Comparing radiation treatments using intensity-modulated beams, multiple arcs, and single arcs

Dosimetric Impact of AAA and AXB Dose Calculation Algorithm in VMAT Treatment Planning for Rectal Tumors

Aim

The study aims to compare the accuracy of Anisotropic Analytical Algorithm (AAA) and acuros XB (AXB) dose calculation algorithms for radiotherapy (RT) planning of rectal tumors.

Materials and Methods

Treatment plans from 20 patients with previously treated rectal cancer were retrospectively analyzed. All patients underwent VMAT treatment planning using the AAA algorithm in Eclipse (v15.6) system. These plans were recalculated with AXB in Eclipse (v15.6) while maintaining the original multileaf collimator fluence. Dosimetric parameters and gamma analysis (3%/3 mm and 2%/2 mm criteria) were compared between the two algorithms. A paired two-tailed t-test was used to statistically compare dosimetric and gamma analysis results between the AAA and AXB algorithms.

Results

The results indicate that AAA could be potentially overestimating the dose to planning target volume (PTV). While the mean bowel dose was marginally lower in AAA plans (P = 0.013), doses to other organs at risk (OARs) were slightly higher, suggesting a general overestimation trend. This implies that AAA could be potentially overestimating the dose to OARs and PTV as compared to AXB. The statistical analysis of the Gamma parameters also shows a significant change.

Conclusion

The results indicate that the dose calculation accuracy of AXB is superior to AAA for rectal cancer RT.

Dosimetric comparison of gamma knife and linear accelerator (VMAT and IMRT) plans of SBRT of Lung tumours

This study evaluates dosimetric differences in Stereotactic Body Radiation Therapy (SBRT) for lung tumors using plans of Gamma Knife, and Volumetric Modulated Arc Therapy (VMAT), Intensity-Modulated Radiation Therapy (IMRT) plans based on Linear Accelerator, aiming to inform the reader of appropriate treatment strategy selection. Ten patients with 23 lung tumor lesions treated with SBRT at Zhongshan Hospital of Dalian University were analyzed. Plans of Gamma Knife, and VMAT, IMRT plans based on Linear Accelerator were created for each lesion, totaling 18 plans per type. Lesions were treated with 30-50 Gy in 5-10 fractions. Dosimetric parameters, including gradient index (GI), heterogeneity index (HI), conformity index (CI), and doses to the plan target volumes (PTVs), the gross tumor volumes (GTVs) and organs at risk (OARs) were compared. Plans of Gamma Knife showed superior HI and GI, higher PTV and GTV doses, and reduced doses to the ipsilateral and contralateral lungs, esophagus, spinal cord, and heart compared to VMAT and IMRT plans (p < 0.05). However, Plans of Gamma Knife required longer delivery times. When comparing VMAT and IMRT plans, VMAT plans had shorter delivery times than IMRT plans, but required more monitor units (MUs). Additionally, IMRT plans delivered a lower mean dose to the ipsilateral lung compared to VMAT plans. Gamma Knife SBRT plans achieves steeper dose falloff and minimizes radiation to normal lung tissue compared to VMAT and IMRT plans, but with longer delivery times. VMAT and IMRT plans displayed similar dose distributions for lung SBRT.

The Capabilities and Characteristics of Helical Tomotherapy and Co-Planar Dual Arcs Volumetric-Modulated arc Therapy Associated with Hippocampal Sparing During Prophylactic Cranial Irradiation

Objective: To investigate the features of helical tomotherapy and co-planar dual Arcs volumetric-modulated arc therapy during prophylactic cranial irradiation associated with bilateral hippocampal tissue sparing. Materials and methods: Helical tomotherapy and co-planar dual arcs volumetric-modulated arc therapy treatment plans were generated with a dose of 30 Gy/10 fractions in 16 patients treated with prophylactic cranial irradiation. The dose to the bilateral hippocampal tissues, organs at risk, and planning target volume were determined when the average dose of bilateral hippocampal tissues was reduced by approximately 4 Gy as an observation point. Changes in dosimetry when sparing the bilateral hippocampal tissues were determined for both modalities. Results: When bilateral hippocampal tissues were restricted to 8 Gy, D40%mean-bilateral hippocampal tissues = 7.64 ± 0.41 Gy in helical tomotherapy, while D40%mean-bilateral hippocampal tissues = 10.96 ± 0.38 Gy in co-planar dual arcs volumetric-modulated arc therapy volumetric-modulated arc therapy. Helical tomotherapy was associated with significantly lower doses to organs at risk, including Dmean-bilateral hippocampal tissues (P = .03), D98%-bilateral hippocampal tissues (P = .01), D2%-bilateral hippocampal tissues (P = .01), Dmean-inner ear (P = .02), Dmean-parotid glands (P = .02), Dmax-lens (P = .02), and Dmax-brainstem (P = .02), but not Dmax-optic nerves (P = .87). Helical tomotherapy provided better target coverage, with lower average D2%-PTV (P = .02), higher average D98%-PTV (P = .02), and better conformal index (0.87 vs 0.84, P = .02) and homogeneity index (0.15 vs 0.21, P = .05). With smaller bilateral hippocampal tissues doses, the planning target volume dose changed across 3 dosimetry regions for both modalities; the plateau region (>20.0 Gy for helical tomotherapy versus >16.0 Gy for co-planar dual arcs volumetric-modulated arc therapy), gradient region (20.0-12.0 Gy vs 16.0-11.0 Gy), and falling region (<12.0 Gy vs <11.0 Gy). The average delivery duration of helical tomotherapy was almost 7.7 times longer than that of co-planar dual arcs volumetric-modulated arc therapy. Conclusions: Helical tomotherapy was better at sparing the bilateral hippocampal tissues and organs at risk and had better target coverage but a significantly longer treatment duration than co-planar dual arcs volumetric-modulated arc therapy. Further dose decreases in the bilateral hippocampal tissues would yield worse target dose coverage.

Evaluation of Healthy Tissue Dose at Different Regions between Volumetric-Modulated Arc Therapy and Intensity-Modulated Radiation Therapy Plans in the Treatment of Various Cancers

Background:

Radiotherapy plays an important role in the management of cancer. Although the improved technologies increase therapeutic index, different delivery techniques deliver different dose pattern to the healthy tissue within and outside treatment volume.

Objective:

The objective of this study was to evaluate the low, intermediate, and high dose to healthy tissue within and outside the treatment volume and to find the relation between tumor volume and various doses received healthy tissue volume.

Materials and Methods:

A total of 150 patients were included. For all patients, planning computed tomography images were acquired. Tumors, critical structures, and healthy tissue volumes at different regions were delineated. Two sets of plans, one with volumetric-modulated arc therapy and another with intensity-modulated radiation therapy (IMRT) were created, optimized for 6 MV photons and dose was calculated. Dosimetry results for tumor, organs at risks (OARs), and healthy tissue from both the techniques were evaluated and compared.

Results:

Tumor coverage and dose to OARs was significantly better with volumetric-modulated arc therapy (VMAT). Volume of healthy tissue received high-dose within the treatment volume as well as volume of healthy tissue received low and intermediate-dose out of treatment volume were significantly (P < 0.002) lesser with VMAT. Besides, the results showed that as the tumor volume increased, the various dose received healthy tissue volume also increased.

Conclusions:

VMAT plan can reduce the risk of secondary malignancy while treating different sites of cancer. VMAT is the most appropriate technique than IMRT, especially in the treatment of large tumor volume. Special attention has to be given, especially while treating women and children.

Dosimetric analysis of tangent-based volumetric modulated arc therapy with deep inspiration breath-hold technique for left breast cancer patients

Background

Tangent-based intensity modulated radiation therapy (TIMRT) is a common adjuvant radiotherapy strategy for breast cancer patients. This study compared the dosimetric characteristics of tangent-based volumetric modulated arc therapy (TVMAT) and TIMRT for left breast cancer patients during deep inspiration breath-hold (DIBH) and free breathing (FB) techniques.

Methods

Fourteen patients with left breast cancer after breast-conserving surgery were included. The first arc started at 331.8–353.6 degrees and stopped at 281.8–315.0 degrees. The third arc started at 123.2–149.1 degrees and stopped at 88.0–96.0 degrees. The second and fourth arcs were reverse arcs of first and third arcs. DIBH-TIMRT inversing plans were generated using opposing tangential fields. Wilcoxon signed rank test and Spearman correlation were used to examine the significance of dose difference.

Results

Compared with FB-TVMAT, the mean heart dose of DIBH-TVMAT plans was reduced from 7.9 Gy to 3.2 Gy (p < 0.001). The average left lung volume receiving 30 Gy or more (V30Gy) was reduced from 12.9 to 5.7% (p < 0.001). DIBH-TVAMT plans resulted in a lower mean dose to the contralateral breast and lung (2 Gy and 0.7 Gy vs 3.4 Gy and 1.5 Gy, respectively) as compared to FB-TVMAT plans. Compared with DIBH-TIMRT, the average left lung V30Gy of DIBH-TVMAT plans was reduced from 8.5 to 5.7% (p = 0.031). As for low-dose areas, exposure of the left lung, right breast, heart and right lung volume with 10 Gy or more was not significantly different between the IMRT- and VMAT-plans.

Conclusions

DIBH-TVMAT for left breast cancer treatment retains treatment plan quality similar to the DIBH-IMRT technique without compromising dose restrictions to the heart, right breast and right lung. DIBH-TVMAT increased left lung protection but still had higher V5Gy to right breast and substantially higher V5Gy to heart. For left breast cancer patients receiving treatment with the DIBH technique, DIBH-TVMAT provides better treatment quality and is a safe and feasible treatment strategy.

Dosimetric analysis of stereotactic rotational versus static intensity-modulated radiation therapy for pancreatic cancer

PURPOSE

Stereotactic body radiation therapy is a promising treatment modality for locally advanced pancreatic cancer. To determine the optimal radiation treatment, we compared the plan characteristics of volumetric-modulated arc therapy and intensity-modulated radiation therapy when administered with stereotactic body radiation therapy to treat pancreatic cancer.

PATIENTS AND METHODS

Fifteen patients with locally advanced pancreatic cancer were treated by stereotactic body radiation therapy at a dose of 24-32Gy in four fractions with marker-guided gated volumetric-modulated arc therapy. Four dimensional-computed tomography scans were used to assess the target and surrounding normal organs. The same images, contours, and dose constraints were used for dual-arc volumetric-modulated arc therapy and 9-field intensity-modulated radiation therapy planning. Plans were compared using dosimetric parameters and treatment performance.

RESULTS

Volumetric-modulated arc therapy required significantly lower monitor units (1726 vs. 4188; P<0.001) and shorter treatment delivery time in comparison with intensity-modulated radiation therapy (22.5min vs. 52.4min; P<0.001). Regarding target volume coverage, both modalities demonstrated comparable results (V_95%, 99.3% vs. 99.4%; P=0.796). Both modalities satisfied the dosimetric determinants for duodenal toxicity and the maximum and mean doses administered to normal organ were also statistically similar.

CONCLUSION

In comparison with 9-field intensity-modulated radiation therapy, volumetric-modulated arc therapy significantly reduces the number of monitoring units and treatment delivery times while administering similar dosimetric quality. Based on these results, volumetric-modulated arc therapy might be an appropriate treatment for locally advanced pancreatic cancer when combined with stereotactic body radiation therapy.

Assessment of multi-criteria optimization (MCO) for volumetric modulated arc therapy (VMAT) in hippocampal avoidance whole brain radiation therapy (HA-WBRT)

This study compared the dosimetric performance of (a) volumetric modulated arc therapy (VMAT) with standard optimization (STD) and (b) multi‐criteria optimization (MCO) to (c) intensity modulated radiation therapy (IMRT) with MCO for hippocampal avoidance whole brain radiation therapy (HA‐WBRT) in RayStation treatment planning system (TPS). Ten HA‐WBRT patients previously treated with MCO‐IMRT or MCO‐VMAT on an Elekta Infinity accelerator with Agility multileaf collimators (5‐mm leaves) were re‐planned for the other two modalities. All patients received 30 Gy in 15 fractions to the planning target volume (PTV), namely, PTV30 expanded with a 2‐mm margin from the whole brain excluding hippocampus with margin. The patients all had metastatic lesions (up to 12) of variable sizes and proximity to the hippocampus, treated with an additional 7.5 Gy from a simultaneous integrated boost (SIB) to PTV37.5. The IMRT plans used eight to eleven non‐coplanar fields, whereas the VMAT plans used two coplanar full arcs and a vertex half arc. The averaged target coverage, dose to organs‐at‐risk (OARs) and monitor unit provided by the three modalities were compared, and a Wilcoxon signed‐rank test was performed. MCO‐VMAT provided statistically significant reduction of D100 of hippocampus compared to STD‐VMAT, and Dmax of cochleas compared to MCO‐IMRT. With statistical significance, MCO‐VMAT improved V30 of PTV30 by 14.2% and 4.8%, respectively, compared to MCO‐IMRT and STD‐VMAT. It also raised D95 of PTV37.5 by 0.4 Gy compared to both MCO‐IMRT and STD‐VMAT. Improved plan quality parameters such as a decrease in overall plan Dmax and total monitor units (MU) were also observed for MCO‐VMAT. MCO‐VMAT is found to be the optimal modality for HA‐WBRT in terms of PTV coverage, OAR sparing and delivery efficiency, compared to MCO‐IMRT or STD‐VMAT.

Analyzing the performance of ArcCHECK diode array detector for VMAT plan

AIM

The aim of this study is to evaluate performance of ArcCHECK diode array detector for the volumetric modulated arc therapy (VMAT) patient specific quality assurance (QA). VMAT patient specific QA results were correlated with ion chamber measurement. Dose response of the ArcCHECK detector was studied.

BACKGROUND

VMAT delivery technique improves the dose distribution. It is complex in nature and requires proper QA before its clinical implementation. ArcCHECK is a novel three dimensional dosimetry system.

MATERIALS AND METHODS

Twelve retrospective VMAT plans were calculated on ArcCHECK phantom. Point dose and dose map were measured simultaneously with ion chamber (IC-15) and ArcCHECK diode array detector, respectively. These measurements were compared with their respective TPS calculated values.

RESULTS

The ion chamber measurements are in good agreement with TPS calculated doses. Mean difference between them is 0.50% with standard deviation of 0.51%. Concordance correlation coefficient (CCC) obtained for ion chamber measurements is 0.9996. These results demonstrate a strong correlation between the absolute dose predicted by our TPS and the measured dose. The CCC between ArcCHECK doses and TPS predictions on the CAX was found to be 0.9978. In gamma analysis of dose map, the mean passing rate was 98.53% for 3% dose difference and 3 mm distance to agreement.

CONCLUSIONS

The VMAT patient specific QA with an ion chamber and ArcCHECK phantom are consistent with the TPS calculated dose. Statistically good agreement was observed between ArcCHECK measured and TPS calculated. Hence, it can be used for routine VMAT QA.

Volumetric-modulated arc therapy planning using multicriteria optimization for localized prostate cancer

The purpose of this work is to evaluate the volumetric‐modulated arc therapy (VMAT) multicriteria optimization (MCO) algorithm clinically available in the RayStation treatment planning system (TPS) and its ability to reduce treatment planning time while providing high dosimetric plan quality. Nine patients with localized prostate cancer who were previously treated with 78 Gy in 39 fractions using VMAT plans and rayArc system based on the direct machine parameter optimization (DMPO) algorithm were selected and replanned using the VMAT‐MCO system. First, the dosimetric quality of the plans was evaluated using multiple conformity metrics that account for target coverage and sparing of healthy tissue, used in our departmental clinical protocols. The conformity and homogeneity index, number of monitor units, and treatment planning time for both modalities were assessed. Next, the effects of the technical plan parameters, such as constraint leaf motion CLM (cm/°) and maximum arc delivery time T (s), on the accuracy of delivered dose were evaluated using quality assurance passing rates (QAs) measured using the Delta⁴ phantom from ScandiDos. For the dosimetric plan's quality analysis, the results show that the VMAT‐MCO system provides plans comparable to the rayArc system with no statistical difference for V95% (p<0.01), D1% (p<0.01), CI (p<0.01), and HI (p<0.01) of the PTV, bladder (p<0.01), and rectum (p<0.01) constraints, except for the femoral heads and healthy tissues, for which a dose reduction was observed using MCO compared with rayArc (p<0.01). The technical parameter study showed that a combination of CLM equal to 0.5 cm/degree and a maximum delivery time of 72 s allowed the accurate delivery of the VMAT‐MCO plan on the Elekta Versa HD linear accelerator. Planning evaluation and dosimetric measurements showed that VMAT‐MCO can be used clinically with the advantage of enhanced planning process efficiency by reducing the treatment planning time without impairing dosimetric quality.

PACS numbers: 87.55.D, 87.55.de, 87.55.Qr

Correlation of phantom-based and log file patient-specific QA with complexity scores for VMAT

The motivation for this study was to reduce physics workload relating to patient‐specific quality assurance (QA). VMAT plan delivery accuracy was determined from analysis of pre‐ and on‐treatment trajectory log files and phantom‐based ionization chamber array measurements. The correlation in this combination of measurements for patient‐specific QA was investigated. The relationship between delivery errors and plan complexity was investigated as a potential method to further reduce patient‐specific QA workload. Thirty VMAT plans from three treatment sites — prostate only, prostate and pelvic node (PPN), and head and neck (H&N) — were retrospectively analyzed in this work. The 2D fluence delivery reconstructed from pretreatment and on‐treatment trajectory log files was compared with the planned fluence using gamma analysis. Pretreatment dose delivery verification was also carried out using gamma analysis of ionization chamber array measurements compared with calculated doses. Pearson correlations were used to explore any relationship between trajectory log file (pretreatment and on‐treatment) and ionization chamber array gamma results (pretreatment). Plan complexity was assessed using the MU/ arc and the modulation complexity score (MCS), with Pearson correlations used to examine any relationships between complexity metrics and plan delivery accuracy. Trajectory log files were also used to further explore the accuracy of MLC and gantry positions. Pretreatment 1%/1 mm gamma passing rates for trajectory log file analysis were 99.1% (98.7%–99.2%), 99.3% (99.1%–99.5%), and 98.4% (97.3%–98.8%) (median (IQR)) for prostate, PPN, and H&N, respectively, and were significantly correlated to on‐treatment trajectory log file gamma results (R=0.989,p<0.001). Pretreatment ionization chamber array (2%/2 mm) gamma results were also significantly correlated with on‐treatment trajectory log file gamma results (R=0.623,p<0.001). Furthermore, all gamma results displayed a significant correlation with MCS (R>0.57,p<0.001), but not with MU/arc. Average MLC position and gantry angle errors were 0.001±0.002mm and 0.025°±0.008° over all treatment sites and were not found to affect delivery accuracy. However, variability in MLC speed was found to be directly related to MLC position accuracy. The accuracy of VMAT plan delivery assessed using pretreatment trajectory log file fluence delivery and ionization chamber array measurements were strongly correlated with on‐treatment trajectory log file fluence delivery. The strong correlation between trajectory log file and phantom‐based gamma results demonstrates potential to reduce our current patient‐specific QA. Additionally, insight into MLC and gantry position accuracy through trajectory log file analysis and the strong correlation between gamma analysis results and the MCS could also provide further methodologies to both optimize the VMAT planning and QA process.

PACS number: 87.53.Bn, 87.55.Kh, 87.55.Qr

Volumetric-modulated arc therapy for oropharyngeal carcinoma: a dosimetric and delivery efficiency comparison with static-field IMRT

The purpose of this study is to evaluate the treatment plan adequacy and delivery efficiency among volumetric-modulated arc therapy (VMAT) with one or two arcs and the conventional static-field dynamic multileaf collimator (dMLC) intensity-modulated radiation therapy (IMRT) in patients undergoing oropharyngeal carcinoma. Fifteen patient cases were included in this investigation. Each of the cases was planned using step-and-shoot IMRT, VMAT with a single arc (Arc1) and VMAT with double arcs (Arc2). A two-dose level prescription for planning target volumes (PTVs) was delivered with 70 Gy/56 Gy in 30 fractions. Comparisons were performed of the dose-volume histograms (DVH) for PTVs, the DVH for organs at risk (OARs), the monitor units per fraction (MU/fx), and delivery time. IMRT and Arc2 achieved similar target coverage, but superior to Arc1. Apart from the oral cavity, Arc1 showed no advantage in sparing of OARs compared with IMRT, while Arc2 obtained equivalent or better sparing of OARs among the three techniques. VMAT reduced MU/fx and shortened delivery time remarkably compared with IMRT. Our results demonstrated that for oropharyngeal cases, Arc2 can achieve superior target coverage and normal tissue sparing, as well as a significant reduction in treatment time.

Efficiency of biological versus physical optimization for single-arc VMAT for prostate and head and neck cases

The aim of this work was to compare different approaches to VMAT optimization (biological vs. physical DVH-based) in two commercial treatment planning systems (TPS) for head and neck and prostate cases, using Pareto fronts. VMAT vs. IMRT Pareto front comparison was additionally performed in order to benchmark the optimizer efficiency and VMAT plan quality for each TPS. Three prostate and three head and neck cancer patients were selected for nine-beam IMRT and single-arc VMAT planning in Monaco 3.00 and Oncentra MasterPlan (OMP) 3.3 planning systems. Pareto fronts for prostate cases were constructed based on PTV coverage by 95% isodose and volume of rectum receiving 60 Gy or more. For head and neck cases, PTV coverage by the same isodose and mean dose to parotid gland were used for the construction of Pareto fronts. DVH analysis was performed together with evaluation of planning and delivery efficiency for all the plans. In the intersystem comparison for prostate plans, Monaco generated very similar IMRT and VMAT solutions. Quality of Monaco VMAT plans was superior compared to Oncentra in terms of conformity, homogeneity, and lower median dose to bladder due to biological formalism of optimization cost functions. For the head and neck cases, IMRT and VMAT plans were similar in both systems, except the case where a very strong modulation was required. In this situation single-arc VMAT plan generated with OMP was inferior compared to IMRT. VMAT OMP solutions were similar to Monaco or slightly better for two less-modulated head and neck cases. However, this advantage was achieved on the cost of lower conformity and homogeneity of the Oncentra VMAT plans. IMRT and VMAT solutions generated by Monaco were very similar for both prostate and head and neck cases. Oncentra system shows a bigger difference, and use of the dual-arc VMAT would be recommended to achieve the same plan quality as nine-field IMRT. Biological optimization seems beneficial in terms of plan conformity and homogeneity and allowed achieving lower OAR doses for prostate cases. In complex anatomical situations represented by head and neck cases, sequencing algorithm in Monaco imposed limitations on VMAT plan quality in the intersystem comparison.

Dosimetric study of uniform scanning proton therapy planning for prostate cancer patients with a metal hip prosthesis, and comparison with volumetric-modulated arc therapy

The main purposes of this study were to 1) investigate the dosimetric quality of uniform scanning proton therapy planning (USPT) for prostate cancer patients with a metal hip prosthesis, and 2) compare the dosimetric results of USPT with that of volumetric‐modulated arc therapy (VMAT). Proton plans for prostate cancer (four cases) were generated in XiO treatment planning system (TPS). The beam arrangement in each proton plan consisted of three fields (two oblique fields and one lateral or slightly angled field), and the proton beams passing through a metal hip prosthesis was avoided. Dose calculations in proton plans were performed using the pencil beam algorithm. From each proton plan, planning target volume (PTV) coverage value (i.e., relative volume of the PTV receiving the prescription dose of 79.2 CGE) was recorded. The VMAT prostate planning was done using two arcs in the Eclipse TPS utilizing 6 MV X‐rays, and beam entrance through metallic hip prosthesis was avoided. Dose computation in the VMAT plans was done using anisotropic analytical algorithm, and calculated VMAT plans were then normalized such that the PTV coverage in the VMAT plan was the same as in the proton plan of the corresponding case. The dose‐volume histograms of calculated treatment plans were used to evaluate the dosimetric quality of USPT and VMAT. In comparison to the proton plans, on average, the maximum and mean doses to the PTV were higher in the VMAT plans by 1.4% and 0.5%, respectively, whereas the minimum PTV dose was lower in the VMAT plans by 3.4%. The proton plans had lower (or better) average homogeneity index (HI) of 0.03 compared to the one for VMAT (HI = 0.04). The relative rectal volume exposed to radiation was lower in the proton plan, with an average absolute difference ranging from 0.1% to 32.6%. In contrast, using proton planning, the relative bladder volume exposed to radiation was higher at high‐dose region with an average absolute difference ranging from 0.4% to 0.8%, and lower at low‐ and medium‐dose regions with an average absolute difference ranging from 2.7% to 10.1%. The average mean dose to the rectum and bladder was lower in the proton plans by 45.1% and 22.0%, respectively, whereas the mean dose to femoral head was lower in VMAT plans by an average difference of 79.6%. In comparison to the VMAT, the proton planning produced lower equivalent uniform dose (EUD) for the rectum (43.7 CGE vs. 51.4 Gy) and higher EUD for the femoral head (16.7 CGE vs. 9.5 Gy), whereas both the VMAT and proton planning produced comparable EUDs for the prostate tumor (76.2 CGE vs. 76.8 Gy) and bladder (50.3 CGE vs. 51.1 Gy). The results presented in this study show that the combination of lateral and oblique fields in USPT planning could potentially provide dosimetric advantage over the VMAT for prostate cancer involving a metallic hip prosthesis.

PACS number: 87.55.D‐, 87.55.ne, 87.55.dk

Radiobiological impact of planning techniques for prostate cancer in terms of tumor control probability and normal tissue complication probability

Background:

The radiobiological models describe the effects of the radiation treatment on cancer and healthy cells, and the radiobiological effects are generally characterized by the tumor control probability (TCP) and normal tissue complication probability (NTCP).

Aim:

The purpose of this study was to assess the radiobiological impact of RapidArc planning techniques for prostate cancer in terms of TCP and normal NTCP.

Subjects and Methods:

A computed tomography data set of ten cases involving low-risk prostate cancer was selected for this retrospective study. For each case, two RapidArc plans were created in Eclipse treatment planning system. The double arc (DA) plan was created using two full arcs and the single arc (SA) plan was created using one full arc. All treatment plans were calculated with anisotropic analytical algorithm. Radiobiological modeling response evaluation was performed by calculating Niemierko's equivalent uniform dose (EUD)-based Tumor TCP and NTCP values.

Results:

For prostate tumor, the average EUD in the SA plans was slightly higher than in the DA plans (78.10 Gy vs. 77.77 Gy; P = 0.01), but the average TCP was comparable (98.3% vs. 98.3%; P = 0.01). In comparison to the DA plans, the SA plans produced higher average EUD to bladder (40.71 Gy vs. 40.46 Gy; P = 0.03) and femoral heads (10.39 Gy vs. 9.40 Gy; P = 0.03), whereas both techniques produced NTCP well below 0.1% for bladder (P = 0.14) and femoral heads (P = 0.26). In contrast, the SA plans produced higher average NTCP compared to the DA plans (2.2% vs. 1.9%; P = 0.01). Furthermore, the EUD to rectum was slightly higher in the SA plans (62.88 Gy vs. 62.22 Gy; P = 0.01).

Conclusion:

The SA and DA techniques produced similar TCP for low-risk prostate cancer. The NTCP for femoral heads and bladder was comparable in the SA and DA plans; however, the SA technique resulted in higher NTCP for rectum in comparison with the DA technique.

FusionArc optimization: a hybrid volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) planning strategy

PURPOSE

To introduce a hybrid volumetric modulated arc therapy/intensity modulated radiation therapy (VMAT/IMRT) optimization strategy called FusionArc that combines the delivery efficiency of single-arc VMAT with the potentially desirable intensity modulation possible with IMRT.

METHODS

A beamlet-based inverse planning system was enhanced to combine the advantages of VMAT and IMRT into one comprehensive technique. In the hybrid strategy, baseline single-arc VMAT plans are optimized and then the current cost function gradients with respect to the beamlets are used to define a metric for predicting which beam angles would benefit from further intensity modulation. Beams with the highest metric values (called the gradient factor) are converted from VMAT apertures to IMRT fluence, and the optimization proceeds with the mixed variable set until convergence or until additional beams are selected for conversion. One phantom and two clinical cases were used to validate the gradient factor and characterize the FusionArc strategy. Comparisons were made between standard IMRT, single-arc VMAT, and FusionArc plans with one to five IMRT∕hybrid beams.

RESULTS

The gradient factor was found to be highly predictive of the VMAT angles that would benefit plan quality the most from beam modulation. Over the three cases studied, a FusionArc plan with three converted beams achieved superior dosimetric quality with reductions in final cost ranging from 26.4% to 48.1% compared to single-arc VMAT. Additionally, the three beam FusionArc plans required 22.4%-43.7% fewer MU∕Gy than a seven beam IMRT plan. While the FusionArc plans with five converted beams offer larger reductions in final cost--32.9%-55.2% compared to single-arc VMAT--the decrease in MU∕Gy compared to IMRT was noticeably smaller at 12.2%-18.5%, when compared to IMRT.

CONCLUSIONS

A hybrid VMAT∕IMRT strategy was implemented to find a high quality compromise between gantry-angle and intensity-based degrees of freedom. This optimization method will allow patients to be simultaneously planned for dosimetric quality and delivery efficiency without switching between delivery techniques. Example phantom and clinical cases suggest that the conversion of only three VMAT segments to modulated beams may result in a good combination of quality and efficiency.

Beam controlled arc therapy--a delivery concept for stationary targets

Volumetric modulated arc therapy (VMAT) presupposes that it is beneficial to deliver radiation from all beam angles as the gantry rotates, requiring the multi-leaf collimator to maintain continuity in shape from one angle to another. In turn, radiation from undesirable beam angles could compromise the dose distribution. In this work, we challenge the notion that the radiation beam must be held on as the gantry rotates around the patient. We propose a new approach for delivering intensity-modulated arc therapy, beam-controlled arc therapy (BCAT), during which the radiation beam is controlled on or off and the dose rate is modulated while the gantry rotates around the patient. We employ linear-programming-based dose optimization to each aperture weight, resulting in some zero weight apertures. During delivery, the radiation beam is held off at control points with zero weights as the MLC shape transits to the next non-zero weight shape. This was tested on ten head and neck cases. Plan quality and delivery efficiency were compared with VMAT. Improvements of up to 17% (p-value 0.001) and 57% (p-value 0.018) in organ-at-risk sparing and target dose uniformity, respectively, were achieved. Compared to the fixed number of apertures used in single-arc and double-arc VMAT, the BCAT used 109 and 175 apertures on average, respectively. The difference in total MUs for VMAT and BCAT plans was less than 4%. Plan quality improvement was confirmed after delivery with γ analysis resulting in over 99% agreement, or 4 in 1099 points that failed.

Comparison study of intensity modulated arc therapy using single or multiple arcs to intensity modulated radiation therapy for high-risk prostate cancer

Purpose

Intensity modulated arc therapy (IMAT) is a form of intensity modulated radiation therapy (IMRT) that delivers dose in single or multiple arcs. We compared IMRT plans versus single-arc field (1ARC) and multi-arc fields (3ARC) IMAT plans in high-risk prostate cancer.

Materials and Methods

Sixteen patients were studied. Prostate (PTV_P), right pelvic (PTV_RtLN) and left pelvic lymph nodes (PTV_LtLN), and organs at risk were contoured. PTV_P, PTV_RtLN, and PTV_LtLN received 50.40 Gy followed by a boost to PTV_B of 28.80 Gy. Three plans were per patient generated: IMRT, 1ARC, and 3ARC. We recorded the dose to the PTV, the mean dose (D_MEAN) to the organs at risk, and volume covered by the 50% isodose. Efficiency was evaluated by monitor units (MU) and beam on time (BOT). Conformity index (CI), Paddick gradient index, and homogeneity index (HI) were also calculated.

Results

Average Radiation Therapy Oncology Group CI was 1.17, 1.20, and 1.15 for IMRT, 1ARC, and 3ARC, respectively. The plans' HI were within 1% of each other. The D_MEAN of bladder was within 2% of each other. The rectum D_MEAN in IMRT plans was 10% lower dose than the arc plans (p < 0.0001). The GI of the 3ARC was superior to IMRT by 27.4% (p = 0.006). The average MU was highest in the IMRT plans (1686) versus 1ARC (575) versus 3ARC (1079). The average BOT was 6 minutes for IMRT compared to 1.3 and 2.9 for 1ARC and 3ARC IMAT (p < 0.05).

Conclusion

For high-risk prostate cancer, IMAT may offer a favorable dose gradient profile, conformity, MU and BOT compared to IMRT.

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% - D(95%)); (ii) degree of conformity (CI9(5%)); (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.

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

PURPOSE

Rotational IMRT has been adopted by many clinics for its promise to deliver treatments in a shorter amount of time than other conventional IMRT techniques. In this paper, the authors investigate whether RapidArc is more susceptible to delivery uncertainties than dynamic IMRT using fixed fields.

METHODS

Dosimetric effects of delivery uncertainties in dose rate, gantry angle, and MLC leaf positions were evaluated by incorporating these uncertainties into RapidArc and sliding window IMRT (SW IMRT) treatment plans for five head-and-neck and five prostate cases. Dose distributions and dose-volume histograms of original and modified plans were recalculated and compared using Gamma analysis and dose indices of planned treatment volumes (PTV) and organs at risk (OAR). Results of Gamma analyses using passing criteria ranging from 1%-1 mm up to 5%-3 mm were reported.

RESULTS

Systematic shifts in MLC leaf bank positions of SW-IMRT cases resulted in 2-4 times higher average percent differences than RapidArc cases. Uniformly distributed random variations of 2 mm for active MLC leaves had a negligible effect on all dose distributions. Sliding window cases were much more sensitive to systematic shifts in gantry angle. Dose rate variations during RapidArc must be much larger than typical machine tolerances to affect dose distributions significantly; dynamic IMRT is inherently not susceptible to such variations.

CONCLUSIONS

RapidArc deliveries were found to be more tolerant to variations in gantry position and MLC leaf position than SW IMRT. This may be attributed to the fact that the average segmental field size or MLC leaf opening is much larger for RapidArc. Clinically acceptable treatments may be delivered successfully using RapidArc despite large fluctuations in dose rate and gantry position.

A novel multifunctional nanocomposite C225-conjugated Fe3O4/Ag enhances the sensitivity of nasopharyngeal carcinoma cells to radiotherapy

Radiotherapy is the major treatment for nasopharyngeal carcinoma, a malignant tumor of epithelial origin. In this process, a tracer with high sensitivity is pivotal for diagnostic imaging in radiotherapy. Here, we designed a novel multifunctional magnetic silver nanocomposite, Fe(3)O(4)/Ag conjugated to an epidermal growth factor receptor-specific antibody (C225), which can be potentially used for synchronous cancer therapy and diagnosis via magnetic resonance imaging. Characteristics of Fe(3)O(4)/Ag/C225 were determined by transmission electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet spectra, and dynamic light scattering. The results demonstrated that Fe(3)O(4)/Ag/C225 nanoparticles were spherical and dispersed well in water. The activity of C225 was preserved ∼80% in the Fe(3)O(4)/Ag/C225 nanoparticles. Futhermore, we tested the cytotoxicity and radiosensitivity of the nanocomposite for human nasopharyngeal carcinoma cell lines (CNEs) in vitro. MTT analysis revealed that Fe(3)O(4)/Ag/C225 could inhibit the proliferation of CNEs in a dose- and time-dependent manner. The clonogenic assay indicated that Fe(3)O(4)/Ag/C225 combined with X-ray treatment could increase the sensitivity of CNEs to irradiation. In a summary, the novel multifunctional nanocomposite Fe(3)O(4)/Ag/C225 might be a potential radiosensitizer for treating malign tumors in the clinic.

Intensity modulated radiation therapy with field rotation--a time-varying fractionation study

This paper proposes a novel mathematical approach to the beam selection problem in intensity modulated radiation therapy (IMRT) planning. The approach allows more beams to be used over the course of therapy while limiting the number of beams required in any one session. In the proposed field rotation method, several sets of beams are interchanged throughout the treatment to allow a wider selection of beam angles than would be possible with fixed beam orientations. The choice of beamlet intensities and the number of identical fractions for each set are determined by a mixed integer linear program that controls jointly for the distribution per fraction and the cumulative dose distribution delivered to targets and critical structures. Trials showed the method allowed substantial increases in the dose objective and/or sparing of normal tissues while maintaining cumulative and fraction size limits. Trials for a head and neck site showed gains of 25%-35% in the objective (average tumor dose) and for a thoracic site gains were 7%-13%, depending on how strict the fraction size limits were set. The objective did not rise for a prostate site significantly, but the tolerance limits on normal tissues could be strengthened with the use of multiple beam sets.

The effect of gantry spacing resolution on plan quality in a single modulated arc optimization

Volumetric‐modulated arc technique (VMAT) is an efficient form of IMRT delivery. It is advantageous over conventional IMRT in terms of treatment delivery time. This study investigates the relation between the number of segments and plan quality in VMAT optimization for a single modulated arc. Five prostate, five lung, and five head‐and‐neck (HN) patient plans were studied retrospectively. For each case, four VMAT plans were generated. The plans differed only in the number of control points used in the optimization process. The control points were spaced 2°, 3°, 4°, and 6° apart, respectively. All of the optimization parameters were the same among the four schemes. The 2° spacing plan was used as a reference to which the other three plans were compared. The plan quality was assessed by comparison of dose indices (DIs) and generalized equivalent uniform doses (gEUDs) for targets and critical structures. All optimization schemes generated clinically acceptable plans. The differences between the majority of reference and compared DIs and gEUDs were within 3%. DIs and gEUDs which differed in excess of 3% corresponded to dose levels well below the organ tolerances. The DI and the gEUD differences increased with an increase in plan complexity from prostates to HNs. Optimization with gantry spacing resolution of 4° seems to be a very balanced alternative between plan quality and plan complexity.

PACS number: 87.55.de

Reduced order constrained optimization (ROCO): clinical application to lung IMRT

PURPOSE

The authors use reduced-order constrained optimization (ROCO) to create clinically acceptable IMRT plans quickly and automatically for advanced lung cancer patients. Their new ROCO implementation works with the treatment planning system and full dose calculation used at Memorial Sloan-Kettering Cancer Center (MSKCC). The authors have implemented mean dose hard constraints, along with the point-dose and dose-volume constraints that the authors used for our previous work on the prostate.

METHODS

ROCO consists of three major steps. First, the space of treatment plans is sampled by solving a series of optimization problems using penalty-based quadratic objective functions. Next, an efficient basis for this space is found via principal component analysis (PCA); this reduces the dimensionality of the problem. Finally, a constrained optimization problem is solved over this basis to find a clinically acceptable IMRT plan. Dimensionality reduction makes constrained optimization computationally efficient.

RESULTS

The authors apply ROCO to 12 stage III non-small-cell lung cancer (NSCLC) cases, generating IMRT plans that meet all clinical constraints and are clinically acceptable, and demonstrate that they are competitive with the clinical treatment plans. The authors also test how many samples and PCA modes are necessary to achieve an adequate lung plan, demonstrate the importance of long-range dose calculation for ROCO, and evaluate the performance of nonspecific normal tissue ("rind") constraints in ROCO treatment planning for the lung. Finally, authors show that ROCO can save time for planners, and they estimate that in the clinic, planning using their approach would save a median of 105 min for the patients in the study.

CONCLUSIONS

New challenges arise when applying ROCO to the lung site, which include the lack of a class solution, a larger treatment site, an increased number of parameters and beamlets, a variable number of beams and beam arrangement, and the customary use of rinds in clinical plans to avoid high-dose areas outside the PTV. In the authors previous work, use of an approximate dose calculation in the hard constraint optimization sometimes meant that clinical constraints were not met when evaluated with the full dose calculation. This difficulty has been removed in the current work by using the full dose calculation in the hard constraint optimization. The authors have demonstrated that ROCO offers a fast and automatic way to create IMRT plans for advanced NSCLC, which extends their previous application of ROCO to prostate cancer IMRT planning.

Intensity-modulated radiosurgery with rapidarc for multiple brain metastases and comparison with static approach

Rotational RapidArc (RA) and static intensity-modulated radiosurgery (IMRS) have been used for brain radiosurgery. This study compares the 2 techniques from beam delivery parameters and dosimetry aspects for multiple brain metastases. Twelve patients with 2-12 brain lesions treated with IMRS were replanned using RA. For each patient, an optimal 2-arc RA plan from several trials was chosen for comparison with IMRS. Homogeneity, conformity, and gradient indexes have been calculated. The mean dose to normal brain and maximal dose to other critical organs were evaluated. It was found that monitor unit (MU) reduction by RA is more pronounced for cases with larger number of brain lesions. The MU-ratio of RA and IMRS is reduced from 104% to 39% when lesions increase from 2 to 12. The dose homogeneities are comparable in both techniques and the conformity and gradient indexes and critical organ doses are higher in RA. Treatment time is greatly reduced by RA in intracranial radiosurgery, because RA uses fewer MUs, fewer beams, and fewer couch angles.

Target tracking using DMLC for volumetric modulated arc therapy: a simulation study

PURPOSE

Target tracking using dynamic multileaf collimator (DMLC) is a promising approach for intrafraction motion management in radiation therapy. The purpose of this work is to develop a DMLC tracking algorithm capable of delivering volumetric-modulated arc therapy (VMAT) to the targets that experience two-dimensional (2D) rigid motion in the beam's eye view.

METHODS

The problem of VMAT delivery to moving targets is formulated as a control problem with constraints. The relationships between gantry speed, gantry acceleration, MLC leaf-velocity, dose rate, and target motion are derived. An iterative search algorithm is developed to find numerical solutions for efficient delivery of a specific VMAT plan to the moving target using 2D DMLC tracking. The delivery of five VMAT lung plans is simulated. The planned and delivered fluence maps in the target-reference frame are calculated and compared.

RESULTS

The simulation demonstrates that the 2D tracking algorithm is capable of delivering the VMAT plan to a moving target fast and accurately without violating the machine constraints and the integrity of the treatment plan. The average delivery time is only 29 s longer than that of no-tracking delivery, 101 versus 72 s, respectively. The fluence maps are normalized to 200 MU and the average root-mean-square error between the desired and the delivered fluence is 2.1 MU, compared to 14.8 MU for no-tracking and 3.6 MU for one-dimensional tracking.

CONCLUSIONS

A locally optimal MLC tracking algorithm for VMAT delivery is proposed, aiming at shortest delivery time while maintaining treatment plan invariant. The inconsequential increase of treatment time due to DMLC tracking is clinically desirable, which makes VMAT with DMLC tracking attractive in treating moving tumors.

When is better best? A multiobjective perspective

PURPOSE

To identify the most informative methods for reporting results of treatment planning comparisons.

METHODS

Seven articles from the past year of International Journal of Radiation Oncology Biology Physics reported on comparisons of treatment plans for IMRT and IMAT. The articles were reviewed to identify methods of comparisons. Decision theoretical concepts were used to evaluate the study methods and highlight those that provide the most information.

RESULTS

None of the studies examined the correlation between objectives. Statistical comparisons provided some information but not enough to provide support for a robust decision analysis.

CONCLUSIONS

The increased use of treatment planning studies to evaluate different methods in radiation therapy requires improved standards for designing the studies and reporting the results.

Intensity-modulated arc therapy: principles, technologies and clinical implementation

Intensity-modulated arc therapy (IMAT) was proposed by Yu (1995 Phys. Med. Biol. 40 1435-49) as an alternative to tomotherapy. Over more than a decade, much progress has been made. The advantages and limitations of the IMAT technique have also been better understood. In recent years, single-arc forms of IMAT have emerged and become commercially adopted. The leading example is the volumetric-modulated arc therapy (VMAT), a single-arc form of IMAT that delivers apertures of varying weights with a single-arc rotation that uses dose-rate variation of the treatment machine. With commercial implementation of VMAT, wide clinical adoption has quickly taken root. However, there remains a lack of general understanding for the planning of such arc treatments, as well as what delivery limitations and compromises are made. Commercial promotion and competition add further confusion for the end users. It is therefore necessary to provide a summary of this technology and some guidelines on its clinical implementation. The purpose of this review is to provide a summary of the works from the radiotherapy community that led to wide clinical adoption, and point out the issues that still remain, providing some perspective on its further developments. Because there has been vast experience in IMRT using multiple intensity-modulated fields, comparisons between IMAT and IMRT are also made in the review within the areas of planning, delivery and quality assurance.

Ultrafast treatment plan optimization for volumetric modulated arc therapy (VMAT)

PURPOSE

To develop a novel aperture-based algorithm for volumetric modulated are therapy (VMAT) treatment plan optimization with high quality and high efficiency.

METHODS

The VMAT optimization problem is formulated as a large-scale convex programming problem solved by a column generation approach. The authors consider a cost function consisting two terms, the first enforcing a desired dose distribution and the second guaranteeing a smooth dose rate variation between successive gantry angles. A gantry rotation is discretized into 180 beam angles and for each beam angle, only one MLC aperture is allowed. The apertures are generated one by one in a sequential way. At each iteration of the column generation method, a deliverable MLC aperture is generated for one of the unoccupied beam angles by solving a subproblem with the consideration of MLC mechanic constraints. A subsequent master problem is then solved to determine the dose rate at all currently generated apertures by minimizing the cost function. When all 180 beam angles are occupied, the optimization completes, yielding a set of deliverable apertures and associated dose rates that produce a high quality plan.

RESULTS

The algorithm was preliminarily tested on five prostate and five head-and-neck clinical cases, each with one full gantry rotation without any couch/collimator rotations. High quality VMAT plans have been generated for all ten cases with extremely high efficiency. It takes only 5-8 min on CPU (MATLAB code on an Intel Xeon 2.27 GHz CPU) and 18-31 s on GPU (CUDA code on an NVIDIA Tesla C1060 GPU card) to generate such plans.

CONCLUSIONS

The authors have developed an aperture-based VMAT optimization algorithm which can generate clinically deliverable high quality treatment plans at very high efficiency.