Wilko F.A.R. Verbakel

Volumetric Intensity-Modulated Arc Therapy Vs. Conventional IMRT in Head-and-Neck Cancer: A Comparative Planning and Dosimetric Study

PURPOSE Volumetric intensity-modulated arc therapy (RA) allows for rapid delivery of highly conformal dose distributions. In this study, planning and dosimetry of RA were compared with conventional intensity-modulated radiation therapy (IMRT) plans of head-and-neck cancer patients. MATERIALS AND METHODS Computed tomography scans of 12 patients who had completed IMRT for advanced tumors of the naso-, oro- and hypopharynx were replanned using RA using either one or two arcs. Calculated doses to planning target volume (PTV) and organs at risk (OAR) were compared between IMRT and RA plans. Dose distributions for single arc (n = 8) and double arc (n = 4) plans were verified using film dosimetry in three to five coronal planes using a quality assurance phantom. RESULTS RA plans allowed for a mean reduction in number of monitor units (MU) by nearly 60%, relative to seven field sliding window IMRT plans. RA plans achieved similar sparing of all OAR as IMRT. Double arc RA provided the best dose homogeneity to PTV with a lower standard deviation of PTV dose (1.4 Gy), vs. single arc plans (2.0 Gy) and IMRT (1.7 Gy). Film measurements showed good correspondence with calculated doses; the mean gamma value was 0.30 (double arc) and area of the film with a gamma exceeding 1 was 0.82%. CONCLUSIONS RA is a fast, safe, and accurate technique that uses lower MUs than conventional IMRT. Double arc plans provided at least similar sparing of OAR and better PTV dose homogeneity than single arc or IMRT.

Rapid delivery of stereotactic radiotherapy for peripheral lung tumors using volumetric intensity-modulated arcs

The delivery of high dose conventional stereotactic body radiotherapy (SBRT) for patients with stage I lung tumors generally takes 30-45min per fraction. The novel volumetric intensity-modulated arc therapy (RA) for planning and delivery enabled much faster treatment for three patients with different fractionation schemes. This reduces the risk of intrafraction motion and is more patient friendly. In addition, in comparison to the conventional plans using 10 static non-coplanar fields, RA plans achieved superior dose conformity around the PTV and reduced chest wall doses.

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.

Treatment of large stage I-II lung tumors using stereotactic body radiotherapy (SBRT): Planning considerations and early toxicity

PURPOSE To study the dosimetric predictors of early clinical toxicity following SBRT in patients with lung tumors and planning target volumes (PTV) exceeding 80 cm(3). METHODS Eighteen consecutive patients who were treated using volumetric modulated arc therapy (RapidArc™) were assessed. All were either unfit or refused to undergo surgery or chemoradiotherapy. PTV planning objectives were as used in the ROSEL study protocol. Clinical toxicity was scored using Common Toxicity Criteria AE4.0. Lung volumes receiving 5, 10, 15, and 20 Gy (V(5), V(10), V(15) and V(20)) and mean lung dose were assessed and correlated to symptomatic radiation pneumonitis (RP). RESULTS Median age, age-adjusted Charlson-comorbidity score and PTV size were 74, 7.5 and 137 cm(3), respectively. At a median follow-up of 12.8 months, 8 deaths were recorded: 5 arising from comorbidity, 2 were potentially treatment-related and 1 had local recurrence. RP was reported in 5 patients (grade 2 in 3 and grade 3 in 2). All RP occurred in plans without a high priority optimization objective on contralateral lung. Acute RP was best predicted by contralateral lung V(5) (p<0.0001). CONCLUSION After SBRT using RapidArc in lung tumors >80 cm(3), the contralateral lung V(5) best predicts RP. Limiting contralateral lung V(5) to <26% may reduce acute toxicity.

New developments in arc radiation therapy: A review

Arc therapies have gained widespread clinical interest in radiation oncology over the past decade. Arc therapies have several potential advantages over standard techniques such as intensity-modulated radiation therapy, with implications for patients, administrators, and oncologists. This review focuses on the rationale for arc therapy, descriptions of the modern arc techniques that are currently clinically available, and highlights some distinguishing features of arc therapies, such as dose distributions, treatment times, and imaging capabilities. Arc therapies are exciting examples of progress in radiotherapy through technological innovation, aimed at ultimately improving the therapeutic ratio for patients receiving radiation.

Volumetric Modulated Arc Radiotherapy for Vestibular Schwannomas

PURPOSE To evaluate volumetric modulated arc radiotherapy (RapidArc [RA]), a novel approach allowing for rapid treatment delivery, for the treatment of vestibular schwannoma (VS). METHODS AND MATERIALS The RA plans were generated for a small (0.5 cm(3)), intermediate (2.8 cm(3)), and large (14.8 cm(3)) VS. The prescription dose was 12.5 Gy to the encompassing 80% isodose. The RA plans were compared with conventional radiosurgery plans using both a single dynamic conformal arc (1DCA) and five noncoplanar dynamic conformal arcs (5DCA). Conformity indices (CI) and dose-volume histograms of critical organs were compared. The RA plan for the medium-sized VS was measured in a phantom using Gafchromic EBT films and compared with calculated dose distributions. RESULTS The RA planning was completed within 30 min in all cases, and calculated treatment delivery time (after patient setup) was 5 min vs. 20 min for 5DCA. A superior CI was achieved with RA, with a substantial decrease in low-dose irradiation of the normal brain achieved relative to 5DCA plans. Maximum doses to critical organs were similar for RA and 5DCA but were higher for 1DCA. Film measurements showed the differences between calculated and measured doses to be smaller than 1.5% in the high-dose area and smaller than 3% in the low-dose area. CONCLUSION The RA plans consistently achieved a higher CI and decrease in areas of low-dose irradiation. This, together with shorter treatment delivery times, has led to RA replacing our conventional five-arc radiosurgery technique for VS.

Lung Density Changes After Stereotactic Radiotherapy: A Quantitative Analysis in 50 Patients

PURPOSE Radiologic lung density changes are observed in more than 50% of patients after stereotactic body radiotherapy (SBRT) for lung cancer. We studied the relationship between SBRT dose and posttreatment computed tomography (CT) density changes, a surrogate for lung injury. METHODS AND MATERIALS The SBRT fractionation schemes used to treat Stage I lung cancer with RapidArc were three fractions of 18 Gy, five fractions of 11 Gy, or eight fractions of 7.5 Gy, prescribed at the 80% isodose. Follow-up CT scans performed at less than 6 months (n = 50) and between 6 and 9 months (n = 30) after SBRT were reviewed. Posttreatment scans were coregistered with baseline scans using a B-spline deformable registration algorithm. Voxel-Hounsfield unit histograms were created for doses between 0.5 and 50 Gy. Linear mixed effects models were used to assess the effects of SBRT dose on CT density, and the influence of possible confounders was tested. RESULTS Increased CT density was associated with higher dose, increasing planning target volume size, and increasing time after SBRT (all p < 0.0001). Density increases were apparent in areas receiving >6 Gy, were most prominent in areas receiving >20 Gy, and seemed to plateau above 40 Gy. In regions receiving >36 Gy, the reduction in air-filled fraction of lung after treatment was up to 18%. No increase in CT density was observed in the contralateral lung receiving ≥3 Gy. CONCLUSIONS A dose-response relationship exists for quantitative CT density changes after SBRT. A threshold of effect is seen at low doses, and a plateau at highest doses.

DOSIMETRIC IMPACT OF INTERPLAY EFFECT ON RAPIDARC LUNG STEREOTACTIC TREATMENT DELIVERY

PURPOSE Volumetric modulated arc therapy (RapidArc; Varian Medical Systems, Palo Alto, CA) allows fast delivery of stereotactic radiotherapy for Stage I lung tumors. We investigated discrepancies between the calculated and delivered dose distributions, as well as the dosimetric impact of leaf interplay with breathing-induced tumor motion. METHODS AND MATERIALS In 20 consecutive patients with Stage I lung cancer who completed RapidArc delivery, 15 had tumor motion exceeding 5 mm on four-dimensional computed tomography scan. Static and dynamic measurements were performed with Gafchromic EBT film (International Specialty Products Inc., Wayne, NJ) in a Quasar motion phantom (Modus Medical Devices, London, Ontario, Canada). Static measurements were compared with calculated dose distributions, and dynamic measurements were compared with the convolution of static measurements with sinusoidal motion patterns. Besides clinical treatment plans, additional cases were optimized to create excessive multileaf collimator modulation and delivered on the phantom with peak-to-peak motions of up to 25 mm. γ Analysis with a 3% dose difference and 2- or 1-mm distance to agreement was used to evaluate the accuracy of delivery and the dosimetric impact of the interplay effect. RESULTS In static mode film dosimetry of the two-arc delivery in the phantom showed that, on average, fewer than 3% of measurements had γ greater than 1. Dynamic measurements of clinical plans showed a high degree of agreement with the convolutions: for double-arc plans, 99.5% met the γ criterion. The degree of agreement was 98.5% for the plans with excessive multileaf collimator modulations and 25 mm of motion. CONCLUSIONS Film dosimetry shows that RapidArc accurately delivers the calculated dose distribution and that interplay between leaves and tumor motion is not significant for single-fraction treatments when RapidArc is delivered with two different arcs.

Evaluation of a Knowledge-Based Planning Solution for Head and Neck Cancer

PURPOSE Automated and knowledge-based planning techniques aim to reduce variations in plan quality. RapidPlan uses a library consisting of different patient plans to make a model that can predict achievable dose-volume histograms (DVHs) for new patients and uses those models for setting optimization objectives. We benchmarked RapidPlan versus clinical plans for 2 patient groups, using 3 different libraries. METHODS AND MATERIALS Volumetric modulated arc therapy plans of 60 recent head and neck cancer patients that included sparing of the salivary glands, swallowing muscles, and oral cavity were evenly divided between 2 models, Model(30A) and Model(30B), and were combined in a third model, Model60. Knowledge-based plans were created for 2 evaluation groups: evaluation group 1 (EG1), consisting of 15 recent patients, and evaluation group 2 (EG2), consisting of 15 older patients in whom only the salivary glands were spared. RapidPlan results were compared with clinical plans (CP) for boost and/or elective planning target volume homogeneity index, using HI(B)/HI(E) = 100 × (D2% - D98%)/D50%, and mean dose to composite salivary glands, swallowing muscles, and oral cavity (D(sal), D(swal), and D(oc), respectively). RESULTS For EG1, RapidPlan improved HI(B) and HI(E) values compared with CP by 1.0% to 1.3% and 1.0% to 0.6%, respectively. Comparable D(sal) and D(swal) values were seen in Model(30A), Model(30B), and Model60, decreasing by an average of 0.1, 1.0, and 0.8 Gy and 4.8, 3.7, and 4.4 Gy, respectively. However, differences were noted between individual organs at risk (OARs), with Model(30B) increasing D(oc) by 0.1, 3.2, and 2.8 Gy compared with CP, Model(30A), and Model60. Plan quality was less consistent when the patient was flagged as an outlier. For EG2, RapidPlan decreased D(sal) by 4.1 to 4.9 Gy on average, whereas HI(B) and HI(E) decreased by 1.1% to 1.5% and 2.3% to 1.9%, respectively. CONCLUSIONS RapidPlan knowledge-based treatment plans were comparable to CP if the patients OAR-planning target volume geometry was within the range of those included in the models. EG2 results showed that a model including swallowing-muscle and oral-cavity sparing can be applied to patients with only salivary gland sparing. This may allow model library sharing between institutes. Optimal detection of inadequate plans and population of model libraries requires further investigation.

RapidArc planning and delivery in patients with locally advanced head-and-neck cancer undergoing chemoradiotherapy.

PURPOSE Volumetric modulated arc therapy (RapidArc, Varian Medical Systems) permits the delivery of highly conformal dose distributions. We studied planning and delivery in patients who underwent RapidArc for locally advanced head-and-neck cancer (HNC). METHODS AND MATERIALS A total of 35 consecutive patients who completed RapidArc with concurrent chemotherapy for Stages III-IV tumors of the oro- and hypopharynx/larynx in our center were identified. All underwent bilateral neck irradiation and 21 patients had at least N2 disease. A simultaneous integrated boost (SIB) delivered 70 Gy (in 2 Gy/fraction) to the planning target volume (PTV)(boost) and elective nodal regions (PTV(elect)) received 57.75 Gy. A standard planning constraint set was used and constraints for parotid glands were individually adapted. Treatments were delivered using two arcs after all plans were verified in a solid water phantom using GafChromic External Beam Therapy films. RESULTS RapidArc planning generally took 1.5-2 h, which was faster than with our previous seven-field intensity-modulated radiotherapy sliding window technique. Film dosimetry revealed that 0.6% of films exceeded a combination of dose differences ≥3% or distance to agreement ≥2 mm. More than 99% of both PTVs received ≥95% of the prescription dose. Average plan conformity index was 1.13 and mean dose to ipsilateral and contralateral parotid glands were 31.4 Gy and 26.1 Gy, respectively. The mean beam-on time was <3 min and mean number of monitor units was 426. CONCLUSIONS RapidArc achieved excellent target coverage and normal tissue sparing, with delivery completed in less than 3 min. RA is currently our standard intensity-modulated radiotherapy approach for advanced HNC.