Validation of pencil beam scanning proton therapy with multi‐leaf collimator calculated by a commercial Monte Carlo dose engine

Tominaga, Yoshiya; Sakurai, Yoshinori; Miyata, Junya; Harada, Shuichi; Akagi, Takashi; Oita, Masataka

doi:10.1002/acm2.13817

Cited by 7 publications

(3 citation statements)

References 38 publications

(93 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…MELTHEA V (Hitachi, Ltd., Tokyo, Japan) at the Medical Corporation, Hakuhokai, Osaka Proton Therapy Clinic (OPTC) was used as the proton beam therapy system. 23 This machine has a synchrotron and gantry room; we can insert a multi-leaf collimator (MLC) for PBS irradiation to improve the lateral penumbra. 24,25 The PBS scan method was raster scanning, which did not interrupt the beam while moving the spot.…”

Section: Proton Beam Therapy Systemmentioning

confidence: 99%

Experimental validation of a 4D dynamic dose calculation model for proton pencil beam scanning without spot time stamp considering free‐breathing motion

Tominaga,

Oita,

Miyata

et al. 2023

Medical Physics

Self Cite

View full text Add to dashboard Cite

PurposeWe developed a 4‐dimensional dynamic dose (4DDD) calculation model for proton pencil beam scanning (PBS). This model incorporates the spill start time for all energies and uses the remaining irradiated spot time model instead of irradiated spot time logs. This study aimed to validate the calculation accuracy of a log file‐based 4DDD model by comparing it with dose measurements performed under free‐breathing conditions, thereby serving as an alternative approach to the conventional log file‐based system.MethodsThree cubic verification plans were created using a heterogeneous block phantom; these plans were created using 10 phase 4D‐CT datasets of the phantom. The CIRS dynamic platform was used to simulate motion with amplitudes of 2.5, 3.75, and 5.0 mm. These plans consisted of eight‐ and two‐layered rescanning techniques. The lateral profiles were measured using a 2D ionization chamber array (2D‐array) and EBT3 Gafchromic films at four starting phases, including three sinusoidal curves (periods of 3, 4, and 6 s) and a representative patient curve during actual treatment. 4DDDs were calculated using in‐house scripting that assigned a time stamp to each spot and performed dose accumulation using deformable image registration. Furthermore, to evaluate the impact of parameter selection on our 4DDD model calculations, simulations were performed assuming a ±10% change in irradiation time stamp (0.8 ± 0.08 s) and spot scan speed. We evaluated the 2D gamma index and the absolute point doses between the calculated values and the measurements.ResultsThe 2D‐array measurements revealed that the gamma scores for the static plans (no motion) and 4DDD plans exceeded 97.5% and 93.9% at 3%/3 mm, respectively. The average gamma score of the 4DDD plans was at least 96.1%. When using EBT3 films, the gamma scores of the 4DDD model exceeded 92.4% and 98.7% at 2%/2 mm and 3%/3 mm, respectively. Regarding the 4DDD point dose differences, more than 95% of the dose regions exhibited discrepancies within ±5.0% for 97.7% of the total points across all plans. The spot time assignment accuracy of our 4DDD model was acceptable even with ±10% sensitivity. However, the accuracy of the scan speed, when varied within ±10% sensitivity, was not acceptable (minimum gamma scores of 82.6% and maximum dose difference of 12.9%).ConclusionsOur 4DDD calculations under free‐breathing conditions using amplitudes of less than 5.0 mm were in good agreement with the measurements regardless of the starting phases, breathing curve patterns (between 3 and 6 s periods), and varying numbers of layered rescanning. The proposed system allows us to evaluate actual irradiated doses in various breathing periods, amplitudes, and starting phases, even on PBS machines without the ability to record spot logs.

show abstract

Section: Proton Beam Therapy Systemmentioning

confidence: 99%

Experimental validation of a 4D dynamic dose calculation model for proton pencil beam scanning without spot time stamp considering free‐breathing motion

Tominaga,

Oita,

Miyata

et al. 2023

Medical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…The LP is influenced by the initial spot size, multiple Coulomb scattering in matter (the patient), and optional beam shaping devices in the treatment head (‘nozzle'), such as range shifter or aperture. A sharper LP could be achieved when combining PBS with apertures or multi‐leaf collimators 3–8 . Winterhalter et al 9 .…”

Section: Introductionmentioning

confidence: 99%

“…A sharper LP could be achieved when combining PBS with apertures or multi-leaf collimators. [3][4][5][6][7][8] Winterhalter et al 9 have evaluated various optimization approaches to improve the LP, recommending the combination of aperture and pencil beam fluence optimization at the edge.…”

Section: Introductionmentioning

confidence: 99%

Optimization of proton pencil beam positioning in collimated fields

et al. 2023

View full text Add to dashboard Cite

Background: The addition of static or dynamic collimator systems to the pencil beam scanning delivery technique increases the number of options for lateral field shaping. The collimator shape needs to be optimized together with the intensity modulation of spots. Purpose: To minimize the proton field's lateral penumbra by investigating the fundamental relations between spot and collimating aperture edge position. Methods: Analytical approaches describing the effect of spot position on the resulting spot profile are presented. The theoretical description is then compared with Monte Carlo simulations in TOPAS and in the RayStation treatment planning system, as well as with radiochromic film measurements at a clinical proton therapy facility.In the model,one single spot profile is analyzed for various spot positions in air. Further, irradiation setups in water with different energies, the combination with a range shifter, and two-dimensional proton fields were investigated in silico. Results:The further the single spot is placed beyond the collimating aperture edge ('overscanning'), the sharper the relative lateral dose fall-off and thus the lateral penumbra. Overscanning up to 5 mm reduced the lateral penumbra by about 20% on average after a propagation of 13 cm in air. This benefit from overscanning is first predicted by the analytical proofs and later verified by simulations and measurements.Corresponding analyses in water confirm the benefit in lateral penumbra with spot position optimization as observed theoretically and in air. The combination of spot overscanning with fluence modulation facilitated an additional improvement. Conclusions: The lateral penumbra of single spots in collimated scanned proton fields can be improved by the method of spot overscanning. This suggests a better sparing of proximal organs at risk in smaller water depths at higher energies, especially in the plateau of the depth dose distribution. All in all, spot overscanning in collimated scanned proton fields offers particular potential in combination with techniques such as fluence modulation or dynamic collimation for optimizing the lateral penumbra to spare normal tissue.

show abstract

Validation of pencil beam scanning proton therapy with multi‐leaf collimator calculated by a commercial Monte Carlo dose engine

Tominaga

Sakurai²,

Miyata

et al. 2022

J Applied Clin Med Phys

View full text Add to dashboard Cite

This study aimed to evaluate the clinical beam commissioning results and lateral penumbra characteristics of our new pencil beam scanning (PBS) proton therapy using a multi‐leaf collimator (MLC) calculated by use of a commercial Monte Carlo dose engine. Eighteen collimated uniform dose plans for cubic targets were optimized by the RayStation 9A treatment planning system (TPS), varying scan area, modulation widths, measurement depths, and collimator angles. To test the patient‐specific measurements, we also created and verified five clinically realistic PBS plans with the MLC, such as the liver, prostate, base‐of‐skull, C‐shape, and head‐and‐neck. The verification measurements consist of the depth dose (DD), lateral profile (LP), and absolute dose (AD). We compared the LPs and ADs between the calculation and measurements. For the cubic plans, the gamma index pass rates (γ‐passing) were on average 96.5% ± 4.0% at 3%/3 mm for the DD and 95.2% ± 7.6% at 2%/2 mm for the LP. In several LP measurements less than 75 mm depths, the γ‐passing deteriorated (increased the measured doses) by less than 90% with the scattering such as the MLC edge and range shifter. The deteriorated γ‐passing was satisfied by more than 90% at 2%/2 mm using uncollimated beams instead of collimated beams except for three planes. The AD differences and the lateral penumbra width (80%–20% distance) were within ±1.9% and ± 1.1 mm, respectively. For the clinical plan measurements, the γ‐passing of LP at 2%/2 mm and the AD differences were 97.7% ± 4.2% on average and within ±1.8%, respectively. The measurements were in good agreement with the calculations of both the cubic and clinical plans inserted in the MLC except for LPs less than 75 mm regions of some cubic and clinical plans. The calculation errors in collimated beams can be mitigated by substituting uncollimated beams.

show abstract

Validation of pencil beam scanning proton therapy with multi‐leaf collimator calculated by a commercial Monte Carlo dose engine

Cited by 7 publications

References 38 publications

Experimental validation of a 4D dynamic dose calculation model for proton pencil beam scanning without spot time stamp considering free‐breathing motion

Experimental validation of a 4D dynamic dose calculation model for proton pencil beam scanning without spot time stamp considering free‐breathing motion

Optimization of proton pencil beam positioning in collimated fields

Validation of pencil beam scanning proton therapy with multi‐leaf collimator calculated by a commercial Monte Carlo dose engine

Contact Info

Product

Resources

About