plans. The diode detector array ArcCHECK was
used for measurement of the real dose distribution of IMRT and VMAT. After acquiring a
CT image of the ArcCHECK, virtual treatment plans were prepared for head-neck, lung
and prostate cases based on the CT images. In each cancer cases, the IMRT and RapidArc
(Varian, Palo Alto, CA, USA) plans were made using photons of 6 MV and 10 MV,
respectively, and 12 plans were prepared. The virtual tumor target and OARs were contoured as
shown in Fig 1. All of the plans were created using an Eclipse (Varian, Palo Alto, CA,
Fig 2. Example of the result of the recalculated dose distribution using the compass program.
Fig 3. Dose measurement with MatriXX through the actual beam delivery of each plan.
USA) planning system and prepared according to the dose prescription, as shown in
Table 1. A clinical linear accelerator (LINAC), Trilogy Tx (Varian, Palo Alto, CA, USA),
was used in this study.
Dose recalculation with compass
The dose distribution within a patient’s body was recalculated for all of the prepared treatment
plans using the two calculation methods in Compass.
First, the plan data including the CT, structures, and plan files created using TPS were
imported into Compass in the format of digital imaging and communications in medicine
Fig 4. Example of the dose reconstruction based on the dose data measured using MatriXX.
(DICOM), and the dose was recalculated using the collapsed cone algorithm established
through the beam commissioning process. Fig 2 shows an example of the results of the
recalculated dose distribution.
Subsequently, the dose in the patient was reconstructed based on the dose data measured
using a 2D ion chamber array MatriXX. Fig 3 shows the process of measuring the dose through
actual beam delivery of each plan using MatriXX, and Fig 4 shows an example of dose
reconstruction based on the dose data measured using MatriXX.
Analysis of the dosimetric accuracy of compass. The dose distribution was measured at
the detector array after beam delivery to ArcCHECK in order to verify the dose accuracy
calculated using Compass. The dosimetric accuracy was evaluated by comparison of the measured
dose distribution with that calculated using Compass at the same position. The dose results
calculated using Eclipse TPS, the Compass recalculation results, and the Compass
reconstruction results were compared with the measured dose distributions, and the dose difference was
evaluated using the gamma evaluation method with a 3% dose difference and a 3-mm
distance-to-agreement criteria. The ArcCHECK tool used in this study was introduced three
years ago and the accuracy of dose measurements was verified by commissioning procedure
before using it in clinical cases. And it can be evaluated as a reliable tool through the DQA
results of VMAT and IMRT so far.
Comparison of the results obtained from compass and 3DVH
In order to analyze the additional characteristics of the dose distribution calculated using
Compass, we performed a comparative evaluation with the results calculated using the 3DVH program
which can reconstruct the dose based on the data measured in the DQA process using
ArcCHECK. The dose calculation results obtained from Compass and 3DVH were compared and
analyzed with 30 RapidArc plans (10 head-neck plans, 10 lung plans, and 10 prostate plans).
The patient dose distribution in 3DVH was calculated based on the actual measured data
by delivering the DQA plan using ArcCHECK as shown in Fig 5. Compass was also used to
reconstruct the patient dose for the same plans. The dose distribution recalculated based on
the plan data imported from Eclipse TPS was obtained and the reconstructed dose distribution
Fig 5. Dose measurement with ArcCHECK for the dose reconstruction with the 3DVH program.
results based on the data measured using MatriXX were also obtained. To evaluate the
similarity between the calculated results of the three dose distributions and the results calculated
Fig 6. Comparison of the pass rate calculated in a gamma evaluation between a measured dose using ArcCHECK and a predicted dose
for each dose calculation tool. (A) 6 MV-RapidArc plans, (B) 6 MV-IMRT plans, (C) 10 MV-RapidArc plans, (D) 10 MV-IMRT plans.
using Eclipse TPS, the pass rates of the gamma evaluation in the tumor target and OARs were
calculated with a 3% dose difference and 3-mm distance-to-agreement criteria. In addition, we
evaluated the variation in the major dose metrics of the tumor target and OARs according to
the results of the three dose calculations.
The gamma evaluation results from the comparison with the dose distribution measured using
ArcCHECK to verify the accuracy of the recalculated dose and reconstructed doses in
Compass are shown in Fig 6.
The average pass rates according to the dose calculation methods were calculated as 98.7
±0.8% in Eclipse TPS, 98.5±0.8% in Compass recalculation and 98.2±0.2% in Compass
reconstruction. This confirms that the Compass calculation results are similar to the doses calculated
using the Eclipse TPS and are accurate without any significant errors compared with the actual
The average pass rate results according to the photon energy, treatment technique, and
treatment legion showed similar accuracy without any significant differences, as shown in Table 2.
The results of the comparative evaluation with the dose calculated using the 3DVH
program are shown in Tables 3–8. Tables 3–5 show the pass rates of the gamma evaluation in the
tumor target and OARs when the calculation results obtained from Compass and 3DVH were
compared with the reference dose distribution calculated using Eclipse TPS.
Fig 7 shows the average pass rates in the tumor target and OARs according to the
calculation method for each treatment site. The average pass rates in the tumor target according to
the dose calculation methods were calculated as 96.5±3.9% in 3DVH, 98.9±2.1% in Compass
recalculation, and 92.3±12.5% in Compass reconstruction. The average pass rates in OARs
according to the dose calculation methods were calculated as 99.6±0.6% in 3DVH, 99.9±0.3%
in Compass recalculation and 99.2±1.0% in Compass reconstruction.
Tables 6–8 show the variation in the major dose metrics of the tumor target and OARs
according to the three dose calculation methods. Compared with the change in the average
pass rate in the gamma evaluation, the changes in the dose metric values occurred more
variously according to the dose calculation methods. Fig 8 shows the difference of a calculated
D90% (CTV) using 3DVH and Compass compared with a reference value calculated in Eclipse
TPS. The average differences of D90% (CTV) were 0.78±1.32% in 3DVH, 0.55±1.04% in
Compass recalculation and 1.84±2.04% in Compass reconstruction. The average differences of
calculated dose metrics in OARs using 3DVH and Compass compared with reference values
calculated in Eclipse TPS were -1.22±8.81% in 3DVH, -2.61±13.11% in Compass recalculation
and 2.58±15.36% in Compass reconstruction. As can be seen from these results, there were
significant variations in the differences of main dose metrics in OARs compared with those of
D90% (CTV). This showed that more attention should be paid to the analysis on the dose
metrics of OARs calculated in the patient’s dose reconstruction QA tool.
In both CTV and OARs, the differences between the results from Compass reconstruction
calculation and the reference value were significantly larger (p < 0.03) than those of 3DVH
and Compass recalculation. This was due to the characteristics of calculating the dose based on
the measurement data that was influenced by the factors which could occur during the
measurement process such as the variation of the output and mechanical accuracy in the linear
accelerator, and the sensitivity variation of the measurement device.
In this study, the dosimetric difference compared with the actual dose data measured using
ArcCHECK was analyzed in order to evaluate the accuracy of dose calculation in Compass to
develop a dose reconstruction program for IMRT DQA. Based on the results of gamma
evaluation for 12 plans, Compass achieved an average pass rate of more than 98% in both
recalculation and reconstruction methods. This showed a dosimetric accuracy similar to that of
Eclipse TPS, which achieved a pass rate of 98.7%. Thus, the dosimetric accuracy related to the
beam commissioning process during the installation of Compass can be confirmed, and the
Fig 7. Comparison of the pass rate calculated in a gamma evaluation between a reference dose calculated using
Eclipse TPS and a calculated dose using 3DVH and compass. (A) average pass rate in the tumor target, (B) average
pass rate in the OARs.
reliability of dose results can be guaranteed when calculating the dose distribution in a patient’s
body before applying it to clinical cases.
Although many studies have demonstrated the accuracy of a commercially available dose
reconstruction program for IMRT DQA [11,19–23], it is reasonable that the accuracy of the
dose calculated using the program should be verified in advance through a comparison with
the actual measured dose distribution before application in practical clinical cases.
Accordingly, the verification of dosimetric accuracy based on the dose measured using the detector
array for IMRT DQA, as devised in this study, can be effectively used in clinical sites.
Fig 8. Difference of D90% (CTV) calculated using 3DVH and compass compared with a reference value calculated
in Eclipse TPS. (A) head-neck plans, (B) lung plans, (C) prostate plans.
Comparing the dose calculation results obtained using Compass and 3DVH, the pass rate
in gamma evaluation was slightly different according to the characteristics of the calculation
program and the positions and shapes of the tumor target and OARs.
In the tumor target, the average pass rate was 98.9±2.1% in the Compass recalculation, 96.5
±3.9% in 3DVH, and 92.3±12.5% in the Compass reconstruction. In the OARs, the average
pass rate was 99.9±0.3% in the Compass recalculation, 99.6±0.6% in 3DVH, and 99.2±1.0% in
the Compass reconstruction, demonstrating no significant difference for the different
calculation methods in this case. The reason for the differences in the pass rate results in cases where
the tumor target is larger is because the dose difference calculated according to the program
algorithm is relatively larger because the target region is irradiated with a larger amount of
dose. The reason for the lowest pass rate in the Compass reconstruction is the occurrence of
various possible errors in the measurement process, which could be included in the calculation
of the dose based on the MatriXX measurement data. The pass rates in the tumor target and
OARs showed acceptable values, guaranteeing a certain level of accuracy, except for a few cases
as shown in Tables 3–5.
Comparisons of important dose metric values on DVH that are related to actual tumor
control and complication probability are also needed rather than a simple comparison of
gamma evaluation values in CTV and OARs. As shown in Tables 6–8, the calculation results
of important dose metrics for tumor target and OARs showed various differences according
to the program calculation method and the position of the target and OARs. This confirmed
that a detailed analysis of the important dose metrics related to tumor control and
complications of OARs should be performed additionally rather than merely relying on the
gamma evaluation results when analyzing the characteristics of the dose distribution
calculated using the dose reconstruction program. And an appropriate tolerance range in the
dose metric analysis should be set up for the proper use of patient dose QA tool such as
The additional study on the dose characteristics calculated by compass according to the
various cases will be performed when the sufficient compass dosimeric results are collected for
more patient cases.
In this study, we designed and verified the validity of a method that utilizes the actual dose
measured using ArcCHECK, the IMRT DQA detector array, to validate the dose accuracy
calculated using Compass, the dose reconstruction program, inside a patient’s body. Before the
commercialized dose reconstruction program is used at a clinical site, it is necessary to verify
the accuracy of the dose calculated using the program. Using the method developed in this
study, the dose accuracy is expected to be determined efficiently by comparing it with the
actual measured dose distribution.
S1 Fig. 6MV-RapidArc Dose Recalculated by Compass for Head-Neck Case.
S2 Fig. 6MV-RapidArc Dose Reconstructed by Compass for Head-Neck Case.
S3 Fig. 6MV-IMRT Dose Recalculated by Compass for Head-Neck Case.
S4 Fig. 6MV-IMRT Dose Reconstructed by Compass for Head-Neck Case.
S5 Fig. 10MV-RapidArc Dose Recalculated by Compass for Head-Neck Case.
S6 Fig. 10MV-RapidArc Dose Reconstructed by Compass for Head-Neck Case.
S7 Fig. 10MV-IMRT Dose Recalculated by Compass for Head-Neck Case.
S8 Fig. 10MV-IMRT Dose Reconstructed by Compass for Head-Neck Case.
S9 Fig. 6MV-RapidArc Dose Recalculated by Compass for Lung Case.
S10 Fig. 6MV-RapidArc Dose Reconstructed by Compass for Lung Case.
S11 Fig. 6MV-IMRT Dose Recalculated by Compass for Lung Case.
S12 Fig. 6MV-IMRT Dose Reconstructed by Compass for Lung Case.
S13 Fig. 10MV-RapidArc Dose Recalculated by Compass for Lung Case.
S14 Fig. 10MV-RapidArc Dose Reconstructed by Compass for Lung Case.
S15 Fig. 10MV-IMRT Dose Recalculated by Compass for Lung Case.
S16 Fig. 10MV-IMRT Dose Reconstructed by Compass for Lung Case.
S17 Fig. 6MV-RapidArc Dose Recalculated by Compass for Prostate Case.
S18 Fig. 6MV-RapidArc Dose Reconstructed by Compass for Prostate Case.
S19 Fig. 6MV-IMRT Dose Recalculated by Compass for Prostate Case.
S20 Fig. 6MV-IMRT Dose Reconstructed by Compass for Prostate Case.
S21 Fig. 10MV-RapidArc Dose Recalculated by Compass for Prostate Case.
S22 Fig. 10MV-RapidArc Dose Reconstructed by Compass for Prostate Case.
S23 Fig. 10MV-IMRT Dose Recalculated by Compass for Prostate Case.
S24 Fig. 10MV-IMRT Dose Reconstructed by Compass for Prostate Case.
Conceptualization: Ju-Young Song, Sung-Ja Ahn.
Data curation: Ju-Young Song.
Formal analysis: Ju-Young Song.
Methodology: Ju-Young Song, Sung-Ja Ahn.
Supervision: Sung-Ja Ahn.
Writing – original draft: Ju-Young Song.
Writing – review & editing: Sung-Ja Ahn.
1. Ezzell GA , Galvin JM , Low D , Palta JR , Rosen I , Sharpe MB , et al. Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT subcommittee of the AAPM radiation therapy committee . Med Phys . 2003 ; 30 : 2089 - 2115 . https://doi.org/10.1118/1.1591194 PMID: 12945975
2. Palta JR , Liu C , Li JG . Quality assurance of intensity-modulated radiation therapy . Int J Radiat Oncol Biol Phys . 2008 ; 71 : S108 - S112 . https://doi.org/10.1016/j.ijrobp. 2007 . 05.092 PMID: 18406906
3. Li JS , Lin T , Chen L , Price RA Jr., Ma CM . Uncertainties in IMRT dosimetry . Med Phys . 2010 ; 37 : 2491 - 2500 . https://doi.org/10.1118/1.3413997 PMID: 20632560
4. Gordon JD , Krafft SP , Jang S , Smith-Raymond L , Stevie MY , Hamilton RJ . Confidence limit variation for a single IMRT system following the TG119 protocol . Med Phys . 2011 ; 38 : 1641 - 1648 . https://doi. org/10.1118/1.3555298 PMID: 21520877
5. Ezzell GA , Burmeister JW , Dogan N , LoSasso TJ , Mechalakos JG , Mihailidis D , et al. IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119 . Med Phys . 2009 ; 36 : 5359 - 5373 . https://doi.org/10.1118/1.3238104 PMID: 19994544
6. Korevaar EW , Wauben DJ , van der Hulst PC , Langendijk JA , van't Veld AA . Clinical introduction of a linac head-mounted 2D detector array based quality assurance system in head and neck IMRT . Radiother Oncol . 2011 ; 100 : 446 - 452 . https://doi.org/10.1016/j.radonc. 2011 . 09.007 PMID: 21963288
7. Nelms BE , Zhen H , Tome WA. Per-beam, planar IMRT QA passing rates do not predict clinically relevant patient dose errors . Med Phys . 2011 ; 38 : 1037 - 1044 . https://doi.org/10.1118/1.3544657 PMID: 21452741
8. Infusino E , Mameli A , Conti R , Gaudino D , Stimato G , Bellesi L , et al. Initial experience of ArcCHECK and 3DVH software for RapidArc treatment plan verification . Med Dosim . 2014 ; 39 : 276 - 281 . https:// doi.org/10.1016/j.meddos. 2014 . 04.004 PMID: 25088815
9. Nakaguchi Y , Ono T , Maruyama M , Nagasue N , Shimohigashi Y , Kai Y. Validation of fluence-based 3D IMRT dose reconstruction on a heterogeneous anthropomorphic phantom using Monte Carlo simulation . J Appl Clin Med Phys . 2015 ; 16 : 264 - 272 .
10. Kadoya N , Saito M , Ogasawara M , Fujita Y , Ito K , Sato K , et al. Evaluation of patient DVH-based QA metrics for prostate VMAT: correlation between accuracy of estimated 3D patient dose and magnitude of MLC misalignment . J Appl Clin Med Phys . 2015 ; 16 : 5251. https://doi.org/10.1120/jacmp. v16i3.5251 PMID: 26103486
11. Opp D , Nelms BE , Zhang G , Stevens C , Feygelman V. Validation of measurement-guided 3D VMAT dose reconstruction on a heterogeneous anthropomorphic phantom . J Appl Clin Med Phys . 2013 ; 14 : 70 - 84 .
12. Hauri P , Verlaan S , Graydon S , Ahnen L , Klo¨ck S , Lang S. Clinical evaluation of an anatomy-based patient specific quality assurance system . J Appl Clin Med Phys . 2014 ; 15 : 181 - 190 .
13. Vikraman S , Manigandan D , Karrthick KP , Sambasivaselli R , Senniandavar V , Ramu M , et al. Quantitative evaluation of 3D dosimetry for stereotactic volumetric-modulated arc delivery using compass . J Appl Clin Med Phys . 2014 ; 16 : 192 - 207 .
14. Nakaguchi Y , Ono T , Onitsuka R , Maruyama M , Shimohigashi Y , Kai Y. Comparison of 3-dimensional dose reconstruction system between fluence-based system and dose measurement-guided system . Med Dosim . 2016 ; 41 : 205 - 211 . https://doi.org/10.1016/j.meddos. 2016 . 03.001 PMID: 27179708
15. Bedford JL , Lee YK , Wai P , South CP , Warrington AP . Evaluation of the delta4 phantom for IMRT and VMAT verification . Phys Med Biol . 2009 ; 54 : N167 - N176 . https://doi.org/10.1088/ 0031 - 9155 /54/9/N04 PMID: 19384007
16. Boggula R , Jahnke L , Wertz H , Lohr F , Wenz F. Patient-specific 3D pretreatment and potential 3D online dose verification of Monte Carlo-calculated IMRT prostate treatment plans . Int J Radiat Oncol Biol Phys . 2011 ; 81 : 1168 - 1175 . https://doi.org/10.1016/j.ijrobp. 2010 . 09.010 PMID: 21093168
17. Asuni G , Jensen JM , McCurdy BM. A Monte Carlo investigation of contaminant electrons due to a novel in vivo transmission detector . Phys Med Biol . 2011 ; 56 : 1207 - 1223 . https://doi.org/10.1088/ 0031 - 9155 / 56/4/020 PMID: 21285480
18. Nakaguchi Y , Araki F , Ono T , Tomiyama Y , Maruyama M , Nagasue N , et al. Validation of a quick threedimensional dose verification system for pre-treatment IMRT QA . Radiol Phys Technol . 2015 ; 8 : 73 - 80 . https://doi.org/10.1007/s12194- 014 - 0294 -x PMID: 25261343
19. Olch AJ . Evaluation of the accuracy of 3DVH software estimates of dose to virtual ion chamber and film in composite IMRT QA . Med Phys . 2012 ; 39 : 81 - 86 . https://doi.org/10.1118/1.3666771 PMID: 22225277
20. Carrasco P , Jornet N , Latorre A , Eudaldo T , Ruiz A , Ribas M. 3D DVH-based metric analysis versus per-beam planar analysis in IMRT pretreatment verification . Med Phys . 2012 ; 39 : 5040 - 5049 . https:// doi.org/10.1118/1.4736949 PMID: 22894429
21. Stasi M , Bresciani S , Miranti A , Maggio A , Sapino V , Gabriele P. Pretreatment patient-specific IMRT quality assurance: a correlation study between gamma index and patient clinical dose volume histogram . Med Phys . 2012 ; 39 : 7626 - 7634 . https://doi.org/10.1118/1.4767763 PMID: 23231310
22. Nakaguchi Y , Araki F , Maruyama M , Saiga S. Dose verification of IMRT by use of a compass transmission detector . Radiol Phys Technol . 2012 ; 5 : 63 - 70 . https://doi.org/10.1007/s12194- 011 - 0137 -y PMID : 22038312
23. Visser R , Wauben DJ , de Groot M , Godart J , Langendijk JA , van't Veld AA , et al. Efficient and reliable 3D dose quality assurance for IMRT by combining independent dose calculations with measurements . Med Phys . 2013 ; 40 : 021710. https://doi.org/10.1118/1.4774048 PMID: 23387733