Improving delivery of segments with small MU in step‐and‐shoot IMRT

Kuperman, Vadim; Lam, W. C.

doi:10.1118/1.2174128

Cited by 14 publications

(18 citation statements)

References 10 publications

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“…This procedure provides a more accurate assessment of the overshooting effect on patient dose compared to simply adding/subtracting a fixed amount of MU from the first/last segment, as it was performed in previous studies. Preceding published studies suggest that the overshooting should have an insignificant dose effect in the high‐dose region because the increased outputs do not tend to accumulate in the same voxels, (1) and that the overdose to prostate PTV is less than 1%, (3) while Kuperman et al (4) reported a 1%–2% overdose. Our cases show a higher dose impact: up to 2.8% in prostate PTV

D_{95}

and 3.0% in bladder

D_{1 cc}

.…”

Section: Discussionmentioning

confidence: 99%

“…While our method shifts the unknown overshooting to an artificially added “closed segment” that essentially has no dosimetric impact, therefore completely removes the systematic error. Kuperman et al (4) proposed a different solution: shift the order of the segments for every fraction. This has the potential to completely remove the systematic error; however, it is relatively more complicated to implement because the number of fractions and the number of segment for each beam both varies, and the delivered plan needs to be changed for every fraction.…”

Section: Discussionmentioning

confidence: 99%

“…Grigorov et al (3) and Kuperman et al (4) studied the impact of the overshoot phenomenon for site specific clinical cases. Grigorov and colleagues manually subtracted 0.65 MU, while Kuperman et al subtracted 0.5 MU from the first segment then added the same MU number to the last segment, and recalculated the patient dose utilizing treatment planning system (TPS).…”

Section: Introductionmentioning

confidence: 99%

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The step‐and‐shoot IMRT overshooting phenomenon: a novel method to mitigate patient overdosage

Zhen

Ouyang

Bao

et al. 2016

J Applied Clin Med Phys

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The goal of this work is to evaluate the dosimetric impact of an overshooting phenomenon in step‐and‐shoot IMRT delivery, and to demonstrate a novel method to mitigate the issue. Five pelvis IMRT patients treated on Varian 2100C EX linacs with larger than +4.5% phantom ion chamber point‐dose difference relative to planned dose were investigated. For each patient plan, 5 fractions were delivered. DynaLog files were recorded and centi‐MU pulses from dose integrator board for every control point (CP) were counted using a commercial pulse counter. The counter recorded CP MU agrees with DynaLog records, both showing an ~0.6 MU overshoot of the first segment of every beam. The 3D patient dose was recalculated from the counter records and compared to the planned dose, showing that the overshoot resulted in on average 2.05% of PTV D95 error, and 2.49%, 2.61% and 2.45% of D1cc error for rectum, bladder, and bowel, respectively. The initial plans were then modified by inserting a specially designed MLC segment to the start of every beam. The modified plans were also delivered five times. The dose from the modified delivery was calculated using counter recorded CP MU. The corresponding Dx parameters were all within 0.31% from the original plan. IMRT QA results also show a 2.2% improvement in ion chamber point‐dose agreement. The results demonstrate that the proposed plan modification method effectively eliminates the overdosage from the overshooting phenomenon.PACS number(s): 87.55.Qr, 87.55.km

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D_{95}

and 3.0% in bladder

D_{1 cc}

.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The step‐and‐shoot IMRT overshooting phenomenon: a novel method to mitigate patient overdosage

Zhen

Ouyang

Bao

et al. 2016

J Applied Clin Med Phys

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“…Several linear-accelerator-based irradiation techniques, such as intensity-modulated radiation therapy (IMRT), stereotactic radiotherapy and conformal arc radiotherapy, deliver a highly accurate dose to the target volume while sparing the surrounding healthy tissue [1] [2]. The latest development in this approach is volumetric modulated radiotherapy (VMAT), where in the gantry speed, dose rate, and multileaf collimator (MLC) leaf speed are varied during gantry rotation, reducing the treatment time per fraction [3] [4].…”

Section: Introductionmentioning

confidence: 99%

“…The latest development in this approach is volumetric modulated radiotherapy (VMAT), where in the gantry speed, dose rate, and multileaf collimator (MLC) leaf speed are varied during gantry rotation, reducing the treatment time per fraction [3] [4]. IMRT is typically categorized into dynamic MLC (DMLC) mode (referred to as sliding window) [1] and static MLC (SMLC) mode (referred to as step-and-shoot) [2].…”

Section: Introductionmentioning

confidence: 99%

Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT

Miura¹,

Ozawa²,

Tsuda³

et al. 2015

IJMPCERO

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The stability of delivery of low monitor unit (MU) setting is important especially for step-andshoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off according to the number of the segments. This study evaluates the dose linearity and profile flatness/symmetry under low MU settings for Vero4DRT, a new linear-accelerator based irradiation system that currently implements step-and-shoot IMRT. To evaluate the dose linearity and flatness/symmetry, the point doses and beam profiles were measured as functions of MU and dose rates. The accuracy of dose delivery depended on the dose rate. Under all dose rates, the dose was linear within 1% above 5 MU and within 2% above 3 MU. The beam symmetry was degraded in-line compared with crossline, although both profiles were symmetric within 2% at all dose settings. The profile flatness was also within 2% above 5 MU at any dose rate and showed no significant variation among the low MU settings. To ensure stable beam delivery without increasing the treatment time of Vero4DRT, we recommend a delivery of 5 MU per segment at a dose rate of 500 MU/min.

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