Characterizing local dose perturbations due to gas cavities in magnetic resonance‐guided radiotherapy

Shortall, Jane; Osorio, Eliana Vásquez; Chuter, Robert; Green, Andrew; McWilliam, A.; Kirkby, K.J.; Mackay, Ranald I; Herk, Marcel van

doi:10.1002/mp.14120

Cited by 3 publications

(7 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Work could be done to explore likely beam configurations covering the rectum. Clinical implementation of the heuristic equation we use to estimate dose effects should always involve applying it to each treatment beam and summing the effect, which can be done in real time 29 …”

Section: Discussionmentioning

confidence: 99%

“…Clinical implementation of the heuristic equation we use to estimate dose effects should always involve applying it to each treatment beam and summing the effect, which can be done in real time. 29 The purpose of this work was to assess if rectal gas present at the beginning of a scan-session remains stable enough throughout a scan-session to result in clinically concerning dose perturbations in the rectum. Additionally, we looked at whether accounting for gas at the beginning of each scan-session is dosimetrically beneficial.…”

Section: C Dose Effects Due To Rectal Gasmentioning

confidence: 99%

“…The equation was derived in Ref. [29] using data fitting techniques, and describes the dosimetrical effects of ERE and attenuation differences for a single beam centered on a spherical air cavity using a modulated sinusoidal and a Gaussian function for ERE and attenuation effects, respectively. The amplitude of both effects depends on the cavity radius, r , either logarithmically (ERE) or linearly (attenuation differences).…”

Section: Intra‐fractional Dose Effects Due To Rectal Gasmentioning

confidence: 99%

“…(), an adapted version of an equation previously presented in Ref. [29]. The equation calculates the dose perturbation, ΔD % , at angles θ , Φ around spherical air cavities (up to 1 cm distance, d , from the cavity surface) for the Elekta Unity system with a 1.5 T transverse magnetic field and 7 MV photon spectrum irradiated with a single beam.…”

Section: Intra‐fractional Dose Effects Due To Rectal Gasmentioning

confidence: 99%

See 3 more Smart Citations

Inter‐ and intra‐fractional stability of rectal gas in pelvic cancer patients during MRIgRT

et al. 2020

View full text Add to dashboard Cite

Purpose Due to the electron return effect (ERE) during magnetic resonance imaging guided radiotherapy (MRIgRT), rectal gas during pelvic treatments can result in hot spots of over‐dosage in the rectal wall. Determining the clinical impact of this effect on rectal toxicity requires estimation of the amount and mobility (and stability) of rectal gas during treatment. We therefore investigated the amount of rectal gas and local inter‐ and intra‐fractional changes of rectal gas in pelvic cancer patients. Methods To estimate the volume of gas present at treatment planning, the rectal gas contents in the planning computed tomography (CT) scans of 124 bladder, 70 cervical and 2180 prostate cancer patients were calculated. To estimate inter‐ and intra‐fractional variations in rectal gas, 174 and 131 T2‐w MRIs for six cervical and eleven bladder cancer patients were used. These scans were acquired during four scan‐sessions (~20–25 min each) at various time‐points. Additionally, 258 T2‐w MRIs of the first five prostate cancer patients treated using MRIgRT at our center, acquired during each fraction, were analyzed. Rectums were delineated on all scans. The area of gas within the rectum delineations was identified on each MRI slice using thresholding techniques. The area of gas on each slice of the rectum was used to calculate the inter‐ and intra‐fractional group mean, systematic and random variations along the length of the rectum. The cumulative dose perturbation as a result of the gas was estimated. Two approaches were explored: accounting or not accounting for the gas at the start of the scan‐session. Results Intra‐fractional variations in rectal gas are small compared to the absolute volume of rectal gas detected for all patient groups. That is, rectal gas is likely to remain stable for periods of 20–25 min. Larger volumes of gas and larger variations in gas volume were observed in bladder cancer patients compared with cervical and prostate cancer patients. For all patients, local cumulative dose perturbations per beam over an entire treatment in the order of 60 % were estimated when gas had not been accounted for in the daily adaption. The calculated dose perturbation over the whole treatment was dramatically reduced in all patients when accounting for the gas in the daily set‐up image. Conclusion Rectal gas in pelvic cancer patients is likely to remain stable over the course of an MRIgRT fraction, and also likely to reappear in the same location in multiple fractions, and can therefore result in clinically relevant over‐dosage in the rectal wall. The over‐dosage is reduced when accounting for gas in the daily adaption.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: C Dose Effects Due To Rectal Gasmentioning

confidence: 99%

Section: Intra‐fractional Dose Effects Due To Rectal Gasmentioning

confidence: 99%

Section: Intra‐fractional Dose Effects Due To Rectal Gasmentioning

confidence: 99%

See 2 more Smart Citations

Inter‐ and intra‐fractional stability of rectal gas in pelvic cancer patients during MRIgRT

et al. 2020

View full text Add to dashboard Cite

show abstract

“…In recent years, with the development and clinical application of magnetic resonance linear accelerators (MR-LINAC), people have become increasingly interested in the effect of magnetic fields on dose distribution, and some research results have appeared [ 8 , 9 ]. The MR-LINAC receives a static magnetic field perpendicular to the beam direction.…”

Section: Introductionmentioning

confidence: 99%

Influence and optimization strategy of the magnetic field in 1.5 T MR-linac liver stereotactic radiotherapy

Liu,

Yin,

et al. 2023

Radiat Oncol

View full text Add to dashboard Cite

Objective To compare intensity reduction plans for liver cancer with or without a magnetic field and optimize field and subfield numbers in the intensity-modulated radiotherapy (IMRT) plans designed for liver masses in different regions. Methods This retrospective study included 62 patients who received radiotherapy for liver cancer at Shandong Cancer Hospital. Based on each patient's original individualized intensity-modulated plan (plan1.5 T), a magnetic field-free plan (plan0 T) and static intensity-modulated plan with four different optimization schemes were redesigned for each patient. The differences in dosimetric parameters among plans were compared. Results In the absence of a magnetic field in the first quadrant, PTV Dmin increased (97.75 ± 17.55 vs. 100.96 ± 22.78)%, Dmax decreased (121.48 ± 29.68 vs. 119.06 ± 28.52)%, D98 increased (101.35 ± 7.42 vs. 109.35 ± 26.52)% and HI decreased (1.14 ± 0.14 vs. 1.05 ± 0.01). In the absence of a magnetic field in the second quadrant, PTV Dmin increased (84.33 ± 19.74 vs. 89.96 ± 21.23)%, Dmax decreased (105 ± 25.08 vs. 104.05 ± 24.86)%, and HI decreased (1.04 ± 0.25 vs. 0.99 ± 0.24). In the absence of a magnetic field in the third quadrant, PTV Dmax decreased (110.21 ± 2.22 vs. 102.31 ± 26)%, L-P V30 decreased (10.66 ± 9.19 vs. 5.81 ± 3.22)%, HI decreased (1.09 ± 0.02 vs. 0.98 ± 0.25), and PTV Dmin decreased (92.12 ± 4.92 vs. 89.1 ± 22.35)%. In the absence of a magnetic field in the fourth quadrant, PTV Dmin increased (89.78 ± 6.72 vs. 93.04 ± 4.86)%, HI decreased (1.09 ± 0.01 vs. 1.05 ± 0.01) and D98 increased (99.82 ± 0.82 vs. 100.54 ± 0.84)%. These were all significant differences. In designing plans for tumors in each liver region, a total number of subfields in the first area of 60, total subfields in the second zone of 80, and total subfields in the third and fourth zones of 60 or 80 can achieve the dose effect without a magnetic field. Conclusion In patients with liver cancer, the effect of a magnetic field on the target dose is more significant than that on doses to organs at risk. By controlling the max total number of subfields in different quadrants, the effect of the magnetic field can be greatly reduced or even eliminated.

show abstract

Why we should care about gas pockets in online adaptive MRgRT: a dosimetric evaluation

Nardini,

Meffe,

Galetto

et al. 2023

Front. Oncol.

View full text Add to dashboard Cite

IntroductionContouring of gas pockets is a time consuming step in the workflow of adaptive radiotherapy. We would like to better understand which gas pockets electronic densitiy should be used and the dosimetric impact on adaptive MRgRT treatment.Materials and methods21 CT scans of patients undergoing SBRT were retrospectively evaluated. Anatomical structures were contoured: Gross Tumour Volume (GTV), stomach (ST), small bowel (SB), large bowel (LB), gas pockets (GAS) and gas in each organ respectively STG, SBG, LBG. Average HU in GAS was converted in RED, the obtained value has been named as Gastrointestinal Gas RED (GIGED). Differences of average HU in GAS, STG, SBG and LBG were computed. Three treatment plans were calculated editing the GAS volume RED that was overwritten with: air RED (0.0012), water RED (1.000), GIGED, generating respectively APLAN, WPLAN and the GPLAN. 2-D dose distributions were analyzed by gamma analysis. Parameter called active gas volume (AGV) was calculated as the intersection of GAS with the isodose of 5% of prescription dose.ResultsAverage HU value contained in GAS results to be equal to -620. No significative difference was noted between the average HU of gas in different organ at risk. Value of Gamma Passing Rate (GPR) anticorrelates with the AGV for each plan comparison and the threshold value for GPR to fall below 90% is 41, 60 and 139 cc for WPLANvsAPLAN, GPLANvsAPLAN and WPLANvsGPLAN respectively.DiscussionsGIGED is the right RED for Gastrointestinal Gas. Novel AGV is a useful parameter to evaluate the effect of gas pocket on dose distribution.

show abstract

Characterizing local dose perturbations due to gas cavities in magnetic resonance‐guided radiotherapy

Cited by 3 publications

References 28 publications

Inter‐ and intra‐fractional stability of rectal gas in pelvic cancer patients during MRIgRT

Inter‐ and intra‐fractional stability of rectal gas in pelvic cancer patients during MRIgRT

Influence and optimization strategy of the magnetic field in 1.5 T MR-linac liver stereotactic radiotherapy

Why we should care about gas pockets in online adaptive MRgRT: a dosimetric evaluation

Contact Info

Product

Resources

About