Verification of Breast Cancer Treatment Planning with Various Radiation Techniques Using Monte Carlo Simulations and Linac Log Files

In the Treatment Planning System (TPS), when the patient is irradiated with one direction of radiation, the Organ At Risk (OAR) around the Planning Target Volume (PTV) receives a high dose and receives an uneven dose. By considering the dose distribution on the PTV and OAR, it is necessary to determine the appropriate radiation direction on the TPS. This study compares the radiation dose achieved by the PTV and OAR of breast cancer patients with radiation directions 3, 5, 7, and 9 on the TPS Intensity Modulated Radiation Therapy (IMRT). This study used 16 retrospective data sets of breast cancer patients consisting of 8 patient data without breast surgery and 8 post-breast surgery data. The data obtained in this study were V95, D2%, D50%, and D98% from the DVH graph. Data analysis was carried out by comparing the average values of the Conformity Index (CI) and Homogeneity Index (HI) and the average dose received by the OAR in four variations of radiation directions. In breast cancer patients without surgery, better CI values were obtained in 9 radiation directions with an average CI = 0.980424; the lowest CI value = 0.957054 and the highest CI value = 0.998541. While in post-operative breast cancer patients, better CI values were obtained in 7 radiation directions with an average CI = 0.983920; the lowest CI value = 0.928394 and the highest CI value = 0.999994. In breast cancer patients without surgery, better HI values were obtained in 9 radiation directions with an average HI = 0.153551; the lowest HI value = 0.086190, and the highest HI value = 0.209303. While in post-operative breast cancer patients, better HI values were obtained in 7 radiation directions with an average HI = 0.121777; the lowest HI value = 0.081539, and the highest HI value 0.158169. The mean dose received by OAR of breast cancer patients without surgery was achieved in 9 radiation directions. In contrast, in post-operative breast cancer patients, it was completed in 5, 7, and 9 radiation directions. Reviewed from the conformity factor (CI) and uniformity (HI), and the mean dose received by breast cancer patients, it can be concluded that planning using IMRT with 9 radiation directions is optimal for use in breast cancer patients without surgery. While radiation with 7 directions is optimal for use in post-operative breast cancer patients. With higher conformity, lower homogeneity, and PTV receiving the maximum dose, the dose received by OAR can be minimized.

ID: 200 Evaluation of key parameters for non-small cell lung cancer treatments using Geant4 as benchmark dose calculation algorithm

Introduction: The functionality and quality of any treatment planning system (TPS) strongly depends on the type of Algorithm which is used by it. Obviously, the role of dose distribution algorithms in calculation of prescribed dose inside the tumor in modern radiotherapy techniques has more important than past to achieve the best clinical outcomes, especially in tumors which are placed in lung or near it like Esophagus cancer. The aim of this study is to evaluate and comparison of efficiency and accuracy of two dose distribution algorithms, Clarkson and Superposition which are using in PCRT 3D treatment planning system to calculate the dose distribution in Three- Dimensional Conformal Radiotherapy (3D-CRT) for Esophagus cancer cases. Materials and Methods: In this study ten patients with esophageal cancer were planned by Clarkson and Superposition algorithms. Treatment plan of the patients were created with a photon beam of 6 MV. Commercially available PCRT3D version6 (made in Spain) Planning system was used to calculate dose in ten planed patients. For this goal and to compare two dose distribution algorithms, the statistical analysis was performed by comparing Conformity Index and Homogeneity Index for target. Results: The maximum value of variation between algorithms for PTV in Dmin, Dmax, and Dmean were 11.7%, 8.3% and 0.73%, respectively. The maximum deviation of variation observed between algorithms in OAR's consist of Dmean is 8.9% for Left lung 7.14% for Right Lung and 2.65% for Spinal cord. Significant variation between algorithms for Homogeneity Index values is 9.06% and highest Percentage oscillation between algorithms for Conformity Index values are 6.33%. Conclusion: According to this study and because of the different results which was driven from treatment planning, significant care should be taken account when calculating treatment plans, due to different dose calculation algorithm may influence treatment planning as well as clinical results.

BackgroundTo improve the quality of plan for the radiation treatment of advanced left breast cancer by introducing the auxiliary structures (ASs) which are used to spare the regions with no intact delineated structures adjacent to the target volume.MethodsCT data from 20 patients with left-sided advanced breast cancer were selected. An AS designated as A1 was created to spare the regions of the aorta, pulmonary artery, superior vena ava, and contralateral tissue of the upper chest and neck, and another, designated as A2, was created in the regions of the cardia and fundus of the stomach, left liver lobe, and splenic flexure of the colon. IMRT and VMAT plans were created for cases with and without the use of the AS dose constraints in plan optimization. Dosimetric parameters of the target and organs at risk (OARs) were compared between the separated groups.ResultsWith the use of AS dose constraints, both the IMRT and VMAT plans were clinically acceptable and deliverable, even showing a slight improvement in dose distribution of both the target and OARs compared with the AS-unused plans. The ASs significantly realized the dose sparing for the regions and brought a better conformity index (p < 0.05) and homogeneity index (p < 0.05) in VMAT plans. In addition, the volume receiving at least 20 Gy (V20) for the heart (p < 0.05), V40 for the left lung (p < 0.05), and V40 for the axillary-lateral thoracic vessel juncture region (p < 0.05) were all lower in VMAT plans.ConclusionThe use of the defined AS dose constraints in plan optimization was effective in sparing the indicated regions, improving the target dose distribution, and sparing OARs for advanced left breast cancer radiotherapy, especially those that utilize VMAT plans.

Purpose: To establish an acceptable quality assurance (QA) criteria for IMRT patient specific QA. There are no established criteria regarding agreement between patient's planned dose distributions versus QA measurements. Method and Materials: A series of MLC QA test patterns were run to detect/correct MLC leaf positional inaccuracies for a Varian 2100C and Elekta Synergy (both with 80 leaf MLC). MapCheck, a 2D diode array system, was used to determine optimal correctional parameter, Dosimetric Leaf Gap (DLG), used in the Varian Eclipse/Helios treatment planning system (TPS) (accounts for effect of MLC rounded‐leaf end geometry). Patient's IMRT plan was checked by resetting all fields to a fixed gantry angle (beam down), delivering summed dose of each beam, measuring with MapCheck, then comparing with TPS calculated dose distribution. QA results for a total of 48 segmented MLC (SMLC) IMRT cases (37 prostate, 9 head and neck, 1 pelvis, and 1 brain) were reviewed. Results:MLC position uncertainties were reduced from 0.3–0.4 mm to 0.1–0.2 mm by a careful calibration. An optimal DLG of 2 mm was determined for Elekta Synergy. Using criteria of ±3% dose agreement or ±3mm distance to agreement (DTA), measured absolute dose distributions agreed with planned dose distributions as follows: prostate: mean 98%, 2.3% S.D.; HN pelvis: mean 90.5%; brain: mean 91.1%; for the total 48 cases, mean 96%, S.D. 5.4%. Conclusion:MLC positional accuracy and having optimal correctional parameter within the TPS are two key factors to ensure IMRT delivered dose in good agreement with calculated dose distribution. Using MapCheck as described, we have implemented the following pass/fail criteria for patient specific QA measurement results: 85% of points within ±3% and ±3 mm DTA in absolute dose. Our clinical experience shows that this is achievable even with the most complicated H&N cases.

Dose-volume histogram (DVH) has become an important tool for evaluation of radiation outcome as reflected from many clinical protocols. While dosimetric accuracy in treatment planning system (TPS) is well quantified, the variability in volume estimation is uncertain due to reconstruction algorithm that is investigated in this study. In addition, the impact of dose distribution and tumor control probability (TCP) were also investigated with CT slice thickness for IMRT planning. A water phantom containing various objects with accurately known volume ranging from 1 to 100 cm(3) was scanned with 1, 2, 3, 5, and 10 mm slice thickness. The CT data sets were sent to Eclipse TPS for contour delineation and volume estimation. The data were compared with known volume for the estimation of error in the volume of each structure. IMRT Plans were generated on phantom containing four objects with different slice thickness (1-5 mm) to calculate TCP. ICRU-83-recommended dose points such as D 2%, D 50%, D 98%, as well as homogeneity and conformity index were also calculated. The variability of volumes with CT slice thickness was significant especially for small volume structures. A maximum error of 92% was noticed for 1 cm(3) volume of object with 10 mm slice thickness, whereas it was ~19% for 1 mm slice thickness. For 2 and 3 cm(3) objects, the maximum error of 99% was noticed with 10 mm slice thickness and ~60% with 5 mm. The differences are smaller for larger volumes with a cutoff at about 20 cm(3). The calculated volume of the objects is a function of reconstruction algorithm and slice thickness. The PTV mean dose and TCP decreased with increasing slice thickness. Maximum variation of ~5% was noticed in mean dose and ~2% in TCP with change in slice thickness from 1 to 5 mm. The relative decrease in target volume receiving 95% of the prescribed dose is ~5% with change in slice thickness from 1 to 5 mm. The homogeneity index increases up to 163% and conformity index decreases by 4% between 1 and 5 mm slice thickness, producing highly inhomogeneous and least conformal treatment plan. Estimation of a volume is dependent on CT slice thickness and the contouring algorithm in a TPS. During commissioning of TPS and for all clinical protocols, evaluation of volume should be included to provide the limit of accuracy in DVH from TPS, especially for small objects. A smaller slice thickness provides superior dosimetry with improved TCP. Thus, the smallest possible slice thickness should be used for IMRT planning, especially when smaller structures are present.

Purpose Because of the poor prognosis for high-grade glioma (HGG) patients, it is important to increase the dose of the tumor to improve the efficacy while minimizing the dose of organs at risk (OARs). Thus, we evaluated the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for high-grade glioma (HGG). Methods A total of 42 HGG patients were retrospectively selected who had undergone helical tomotherapy; then, IMRT and VMAT plans were generated and optimized for comparison after contouring crucial neuronal structures for neurogenesis and neurocognitive function. IMRT and VMAT were optimized with the Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60 Gy to planning target volume (PTV) 1 and 50-54 Gy to PTV2. We also analyzed the homogeneity index (HI) and conformity index (CI) of PTVs and organ at risk (OAR) sparing. Results There was no significant difference in the PTV coverage among IMRT, VMAT, or HT. As for the HI, HT plans (PTV1 HI: 0.09 ± 0.03, PTV2 HI: 0.17 ± 0.05) had the best homogeneity when compared to IMRT plans (PTV1 HI: 0.10 ± 0.04, PTV2 HI: 0.18 ± 0.04) and VMAT plans (PTV1 HI: 0.11 ± 0.03, PTV2 HI: 0.20 ± 0.03). The CI value of HT (PTV1 CI: 0.98 ± 0.03, PTV2: 0.98 ± 0.05) was closest to the optimal value. Except for the IMRT and VMAT groups, there were statistically significant differences between the other two groups of the CI values in both PTV1 and PTV2. The other comparison values were statistically significant except for the optic nerve, and VMAT had the best sparing of the optic chiasm. The mean and max doses of OARs declined significantly in HT. Conclusions For high-grade glioma patients, HT had superior outcomes in terms of PTV coverage and OAR sparing as compared with IMRT/VMAT.

The aim of this study was to verify the advanced inhomogeneous dose distribution produced by a volumetric arc therapy technique (RapidArc™) using 3D gel measurements and Monte Carlo (MC) simulations. The TPS (treatment planning system)-calculated dose distribution was compared with gel measurements and MC simulations, thus investigating any discrepancy between the planned dose delivery and the actual delivery. Additionally, the reproducibility of the delivery was investigated using repeated gel measurements. A prostate treatment plan was delivered to a 1.3 liter nPAG gel phantom using one single arc rotation and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using a 1.5 T scanner. The MC dose distributions were calculated using the VIMC-Arc code. The relative absorbed dose differences were calculated voxel-by-voxel, within the volume enclosed by the 90% isodose surface (VOI90), for the TPS versus gel and TPS versus MC. The differences between the verification methods, MC versus gel, and between two repeated gel measurements were investigated in the same way. For all volume comparisons, the mean value was within 1% and the standard deviation of the differences was within 2.5% (1SD). A 3D gamma analysis between the dose matrices were carried out using gamma criteria 3%/3 mm and 5%/5 mm (% dose difference and mm distance to agreement) within the volume enclosed by the 50% isodose surface (VOI50) and the 90% isodose surface (VOI90), respectively. All comparisons resulted in very high pass rates. More than 95% of the TPS points were within 3%/3 mm of both the gel measurement and MC simulation, both inside VOI50 and VOI90. Additionally, the repeated gel measurements showed excellent consistency, indicating reproducible delivery. Using MC simulations and gel measurements, this verification study successfully demonstrated that the RapidArc™ plan was both accurately calculated and delivered as planned.

The dynamic collimation system (DCS) provides energy layer-specific collimation for pencil beam scanning (PBS) proton therapy using two pairs of orthogonal nickel trimmer blades. While excellent measurement-to-calculation agreement has been demonstrated for simple cube-shaped DCS-trimmed dose distributions, no comparison of measurement and dose calculation has been made for patient-specific treatment plans. To validate a patient-specific quality assurance (PSQA) process for DCS-trimmed PBS treatment plans and evaluate the agreement between measured and calculated dose distributions. Three intracranial patient cases were considered. Standard uncollimated PBS and DCS-collimated treatment plans were generated for each patient using the Astroid treatment planning system (TPS). Plans were recalculated in a water phantom and delivered at the Miami Cancer Institute (MCI) using an Ion Beam Applications (IBA) dedicated nozzle system and prototype DCS. Planar dose measurements were acquired at two depths within low-gradient regions of the target volume using an IBA MatriXX ion chamber array. Measured and calculated dose distributions were compared using 2D gamma analysis with 3%/3mm criteria and low dose threshold of 10% of the maximum dose. Median gamma pass rates across all plans and measurement depths were 99.0% (PBS) and 98.3% (DCS), with a minimum gamma pass rate of 88.5% (PBS) and 91.2% (DCS). The PSQA process has been validated and experimentally verified for DCS-collimated PBS. Dosimetric agreement between the measured and calculated doses was demonstrated to be similar for DCS-collimated PBS to that achievable with noncollimated PBS.

PurposeA new development on the RayStation treatment planning system (TPS) allows a plan to be planned by imposing a constraint on the leaf sequencing: all leaves move in the same direction before moving again in the opposite direction to create a succession of sliding windows (SWs). The study aims to investigate this new leaf sequencing, coupled with standard optimization (SO) and multi‐criteria optimization (MCO) and to compare it with the standard sequencing (STD).MethodsSixty plans were replanned for 10 head and neck cancer patients (two dose levels simultaneously SIB, 56 and 70 Gy in 35 fractions). All plans were compared, and a Wilcoxon signed‐rank test was performed. Pre‐processing QA and metrics of multileaf collimator (MLC) complexity were studied.ResultsAll methodologies met the dose requirements for the planning target volumes (PTVs) and organs at risk (OARs). SO demonstrates significantly best results for homogeneity index (HI), conformity index (CI), and target coverage (TC). SO‐SW gives best results for PTVs (D98% and D2%) but the differences between techniques are less than 1%. Only the D2%,PTV‐56 Gy is higher with both MCO methods. MCO‐STD offer the best sparing OARs (parotids, spinal cord, larynx, oral cavity). The gamma passing rates (GPRs) with 3%/3 mm criteria between the measured and calculated dose distributions are higher than 95%, slightly lowest with SW. The number of monitor units (MUs) and MLC metrics are higher in SW show a higher modulation.ConclusionsAll plans are feasible for the treatment. A clear advantage of SO‐SW is that the treatment plan is more straightforward to planning by the user due to the more advanced modulation. MCO stands out for its ease of use and will allow a less experienced user to offer a better plan than in SO. In addition, MCO‐STD will reduce the dose to the OARs while maintaining good TC.

Cervical cancer which attacks the cervix is triggered by a virus called human papilloma virus (HPV). One effective treatment method for cervical cancer is external radiotherapy using a Linear Accelerator (Linac). This research aims to obtain radiation dose distribution by comparing the effectiveness of two treatment techniques cervical cancer, through Conformity Index (CI), Homogenity Index (HI), and radiation protection against Organ at Risk (OAR) in accordance with QUANTEC rules. The techniques used is Three Dimensional Conformal Radiation Therapy (3DCRT) with 2 directions of irradiation (anterior – posterior) and 4 directions of irradiation (box). Research data was obtained from 15 images of cervical cancer patients who have contoured by a Radiation Onkology Doctor at Indriati Hospital Solo Baru. From the result of the research, it can be said that the 3DCRT technique with 4 directions It can be seen from a higher Conformity Index (CI) value indicating a better level of conformity, and a lower Homogenity Index (HI) value indicating a higher level of homogenity. In addition, the 3DCRT technique with 4 directions of irradiation is also considered more effective in protecting OAR compared to 2 directions of irradiation.

To optimize NTO parameters in non-coplanar RapidArc (RA) stereotactic radiosurgery (SRS) for multiple brain metastases and compare them with HyperArc (HA) plans. Thirty patients with multiple brain metastases, receiving 21Gy prescriptions, were retrospectively enrolled, with lesions ranging from two to eight and volumes between 0.27 and 10.56 cm3. Non-coplanar RapidArc plans utilized manual NTO (RA-mNTO) with varying dose fall-off values (0.1mm-1, 0.5mm-1, 1.0mm-1, 2.0mm-1, 3.0mm-1) and end doses (50%, 25% & 10%). Additionally, two HyperArc plans were generated: HA-ALDO used Automatic Lower Dose Objectives with SRS NTO, while HA-mNTO used the same beam geometry with manual NTO parameters optimized from RA-mNTO plans. TrueBeam with High-Definition Multi-leaf Collimators (HDMLC), 6 MV Flattening Filter Free (FFF) Beam at a maximum dose rate of 1400 MU/min, and Eclipse version 16.1 TPS were used. Plans were assessed for Paddick Conformity Index (CI), Gradient Index (GI), Homogeneity Index (HI), normal brain doses (V18Gy, V15Gy, and V12Gy), Monitor Units (MUs), and delivery accuracy using aS1200 Digital Megavolt Imager (DMI) with 2%/2mm gamma criteria. Statistical analysis utilized integrated scoring and the Wilcoxon signed-rank test. RA-mNTO plans with 0.5mm⁻1 dose fall-off and 10% end-dose showed superior dosimetric outcomes: CI (0.85 ± 0.08), GI (3.63 ± 0.87), and HI (0.36 ± 0.06) compared to HA-ALDO (CI 0.84 ± 0.09, GI: 3.97 ± 0.85, HI: 0.39 ± 0.07) and HA-mNTO (CI 0.83 ± 0.08, GI: 3.60 ± 0.93, HI: 0.40 ± 0.06). MUs were comparable: RA-mNTO (9679 ± 1882), HA-ALDO (9509 ± 1315), and higher for HA-mNTO (10,457 ± 1980). RA-mNTO plans exhibited significantly lower normal brain doses (V18Gy: 1.78 ± 1.23, V15Gy: 3.54 ± 2.37, V12Gy: 6.21 ± 4.09) compared to HA-ALDO (V18Gy: 2.02 ± 1.34, V15Gy: 4.09 ± 2.66, V12Gy: 7.15 ± 4.56) and HA-mNTO (V18Gy: 1.85 ± 1.20, V15Gy: 3.68 ± 2.33, V12Gy: 6.36 ± 3.97). All techniques achieved > 98% gamma pass rate. Non-coplanar RA plans with optimized mNTO settings outperformed HyperArc plans in all studied dosimetric parameters for SRS treatment of multiple brain metastases.

Purpose: To evaluate the differences between relative biological effectiveness (RBE)‐weighted doses calculated with either the linear quadratic (LQ) or repair‐misrepair‐fixation (RMF) RBE model for intensity modulated proton therapy (IMPT) treatment plans. Methods: The commercial treatment planning system (TPS) used at MD Anderson Cancer Center (MDACC) does not provide the LET information necessary in order to utilize variable RBE models to calculate RBE‐weighted dose for treatment plans. To obtain this information the Monte Carlo code MCNPX was used to recalculate IMPT treatment plans for patients with central nervous system (CNS) disease taken from the TPS and record the track‐averaged LET in each voxel of the dose distribution. The dose‐averaged LET was approximated from the track‐averaged LET by use of an appropriate scaling factor. The Monte Carlo Damage Simulation (MCDS) software was used to parameterize the number of double‐strand breaks generated in cells by protons according to their stopping power. This information, along with relevant biological coefficients, was then used to generate RBE‐weighted dose distributions according to the LQ and RMF RBE models. Plan evaluation metrics, such as a conformality index and heterogeneity index, were used for plan comparison. Results: The LQ RBE model produces higher RBE‐weighted doses, particularly in the target volume, compared to the RMF model. Doses predicted by the RMF model in nearby organs at risk can at times be several Gray lower than those predicted by the LQ model. Both models predict equivalently heterogeneous target dose distributions, while the RMF model predicts more conformal target dose. Conclusion: Calculation of proton treatment plan dose incorporating either the LQ or RMF models of variable RBE produces observable differences in the resultant dose distributions. Further investigation, including utilization of different biological coefficients, is required to determine the implications for all of the associated normal tissues. UTMDACC Sister Institution Network Fund Grant (SINF MDACC‐DKFZ)

Purpose:To evaluate the conformity index for SBRT lung plan in Eclipse (version 11) treatment planning system.Methods:In the Eclipse treatment planning system the conformity index was defined as VRI/TV, where VRI is prescription isodose surface, and TV is the target volume. In 1997, Van't Riet et al introduced TVRI/TV × TVRI/VRI as a conformal index, where TVRI is the target volume closed by the prescription isodose surface. We chose a lung cancer patient who was assigned to be treated with SBRT. SBRT immobilization device was used and non‐gated CT/4DCT was performed. The tumor movement was less than 1 cm based on 4DCT. A MIP image set was generated and used to delineate the internal target volume (ITV). A 5 mm margin was added on the ITV to generate the PTV. The prescription was 5000 cGy in 5 fractions and 100% prescription dose covered 95% of the PTV. A VMAT plan (plan I) was made to achieve the physician's goal. Then a high dose structure was generated by VRI subtracting the TV, a low dose structure was generated by TV subtracting VRI, and medium dose structure was named for the overlapping area between VRI and TV. The other VMAT plan (plan II) was made by adding constraints to high/low/medium dose structures, respectively. The conformity index was determined and compared between plan I and plan II.Results:For plan I, the Eclipse's conformal index was 1.06; the Van't Riet's conformal index was 0.82. For plan II, the Eclipse's conformal index was 1.02; the Van't Riet's conformal index was 0.85. The conformal index was improved in plan II.Conclusion:The high/low dose/medium dose structures may be useful to make more conformal plans to treat lung area using SBRT based on the conformal index values.

222. Optimization of pretreatment IMRT dose distribution verification: Bidimensional gaussian kernel implementation