A treatment planning study comparing volumetric arc modulation with RapidArc and fixed field IMRT for cervix uteri radiotherapy

Comparative analysis of SmartArc-based dual arc volumetric-modulated arc radiotherapy (VMAT) versus intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma

The purpose of this study was to evaluate and quantify the planning performance of SmartArc‐based volumetric‐modulated arc radiotherapy (VMAT) versus fixed‐beam intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) using a sequential mode treatment plan. The plan quality and performance of dual arc‐VMAT (DA‐VMAT) using the Pinnacle3 Smart‐Arc system (clinical version 9.0; Philips, Fitchburg, WI, USA) were evaluated and compared with those of seven‐field (7F)‐IMRT in 18 consecutive NPC patients. Analysis parameters included the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), maximum and mean dose, normal tissue complication probability (NTCP) for the specified organs at risk (OARs), and comprehensive quality index (CQI) for an overall evaluation in the 11 OARs. Treatment delivery time, monitor units per fraction (MU/fr), and gamma (Γ3mm,3%) evaluations were also analyzed. DA‐VMAT achieved similar target coverage and slightly better homogeneity than conventional 7F‐IMRT with a similar CI and HI. NTCP values were only significantly lower in the left parotid gland (for xerostomia) for DA‐VMAT plans. The mean value of CQI at 0.98±0.02 indicated a 2% benefit in sparing OARs by DA‐VMAT. The MU/fr used and average delivery times appeared to show improved efficiencies in DA‐VMAT. Each technique demonstrated high accuracy in dose delivery in terms of a high‐quality assurance (QA) passing rate (>98%) of the (Γ3mm,3%) criterion. The major difference between DA‐VMAT and 7F‐IMRT using a sequential mode for treating NPC cases appears to be improved efficiency, resulting in a faster delivery time and the use of fewer MU/fr.

PACS number: 87.53.Tf, 87.55.x, 87.55.D, 87.55.dk

Implementing RapidArc into clinical routine: a comprehensive program from machine QA to TPS validation and patient QA

PURPOSE

With the increased commercial availability of intensity modulated arc therapy (IMAT) comes the need for comprehensive QA programs, covering the different aspects of this newly available technology. This manuscript proposes such a program for the RapidArc (RA) (Varian Medical Systems, Palo Alto) IMAT solution.

METHODS

The program was developed and tested out for a Millennium120 MLC on iX Clinacs and a HighDefinition MLC on a Novalis TX, using a variety of measurement equipment including Gafchromic film, 2D ion chamber arrays (Seven29 and StarCheck, PTW, Freiburg, Germany) with inclinometer and Octavius phantom, the Delta4 systam (ScandiDos, Uppsala, Sweden) and the portal imager (EPID). First, a number of complementary machine QA tests were developed to monitor the correct interplay between the accelerating/decelerating gantry, the variable dose rate and the MLC position, straining the delivery to the maximum allowed limits. Second, a systematic approach to the validation of the dose calculation for RA was adopted, starting with static gantry and RA specific static MLC shapes and gradually moving to dynamic gantry, dynamic MLC shapes. RA plans were then optimized on a series of artificial structures created within the homogeneous Octavius phantom and within a heterogeneous lung phantom. These served the double purpose of testing the behavior of the optimization algorithm (PRO) as well as the precision of the forward dose calculation. Finally, patient QA on a series of clinical cases was performed with different methods. In addition to the well established in-phantom QA, we evaluated the portal dosimetry solution within the Varian approach.

RESULTS

For routine machine QA, the "Snooker Cue" test on the EPID proved to be the most sensitive to overall problem detection. It is also the most practical one. The "Twinkle" and "Sunrise" tests were useful to obtain well differentiated information on the individual treatment delivery components. The AAA8.9 dose calculations showed excellent agreement with all corresponding measurements, except in areas where the 2.5 mm fixed fluence resolution was insufficient to accurately model the tongue and groove effect or the dose through nearly closed opposing leafs. Such cases benefited from the increased fluence resolution in AAA10.0. In the clinical RA fields, these effects were smeared out spatially and the impact of the fluence resolution was considerably less pronounced. The RA plans on the artificial structure sets demonstrated some interesting characteristics of the PRO8.9 optimizer, such as a sometimes unexpected dependence on the collimator rotation and a suboptimal coverage of targets within lung tissue. Although the portal dosimetry was successfully validated, we are reluctant to use it as a sole means of patient QA as long as no gantry angle information is embedded.

CONCLUSIONS

The all-in validation program allows a systematic approach in monitoring the different levels of RA treatments. With the systematic approach comes a better understanding of both the capabilities and the limits of the used solution. The program can be useful for implementation, but also for the validation of major upgrades.

Bilateral kidney preservation by volumetric-modulated arc therapy (RapidArc) compared to conventional radiation therapy (3D-CRT) in pancreatic and bile duct malignancies

Background

To compare volumetric-modulated arc therapy plans with conventional radiation therapy (3D-CRT) plans in pancreatic and bile duct cancers, especially for bilateral kidney preservation.

Methods

A dosimetric analysis was performed in 21 patients who had undergone radiotherapy for pancreatic or bile duct carcinoma at our institution. We compared 4-field 3D-CRT and 2 arcs RapidArc (RA) plans. The treatment plan was designed to deliver a dose of 50.4 Gy to the planning target volume (PTV) based on the gross disease in a 1.8 Gy daily fraction, 5 days a week. Planning objectives were 95% of the PTV receiving 95% of the prescribed dose and no more than 2% of the PTV receiving more than 107%. Dose-volume histograms (DVH) for the target volume and the organs at risk (right and left kidneys, bowel tract, liver and healthy tissue) were compared. Monitor units and delivery treatment time were also reported.

Results

All plans achieved objectives, with 95% of the PTV receiving ≥ 95% of the dose (D95% for 3D-CRT = 48.9 Gy and for RA = 48.6 Gy). RapidArc was shown to be superior to 3D-CRT in terms of organ at risk sparing except for contralateral kidney: for bowel tract, the mean dose was reduced by RA compared to 3D-CRT (16.7 vs 20.8 Gy, p = 0.0001). Similar result was observed for homolateral kidney (mean dose of 4.7 Gy for RA vs 12.6 Gy for 3D-CRT, p < 0.0001), but 3D-CRT significantly reduced controlateral kidney dose with a mean dose of 1.8 Gy vs 3.9 Gy, p < 0.0007. Compared to 3D-CRT, mean MUs for each fraction was significantly increased with RapidArc: 207 vs 589, (p < 0.0001) but the treatment time was not significantly different (2 and 2.66 minutes, p = ns).

Conclusion

RapidArc allows significant dose reduction, in particular for homolateral kidney and bowel, while maintaining target coverage. This would have a promising impact on reducing toxicities.

Dosimetric comparison of helical tomotherapy, RapidArc, and a novel IMRT & Arc technique for esophageal carcinoma

PURPOSE

To compare radiotherapy treatment plans for mid- and distal-esophageal cancer with primary involvement of the gastroesophageal (GE) junction using a novel IMRT & Arc technique (IMRT & Arc), helical tomotherapy (HT), and RapidArc (RA1 and RA2).

METHODS AND MATERIALS

Eight patients treated on HT for locally advanced esophageal cancer with radical intent were re-planned for RA and IMRT&Arc. RA plans employed single and double arcs (RA1 and RA2, respectively), while IMRT&Arc plans had four fixed-gantry IMRT fields and a conformal arc. Dose-volume histogram statistics, dose uniformity, and dose homogeneity were analyzed to compare treatment plans.

RESULTS

RA2 plans showed significant improvement over RA1 plans in terms of OAR dose and PTV dose uniformity and homogeneity. HT plan provided best dose uniformity (p=0.001) and dose homogeneity (p=0.002) to planning target volume (PTV), while IMRT&Arc and RA2 plans gave lowest dose to lungs among four radiotherapy techniques with acceptable PTV dose coverage. Mean V(10) of the lungs was significantly reduced by the RA2 plans compared to IMRT&Arc (40.3%, p=0.001) and HT (66.2%, p<0.001) techniques. Mean V(15) of the lungs for the RA2 plans also showed significant improvement over the IMRT&Arc (25.2%, p=0.042) and HT (34.8%, p=0.027) techniques. These improvements came at the cost of higher doses to the heart volume compared to HT and IMRT&Arc techniques. Mean lung dose (MLD) for the IMRT&Arc technique (21.2 ± 5.0% of prescription dose) was significantly reduced compared to HT (26.3%, p=0.004), RA1 (23.3%, p=0.028), and RA2 (23.2%, p=0.017) techniques.

CONCLUSION

The IMRT&Arc technique is a good option for treating esophageal cancer with thoracic involvement. It achieved optimal low dose to the lungs and heart with acceptable PTV coverage. HT is a good option for treating esophageal cancer with little thoracic involvement as it achieves superior dose conformality and uniformity. The RA2 technique provided for improved treatment plans using additional arcs with low doses to the lungs at the cost of increased heart dose. Plan quality could still be improved through the use of additional arcs.

Commissioning and early experience with a new-generation low-energy linear accelerator with advanced delivery and imaging functionalities

Background

A new-generation low-energy linear accelerator (UNIQUE) was introduced in the clinical arena during 2009 by Varian Medical Systems. The world's first UNIQUE was installed at Oncology Institute of Southern Switzerland and put into clinical operation in June 2010. The aim of the present contribution was to report experience about its commissioning and first year results from clinical operation.

Methods

Commissioning data, beam characteristics and the modeling into the treatment planning system were summarized. Imaging system of UNIQUE included a 2D-2D matching capability and tests were performed to identify system repositioning capability. Finally, since the system is capable of delivering volumetric modulated arc therapy with RapidArc, a summary of the tests performed for such modality to assess its performance in preclinical settings and during clinical usage was included.

Results

Isocenter virtual diameter was measured as less than 0.2 mm. Observed accuracy of isocenter determination and repositioning for 2D-2D matching procedures in image guidance was <1.2 mm. Concerning reproducibility and stability over a period of 1 year, deviations from reference were found <0.3 ± 0.2% for linac output, <0.1% for homogeneity, similarly to symmetry. Rotational accuracy of the entire gantry-portal imager system showed a maximum deviation from nominal 0.0 of <1.2 mm. Pre treatment quality assurance of RapidArc plans resulted with a Gamma Agreement Index (fraction of points passing the gamma criteria) of 97.0 ± 1.6% on the first 182 arcs verified.

Conclusions

The results of the commissioning tests and of the first period of clinical operation, resulted meeting specifications and having good margins respect to tolerances. UNIQUE was put into operation for all delivery techniques; in particular, as shown by the pre-treatment quality assurance results, it enabled accurate and safe delivery of RapidArc plans.

Volumetric modulated arc radiotherapy for esophageal cancer

A treatment planning study was performed to evaluate the performance of volumetric arc modulation with RapidArc (RA) against 3D conformal radiation therapy (3D-CRT) and conventional intensity-modulated radiation therapy (IMRT) techniques for esophageal cancer. Computed tomgraphy scans of 10 patients were included in the study. 3D-CRT, 4-field IMRT, and single-arc and double-arc RA plans were generated with the aim to spare organs at risk (OAR) and healthy tissue while enforcing highly conformal target coverage. The planning objective was to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Plans were evaluated based on target conformity and dose-volume histograms of organs at risk (lung, spinal cord, and heart). The monitor unit (MU) and treatment delivery time were also evaluated to measure the treatment efficiency. The IMRT plan improves target conformity and spares OAR when compared with 3D-CRT. Target conformity improved with RA plans compared with IMRT. The mean lung dose was similar in all techniques. However, RA plans showed a reduction in the volume of the lung irradiated at V(₂₀Gy) and V(₃₀Gy) dose levels (range, 4.62-17.98%) compared with IMRT plans. The mean dose and D(₃₅%) of heart for the RA plans were better than the IMRT by 0.5-5.8%. Mean V(₁₀Gy) and integral dose to healthy tissue were almost similar in all techniques. But RA plans resulted in a reduced low-level dose bath (15-20 Gy) in the range of 14-16% compared with IMRT plans. The average MU needed to deliver the prescribed dose by RA technique was reduced by 20-25% compared with IMRT technique. The preliminary study on RA for esophageal cancers showed improvements in sparing OAR and healthy tissue with reduced beam-on time, whereas only double-arc RA offered improved target coverage compared with IMRT and 3D-CRT plans.

Quality assurance of RapidArc in clinical practice using portal dosimetry

OBJECTIVE

Quality assurance data from five centres were analysed to assess the reliability of RapidArc radiotherapy delivery in terms of machine and dosimetric performance.

METHODS

A large group of patients was treated with RapidArc radiotherapy and treatment data recorded. Machine quality assurance was performed according to Ling et al (Int J Radiat Oncol Biol Phys 2008;72:575-81). In addition, treatment to a typical clinical case was delivered biweekly as a constancy check. Pre-treatment dosimetric validation of plan delivery was performed for each patient. All measurements and computations were performed at the depth of the maximum dose in water according to the GLAaS method using electronic portal imaging device measurements. Evaluation was carried out according to a gamma agreement index (GAI, the percentage of field area passing the test); the threshold dose difference was 3% and the threshold distance to agreement was 3 mm.

RESULTS

A total of 275 patients (395 arcs) were included in the study. Mean delivery parameters were 31.0±20.0° (collimator angle), 4.7±0.5° s(-1) (gantry speed), 343±134 MU min(-1) (dose rate) and 1.6±1.4 min (beam-on time) for prescription doses ranging from 1.8 to 16.7 Gy/fraction. Mean deviations from the baseline dose rate and gantry speed ranged from -0.61% to 1.75%. Mean deviations from the baseline for leaf speed variation ranged from -0.73% to 0.41%. The mean GAI of repeated clinical fields was 99.2±0.2%. GAI varied from 84.7% to 100%; the mean across all patients was 97.1±2.4%.

CONCLUSION

RapidArc can provide a reliable and accurate delivery of radiotherapy for a variety of clinical conditions.

Comparison of modulated electron radiotherapy to conventional electron boost irradiation and volumetric modulated photon arc therapy for treatment of tumour bed boost in breast cancer

BACKGROUND AND PURPOSE

To compare few leaf electron collimator (FLEC)-based modulated electron radiotherapy (MERT) to conventional direct electron (DE) and volumetric modulated photon arc therapy (VMAT) for the treatment of tumour bed boost in breast cancer.

MATERIALS AND METHODS

Fourteen patients with breast cancer treated by lumpectomy and requiring post-operative whole breast radiotherapy with tumour bed boost were planned retrospectively using conventional DE, VMAT and FLEC-based MERT. The planning goal was to deliver 10Gy to at least 95% of the tumour bed volume. Dosimetry parameters for all techniques were compared.

RESULTS

Dose evaluation volume (DEV) coverage and homogeneity were best for MERT (D(98)=9.77Gy, D(2)=11.03Gy) followed by VMAT (D(98)=9.56Gy, D(2)=11.07Gy) and DE (D(98)=9.81Gy, D(2)=11.52Gy). Relative to the DE plans, the MERT plans predicted a reduction of 35% in mean breast dose (p<0.05), 54% in mean lung dose (p<0.05) and 46% in mean body dose (p<0.05). Relative to the VMAT plans, the MERT plans predicted a reduction of 24%, 36% and 39% in mean breast dose, heart dose and body dose, respectively (p<0.05).

CONCLUSIONS

MERT plans were a considerable improvement in dosimetry over DE boost plans. There was a dosimetric advantage in using MERT over VMAT for increased DEV conformity and low-dose sparing of healthy tissue including the integral dose; however, the cost is often an increase in the ipsilateral lung high-dose volume.

Two-step intensity modulated arc therapy (2-step IMAT) with segment weight and width optimization

Background

2-step intensity modulated arc therapy (IMAT) is a simplified IMAT technique which delivers the treatment over typically two continuous gantry rotations. The aim of this work was to implement the technique into a computerized treatment planning system and to develop an approach to optimize the segment weights and widths.

Methods

2-step IMAT was implemented into the Prism treatment planning system. A graphical user interface was developed to generate the plan segments automatically based on the anatomy in the beam's-eye-view. The segment weights and widths of 2-step IMAT plans were subsequently determined in Matlab using a dose-volume based optimization process. The implementation was tested on a geometric phantom with a horseshoe shaped target volume and then applied to a clinical paraspinal tumour case.

Results

The phantom study verified the correctness of the implementation and showed a considerable improvement over a non-modulated arc. Further improvements in the target dose uniformity after the optimization of 2-step IMAT plans were observed for both the phantom and clinical cases. For the clinical case, optimizing the segment weights and widths reduced the maximum dose from 114% of the prescribed dose to 107% and increased the minimum dose from 87% to 97%. This resulted in an improvement in the homogeneity index of the target dose for the clinical case from 1.31 to 1.11. Additionally, the high dose volume V₁₀₅ was reduced from 57% to 7% while the maximum dose in the organ-at-risk was decreased by 2%.

Conclusions

The intuitive and automatic planning process implemented in this study increases the prospect of the practical use of 2-step IMAT. This work has shown that 2-step IMAT is a viable technique able to achieve highly conformal plans for concave target volumes with the optimization of the segment weights and widths. Future work will include planning comparisons of the 2-step IMAT implementation with fixed gantry intensity modulated radiotherapy (IMRT) and commercial IMAT implementations.

Understanding the impact of RapidArc therapy delivery errors for prostate cancer

The purpose of this study is to simulate random and systematic RapidArc delivery errors for external beam prostate radiotherapy plans in order to determine the dose sensitivity for each error type. Ten prostate plans were created with a single 360° arc. The DICOM files for these treatment plans were then imported into an in‐house computer program that introduced delivery errors. Random and systematic gantry position (0.25°, 0.5°, 1°), monitor unit (MU) (1.25%, 2.5%, 5%), and multileaf collimator (MLC) position (0.5, 1, 2 mm) errors were introduced. The MLC errors were either random or one of three types of systematic errors, where the MLC banks moved in the same (MLC gaps remain unchanged) or opposing directions (increasing or decreasing the MLC gaps). The generalized equivalent uniform dose (gEUD) was calculated for the original plan and all treatment plans with errors introduced. The dose sensitivity for the cohort was calculated using linear regression for the gantry position, MU, and MLC position errors. Because there was a large amount of variability for systematic MLC position errors, the dose sensitivity of each plan was calculated and correlated with plan MU, mean MLC gap, and the percentage of MLC leaf gaps less than 1 and 2 cm for each individual plan. We found that random and systematic gantry position errors were relatively insignificant (< 0.1% gEUD change) for gantry errors up to 1°. Random MU errors were also insignificant, and systematic MU increases caused a systematic increase in gEUD. For MLC position errors, random MLC errors were relatively insignificant up to 2 mm as had been determined in previous IMRT studies. Systematic MLC shift errors caused a decrease of approximately −1% in the gEUD per mm. For systematic MLC gap open errors, the dose sensitivity was 8.2%/mm and for MLC gap close errors the dose sensitivity was −7.2%/mm. There was a large variability for MLC gap open/close errors for the ten RapidArc plans which correlated strongly with MU, mean gap width, and percentage of MLC gaps less than 1 or 2 cm. This study evaluates the magnitude of various simulated RapidArc delivery errors by calculating gEUED on various prostate plans.

PACS numbers: 87.55.x, 87.55.D, 87.55.de, 87.55.dk

Intensity-modulated arc therapy for pediatric posterior fossa tumors

PURPOSE

To compare intensity-modulated arc therapy (IMAT) to noncoplanar intensity-modulated radiation therapy (IMRT) in the treatment of pediatric posterior fossa tumors.

METHODS AND MATERIALS

Nine pediatric patients with posterior fossa tumors, mean age 9 years (range, 6-15 years), treated using IMRT were chosen for this comparative planning study because of their tumor location. Each patient's treatment was replanned to receive 54 Gy to the planning target volume (PTV) using five different methods: eight-field noncoplanar IMRT, single coplanar IMAT, double coplanar IMAT, single noncoplanar IMAT, and double noncoplanar IMAT. For each method, the dose to 95% of the PTV was held constant, and the doses to surrounding critical structures were minimized. The different plans were compared based on conformity, total linear accelerator dose monitor units, and dose to surrounding normal tissues, including the entire body, whole brain, temporal lobes, brainstem, and cochleae.

RESULTS

The doses to the target and critical structures for the various IMAT methods were not statistically different in comparison with the noncoplanar IMRT plan, with the following exceptions: the cochlear doses were higher and whole brain dose was lower for coplanar IMAT plans; the cochleae and temporal lobe doses were lower and conformity increased for noncoplanar IMAT plans. The advantage of the noncoplanar IMAT plan was enhanced by doubling the treatment arc.

CONCLUSION

Noncoplanar IMAT results in superior treatment plans when compared to noncoplanar IMRT for the treatment of posterior fossa tumors. IMAT should be considered alongside IMRT when treatment of this site is indicated.

Stereotactic body radiation therapy for abdominal targets using volumetric intensity modulated arc therapy with RapidArc: feasibility and clinical preliminary results

PURPOSE

To report early clinical experience in stereotactic body radiation therapy (SBRT) delivered using volumetric intensity modulated arc therapy with RapidArc (RA) in patients with primary or metastatic tumours at abdominal sites.

MATERIAL AND METHODS

Thirty-seven consecutive patients were treated using RA. Of these, 16 had primary or metastatic liver tumours, nine had pancreatic cancer and 12 a nodal metastasis in the retro-peritoneum. Dose prescription varied from 45 to 75 Gy to the Clinical Target Volume in 3 to 6 fractions. The median follow-up was 12 months (6-22). Early local control and toxicity were investigated and reported.

RESULTS

Planning objectives on target volumes and organs at risk were met in most cases. Delivery time ranged from 2.8 ± 0.3 to 9.2 ± 2.4 minutes and pre-treatment plan verification resulted in a Gamma Agreement Index from 95.3 ± 3.8 to 98.3 ± 1.7%. At the time of analysis, local control (freedom from progression) at six months, was assessable in 24 of 37 patients and was achieved in 19 patients with a crude rate of 79.2%. Seven patients experienced treatment-related toxicity. Three patients experienced a mild and transient G1 enteritis and two showed a transient G1 liver damage. Two had late toxicity: one developed chronic enteritis causing G1 diarrhoea and G1 abdominal pain and one suffered at three months a G3 gastric bleeding. No patients experienced G4 acute toxicity.

CONCLUSIONS

SBRT for abdominal targets delivered by means of RA resulted to be feasible with good early clinical results in terms of local control rate and acute toxicity profile. RA allowed to achieve required target coverage as well as to keep within normal tissue dose/volume constraints.

Bone marrow-sparing intensity-modulated radiation therapy for Stage I seminoma

BACKGROUND

A direct association between radiotherapy dose, side-effects and secondary cancers has been described in patients with seminoma. A treatment planning study was performed in order to compare computed tomography-based traditional radiotherapy (CT-tRT) versus bone marrow-sparing intensity-modulated radiation therapy (BMS-IMRT) in patients with Stage I seminoma.

MATERIAL AND METHODS

We optimized in 10 patients a CT-tRT and a BMS-IMRT treatment plan to deliver 20 Gy to the para-aortic nodes. CT-tRT and IMRT consisted of anteroposterior-posterioranterior parallel-opposed and seven non-opposed coplanar fields using 16 and 6-MV photon energies, respectively. Dose-Volume Histograms for clinical target volume (CTV), planning target volume (PTV) and organs at risk (OARs) were compared for both techniques using Wilcoxon matched-pair signed rank-test.

RESULTS

D(mean) to CTV and PTV were similar for both techniques, even if CT-tRT showed a slightly improved target coverage in terms of PTV-D(95%) (19.7 vs. 19.5 Gy, p = 0.005) and PTV-V(95%) (100 vs. 99.7%, p = 0.011) compared to BMS-IMRT. BMS-IMRT resulted in a significant reduction (5.2 Gy, p = 0.005) in the D(mean) to the active bone marrow (ABM). The V(100%) and V(75%) of the OARs were reduced with BMS-IMRT by: ABM-V(100%) = 51.7% and ABM-V(75%) = 42.3%; bowel-V(100%) = 15.7% and bowel-V(75%) = 16.8%; stomach-V(100%) = 22% and stomach-V(75%) = 27.7%; pancreas-V(100%) = 37.1% and pancreas-V(75%) = 35.9% (p = 0.005 for all variables).

CONCLUSIONS

BMS-IMRT reduces markedly the dose to the OARs compared to CT-tRT. This should translate into a reduction in acute and long-term toxicity, as well as into the risk of secondary solid and hematological cancers.

Dosimetric comparison of RapidArc with fixed gantry intensity-modulated radiotherapy treatment for multiple liver metastases radiotherapy

We wanted to compare the dosimetric difference and treatment efficiency of RapidArc and fixed gantry intensity-modulated radiotherapy treatment (IMRT) for multiple liver metastases. Computed tomography datasets of 10 patients were studied retrospectively. IMRT plans were generated using 5 fields and RapidArc using either 1 or 2 arcs. The dose distribution of planning target volume (PTV), organs at risk (OARs), and the normal tissue were compared. Monitor units and treatment time were scored to measure expected treatment efficiency. Both RapidArc and IMRT plans resulted in equivalent target coverage. There was no statistically significant difference for the maximum and the minimum dose of PTV. RapidArc plans achieved an improved conformity index compared with IMRT (RA1 = 1.68 ± 0.27, RA2 = 1.61 ± 0.25, IMRT = 1.80 ± 0.37). For OARs, all techniques respected planning objectives. RapidArc plans had a lower dose in V(40) of small bowel than IMRT, but were higher in mean dose of kidneys. Concerning the V(5), V(10), and V(15) of healthy tissue, RapidArc plans were higher than IMRT. However, the V(20), V(25), and V(30) of healthy tissue in RapidArc plans were lower than IMRT. Monitor units per fraction of RapidArc plans were about 40% or 46% of IMRT. Compared with IMRT plans, treatment time of RapidArc plans were reduced by 60% or 70%. All techniques respected planning objectives. RapidArc showed statistical improvements in conformity index and healthy tissue sparing with uncompromised target coverage. This, in combination with fewer monitor units and short delivery time, can lead to clinically significant advances for the treatment of multiple liver metastases.

Volumetric-modulated arc therapy: effective and efficient end-to-end patient-specific quality assurance

PURPOSE

To explore an effective and efficient end-to-end patient-specific quality-assurance (QA) protocol for volumetric modulated arc radiotherapy (VMAT) and to evaluate the suitability of a stationary radiotherapy QA device (two-dimensional [2D] ion chamber array) for VMAT QA.

METHODS AND MATERIALS

Three methods were used to analyze 39 VMAT treatment plans for brain, spine, and prostate: ion chamber (one-dimensional absolute, n = 39), film (2D relative, coronal/sagittal, n = 8), and 2D ion chamber array (ICA, 2D absolute, coronal/sagittal, n = 39) measurements. All measurements were compared with the treatment planning system dose calculation either via gamma analysis (3%, 3- to 4-mm distance-to-agreement criteria) or absolute point dose comparison. The film and ion chamber results were similarly compared with the ICA measurements.

RESULTS

Absolute point dose measurements agreed well with treatment planning system computed doses (ion chamber: median deviation, 1.2%, range, -0.6% to 3.3%; ICA: median deviation, 0.6%, range, -1.8% to 2.9%). The relative 2D dose measurements also showed good agreement with computed doses (>93% of pixels in all films passing gamma, >90% of pixels in all ICA measurements passing gamma). The ICA relative dose results were highly similar to those of film (>90% of pixels passing gamma). The coronal and sagittal ICA measurements were statistically indistinguishable by the paired t test with a hypothesized mean difference of 0.1%. The ion chamber and ICA absolute dose measurements showed a similar trend but had disparities of 2-3% in 18% of plans.

CONCLUSIONS

After validating the new VMAT implementation with ion chamber, film, and ICA, we were able to maintain an effective yet efficient patient-specific VMAT QA protocol by reducing from five (ion chamber, film, and ICA) to two measurements (ion chamber and single ICA) per plan. The ICA (Matrixx®, IBA Dosimetry) was validated for VMAT QA, but ion chamber measurements are recommended for absolute dose comparison until future developments correct the ICA angular dependence.

Volumetric modulated arc therapy vs. IMRT for the treatment of distal esophageal cancer

Several studies have demonstrated that volumetric modulated arc therapy (VMAT) has the ability to reduce monitor units and treatment time when compared with intensity-modulated radiation therapy (IMRT). This study aims to demonstrate that VMAT is able to provide adequate organs at risk (OAR) sparing and planning target volume (PTV) coverage for adenocarcinoma of the distal esophagus while reducing monitor units and treatment time. Fourteen patients having been treated previously for esophageal cancer were planned using both VMAT and IMRT techniques. Dosimetric quality was evaluated based on doses to several OARs, as well as coverage of the PTV. Treatment times were assessed by recording the number of monitor units required for dose delivery. Body V(5) was also recorded to evaluate the increased volume of healthy tissue irradiated to low doses. Dosimetric differences in OAR sparing between VMAT and IMRT were comparable. PTV coverage was similar for the 2 techniques but it was found that IMRT was capable of delivering a slightly more homogenous dose distribution. Of the 14 patients, 12 were treated with a single arc and 2 were treated with a double arc. Single-arc plans reduced monitor units by 42% when compared with the IMRT plans. Double-arc plans reduced monitor units by 67% when compared with IMRT. The V(5) for the body was found to be 18% greater for VMAT than for IMRT. VMAT has the capability to decrease treatment times over IMRT while still providing similar OAR sparing and PTV coverage. Although there will be a smaller risk of patient movement during VMAT treatments, this advantage comes at the cost of delivering small doses to a greater volume of the patient.

Apparatus-dependent dosimetric differences in spine stereotactic body radiotherapy

The purpose of this investigation was to study apparatus-dependent dose distribution differences specific to spine stereotactic body radiotherapy (SBRT) treatment planning. This multi-institutional study was performed evaluating an image-guided robotic radiosurgery system (CK), intensity modulated protons (IMP), multileaf collimator (MLC) fixed-field IMRT with 5 mm (11 field), 4 mm (9 field), and 2.5 mm (8- and 9-field) leaf widths and intensity modulated volumetric arc therapy (IMVAT) with a 2.5 mm MLC. Treatment plans were systematically developed for targets consisting of one, two and three consecutive thoracic vertebral bodies (VBs) with the esophagus and spinal cord contoured as the organs at risk. It was found that all modalities achieved acceptable treatment planning constraints. However, following normalization fixed field IMRT with a 2.5 mm MLC, IMVAT and IMP systems yielded the smallest ratio of maximum dose divided by the prescription dose (MD/PD) for one-, two- and three-VB PTVs (ranging from 1.1-1.16). The 2.5 mm MLC 9-field IMRT, IMVAT and CK plans resulted in the least dose to 0.1 cc volumes of spinal cord and esophagus. CK plans had the greatest degree of target dose inhomogeneity. As the level of complexity increased with an increasing number of vertebral bodies, distinct apparatus features such as the use of a high number of beams and a finer leaf size MLC were favored. Our study quantified apparatus-dependent dose-distribution differences specific to spine SBRT given strict, but realistic, constraints and highlights the need to benchmark physical dose distributions for multi-institutional clinical trials.

Two years experience with quality assurance protocol for patient related Rapid Arc treatment plan verification using a two dimensional ionization chamber array

PURPOSE

To verify the dose distribution and number of monitor units (MU) for dynamic treatment techniques like volumetric modulated single arc radiation therapy-Rapid Arc-each patient treatment plan has to be verified prior to the first treatment. The purpose of this study was to develop a patient related treatment plan verification protocol using a two dimensional ionization chamber array (MatriXX, IBA, Schwarzenbruck, Germany).

METHOD

Measurements were done to determine the dependence between response of 2D ionization chamber array, beam direction, and field size. Also the reproducibility of the measurements was checked. For the patient related verifications the original patient Rapid Arc treatment plan was projected on CT dataset of the MatriXX and the dose distribution was calculated. After irradiation of the Rapid Arc verification plans measured and calculated 2D dose distributions were compared using the gamma evaluation method implemented in the measuring software OmniPro (version 1.5, IBA, Schwarzenbruck, Germany).

RESULTS

The dependence between response of 2D ionization chamber array, field size and beam direction has shown a passing rate of 99% for field sizes between 7 cm×7 cm and 24 cm×24 cm for measurements of single arc. For smaller and larger field sizes than 7 cm×7 cm and 24 cm×24 cm the passing rate was less than 99%. The reproducibility was within a passing rate of 99% and 100%. The accuracy of the whole process including the uncertainty of the measuring system, treatment planning system, linear accelerator and isocentric laser system in the treatment room was acceptable for treatment plan verification using gamma criteria of 3% and 3 mm, 2D global gamma index.

CONCLUSION

It was possible to verify the 2D dose distribution and MU of Rapid Arc treatment plans using the MatriXX. The use of the MatriXX for Rapid Arc treatment plan verification in clinical routine is reasonable. The passing rate should be 99% than the verification protocol is able to detect clinically significant errors.

Rotational IMRT techniques compared to fixed gantry IMRT and tomotherapy: multi-institutional planning study for head-and-neck cases

BACKGROUND

Recent developments enable to deliver rotational IMRT with standard C-arm gantry based linear accelerators. This upcoming treatment technique was benchmarked in a multi-center treatment planning study against static gantry IMRT and rotational IMRT based on a ring gantry for a complex parotid gland sparing head-and-neck technique.

METHODS

Treatment plans were created for 10 patients with head-and-neck tumours (oropharynx, hypopharynx, larynx) using the following treatment planning systems (TPS) for rotational IMRT: Monaco (ELEKTA VMAT solution), Eclipse (Varian RapidArc solution) and HiArt for the helical tomotherapy (Tomotherapy). Planning of static gantry IMRT was performed with KonRad, Pinnacle and Panther DAO based on step&shoot IMRT delivery and Eclipse for sliding window IMRT. The prescribed doses for the high dose PTVs were 65.1Gy or 60.9Gy and for the low dose PTVs 55.8Gy or 52.5Gy dependend on resection status. Plan evaluation was based on target coverage, conformity and homogeneity, DVHs of OARs and the volume of normal tissue receiving more than 5Gy (V5Gy). Additionally, the cumulative monitor units (MUs) and treatment times of the different technologies were compared. All evaluation parameters were averaged over all 10 patients for each technique and planning modality.

RESULTS

Depending on IMRT technique and TPS, the mean CI values of all patients ranged from 1.17 to 2.82; and mean HI values varied from 0.05 to 0.10. The mean values of the median doses of the spared parotid were 26.5Gy for RapidArc and 23Gy for VMAT, 14.1Gy for Tomo. For fixed gantry techniques 21Gy was achieved for step&shoot+KonRad, 17.0Gy for step&shoot+Panther DAO, 23.3Gy for step&shoot+Pinnacle and 18.6Gy for sliding window.V5Gy values were lowest for the sliding window IMRT technique (3499 ccm) and largest for RapidArc (5480 ccm). The lowest mean MU value of 408 was achieved by Panther DAO, compared to 1140 for sliding window IMRT.

CONCLUSIONS

All IMRT delivery technologies with their associated TPS provide plans with satisfying target coverage while at the same time respecting the defined OAR criteria. Sliding window IMRT, RapidArc and Tomo techniques resulted in better target dose homogeneity compared to VMAT and step&shoot IMRT. Rotational IMRT based on C-arm linacs and Tomotherapy seem to be advantageous with respect to OAR sparing and treatment delivery efficiency, at the cost of higher dose delivered to normal tissues. The overall treatment plan quality using Tomo seems to be better than the other TPS technology combinations.

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.

Preclinical assessment of volumetric modulated arc therapy for total marrow irradiation

PURPOSE

A preclinical investigation was undertaken to explore a treatment technique for total marrow irradiation using RapidArc, a volumetric modulated arc technique.

MATERIALS AND METHODS

Computed tomography datasets of 5 patients were included. Plans with eight overlapping coaxial arcs were optimized for 6-MV photon beams. Dose prescription was 12 Gy in 2 Gy per fraction, normalized so that 100% isodose covered 85% of the planning target volume (PTV). The PTV consisted of the whole skeleton (including ribs and sternum), from the top of the skull to the medium distal third of the femurs. Planning objectives for organs at risk (OARs) were constrained to a median dose <6 to 7 Gy. OARs included brain, eyes, oral cavity, parotids, thyroid, lungs, heart, kidneys, liver, spleen, stomach, abdominal cavity, bladder, rectum, and genitals. Pretreatment quality assurance consisted of portal dosimetry comparisons, scoring the delivery to calculation agreement with the gamma agreement index.

RESULTS

The median total body volume in the study was 57 liters (range, 49-81 liters), for an average diameter of 47 cm (range, 46-53 cm) and a total length ranging from 95 to 112 cm. The median PTV volume was 6.8 liters (range, 5.8-10.8 liters). The mean dose to PTV was 109% (range, 107-112%). The global mean of median dose to all OARs was 4.9 Gy (range, 4.5-5.1 Gy over the 5 patients). The individual mean of median doses per organ ranged from 2.3 Gy (oral cavity) to 7.3 Gy (bowels cavity). Preclinical quality assurance resulted in a mean gamma agreement index of 94.3 ± 5.1%. The delivery time measured from quality assurance runs was 13 minutes.

CONCLUSION

Sparing of normal tissues with adequate coverage of skeletal bones was shown to be feasible with RapidArc. Pretreatment quality assurance measurements confirmed the technical agreement between expected and actually delivered dose distributions, suggesting the possibility of incorporating this technique in the treatment options for patients.

Helical tomotherapy versus single-arc intensity-modulated arc therapy: a collaborative dosimetric comparison between two institutions

PURPOSE

Both helical tomotherapy (HT) and single-arc intensity-modulated arc therapy (IMAT) deliver radiation using rotational beams with multileaf collimators. We report a dual-institution study comparing dosimetric aspects of these two modalities.

METHODS AND MATERIALS

Eight patients each were selected from the University of Maryland (UMM) and the University of Wisconsin Cancer Center Riverview (UWR), for a total of 16 cases. Four cancer sites including brain, head and neck (HN), lung, and prostate were selected. Single-arc IMAT plans were generated at UMM using Varian RapidArc (RA), and HT plans were generated at UWR using Hi-Art II TomoTherapy. All 16 cases were planned based on the identical anatomic contours, prescriptions, and planning objectives. All plans were swapped for analysis at the same time after final approval. Dose indices for targets and critical organs were compared based on dose-volume histograms, the beam-on time, monitor units, and estimated leakage dose. After the disclosure of comparison results, replanning was done for both techniques to minimize diversity in optimization focus from different operators.

RESULTS

For the 16 cases compared, the average beam-on time was 1.4 minutes for RA and 4.8 minutes for HT plans. HT provided better target dose homogeneity (7.6% for RA and 4.2% for HT) with a lower maximum dose (110% for RA and 105% for HT). Dose conformation numbers were comparable, with RA being superior to HT (0.67 vs. 0.60). The doses to normal tissues using these two techniques were comparable, with HT showing lower doses for more critical structures. After planning comparison results were exchanged, both techniques demonstrated improvements in dose distributions or treatment delivery times.

CONCLUSIONS

Both techniques created highly conformal plans that met or exceeded the planning goals. The delivery time and total monitor units were lower in RA than in HT plans, whereas HT provided higher target dose uniformity.

Applications of IMAT in cervical esophageal cancer radiotherapy: a comparison with fixed-field IMRT in dosimetry and implementation

This study aimed to compare fixed-field, intensity-modulated radiotherapy (f-IMRT) with intensity-modulated arc therapy (IMAT) treatment plans in dosimetry and practical application for cervical esophageal carcinoma. For ten cervical esophageal carcinoma cases, f-IMRT plan (seven fixed-fields) and two IMAT plans, namely RA (coplanar 360° arcs) and RAx (coplanar 360° arcs without sectors from 80° to 110°, and 250° to 280°), were generated. DVHs were adopted for the statistics of above parameters, as well as conformal index (CI), homogeneity index (HI), dose-volumetric parameters of normal tissues, total accelerator output MUs and total treatment time. There were differences between RAx and f-IMRT, as well as RA in PTV parameters such as HI, V(95%) and V(110%), but not in CI. RAx reduced lung V₅ from (50.9% ± 9.8% in f-IMRT and (51.4% ± 10.8% in RA to (49.3% ± 10.4% in RAx (p < 0.05). However, lung V₃₀, V₄₀, V₅₀ and MLD increased in RAx. There was no difference in the mean heart dose in three plans. Total MU was reduced from 1174.8 ± 144.6 in f-IMRT to 803.8 ± 122.2 in RA and 736.2 ± 186.9 in RAx (p < 0.05). Compared with f-IMRT, IMAT reduced low dose volumes of lung and total MU on the basis of meeting clinical requirements.

A radiotherapy planning study of RapidArc, intensity modulated radiotherapy, three-dimensional conformal radiotherapy, and parallel opposed beams in the treatment of pediatric retroperitoneal tumors

BACKGROUND

This planning study compared RapidArc, fixed-field IMRT (cIMRT), 3D conformal radiotherapy (3D-CRT), and a parallel-opposed pair (POP) for children with retroperitoneal tumors.

PROCEDURE

Plans were generated in eight patients to treat the PTV (dose range 19.8-45 Gy) while limiting kidney and liver doses. In selected patients, vertebral body (VB) dose heterogeneity was minimized. Cumulative DVH parameters, monitor units (MU), and treatment times were compared for the four techniques using the Wilcoxon matched pairs test.

RESULTS

RapidArc and cIMRT covered target volumes more conformally than 3D-CRT and POP (P = 0.012). There was no difference in the ability to meet kidney dose constraints. A significantly lower volume of the liver received 12 Gy with cIMRT or RapidArc compared with 3D-CRT (P = 0.028). Where VB was included in PTV, VB dose homogeneity was generally within 94-104% of the prescription dose. Time to deliver a single fraction with RapidArc, POP, 3D-CRT, and cIMRT was 1.25 ± 0.01, 1.38 ± 0.10, 2.6 ± 0.45, and 4.02 ± 1.12 min, respectively (P = 0.012). Monitor units for a single fraction with POP, 3D-CRT, RapidArc, and cIMRT were 203 ± 26, 235 ± 32, 325 ± 71, and 665 ± 215, respectively (P < 0.05).

CONCLUSIONS

POP resulted in favorable MU, treatment time and dosimetry but had poor conformality. 3D-CRT was more conformal but had higher MU and treatment time. RapidArc and cIMRT were generally no better dosimetrically than conformal techniques. RapidArc was dosimetrically very similar to cIMRT, but resulted in a major reduction in time and MU used to deliver the radiation.

Hypofractionated stereotactic radiotherapy for brain metastases: a dosimetric and treatment efficiency comparison between volumetric modulated arc therapy and intensity modulated radiotherapy

A treatment planning comparison study was performed to evaluate the dosimetric characteristic and treatment efficiency of volumetric modulated arc therapy with step-and-shoot intensity modulated radiotherapy (IMRT) for the hypofractionated stereotactic radiotherapy (HFSRT) in patients with multiple brain metastases. CT datasets of 10 patients with two to four brain metastases were selected for the comparison. Three plans were generated for each case: seven-field step-and-shoot IMRT, single (RA1) and double (RA2) arcs with RapidArc technique (RA, Varian Medical System). The prescribed dose was 50 Gy in 10 fractions and plans were all normalized to the mean dose to the PTV. For PTV, plans aim to achieve at least 98% of PTV was covered with the 95% of prescription dose, at least 95% of PTV was encompassed by the prescription dose, and an over-dosage of 110% of the prescription dose was allowed to 5% volume of the PTV. The plans generated using three techniques were clinically acceptable. The target conformity and homogeneity were improved slightly with RA2 compared to IMRT and RA1. The Paddick CI was 0.868 (IMRT), 0.863 (RA1) and 0.895 (RA2), and HI was 7.7 (IMRT), 7.5 (RA1) and 6.5 (RA2), respectively. Compared with IMRT, the maximum dose in RA2 plans to the brainstem, left and right optic nerves, left and right lens was reduced by 1.6 Gy, 6 Gy, 3 Gy, 1.5 Gy, 1.3 Gy, respectively. The percentage of healthy tissue volume receiving 5 Gy was larger with RA1 (56.7%) and RA2 (57.1%) than with IMRT (52.9%), while the percentages of volume receiving 15 Gy and 20 Gy were smaller with RA1 (27.1%, 18.7%) and RA2 (25%, 16.3%) than with IMRT (28.8%, 19.1%). No significant difference was observed between RA1 and RA2. The mean number of MU per fraction of 5 Gy was 1944 +/- 374 (IMRT), 1199 +/- 173 (RA1) and 1387 +/- 186 (RA2), respectively. Compared with IMRT, the MUs were reduced by 36.8% and 27.2% with RA1 and RA2. The pure beam-on time needed per fraction was 6.5 +/- 1.2 min (IMRT), 1.25 min (RA1) and 2.5 min (RA2), respectively. The beam-on time for RA1 and RA2 was approximately 80% and 40% less compared to IMRT. In conclusion, RA, single arc or double arcs, is a feasible technique with highly conformal dose distribution for the HFSRT in patients with oligo brain metastases. Compared with IMRT, RA1 provides similar plan quality, while RA2 achieves slight improvements in PTV coverage and sparing of organs at risk. The treatment efficiency, using less monitor units and shorter treatment delivery time, is the most obvious advantage.

Cone beam CT pre- and post-daily treatment for assessing geometrical and dosimetric intrafraction variability during radiotherapy of prostate cancer

The purpose of this study was to quantify the relationship between treatment time and dose uncertainty due to intrafraction organ motion in prostate cancer radiotherapy (RT). Ten consecutive patients with prostate cancer treated by radical RT by volumetric modulated arc therapy (RapidArc) were considered. For each patient, pre- and post-treatment cone beam computed tomography (CBCT) was performed in 10 fractions. The prostate, rectum and bladder were contoured on each CBCT. The change in organ position, volume and dosimetric uncertainty induced by organ motion were evaluated. Interval time between the two CBCTs ranged between 4 and 16 min (mean 7.3 ± 0.7 min). Treatment with intrafraction prostate motion >3mm and > 5 mm were 24% and 5%, respectively. Regarding change in centroid position and volume, a poor time correlation was found for target and rectum, while a constant increase was obtained for bladder. The agreement index was highly correlated to time (r = -0.89 for bladder, r = -0.95 for rectum, and r= -0.84 for prostate). In terms of difference in dose volume histogram between pre- and post-CBCT, the dose uncertainties for the targets and rectum amplified with the increasing time. The increasing intrafraction dose uncertainty with time requires the use of an RT technique with minimization of treatment time to improve confidence in planning dose distribution.

A method for optimizing LINAC treatment geometry for volumetric modulated arc therapy of multiple brain metastases

PURPOSE

Volumetric modulated arc therapy (VMAT) is a rotational delivery technique in which MLC shapes, dose rate, and gantry rotation speed are optimized to produce conformal dose distributions. The aim of this work is to develop a beam projection method for deriving the optimal table and collimator angles for multilesion treatment planning.

METHODS

The method consists of four steps. The first step is to define the vector of beam-eye-view (BEV)-Y-axis in the treatment planning CT coordinates. The second step is to project each target onto the BEV-Y-axis vector. In the third step, the best table and collimator angle are found with a brute-force optimization technique that minimizes MLC leaf sharing between lesions. The fourth step is to generate an optimized VMAT plan with appropriate table/collimator angles and evaluate the plan quality.

RESULTS

The authors tested the method on three example cases with targets of various locations in the brain and sizes ranging from 1.18 to 17.86 cm(3). Applying the optimized geometric parameter to generate VMAT plan, a reduction of the 12 Gy volume was more than 6.1% for all cases; the plan homogeneity (D2%-D95%) was improved from 5.88 +/- 1.21 to 5.21 +/- 0.93 Gy vs a VMAT plan with the manufacturer recommended table and collimator angles.

CONCLUSIONS

The authors conclude that the use of the projection method minimizes the sharing of MLC leaves between lesions and improves the plan quality for multilesion VMAT delivery.

Whole abdomen radiation therapy in ovarian cancers: a comparison between fixed beam and volumetric arc based intensity modulation

Purpose

A study was performed to assess dosimetric characteristics of volumetric modulated arcs (RapidArc, RA) and fixed field intensity modulated therapy (IMRT) for Whole Abdomen Radiotherapy (WAR) after ovarian cancer.

Methods and Materials

Plans for IMRT and RA were optimised for 5 patients prescribing 25 Gy to the whole abdomen (PTV_WAR) and 45 Gy to the pelvis and pelvic nodes (PTV_Pelvis) with Simultaneous Integrated Boost (SIB) technique. Plans were investigated for 6 MV (RA6, IMRT6) and 15 MV (RA15, IMRT15) photons. Objectives were: for both PTVs V_90% > 95%, for PTV_Pelvis: D_max < 105%; for organs at risk, maximal sparing was required. The MU and delivery time measured treatment efficiency. Pre-treatment Quality assurance was scored with Gamma Agreement Index (GAI) with 3% and 3 mm thresholds.

Results

IMRT and RapidArc resulted comparable for target coverage. For PTV_WAR, V_90% was 99.8 ± 0.2% and 93.4 ± 7.3% for IMRT6 and IMRT15, and 98.4 ± 1.7 and 98.6 ± 0.9% for RA6 and RA15. Target coverage resulted improved for PTV_Pelvis. Dose homogeneity resulted slightly improved by RA (Uniformity was defined as U_5-95% = D_5%-D_95%/D_mean). U₅-_95% for PTV_WAR was 0.34 ± 0.05 and 0.32 ± 0.06 (IMRT6 and IMRT15), 0.30 ± 0.03 and 0.26 ± 0.04 (RA6 and RA15); for PTV_Pelvis, it resulted equal to 0.1 for all techniques. For organs at risk, small differences were observed between the techniques. MU resulted 3130 ± 221 (IMRT6), 2841 ± 318 (IMRT15), 538 ± 29 (RA6), 635 ± 139 (RA15); the average measured treatment time was 18.0 ± 0.8 and 17.4 ± 2.2 minutes (IMRT6 and IMRT15) and 4.8 ± 0.2 (RA6 and RA15). GAI_IMRT6 = 97.3 ± 2.6%, GAI_IMRT15 = 94.4 ± 2.1%, GAI_RA6 = 98.7 ± 1.0% and GAI_RA15 = 95.7 ± 3.7%.

Conclusion

RapidArc showed to be a solution to WAR treatments offering good dosimetric features with significant logistic improvements compared to IMRT.

Collimator angle influence on dose distribution optimization for vertebral metastases using volumetric modulated arc therapy

PURPOSE

The cylindrical symmetry of vertebrae favors the use of volumetric modulated are therapy in generating a dose "hole" on the center of the vertebrae limiting the dose to the spinal cord. The authors have evaluated if collimator angle is a significant parameter for dose distribution optimization in vertebral metastases.

METHODS

Three patients with one-three vertebrae involved were considered. Twenty-one differently optimized plans (nine single-arc and 12 double-arc plans) were performed, testing various collimator angle positions. Clinical target volume was defined as the whole vertebrae, excluding the spinal cord canal. The planning target volume (PTV) was defined as CTV+5 mm. Dose prescription was 5 x 4 Gy(2) with normalization to PTV mean dose. The dose at 1 cm(3) of spinal cord was limited to 11.5Gy.

RESULTS

The best plans in terms of target coverage and spinal cord sparing were achieved by two arcs and Arcl-80 degrees and Arc2-280 degrees collimator angles for all the cases considered (i.e., leaf travel parallel to the spinal cord primary orientation). If one arc is used, only 80 degrees reached the objectives.

CONCLUSIONS

This study demonstrated the role of collimation rotation for the vertebrae metastasis irradiation, with the leaf travel parallel to the spinal cord primary orientation to be better than other solutions. Thus, optimal choice of collimator angle increases the optimization freedom to shape a desired dose distribution.

Stereotactic radiotherapy for peripheral lung tumors: a comparison of volumetric modulated arc therapy with 3 other delivery techniques

PURPOSE

Volumetric modulated arc therapy (RapidArc) allows for fast delivery of stereotactic body radiotherapy (SBRT) delivery in stage I lung tumors. We compared dose distributions and delivery times between RapidArc and common delivery techniques in small tumors.

METHODS

In 18 patients who completed RapidArc SBRT for tumors measuring <70 cm(3), new treatment plans were generated using non-coplanar 3D conformal fields (conf-SBRT) and dynamic conformal arc radiotherapy (DCA). For 9 patients with tumors adjacent to the chest wall, co-planar intensity-modulated radiotherapy (IMRT) plans were also generated. PTV dose coverage, organs at risk (OAR) doses and treatment delivery times were assessed.

RESULTS

RapidArc plans achieved a superior conformity index (CI) and lower V(45 Gy) to chest wall (p<0.05) compared to all other techniques. RapidArc led to a small increase in V(5 Gy) to contralateral lung compared to conf-SBRT (4.4±4% versus 1.2±1.8%, p=0.011). For other OAR, RapidArc and conf-SBRT plans were comparable, and both were superior to DCA plans. Delivery of a 7.5 Gy-fraction required 3.9 min (RapidArc), 11.6 min (conf-SBRT), and 12 min (IMRT).

CONCLUSIONS

In stage I lung tumors measuring <70 cm(3), RapidArc plans achieved both the highest dose conformity and shortest delivery times.

Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment

Background and Purpose

The purpose of this study was to assess plan quality and treatment time achievable with the new VMAT optimization tool implemented in the treatment planning system Oncentra MasterPlan^® as compared to IMRT for Elekta SynergyS^® linear accelerators.

Materials and methods

VMAT was implemented on a SynergyS^® linear accelerator (Elekta Ltd., Crawley, UK) with Mosaiq^® record and verify system (IMPAC Medical Systems, Sunnyvale, CA) and the treatment planning system Oncentra MasterPlan^® (Nucletron BV, Veenendaal, the Netherlands). VMAT planning was conducted for three typical target types of prostate cancer, hypopharynx/larynx cancer and vertebral metastases, and compared to standard IMRT with respect to plan quality, number of monitor units (MU), and treatment time.

Results

For prostate cancer and vertebral metastases single arc VMAT led to similar plan quality as compared to IMRT. For treatment of the hypopharynx/larynx cancer, a second arc was necessary to achieve sufficient plan quality. Treatment time was reduced in all cases to 35% to 43% as compared to IMRT. Times required for optimization and dose calculation, however, increased by a factor of 5.0 to 6.8.

Conclusion

Similar or improved plan quality can be achieved with VMAT as compared to IMRT at reduced treatment times but increased calculation times.

Large volume unresectable locally advanced non-small cell lung cancer: acute toxicity and initial outcome results with rapid arc

BACKGROUND

To report acute toxicity, initial outcome results and planning therapeutic parameters in radiation treatment of advanced lung cancer (stage III) with volumetric modulated arcs using RapidArc (RA).

METHODS

Twenty-four consecutive patients were treated with RA. All showed locally advanced non-small cell lung cancer with stage IIIA-IIIB and with large volumes (GTV:299 ± 175 cm3, PTV:818 ± 206 cm3). Dose prescription was 66Gy in 33 fractions to mean PTV. Delivery was performed with two partial arcs with a 6 MV photon beam.

RESULTS

From a dosimetric point of view, RA allowed us to respect most planning objectives on target volumes and organs at risk. In particular: for GTV D1% = 105.6 ± 1.7%, D99% = 96.7 ± 1.8%, D5%-D95% = 6.3 ± 1.4%; contra-lateral lung mean dose resulted in 13.7 ± 3.9Gy, for spinal cord D1% = 39.5 ± 4.0Gy, for heart V45Gy = 9.0 ± 7.0Gy, for esophagus D1% = 67.4 ± 2.2Gy. Delivery time was 133 ± 7s. At three months partial remission > 50% was observed in 56% of patients. Acute toxicities at 3 months showed 91% with grade 1 and 9% with grade 2 esophageal toxicity; 18% presented grade 1 and 9% with grade 2 pneumonia; no grade 3 acute toxicity was observed. The short follow-up does not allow assessment of local control and progression free survival.

CONCLUSIONS

RA proved to be a safe and advantageous treatment modality for NSCLC with large volumes. Long term observation of patients is needed to assess outcome and late toxicity.

Early clinical experience with volumetric modulated arc therapy in head and neck cancer patients

BACKGROUND

To report about early clinical experience in radiation treatment of head and neck cancer of different sites and histology by volumetric modulated arcs with the RapidArc technology.

METHODS

During 2009, 45 patients were treated at Istituto Clinico Humanitas with RapidArc (28 males and 17 females, median age 65 years). Of these, 78% received concomitant chemotherapy. Thirty-six patients were treated as exclusive curative intent (group A), three as postoperative curative intent (group B) and six with sinonasal tumours (group C). Dose prescription was at Planning Target Volumes (PTV) with simultaneous integrated boost: 54.45 Gy and 69.96 Gy in 33 fractions (group A); 54.45 Gy and 66 Gy in 33 fractions (group B) and 55 Gy in 25 fractions (group C).

RESULTS

Concerning planning optimization strategies and constraints, as per PTV coverage, for all groups, D98% > 95% and V95% > 99%. As regards organs at risk, all planning objectives were respected, and this was correlated with observed acute toxicity rates. Only 28% of patients experienced G3 mucositis, 14% G3 dermitis 44% had G2 dysphagia. Nobody required feeding tubes to be placed during treatment. Acute toxicity is also related to chemotherapy. Two patients interrupted the course of radiotherapy because of a quick worsening of general clinical condition.

CONCLUSIONS

These preliminary results stated that volumetric modulated arc therapy in locally advanced head and neck cancers is feasible and effective, with acceptable toxicities.

Analysis of second malignancies after modern radiotherapy versus prostatectomy for localized prostate cancer

PURPOSE

To clarify the risk of developing second primary cancers (SPCs) after radiotherapy (RT) versus prostatectomy for localized prostate cancer (PCa) in the modern era.

METHODS

The RT cohort consisted of 2120 patients matched on a 1:1 basis with surgical patients according to age and follow-up time. RT techniques consisted of conventional or two-dimensional RT (2DRT, 36%), three-dimensional conformal RT and/or intensity modulated RT (3DCRT/IMRT, 29%), brachytherapy (BT, 16%), and a combination of 2DRT and BT (BT boost, 19%).

RESULTS

The overall SPC risk was not significantly different between the matched-pair (HR 1.14, 95% CI 0.94-1.39), but the risk became significant >5years or >10years after RT (HR 1.86, 95% CI 1.36-2.55; HR 4.94, 95% CI 2.18-11.2, respectively). The most significant sites of increased risk were bladder, lymphoproliferative, and sarcoma. Of the different RT techniques, only 2DRT was associated with a significantly higher risk (HR 1.76, 95% CI 1.32-2.35), but not BT boost (HR 0.83, 95% CI 0.50-1.38), 3DCRT/IMRT (HR 0.81, 95% CI 0.55-1.21), or BT (HR 0.53, 95% CI 0.28-1.01).

CONCLUSIONS

Radiation-related SPC risk varies depending on the RT technique and may be reduced by using BT, BT boost, or 3DCRT/IMRT.