InCise™ multileaf collimator (MLC) was introduced for CyberKnife^® (CK) Robotic Radiosurgery System (CK-MLC) in 2015, and finite size pencil beam (FSPB) was the only available dose computation algorithm for treatment plans of CK-MLC system. The more advanced Monte Carlo (MC) dose calculation algorithm of lnCise™ was initially released in 2017 for the CK Precision™ treatment planning system (TPS) (v1.1) with new graphic processing unit (GPU) platform. GPU based TPS of the CK offers more accurate, faster treatment planning time and intuitive user interface with smart three-dimensional editing tools and fully automated autosegmentation tools. The MC algorithm used in CK TPS simulates the energy deposited by each individual photon and secondary particles to calculate more accurate dose. In the present study, the dose disparities between MC and FSPB algorithms for selected Stereotactic Ablative Radiation Therapy (SABR) CK-MLC treatment plans are quantified.

A total of 80 CK-MLC SABR plans computed with FSPB were retrospectively reviewed and compared with MC computed results, including plans for detached lung cancer (or tumors fully surrounded by lung tissues, n = 21), nondetached lung cancer (or tumor touched the chest wall or mediastinum, n = 23), intracranial (n = 21), and pancreas lesions (n = 15). Dosimetric parameters of each planning target volume and major organs at risk (OAR) are compared in terms of normalized percentage deviations (N_dev).

This study revealed an average of 24.4% overestimated D₉₅ values in plans using FSPB over MC for detached lung (n = 21) and 14.9% for nondetached lung (n = 23) lesions. No significant dose differences are found in intracranial (0.3%, n = 21) and pancreatic (0.9%, n = 15) cases. Furthermore, no significant differences were found in N_dev of OARs.

In this study, it was found that FSPB overestimates dose to inhomogeneous treatment sites. This indicates, the employment of MC algorithm in CK-MLC-based lung SABR treatment plans is strongly suggested.

• Conformity Index
• CyberKnife
• Monte Carlo
• finite size pencil beam
• homogeneity index
• stereotactic ablative radiation therapy
• tissue heterogeneity

• 3D conformal radiotherapy
• Monte Carlo
• collapsed cone convolution
• treatment planning

• Algorithms
• Humans
• Lung/radiation effects
• Monte Carlo Method
• Particle Accelerators/instrumentation
• Phantoms, Imaging
• Radiometry/methods
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted/instrumentation
• Radiotherapy Planning, Computer-Assisted/methods
• Radiotherapy, Conformal

• Non-small cell lung cancer (NSCLC)
• intensity-modulated radiation therapy (IMRT)
• proton therapy
• stereotactic body radiation therapy (SBRT)

Stereotactic body radiation therapy (SBRT) aims to deliver a highly conformal ablative dose to a small target. Dosimetric verification of SBRT for lung tumors presents a challenge due to heterogeneities, moving targets, and small fields. Recent software (M3D) designed for dosimetric verification of lung SBRT treatment plans using an advanced convolution–superposition algorithm was evaluated. Ten lung SBRT patients covering a range of tumor volumes were selected. 3D CRT plans were created using the XiO treatment planning system (TPS) with the superposition algorithm. Dose was recalculated in the Eclipse TPS using the AAA algorithm, M3D verification software using the collapsed‐cone‐convolution algorithm, and in‐house Monte Carlo (MC). Target point doses were calculated with RadCalc software. Near‐maximum, median, and near‐minimum target doses, conformity indices, and lung doses were compared with MC as the reference calculation. M3D 3D gamma passing rates were compared with the XiO and Eclipse. Wilcoxon signed‐rank test was used to compare each calculation method with XiO with a threshold of significance of p<0.05. M3D and RadCalc point dose calculations were greater than MC by up to 7.7% and 13.1%, respectively, with M3D being statistically significant (s.s.). AAA and XiO calculated point doses were less than MC by 11.3% and 5.2%, respectively (AAA s.s.). Median and near‐minimum and near‐maximum target doses were less than MC when calculated with AAA and XiO (all s.s.). Near‐maximum and median target doses were higher with M3D compared with MC (s.s.), but there was no difference in near‐minimum M3D doses compared with MC. M3D‐calculated ipsilateral lung V20 Gy and V5 Gy were greater than that calculated with MC (s.s.); AAA‐ and XiO‐calculated V20 Gy was lower than that calculated with MC, but not statistically different to MC for V5 Gy. Nine of the 10 plans achieved M3D gamma passing rates greater than 95% and 80%for 5%/1 mm and 3%/1 mm criteria, respectively. M3D typically calculated a higher target and lung dose than MC for lung SBRT plans. The results show a range of calculated doses with different algorithms and suggest that M3D is in closer agreement with Monte Carlo, thus discrepancies between the TPS and M3D software will be observed for lung SBRT plans. M3D provides a useful supplement to verification of lung SBRT plans by direct measurement, which typically excludes patient specific heterogeneities.

PACS number(s): 87.55.D‐, 87.55.Qr, 87.55.K‐

• Lung SBRT
• Monte Carlo
• Prescription
• Target dose variation

• Cohort Studies
• Four-Dimensional Computed Tomography
• Humans
• Lung Neoplasms/surgery
• Monte Carlo Method
• Pilot Projects
• Prognosis
• Radiosurgery
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted/methods

• University of Nebraska Medical Center

• Animals
• Beta Particles
• Computer Simulation
• Gamma Rays
• Humans
• Iodine Radioisotopes
• Mice
• Monte Carlo Method
• Phantoms, Imaging
• Photons
• Positron-Emission Tomography/methods
• Tomography Scanners, X-Ray Computed

The quality of radiation therapy depends on the ability to maximize the tumor control probability while minimize the normal tissue complication probability. Both of these two quantities are directly related to the accuracy of dose distributions calculated by treatment planning systems. The commonly used dose calculation algorithms in the treatment planning systems are reviewed in this work. The accuracy comparisons among these algorithms are illustrated by summarizing the highly cited research papers on this topic. Further, the correlation between the algorithms and tumor control probability/normal tissue complication probability values are manifested by several recent studies from different groups. All the cases demonstrate that dose calculation algorithms play a vital role in radiation therapy.

• Dose calculation
• Algorithm
• Radiation therapy
• Tumor control probability
• Normal tissue complication probability

Our work on stereotactic body radiation therapy (SBRT) for primary and metastatic lung tumors will be described. The eligibility criteria for SBRT, our previous SBRT method, the definition of target volume, heterogeneity correction, the position adjustment using four-dimensional cone-beam computed tomography (4D CBCT) immediately before SBRT, volumetric modulated arc therapy (VMAT) method for SBRT, verifying of tumor position within internal target volume (ITV) using in-treatment 4D-CBCT during VMAT-SBRT, shortening of treatment time using flattening-filter-free (FFF) techniques, delivery of 4D dose calculation for lung-VMAT patients using in-treatment CBCT and LINAC log data with agility multileaf collimator, and SBRT method for centrally located lung tumors in our institution will be shown. In our institution, these efforts have been made with the goal of raising the local control rate and decreasing adverse effects after SBRT.

To report the result of independent absorbed-dose calculations based on a Monte Carlo (MC) algorithm in volumetric modulated arc therapy (VMAT) for various treatment sites.

All treatment plans were created by the superposition/convolution (SC) algorithm of SmartArc (Pinnacle V9.2, Philips). The beam information was converted into the format of the Monaco V3.3 (Elekta), which uses the X-ray voxel-based MC (XVMC) algorithm. The dose distribution was independently recalculated in the Monaco. The dose for the planning target volume (PTV) and the organ at risk (OAR) were analyzed via comparisons with those of the treatment plan.

Before performing an independent absorbed-dose calculation, the validation was conducted via irradiation from 3 different gantry angles with a 10- × 10-cm² field. For the independent absorbed-dose calculation, 15 patients with cancer (prostate, 5; lung, 5; head and neck, 3; rectal, 1; and esophageal, 1) who were treated with single-arc VMAT were selected. To classify the cause of the dose difference between the Pinnacle and Monaco TPSs, their calculations were also compared with the measurement data.

In validation, the dose in Pinnacle agreed with that in Monaco within 1.5%. The agreement in VMAT calculations between Pinnacle and Monaco using phantoms was exceptional; at the isocenter, the difference was less than 1.5% for all the patients. For independent absorbed-dose calculations, the agreement was also extremely good. For the mean dose for the PTV in particular, the agreement was within 2.0% in all the patients; specifically, no large difference was observed for high-dose regions. Conversely, a significant difference was observed in the mean dose for the OAR. For patients with prostate cancer, the mean rectal dose calculated in Monaco was significantly smaller than that calculated in Pinnacle.

There was no remarkable difference between the SC and XVMC calculations in the high-dose regions. The difference observed in the low-dose regions may have arisen from various causes such as the intrinsic dose deviation in the MC calculation, modeling accuracy, and CT-to-density table used in each planning system It is useful to perform independent absorbed-dose calculations with the MC algorithm in intensity-modulated radiation therapy commissioning.

• Inhomogeneity corrections
• Lung SBRT
• Monte Carlo
• Pencil beam

• Humans
• Image Processing, Computer-Assisted/methods
• Monte Carlo Method
• Positron-Emission Tomography/methods

• heterogeneity correction
• lung tumor
• monte carlo dose calculation
• stereotactic body radiation therapy

• Algorithms
• Humans
• Lung Neoplasms/diagnostic imaging
• Lung Neoplasms/surgery
• Monte Carlo Method
• Radiosurgery/statistics & numerical data
• Retrospective Studies
• Surgery, Computer-Assisted/statistics & numerical data
• Tomography, X-Ray Computed

Stereotactic lung radiotherapy (SLRT) has emerged as a curative treatment for medically inoperable patients with early-stage non-small cell lung cancer (NSCLC) and the use of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc treatments (VMAT) have been proposed as the best practical approaches for the delivery of SLRT. However, a large number of narrow field shapes are needed in the dose delivery of intensity-modulated techniques and the probability of underdosing the tumour periphery increases as the effective field size is decreased. The purpose of this study was to evaluate small lung tumour doses irradiated by intensity-modulated techniques to understand the risk for dose calculation errors in precision radiotherapy such as SLRT.

The study was executed with two heterogeneous phantoms with targets of Ø1.5 and Ø4.0 cm. Dose distributions in the simulated tumours delivered by small sliding window apertures (SWAs), IMRT and RapidArc treatment plans were measured with radiochromic film. Calculation algorithms of pencil beam convolution (PBC) and anisotropic analytic algorithm (AAA) were used to calculate the corresponding dose distributions.

Peripheral doses of the tumours were decreased as SWA decreased, which was not modelled by the calculation algorithms. The smallest SWA studied was 2 mm, which reduced the 90% isodose line width by 4.2 mm with the Ø4.0 cm tumour as compared to open field irradiation. PBC was not able to predict the dose accurately as the gamma evaluation failed to meet the criteria of ±3%/±1 mm on average in 61% of the defined volume with the smaller tumour. With AAA the corresponding value was 16%. The dosimetric inaccuracy of AAA was within ±3% with the optimized treatment plans of IMRT and RapidArc. The exception was the clinical RapidArc plan with dose overestimation of 4%.

Overall, the peripheral doses of the simulated lung tumours were decreased by decreasing the SWA. To achieve adequate surface dose coverage to small lung tumours with a difference less than 1 mm in the isodose line radius between the open and modulated field, a larger than 6 mm SWA should be used in the dose delivery of SLRT.

The purpose of this study was to compare dose distributions from three different algorithms with the x-ray Voxel Monte Carlo (XVMC) calculations, in actual computed tomography (CT) scans for use in stereotactic radiotherapy (SRT) of small lung cancers.

Slow CT scan of 20 patients was performed and the internal target volume (ITV) was delineated on Pinnacle³. All plans were first calculated with a scatter homogeneous mode (SHM) which is compatible with Clarkson algorithm using Pinnacle³ treatment planning system (TPS). The planned dose was 48 Gy in 4 fractions. In a second step, the CT images, structures and beam data were exported to other treatment planning systems (TPSs). Collapsed cone convolution (CCC) from Pinnacle³, superposition (SP) from XiO, and XVMC from Monaco were used for recalculating. The dose distributions and the Dose Volume Histograms (DVHs) were compared with each other.

The phantom test revealed that all algorithms could reproduce the measured data within 1% except for the SHM with inhomogeneous phantom. For the patient study, the SHM greatly overestimated the isocenter (IC) doses and the minimal dose received by 95% of the PTV (PTV95) compared to XVMC. The differences in mean doses were 2.96 Gy (6.17%) for IC and 5.02 Gy (11.18%) for PTV95. The DVH's and dose distributions with CCC and SP were in agreement with those obtained by XVMC. The average differences in IC doses between CCC and XVMC, and SP and XVMC were -1.14% (p = 0.17), and -2.67% (p = 0.0036), respectively.

Our work clearly confirms that the actual practice of relying solely on a Clarkson algorithm may be inappropriate for SRT planning. Meanwhile, CCC and SP were close to XVMC simulations and actual dose distributions obtained in lung SRT.

• Aged
• Aged, 80 and over
• Clinical Trials, Phase II as Topic
• Dose Fractionation, Radiation
• Female
• Humans
• Linear Models
• Lung/pathology
• Lung/radiation effects
• Lung Neoplasms/diagnostic imaging
• Lung Neoplasms/pathology
• Lung Neoplasms/radiotherapy
• Male
• Middle Aged
• Multicenter Studies as Topic
• Prognosis
• Radiation Injuries/etiology
• Radiography
• Radiosurgery/adverse effects
• Survival Rate

• Humans
• Neoplasms/radiotherapy
• Radiosurgery

• Algorithms
• Artifacts
• Breast Neoplasms/diagnostic imaging
• Breast Neoplasms/radiotherapy
• Breast Neoplasms/surgery
• Female
• Humans
• Image Processing, Computer-Assisted/methods
• Imaging, Three-Dimensional/methods
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted/methods
• Radiotherapy, Adjuvant
• Respiration
• Sensitivity and Specificity
• Software
• Technology, Radiologic/methods
• Tomography, X-Ray Computed/methods

• Models, Biological
• Monte Carlo Method
• Positron-Emission Tomography/methods
• Reproducibility of Results
• Software