Evaluation of the interplay effect when using RapidArc to treat targets moving in the craniocaudal or right‐left direction

Court, Laurence Edward; Wagar, Matthew; Berbeco, R.; Reisner, A.; Winey, B.; Schofield, Deborah; Ionascu, Dan; Allen, Aaron M.; Popple, Richard A.; Lingos, Tania

doi:10.1118/1.3263614

Cited by 72 publications

(71 citation statements)

References 21 publications

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“…This effect has been studied in only two publications for tangential fields techniques39, 40 but not for VMAT for breast. However, the interplay effect has been largely studied in the case of lung RT41, 42, 43, 44, 45, 46 with motion amplitude being largely superior to those encountered in breast treatment. Those studies show that the interplay effect generates a blurring effect on the dose distribution.…”

Section: Discussionmentioning

confidence: 99%

Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy

Tyran

Tallet

Resbeut

et al. 2018

J Applied Clin Med Phys

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PurposeThis study evaluates the benefit of a virtual bolus method for volumetric modulated arc therapy (VMAT) plan optimization to compensate breast modifications that may occur during breast treatment.MethodsTen files were replanned with VMAT giving 50 Gy to the breast and 47 Gy to the nodes within 25 fractions. The planning process used a virtual bolus for the first optimization, then the monitors units were reoptimized without bolus, after fixing the segments shapes. Structures and treatment planning were exported on a second scanner (CT) performed during treatment as a consequence to modifications in patient's anatomy. The comparative end‐point was clinical target volume's coverage. The first analysis compared the VMAT plans made using the virtual bolus method (VB‐VMAT) to the plans without using it (NoVB‐VMAT) on the first simulation CT. Then, the same analysis was performed on the second CT. Finally, the level of degradation of target volume coverage between the two CT using VB‐VMAT was compared to results using a standard technique of forward‐planned multisegment technique (Tan‐IMRT).ResultsUsing a virtual bolus for VMAT does not degrade dosimetric results on the first CT. No significant result in favor of the NoVB‐VMAT plans was noted. The VB‐VMAT method led to significant better dose distribution on a second CT with modified anatomies compared to NoVB‐VMAT. The clinical target volume's coverage by 95% (V95%) of the prescribed dose was 98.9% [96.1–99.6] on the second CT for VB‐VMAT compared to 92.6% [85.2–97.7] for NoVB‐VMAT (P = 0.0002). The degradation of the target volume coverage for VB‐VMAT is not worse than for Tan‐IMRT: the median differential of V95% between the two CT was 0.9% for VMAT and 0.7% for Tan‐IMRT (P = 1).ConclusionThis study confirms the safety and benefit of using a virtual bolus during the VMAT planning process to compensate potential breast shape modifications.

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Section: Discussionmentioning

confidence: 99%

Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy

Tyran

Tallet

Resbeut

et al. 2018

J Applied Clin Med Phys

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“…Complex treatments (e.g., dose painting 7 ) with inversely optimized arc radiotherapy are generally characterized by highly modulated beams and the interplay between the motion of the tumor and the linac motions during treatment has been shown to give errors in the delivered dose. 8 Gating 9,10 has been used frequently in the last decade for treatment of breast cancer but has limitations in the treatment time efficiency, since the radiation delivery is interrupted when the tumor motion exceeds the predefined range.…”

Section: Discussionmentioning

confidence: 99%

The dosimetric impact of inversely optimized arc radiotherapy plan modulation for real-time dynamic MLC tracking delivery

et al. 2012

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Purpose: Real-time dynamic multileaf collimator (MLC) tracking for management of intrafraction tumor motion can be challenging for highly modulated beams, as the leaves need to travel far to adjust for target motion perpendicular to the leaf travel direction. The plan modulation can be reduced by using a leaf position constraint (LPC) that reduces the difference in the position of adjacent MLC leaves in the plan. The purpose of this study was to investigate the impact of the LPC on the quality of inversely optimized arc radiotherapy plans and the effect of the MLC motion pattern on the dosimetric accuracy of MLC tracking delivery. Specifically, the possibility of predicting the accuracy of MLC tracking delivery based on the plan modulation was investigated. Methods: Inversely optimized arc radiotherapy plans were created on CT-data of three lung cancer patients. For each case, five plans with a single 358 arc were generated with LPC priorities of 0 (no LPC), 0.25, 0.5, 0.75, and 1 (highest possible LPC), respectively. All the plans had a prescribed dose of 2 Gy Â 30, used 6 MV, a maximum dose rate of 600 MU/min and a collimator angle of 45 or 315. To quantify the plan modulation, an average adjacent leaf distance (ALD) was calculated by averaging the mean adjacent leaf distance for each control point. The linear relationship between the plan quality [i.e., the calculated dose distributions and the number of monitor units (MU)] and the LPC was investigated, and the linear regression coefficient as well as a two tailed confidence level of 95% was used in the evaluation. The effect of the plan modulation on the performance of MLC tracking was tested by delivering the plans to a cylindrical diode array phantom moving with sinusoidal motion in the superior-inferior direction with a peak-to-peak displacement of 2 cm and a cycle time of 6 s. The delivery was adjusted to the target motion using MLC tracking, guided in real-time by an infrared optical system. The dosimetric results were evaluated using gamma index evaluation with static target measurements as reference. Results: The plan quality parameters did not depend significantly on the LPC (p ! 0.066), whereas the ALD depended significantly on the LPC (p < 0.001). The gamma index failure rate depended significantly on the ALD, weighted to the percentage of the beam delivered in each control point of the plan (ALD w ) when MLC tracking was used (p < 0.001), but not for delivery without MLC tracking (p ! 0.342). The gamma index failure rate with the criteria of 2% and 2 mm was decreased from > 33.9% without MLC tracking to <31.4% (LPC 0) and <2.2% (LPC 1) with MLC tracking. Conclusions:The results indicate that the dosimetric robustness of MLC tracking delivery of an inversely optimized arc radiotherapy plan can be improved by incorporating leaf position constraints in the objective function without otherwise affecting the plan quality. The dosimetric robustness may be estimated prior to delivery by evaluating the ALD w of the plan.

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“…(b) Two indices combining the MCSv, amplitude, and NBs were introduced. The magnitude of interplay effect cannot be evaluated from only one factor, because the interplay effect is caused by combination of various factors such as amplitude, breathing cycle, dose rates, and MLC sequence 4, 5, 6. Therefore, the combination of tumor motion and MCSv (TMMCSv) is calculated as the quotient of the MCSv and amplitude.…”

Section: Methodsmentioning

confidence: 99%

“…showed that the maximum dose variation due to the interplay effect can be up to 30% for one intensity modulated radiation therapy (IMRT) field over one fraction, and 18% for all five IMRT fields over one fraction. Court et al 5. showed that dose error could be >5% for the area of 40% in the target when target motion was 2 cm for VMAT plans (2 Gy/1 fraction).…”

Section: Introductionmentioning

confidence: 99%

Minimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer

Kubo

Monzen

Tamura

et al. 2018

J Applied Clin Med Phys

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It is important to improve the magnitude of dose variation that is caused by the interplay effect. The aim of this study was to investigate the impact of the number of breaths (NBs) to the dose variation for VMAT‐SBRT to lung cancer. Data on respiratory motion and multileaf collimator (MLC) sequence were collected from the cases of 30 patients who underwent radiotherapy with VMAT‐SBRT for lung cancer. The NBs in the total irradiation time with VMAT and the maximum craniocaudal amplitude of the target were calculated. The MLC sequence complexity was evaluated using the modulation complexity score for VMAT (MCSv). Static and dynamic measurements were performed using a cylindrical respiratory motion phantom and a micro ionization chamber. The 1 standard deviation which were obtained from 10 dynamic measurements for each patient were defined as dose variation caused by the interplay effect. The dose distributions were also verified with radiochromic film to detect undesired hot and cold dose spot. Dose measurements were also performed with different NBs in the same plan for 16 patients in 30 patients. The correlations between dose variations and parameters assessed for each treatment plan including NBs, MCSv, the MCSv/amplitude quotient (TMMCSv), and the MCSv/amplitude quotient × NBs product (IVS) were evaluated. Dose variation was decreased with increasing NBs, and NBs of >40 times maintained the dose variation within 3% in 15 cases. The correlation between dose variation and IVS which were considered NBs was shown stronger (R 2 = 0.43, P < 0.05) than TMMCSv (R 2 = 0.32, P < 0.05). The NBs is an important factor to reduce the dose variation. The patient who breathes >40 times during irradiation of two partial arcs VMAT (i.e., NBs = 16 breaths per minute) may be suitable for VMAT‐SBRT for lung cancer.

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Evaluation of the interplay effect when using RapidArc to treat targets moving in the craniocaudal or right‐left direction

Abstract: The interplay between the motions of the LINAC and the target can result in an error in the delivered dose. This effect increases with plan complexity, and with target magnitude and period. It may average out after many fractions.

Cited by 72 publications

References 21 publications

Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy

Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy

The dosimetric impact of inversely optimized arc radiotherapy plan modulation for real-time dynamic MLC tracking delivery

Minimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer

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