Fixed-beam Intensity-modulated Radiotherapy Research Articles

TransDose: a transformer-based UNet model for fast and accurate dose calculation for MR-LINACs

Objective. To present a transformer-based UNet model (TransDose) for fast and accurate dose calculation for magnetic resonance-linear accelerators (MR-LINACs). Approach. A 2D fluence map from each beam was first projected into a 3D fluence volume and then fed into the TransDose model together with patient density volume and output predicted beam dose. The proposed TransDose model combined a 3D residual UNet with a transformer encoder, where convolutional layers extracted the volumetric spatial features, and the transformer encoder processed the long-range dependencies in a global space. Ninety-eight cases with four tumor sites (brain, nasopharynx, lung, and rectum) treated with fixed-beam intensity-modulated radiotherapy were included in the dataset; 78 cases were used for model training and validation; and 20 cases were used for testing. The ground-truth beam doses were calculated with Monte Carlo (MC) simulations within 1% statistical uncertainty and magnetic field strength B = 1.5 T in the superior and inferior direction. Beam angles from the training and validation datasets were rotated 2–5 times, and doses were recalculated to augment the datasets. Results. The dose-volume histograms and indices between the predicted and MC doses showed good consistency. The average 3D γ-passing rates (3%/2 mm, for dose regions above 10% of maximum dose) were 99.13 ± 0.89% (brain), 98.31 ± 1.92% (nasopharynx), 98.74 ± 0.70% (lung), and 99.28 ± 0.25% (rectum). The average dose calculation time, which included the fluence projection and model prediction, was less than 310 ms for each beam. Significance. We successfully developed a transformer-based UNet dose calculation model—TransDose in magnetic fields. Its accuracy and efficiency indicated its potential for use in online adaptive plan optimization for MR-LINACs.

Deep learning-based 3D in vivo dose reconstruction with an electronic portal imaging device for magnetic resonance-linear accelerators: a proof of concept study

Objective. To develop a novel deep learning-based 3D in vivo dose reconstruction framework with an electronic portal imaging device (EPID) for magnetic resonance-linear accelerators (MR-LINACs). Approach. The proposed method directly back-projected 2D portal dose into 3D patient coarse dose, which bypassed the complicated patient-to-EPID scatter estimation step used in conventional methods. A pre-trained convolutional neural network (CNN) was then employed to map the coarse dose to the final accurate dose. The electron return effect caused by the magnetic field was captured with the CNN model. Patient dose and portal dose datasets were synchronously generated with Monte Carlo simulation for 96 patients (78 cases for training and validation and 18 cases for testing) treated with fixed-beam intensity-modulated radiotherapy in four different tumor sites, including the brain, nasopharynx, lung, and rectum. Beam angles from the training dataset were further rotated 2–3 times, and doses were recalculated to augment the datasets. Results. The comparison between reconstructed doses and MC ground truth doses showed mean absolute errors <0.88% for all tumor sites. The averaged 3D γ-passing rates (3%, 2 mm) were 97.42%±2.66% (brain), 98.53%±0.95% (nasopharynx), 99.41%±0.46% (lung), and 98.63%±1.01% (rectum). The dose volume histograms and indices also showed good consistency. The average dose reconstruction time, including back projection and CNN dose mapping, was less than 3 s for each individual beam. Significance. The proposed method can be potentially used for accurate and fast 3D dosimetric verification for online adaptive radiotherapy using MR-LINACs.

Postmastectomy radiotherapy for left-sided breast cancer patients: Comparison of advanced techniques

Postmastectomy radiotherapy (PMRT) has been shown to improve the overall survival for invasive breast cancer patients, and many advanced radiotherapy technologies were adopted for PMRT. The purpose of our study is to compare various advanced PMRT techniques including fixed-beam intensity-modulated radiotherapy (IMRT), non-coplanar volumetric modulated arc therapy (NC-VMAT), multiple arc VMAT (MA-VMAT), and tomotherapy (TOMO). Results of standard VMAT and mixed beam therapy that were published by our group previously were also included in the plan comparisons. Treatment plans were produced for nine PMRT patients previously treated in our clinic. The plans were evaluated based on planning target volume (PTV) coverage, dose homogeneity index (DHI), conformity index (CI), dose to organs at risk (OARs), normal tissue complication probability (NTCP) of pneumonitis, lifetime attributable risk (LAR) of second cancers, and risk of coronary events (RCE). All techniques produced clinically acceptable PMRT plans. Overall, fixed-beam IMRT delivered the lowest mean dose to contralateral breast (1.56 ± 0.4 Gy) and exhibited lowest LAR (0.6 ± 0.2%) of secondary contralateral breast cancer; NC-VMAT delivered the lowest mean dose to lungs (7.5 ± 0.8 Gy), exhibited lowest LAR (5.4 ± 2.8%) of secondary lung cancer and lowest NTCP (2.1 ± 0.4%) of pneumonitis; mixed beam therapy delivered the lowest mean dose to heart (7.1 ± 1.3 Gy) and exhibited lowest RCE (8.6 ± 7.1%); TOMO plans provided the most optimal target coverage while delivering higher dose to OARs than other techniques. Both NC-VMAT and MA-VMAT exhibited lower values of all OARs evaluation metrics compare to standard VMAT. Fixed-beam IMRT, NC-VMAT, and mixed beam therapy could be the optimal radiation technique for certain breast cancer patients after mastectomy.

Comparison of biologically effective dose for treatment planning in the fixed-beam intensity-modulated radiotherapy and the volumetric-modulated arc therapy for the typical types of cancer

PurposeTo compare the fixed-beam intensity-modulated radiotherapy (IMRT) with the volumetric-modulated arc therapy (VMAT) plans for different cancers using the biologically effective dose (BED). MethodsRecruited patients were divided into three groups in terms of tumor anatomic site, including head and neck, thoracic, and abdominal cancers. All of plans were generated using the fixed-beam IMRT and the VMAT techniques. The qualities of the plans were assessed using the conformity index (CI) and the homogeneous index (HI) with respect to the dose delivered to the tumors. Some selected organs-at-risk (OARs) were analyzed. For the efficiency of the plan, monitor units (MUs) were compared between the paired plans. All parameters were collected and evaluated based on the conventional dose-volume histogram (DVH) of the paired plans. All BED were calculated from the physical dose. ResultsFor CI and HI, the fixed-beam IMRT and the VMAT gained significant differences (p < 0.05), mainly in the head and neck (HN) group, with the exception of the CI of the plan gross tumor volume (PGTV) in the nasopharyngeal carcinoma (NPC) site. In the thoracic group, the HI gained significant differences (p < 0.05) in the plans of the lung cancer with the central tumor without lymph node metastasis. The CI gained significant differences (p < 0.05) in the plans of the lung cancer with the surrounding tumor without lymph node metastasis. The MUs were higher in the VMAT plans compared with the fixed-beam IMRT plans in only two types of cancers. Analysis of the statistical significances regarding the BED values between the fixed-beam IMRT and the VMAT plans were the same as the values of the physical doses when the two paired plans were analyzed. ConclusionThere is no difference in the data comparison of the paired plans using the BED values compared with the physical doses.

Technological Development, Clinical Application, Quality Assurance and Dosimetric Validation of Volumetric Modulated Arc Therapy (VMAT): A Comprehensive Literature Review

Volumetric Modulated Arc Therapy (VMAT) is a recently developed technology which, similar to Intensity Modulated Radiotherapy (IMRT), utilizes optimization algorithms to find an acceptable solution. VMAT optimization algorithms are more complex and resource intensive than IMRT algorithms, as the former have to account for many more variables including machine-specific limitations. VMAT is distinguished from traditional fixed-beam IMRT in that radiation is delivered while the gantry rotates around the patient. It is a significant advancement over fixed gantry angle IMRT in terms of the efficiency of delivery of desired complex dose distributions (dose painting) in modern-day radiotherapy. The purpose of this review is to discuss the technological development, clinical applications and quality assurance of VMAT.

Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy

The integration of MRI with a linear accelerator (MR-linac) offers great potential for high-precision delivery of radiation therapy (RT). However, the electron deflection resulting from the presence of a transverse magnetic field (TMF) can affect the dose distribution, particularly the electron return effect (ERE) at tissue interfaces. The purpose of the study is to investigate the dose effects of ERE at air-tissue and lung-tissue interfaces during intensity-modulated radiation therapy (IMRT) planning. IMRT and volumetric modulated arc therapy (VMAT) plans for representative pancreas, lung, breast, and head and neck (HN) cases were generated following commonly used clinical dose volume (DV) criteria. In each case, three types of plans were generated: (1) the original plan generated without a TMF; (2) the reconstructed plan generated by recalculating the original plan with the presence of a TMF of 1.5 T (no optimization); and (3) the optimized plan generated by a full optimization with TMF = 1.5 T. These plans were compared using a variety of DV parameters, including V100%, D95%, DHI [dose heterogeneity index: (D20%-D80%)/Dprescription], Dmax, and D1cc in OARs (organs at risk) and tissue interface. All the optimizations and calculations in this work were performed on static data. The dose recalculation under TMF showed the presence of the 1.5 T TMF can slightly reduce V100% and D95% for PTV, with the differences being less than 4% for all but one lung case studied. The TMF results in considerable increases in Dmax and D1cc on the skin in all cases, mostly between 10% and 35%. The changes in Dmax and D1cc on air cavity walls are dependent upon site, geometry, and size, with changes ranging up to 15%. The VMAT plans lead to much smaller dose effects from ERE compared to fixed-beam IMRT in pancreas case. When the TMF is considered in the plan optimization, the dose effects of the TMF at tissue interfaces (e.g., air-cavity wall, lung-tissue interfaces, skin) are significantly reduced in most cases. The doses on tissue interfaces can be significantly changed by the presence of a TMF during MR-guided RT when the magnetic field is not included in plan optimization. These changes can be substantially reduced or even eliminated during VMAT/IMRT optimization that specifically considers the TMF, without deteriorating overall plan quality.

A dosimetric comparison of the fixed-beam IMRT plans using different leaf width of multileaf collimators for the intermediate risk prostate cancer

PurposeTo evaluate the impacts of different leaf-width of multileaf collimator (MLC) on the fixed-beam intensity-modulated radiotherapy (IMRT) planning for prostate cancer patients with intermediate risk factors. Materials and methodsSixteen prostate cancer patients with intermediate risk factors were retrospectively recruited. For each patient, the two IMRT plans using MLC leaf width of 10mm and 4mm (sIMRT and mIMRT) were compared. All of plans were generated with the same setup and optimized parameters and methods. Homogeneity index (HI), conformity index (CI), dose distribution for planning tumor volume (PTV) and organs at risk (OARs) were analyzed to evaluate the quality of the plans. Delivery time (DT), monitor units (MUs) and control points (CPs) were used to assess the efficiency of treatment. ResultsFor the target dose distribution, the mean HI values of the two plans for 16 patients are similar (sIMRT vs. mIMRT: 1.120±0.13 vs. 1.103±0.099, p>0.05). The mean CI of the mIMRT plans was significantly better than that of the sIMRT plans (sIMRT vs. mIMRT: 0.648±0.11 vs. 0.688±0.10, p<0.05). For the OARs sparing, the mIMRT plans failed to reduce the dose to OARs compared to the sIMRT plans, except for the rectum, in which the mIMRT plans gained significantly lower V40, V50 and V70 (percentage of countered volume receiving ≥40, 50 and 70Gy). For the efficiency of treatment, the mean DTs and CPs of the mIMRT plans were obviously higher than that of the sIMRT plans. ConclusionsFor the IMRT of the prostate cancer patients with intermediate risk factors, the plans with the narrower leaf-width MLC failed to promote the quality of plans, OARs dose sparing and the efficiency of treatment, and could only improve the conformity of the plans.

Reducing the probability of radiation-induced hepatic toxicity by changing the treatment modality from helical tomotherapy to fixed-beam intensity-modulated radiotherapy.

To estimate and compare the risk of radiation-induced hepatic toxicity (RIHT) in helical tomotherapy and fixed-beam intensity-modulated radiotherapy (IMRT) for the treatment of hepatocellular carcinoma (HCC). Twenty patients with unresectable HCC treated with tomotherapy were selected. We performed tomotherapy re-planning to reduce the non-target normal liver volume receiving a dose of more than 15 Gy (NTNL-V15Gy), and we created a fixed-beam IMRT plan (FB-P). We compared the dosimetric results as well as the estimated probability of RIHT among the tomotherapy initial plan (T-IP), the tomotherapy re-plan (T-RP), and the FB-P. Comparing the T-RP and FB-P, the homogeneity index was 0.11 better with the T-RP. However, the mean NTNL-V15Gy was 6.3% lower with the FB-P. These differences result in a decline in the probability of RIHT from 0.216 in the T-RP to 0.115 in the FB-P. In patients whose NTNL-V15Gy was higher than 43.2% with the T-RP, the probability of RIHT markedly reduced from 0.533 to 0.274. By changing the treatment modality from tomotherapy to fixed-beam IMRT, we could reduce the liver dose and the probability of RIHT without scarifying the target coverage, especially in patients whose liver dose is high.

VMAT planning study in rectal cancer patients.

BackgroundTo compare the dosimetric differences among fixed field intensity-modulated radiation therapy (IMRT), single-arc volumetric-modulated arc therapy (SA-VMAT) and double-arc volumetric-modulated arc therapy (DA-VMAT) plans in rectal cancer.MethodFifteen patients with rectal cancer previously treated with IMRT in our institution were selected for this study. For each patient, three plans were generated with the planning CT scan: one using a fixed beam IMRT, and two plans using the VMAT technique: SA-VMAT and DA-VMAT. Dose prescription to the PTV was 50 Gy in 2 Gy per fraction. Dose volume histograms (DVH) for the target volume and the organs at risk (small bowel, bladder, femoral heads and healthy tissue) were compared for these different techniques. Monitor units (MU) and delivery treatment time were also reported.ResultsDA-VMAT achieved the highest minimum planning target volume (PTV) dose and the lowest maximal dose, resulting in the most homogeneous PTV dose distribution. DA-VMAT also yielded the best CI, although the difference was not statistically significant. Between SA-VMAT and IMRT, the target dose coverage was largely comparable; however, SA-VMAT was able to achieve a better V95 and V107. VMAT showed to be inferior to IMRT in terms of organ at risk sparing, especially for the small bowel. Compared with IMRT, DA-VMAT increased the V15 of small bowel nearly 55 cc. The MU and treatment delivery time were significantly reduced by the use of VMAT techniques.ConclusionVMAT is a new radiation technique that combines the ability to achieve highly conformal dose distributions with highly efficient treatment delivery. Considering the inferior role of normal tissue sparing, especially for small bowel, VMAT need further investigation in rectal cancer treatment.

Target splitting non-coplanar RapidArc radiation therapy for a diffuse sebaceous carcinoma of the scalp: a novel delivery technique.

Background and purposeTo compare conventional lateral photon-electron, fixed-beam intensity modulated radiation therapy (IMRT), coplanar and non-coplanar RapidArc for the treatment of a diffuse sebaceous gland carcinoma of the scalp.MethodsComprehensive dosimetry comparisons were performed among 3D-CRT, IMRT and various RapidArc plans. Target coverage, conformity index (CI), homogeneity index (HI) and doses to organs at risk (OAR) were calculated. Monitor unites (MUs) and delivery time of each treatment were also recorded to evaluate the execution efficiency. The influence of target splitting technique and non-coplanar planning on plan quality was discussed.ResultsIMRT was superior to 3D-CRT concerning targets’ coverage at the sacrifice of larger irradiated brain volumes to low doses. CIs and HIs were better in coplanar RapidArc and non-coplanar RapidArc plans than 3D-CRT and IMRT. Best dose coverage and sparing of OARs were achieved in non-coplanar plans using target splitting technique. Treatment delivery time was longest in the IMRT plan and shortest in the coplanar RapidArc plan without target splitting. The 3%/3 mm gamma test pass rates were above 95% for all the plans.ConclusionsTarget splitting technique and non-coplanar arcs are recommended for total scalp irradiation.

Volumetric intensity-modulated arc therapy vs conventional intensity-modulated radiation therapy in nasopharyngeal carcinoma: a dosimetric study

Dosimetric comparisons between RapidArc (RA) and conventional Intensity-Modulated Radiation Therapy (IMRT) techniques for nasopharyngeal carcinoma (NPC) were performed to address differences in dose coverage of the target, sparing of organs-at-risk (OARs), delivery of monitor units (MUs) and time, to assess whether the RA technique was more beneficial for treatment of NPC. Eight NPC patients (Stages I–IV), who had completed RA treatment, were selected for this study. Computed tomography data sets were re-planned using 7-fields fixed beam IMRT. Quantitative measurements of dose-endpoint values on the dose-volume histograms were carried out for evaluation of: (i) dose homogeneity (D5% – D95%); (ii) degree of conformity (CI95%); (iii) tumor control probability (TCP); (iv) doses to OARs; (v) normal tissue complication probability (NTCP); (vi) treatment time; and (vii) MUs. RA plans achieved better dose conformity and TCP in planning target volumes (PTVs). Target dose homogeneity was not as high as for IMRT plans. Doses to tempero-mandibular joints, clavicles, parotid glands and posterior neck, and their NTCPs were significantly lower in RA plans (P < 0.05). Mean doses to the brainstem and spinal cord were slightly lower in IMRT plans. RA plans allowed for a mean reduction in MUs by 78% (P = 0.006), and a four-fold reduction in treatment delivery times, relative to IMRT plans. RA plans showed superior, or comparable, target coverage and dose conformity in PTVs, but at the expense of inferior dose homogeneity. RA plans also achieved significant improvements in dose reduction to OARs and healthy tissue sparing. A significant reduction in treatment delivery time for RA treatment technique was also noted.

Single-arc volumetric-modulated arc therapy can provide dose distributions equivalent to fixed-beam intensity-modulated radiation therapy for prostatic irradiation with seminal vesicle and/or lymph node involvement

Volumetric-modulated arc therapy (VMAT) is becoming an increasingly utilised modality for treating a variety of anatomical sites. However, the efficacy of single-arc VMAT to treat prostate cancer suspicious for extraprostatic extension was heretofore unknown. In this work, we report our institutional experience with single-arc VMAT and fixed-beam intensity-modulated radiation therapy (IMRT) for prostate cancer patients treated for seminal vesicle and/or lymph node involvement. Single-arc VMAT and 7- or 9-field IMRT treatment plans were compared for 10 prostate cancer patients treated for seminal vesicle involvement and/or lymph node involvement. All treatment plans were constructed using the Philips Pinnacle treatment planning system (v.9.0, Fitchburg, WI) and delivered on an Elekta Infinity radiotherapy accelerator (Crawley, UK). Resulting plans were compared using metrics that characterised dosimetry and delivery efficiency. No statistically significant differences in target coverage, target homogeneity or normal tissue doses were noted between the plans (p>0.05). For prostate patients treated for seminal vesicle involvement, VMAT plans were delivered in 1.4±0.1 min (vs 9.5±2.4 min for fixed-beam IMRT) (p<0.01) and required approximately 20% fewer monitor units (p=0.01). For prostate patients treated for lymph node involvement, VMAT plans were delivered in 1.4±0.1 min (vs 11.7±1.3 min for fixed-beam IMRT) (p<0.01) and required approximately 45% fewer monitor units (p<0.01). Single-arc VMAT plans were dosimetrically equivalent to fixed-beam IMRT plans with significantly improved delivery efficiency.

Plan comparison of volumetric-modulated arc therapy (RapidArc) and conventional intensity-modulated radiation therapy (IMRT) in anal canal cancer

BackgroundTo compare volumetric-modulated arc therapy (RapidArc) plans with conventional intensity-modulated radiation therapy (IMRT) plans in anal canal cancers.MethodsTen patients with anal canal carcinoma previously treated with IMRT in our institution were selected for this study. For each patient, three plans were generated with the planning CT scan: one using a fixed beam IMRT, and two plans using the RapidArc technique: a single (RA1) and a double (RA2) modulated arc therapy. The treatment plan was designed to deliver in one process with simultaneous integrated boost (SIB) a dose of 59.4 Gy to the planning target volume (PTV2) based on the gross disease in a 1.8 Gy-daily fraction, 5 days a week. At the same time, the subclinical disease (PTV1) was planned to receive 49.5 Gy in a 1.5 Gy-daily fraction. Plans were normalized to 99% of the PTV2 that received 95% of the prescribed dose. Planning objectives were 95% of the PTV1 will receive 95% of the prescribed dose and no more than 2% of the PTV will receive more than 107%. Dose-volume histograms (DVH) for the target volume and the organs at risk (bowel tract, bladder, iliac crests, femoral heads, genitalia/perineum, and healthy tissue) were compared for these different techniques. Monitor units (MU) and delivery treatment time were also reported.ResultsAll plans achieved fulfilled objectives. Both IMRT and RA2 resulted in superior coverage of PTV than RA1 that was slightly inferior for conformity and homogeneity (p < 0.05).Conformity index (CI95%) for the PTV2 was 1.15 ± 0.15 (RA2), 1.28 ± 0.22 (IMRT), and 1.79 ± 0.5 (RA1). Homogeneity (D5% - D95%) for PTV2 was 3.21 ± 1.16 Gy (RA2), 2.98 ± 0.7 Gy (IMRT), and 4.3 ± 1.3 Gy (RA1). RapidArc showed to be superior to IMRT in terms of organ at risk sparing. For bowel tract, the mean dose was reduced of 4 Gy by RA2 compared to IMRT. Similar trends were observed for bladder, femoral heads, and genitalia. The DVH of iliac crests and healthy tissue resulted in comparable sparing for the low doses (V10 and V20). Compared to IMRT, mean MUs for each fraction was significantly reduced with RapidArc (p = 0.0002) and the treatment time was reduced by a 6-fold extent.ConclusionFor patients suffering from anal canal cancer, RapidArc with 2 arcs was able to deliver equivalent treatment plan to IMRT in terms of PTV coverage. It provided a better organ at risk sparing and significant reductions of MU and treatment time per fraction.

WE-E-BRA-07: How Could Fixed-Beam Intensity-Modulated Radiation-Therapy Exceed SmartArc?

Purpose: To discover the number of beams required in fixed‐beam IMRT to achieve similar plan quality to SmartArc in prostate cancertreatment.Method and Materials: Previous study showed that IMRT with as many as 24, uniformly‐distributed, beams still could not exceed SmartArc. In this work, we first studied the dose distributions of IMRT and SmartArc plans in a cylindrical water phantom, which provided guidelines for the beam‐angle‐selection in the patient study. Then, IMRT with respectively 8 to 16 beams and a SmartArc plan were generated for each of five prostate‐cancer patients. The 8‐beam plan used our Institution's standard configuration; other IMRT plans applied re‐selected gantry angles for better rectum sparing. All plans were generated using our in‐house developed automatic inverse‐planning algorithm and were optimized to at least similar quality as the clinical plan for each patient. Dose distributions in the OARs from each plan were compared. Results: The phantom study shows that SmartArc produced generally uniform penumbra in dose profile all around the target; in contrast, the fixed‐beam plans resulted in narrower penumbra perpendicular to beam directions whereas wider penumbra at other directions, which indicates that, for IMRT to achieve better sparing of OAR, beams along the tangent direction of the connection between the OAR and PTV should be included. The IMRT plans in the patient study shows obvious dose reduction in the rectum when more beams were selected based on such principle; when the number of beams reaches 16, the rectum starts to receive comparable dose to SmartArc with similar PTV coverage. Conclusion: Fixed‐beam IMRT is capable of exceeding the performance of SmartArc in prostate cancertreatment as long as 16 or more beams with properly selected gantry angles are used. Considering the superior delivery efficiency of SmartArc, however, SmartArc may still be preferable in clinical applications.

Pulmonary Toxicity of Chemotherapy

To compare the fixed-beam intensity-modulated radiotherapy (IMRT) with the volumetric-modulated arc therapy (VMAT) plans for different cancers using the biologically effective dose (BED).Recruited patients were divided into three groups in terms of tumor anatomic site, including head and neck, thoracic, and abdominal cancers. All of plans were generated using the fixed-beam IMRT and the VMAT techniques. The qualities of the plans were assessed using the conformity index (CI) and the homogeneous index (HI) with respect to the dose delivered to the tumors. Some selected organs-at-risk (OARs) were analyzed. For the efficiency of the plan, monitor units (MUs) were compared between the paired plans. All parameters were collected and evaluated based on the conventional dose-volume histogram (DVH) of the paired plans. All BED were calculated from the physical dose.For CI and HI, the fixed-beam IMRT and the VMAT gained significant differences (p < 0.05), mainly in the head and neck (HN) group, with the exception of the CI of the plan gross tumor volume (PGTV) in the nasopharyngeal carcinoma (NPC) site. In the thoracic group, the HI gained significant differences (p < 0.05) in the plans of the lung cancer with the central tumor without lymph node metastasis. The CI gained significant differences (p < 0.05) in the plans of the lung cancer with the surrounding tumor without lymph node metastasis. The MUs were higher in the VMAT plans compared with the fixed-beam IMRT plans in only two types of cancers. Analysis of the statistical significances regarding the BED values between the fixed-beam IMRT and the VMAT plans were the same as the values of the physical doses when the two paired plans were analyzed.There is no difference in the data comparison of the paired plans using the BED values compared with the physical doses.

A quality assurance method for analyzing and verifying intensity modulated fields

A quality assurance method is developed for measuring, verifying and analyzing intensity modulated radiation fields. It is applicable for rotational and fixed-beam intensity modulated radiation therapy (IMRT) treatments. A gantry-mount device was constructed to measure the transmission dose of an IMRT field using radiographic films. A double-exposure technique with optimal kernel estimate method was developed to minimize the errors from measurements. A chi2 confidence level test method was developed to detect the discrepancies between measured and prescribed IMRT fluence distributions. Our method was tested for rotational and fixed-beam IMRT treatment verifications. The method was found insensitive to the hardware-related parameters for rotational and fixed-beam IMRT deliveries. The chi2 confidence level test was found to be more sensitive than linear correlation method in detecting relative small errors for cases with a few segments or narrow regions of interest. In conclusion, we demonstrated a quantitative method for verifying and analyzing IMRT treatment deliveries.