Volumetric Modulated Arc Therapy: Planning and Evaluation for Prostate Cancer Cases

doi:10.1016/j.ijrobp.2009.03.033

International Journal of Radiation OncologyBiologyPhysics

Volume 76, Issue 5, April 2010, Pages 1456-1462

Presented at the annual meeting of American Association of Physicists in Medicine, Houston, July 2008.

https://doi.org/10.1016/j.ijrobp.2009.03.033 Get rights and content

Purpose

To develop an optimization method using volumetric modulated arc therapy (VMAT) and evaluate VMAT plans relative to the standard intensity-modulated radiotherapy (IMRT) approach in prostate cancer.

Methods and Materials

A single gantry rotation was modeled using 177 equispaced beams. Multileaf collimator apertures and dose rates were optimized with respect to gantry angle subject to dose-volume–based objectives. Our VMAT implementation used conjugate gradient descent to optimize dose rate, and stochastic sampling to find optimal multileaf collimator leaf positions. A treatment planning study of 11 prostate cancer patients with a prescription dose of 86.4 Gy was performed to compare VMAT with a standard five-field IMRT approach. Plan evaluation statistics included the percentage of planning target volume (PTV) receiving 95% of prescribed dose (V95), dose to 95% of PTV (D95), mean PTV dose, tumor control probability, and dosimetric endpoints of normal organs, whereas monitor unit (MU) and delivery time were used to assess delivery efficiency.

Results

Patient-averaged PTV V95, D95, mean dose, and tumor control probability in VMAT plans were 96%, 82.6 Gy, 88.5 Gy, and 0.920, respectively, vs. 97%, 84.0 Gy, 88.9 Gy, and 0.929 in IMRT plans. All critical structure dose requirements were met. The VMAT plans presented better rectal wall sparing, with a reduction of 1.5% in normal tissue complication probability. An advantage of VMAT plans was that the average number of MUs (290 MU) was less than for IMRT plans (642 MU).

Conclusion

The VMAT technique can reduce beam on time by up to 55% while maintaining dosimetric quality comparable to that of the standard IMRT approach.

Introduction

Volumetric modulated arc therapy (VMAT) proposed by Otto (1) is an emerging treatment paradigm. Currently there are three mechanical variables in VMAT delivery: (a) gantry rotation, (b) multileaf collimator (MLC) motion, and (c) dose rate modulation. In the current platform of the Trilogy 2300I linear accelerator (Varian Medical Systems, Palo Alto, CA), both MLC aperture and dose rate can be simultaneously adjusted in an arc of 360° or less, whereas gantry speed is modulated as needed. As described by Ling et al.(2), the current mechanical constraints imposed by the maximum MLC leaf speed is 5 mm/°, corresponding to about 2.5 cm/sec. The allowable dose rate modulation range is 30–600 monitor units (MU)/min, corresponding to 0.1–2 MU/°. When more than 2 MU/° is needed at certain beam angles, the gantry will decelerate to allow delivery of more radiation dose.

The VMAT optimization algorithm is an expansion of the direct aperture optimization (DAO) algorithm proposed and tested by Shepard et al.(3) and Earl et al.(4). The DAO was designed for step-and-shoot intensity-modulated radiation therapy (IMRT) 5, 6, 7, 8, 9, 10. In the DAO approach, a predefined number of beam apertures and their MUs are optimized with respect to a fixed number of beam angles. The VMAT is more efficient and powerful than DAO-based step-and-shoot IMRT because the VMAT (a) takes advantage of the full range of 360° beam directions, (b) allows dose rate modulation during delivery, and (c) integrates the treatment delivery into a continuous procedure. These improvements are allowed by the current advancements in the design of MLC and Linac control system. Another well-studied paradigm of arc therapy is intensity-modulated arc therapy (IMAT) proposed by Yu (11), Yu et al.(12), and other investigators 13, 14, 15, 16, 17. Unlike IMAT, VMAT combines intensity map optimization and leaf sequencing as one process. The VMAT optimizes the treatment machine parameters directly; thus, the resultant optimized plan can be delivered without an additional MLC sequencing algorithm that often compromises the plan quality. Therefore, VMAT optimization is more intuitive and efficient.

The purpose of this study is first to describe the implementation of VMAT optimization on the current Memorial Sloan Kettering Cancer Center (MSKCC) treatment planning system and second to compare VMAT treatment plans with the standard five-field IMRT approach under MSKCC prostate treatment protocol by evaluating both dosimetric and delivery efficiency parameters.

Section snippets

Optimization algorithm

We describe our optimization method for VMAT treatment plans. A single gantry rotation up to 360° is modeled using 177 equispaced beams. The maximum number of 177 beams is the technical limit of the delivery system on the current Trilogy platform. Optimization parameters in VMAT planning are the beam apertures (MLC positions) and dose rate at each beam gantry angle. The optimization algorithm uses a dose–volume histogram (DVH) constraint-based objective function: $\begin{matrix} Obj = \frac{1}{N_{T}} \sum_{i = 1}^{N_{T}} [r^{T} {(D_{i} - D_{p})}^{2} + r_{L}^{T} H (D_{L} - \end{matrix}$

Results

The PTV volume in the 11-patient planning study ranged from 130 cc to 213 cc (median, 178 cc). The averaged PTV, rectal wall, bladder wall, and body DVHs are illustrated in Fig. 3a, b, c, d, respectively. Zones in which IMRT plans were statistically better than VMAT (p < 0.05) are marked with light gray, whereas zones in which VMAT plans were statistically better are marked with dark gray. Fig. 4 shows a dose distribution comparison between VMAT and IMRT of a typical case. Comparison of

Discussion

In this article we have reported on a prototype VMAT plan optimization system that is integrated in the existing MSKCC treatment planning platform. We have demonstrated the capability of our VMAT optimization algorithm in a treatment planning study of 11 prostate cancer patients planned according to the standard MSKCC prostate treatment technique. Our optimization method differs from that reported by Otto (1) in the following ways: (a) the use of conjugate gradient search in the beam weight

Conclusion

In the treatment of prostate cancer, VMAT techniques can increase treatment time efficiency by up to 55% while maintaining comparable dosimetric quality to that of standard IMRT approaches, even when challenged by high prescription doses and tight normal tissue constraints.

Acknowledgment

The authors thank Yves Archimbault from Varian Medical Systems, Palo Alto, CA, for his help and discussion regarding Varian's implementation of RapidArc.

References (30)

W. De Gersem et al.
Leaf position optimization for step-and-shoot IMRT
Int J Radiat Oncol Biol Phys
(2001)
C.X. Yu et al.
Clinical implementation of intensity-modulated arc therapy
Int J Radiat Oncol Biol Phys
(2002)
E. Wong et al.
Intensity-modulated arc therapy simplified
Int J Radiat Oncol Biol Phys
(2002)
D. Cao et al.
Comparison of plan quality provided by intensity-modulated arc therapy and helical tomotherapy
Int J Radiat Oncol Biol Phys
(2007)
O. Cahlon et al.
Ultra-high dose (86.4 Gy) IMRT for localized prostate cancer: toxicity and biochemical outcomes
Int J Radiat Oncol Biol Phys
(2008)
S. Levegrun et al.
Risk group dependence of dose-response for biopsy outcome after three-dimensional conformal radiation therapy of prostate cancer
Radiother Oncol
(2002)
S. Levegrun et al.
Fitting tumor control probability models to biopsy outcome after three-dimensional radiation therapy of prostate cancer: Pitfalls in deducing radiobiological parameters for tumor from clinical data
Int J Radiat Oncol Biol Phys
(2001)
G.J. Kutcher et al.
Calculation of complication probability factors for non-uniform normal tissue radiation: The effective volume method
Int J Radiat Oncol Biol Phys
(1989)
C. Burman et al.
Fitting of normal tissue tolerance data to an analytic function
Int J Radiat Oncol Biol Phys
(1991)
E.J. Hall et al.
Radiation-induced second cancers: The impact of 3D-CRT and IMRT
Int J Radiat Oncol Biol Phys
(2003)

E.J. Hall

Intensity-modulated radiation therapy, protons, and the risk of second cancers

Int J Radiat Ooncol Biol Phys

(2006)

D. Palma et al.

Volumetric modulated arc therapy for delivery of prostate radiotherapy: Comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy

Int J Radiat Oncol Biol Phys

(2008)

A. Pirzkall et al.

The effect of beam energy and number of fields on photon-based IMRT for deep-seated targets

Int J Radiat Ooncol Biol Phys

(2002)

D.J. Godfrey et al.

Digital tomosynthesis with an on-board kilovoltage imaging device

Int J Radiat Oncol Biol Phys

(2006)

K. Otto

Volumetric modulated arc therapy: IMRT in a single gantry arc

Med Phys

(2008)

Cited by (183)

Treatment related factors associated with the risk of breast radio-induced-sarcoma
2022, Radiotherapy and Oncology
The Radiation Induced Sarcoma (RIS) is a rare but serious adverse event following radiotherapy (RT). Current RT techniques are more precise, but irradiate a larger volume at a low dose. This study aimed to describe radiation characteristics in a large series of patients suffering from RIS.
Patient-representative voxel-based anthropomorphic phantoms were used to reconstruct patient-specific RT fields for 125 patients diagnosed with RIS after primary breast cancer. For each patient, the location of the RIS onset site was determined and transferred onto the phantom as a contour. Using a treatment planning system (TPS), the dose distribution on the RIS in the phantom was calculated.
The mean dose (Dmean) received in the area where RIS subsequently developed was 47.8 ± 11.6 Gy. The median dose in the zones where RIS later developed ranged from 11 Gy to 58.8 Gy. The median time from RT to RIS development was 8 years (range 2–32 years). Analysis for predictors of time to radiation-induced sarcoma development highlighted a significant impact of age of patient during the RT whereas in multivariable analysis chemotherapy and hormonotherapy for primary breast cancer were not associated with a significant difference in time to diagnosis of RIS.
This study highlights that the dose received by the tissue in which the RIS developed was almost 47 Gy. These results are encouraging for the use of new RT techniques increasing volumes receiving low doses, without fear of an excess of RIS over the next 10 years.
Adaptive sequential plan-on-plan optimization during prostate-specific antigen response guided radiotherapy of recurrent prostate cancer
2021, Physics and Imaging in Radiation Oncology
Treatment adaptation based on tumour biomarker response during radiotherapy of prostate cancer, could be used for both escalation and de-escalation of radiation doses and volumes. To execute an adaptation involving extension of treatment volumes during radiation can however be restricted by the doses already delivered. The aim of this work was to develop a treatment planning method that addresses this challenge.
A volumetric-modulated-arc-therapy (VMAT) planning method with sequential plan-on-plan optimization was developed for a prospective phase II trial including 100 patients on salvage radiotherapy (SRT) for prostate cancer recurrence. A treatment adaptation was performed after five weeks of SRT based on prostate-specific antigen response during this phase of the treatment. This involved extension of treatment volumes for non-responders (n = 64) to include pelvic lymph nodes and boost to ⁶⁸Gallium-Prostate-Specific-Membrane-Antigen-Positron-Emission-Tomography positive lesions. This method was evolved by introducing an EQD2 (equivalent dose in 2.0 Gy fractions) correction of the base plan for improved dose coverage.
All dose-volume criteria for target coverage were met for the non-responders when based on physical dose. An EQD2 correction of the base plan for non-responders, implemented for the final 29 patients, led to a statistically significant improvement in dose coverage as compared to the 35 patients treated without EQD2 correction.
This is to our knowledge the only study presented on biomarker-guided sequential VMAT radiotherapy using a plan-on-plan technique in the pelvis. By using a biologically adapted technique an improved target coverage was achieved without compromising doses to organs at risk.
Urethra-Sparing Stereotactic Body Radiation Therapy for Prostate Cancer: Quality Assurance of a Randomized Phase 2 Trial
2020, International Journal of Radiation Oncology Biology Physics
To present the radiation therapy quality assurance results from a prospective multicenter phase 2 randomized trial of short versus protracted urethra-sparing stereotactic body radiation therapy (SBRT) for localized prostate cancer.
Between 2012 and 2015, 165 patients with prostate cancer from 9 centers were randomized and treated with SBRT delivered either every other day (arm A, n = 82) or once a week (arm B, n = 83); 36.25 Gy in 5 fractions were prescribed to the prostate with (n = 92) or without (n = 73) inclusion of the seminal vesicles (SV), and the urethra planning-risk volume received 32.5 Gy. Patients were treated either with volumetric modulated arc therapy (VMAT; n = 112) or with intensity modulated radiation therapy (IMRT; n = 53). Deviations from protocol dose constraints, planning target volume (PTV) homogeneity index, PTV Dice similarity coefficient, and number of monitor units for each treatment plan were retrospectively analyzed. Dosimetric results of VMAT versus IMRT and treatment plans with versus without inclusion of SV were compared.
At least 1 major protocol deviation occurred in 51 patients (31%), whereas none was observed in 41. Protocol violations were more frequent in the IMRT group (P < .001). Furthermore, the use of VMAT yielded better dosimetric results than IMRT for urethra planning-risk volume D_98% (31.1 vs 30.8 Gy, P < .0001), PTV D_2% (37.9 vs 38.7 Gy, P < .0001), homogeneity index (0.09 vs 0.10, P < .0001), Dice similarity coefficient (0.83 vs 0.80, P < .0001), and bladder wall V_50% (24.5% vs 33.5%, P = .0001). To achieve its goals volumetric modulated arc therapy required fewer monitor units than IMRT (2275 vs 3378, P <.0001). The inclusion of SV in the PTV negatively affected the rectal wall V_90% (9.1% vs 10.4%, P = .0003) and V_80% (13.2% vs 15.7%, P = .0003).
Protocol deviations with potential impact on tumor control or toxicity occurred in 31% of patients in this prospective clinical trial. Protocol deviations were more frequent with IMRT. Prospective radiation therapy quality assurance protocols should be strongly recommended for SBRT trials to minimize potential protocol deviations.
Artifact-free CT images for electron beam therapy using a patient-specific non metallic shield
2020, Physica Medica
Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts. Furthermore, the treatment planning system (TPS) has a limitation on accurate dose calculations for high density materials. In this study, a Monte Carlo (MC)-based method was developed to accurately evaluate the dosimetric effect of the metallic shield. Two patients with a commercial tungsten shield of lens and two patients with a custom-made lead shield of lip were chosen to produce their non-metallic dummy shields using 3D scanner and printer. With these dummy shields, we generated artifact-free CT images. The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations with real material information were carried out. In addition, clinically relevant dose-volumetric parameters were calculated for the comparison between MC and TPS. Relative dosimetry was performed using radiochromic films. The dose reductions below metallic structures were shown on MC dose distributions, but not evident on TPS dose distributions. The differences in dose-volumetric parameters of PTV between TPS and MC for eye shield cases were not clearly shown. However, the mean dose of lens from TPS and MC was different. The MC results were in superior agreement with measured data in relative dosimetry. The lens dose could be overestimated by TPS. The differences in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip cases than in eye cases. The developed method is useful in predicting the realistic dose distributions around the organs blocked by the metallic shields.
VMAT partial arc technique decreases dose to organs at risk in whole pelvic radiotherapy for prostate cancer when compared to full arc VMAT and IMRT
2023, Medical Dosimetry
Whole pelvic radiotherapy (WPRT) can sterilize microscopic lymph node metastases in treatment of prostate cancer. WPRT, compared to prostate only radiotherapy (PORT), is associated with increased acute gastrointestinal, and hematological toxicities. To further explore minimizing normal tissue toxicities associated with WPRT in definitive IMRT for prostate cancer, this planning study compared dosimetric differences between static 9-field-IMRT, full arc VMAT, and mixed partial-full arc VMAT techniques. In this retrospective study, 12 prostate cancer patients who met the criteria for WPRT were randomly selected for this study. The initial volume, PTV46, included the prostate, seminal vesicles, and pelvic nodes with margin and was prescribed to 4600 cGy. The cone-down volume, PTV78, included the prostate and proximal seminal vesicles with margin to a total dose of 7800 cGy. For each CT image set, 3 plans were generated for each of the PTVs: an IMRT plan, a full arc (FA) VMAT plan, and a mixed partial-full arc (PFA) VMAT plan, using 6MV photons energy. According to RTOG protocols none of the plans had a major Conformity Index (CI) violation by any of the 3 planning techniques. PFA plan had the best mean CI index of 1.00 and significantly better than IMRT (p = 0.03) and FA (p = 0.007). For equivalent PTV coverage, the average composite gradient index of the PFA plans was better than the IMRT and the FA plans with values 1.92, 2.03, and 2.01 respectively. The defference was statistically significant between PFA/IMRT and PFA/FA, with p- values of < 0.001. The IMRT plans and the PFA plans provided very similar doses to the rectum, bladder, sigmoid colon, and femoral heads, which were lower than the dose in the FA plans. There was a significant decrease in the mean dose to the rectum from 4524 cGy with the FA to 4182 cGy with the PFA and 4091 cGy with IMRT (p < 0.001). The percent of rectum receiving 4000 cGy was also the highest with FA at 66.1% compared to 49.9% (PFA) and 47.5% (IMRT). There was a significant decrease in the mean dose to the bladder from 3922 cGy (FA) to 3551 cGy (PFA) and 3612 cGy (IMRT) (p < 0.001). The percent of bladder receiving 4000 cGy was also the highest with FA at 45.4% compared to 36.6% (PFA) and 37.4% (IMRT). The average mean dose to the sigmoid colon decreased from 4177 cGy (FA) to 3893 cGy (PFA) and 3819 cGy (IMRT). The average mean dose to the femoral heads decreased from 2091 cGy (FA) to 2026 cGy (PFA) and 1987 cGy (IMRT). Considering the improvement in plan quality indices recorded in this study including the dose gradient and the dose to organs at risk, mixed partial-full arc plans may be the preferred VMAT treatment technique over full arc plans for prostate cancer treatments that include nodal volumes.
Treatment planning comparison between dynamic wave arc and volumetric modulated arc therapies for prostate-cancer treatment
2022, Medical Dosimetry
The aim of this study was to compare the quality of dynamic wave arc (DWA) and coplanar volumetric modulated arc therapy (co-VMAT) plans for the treatment of localized prostate cancer. The planning target volume (PTV)-rectum, a section of the PTV comprising the PTV minus that of the rectum, received 78 Gy in 39 fractions as the mean dose to the PTV-rectum. The DWA and co-VMAT plans were generated for each patient using the RayStation treatment planning system for the Vero4DRT system. The PTV-rectum dose (D_95%: the percent dose irradiating 95% of the volume), homogeneity index (HI), conformity index (CI), as well as doses to the bladder wall, rectum wall (V_10–70 Gy: the percent volume receiving 10–70 Gy), and bilateral femoral heads of the DWA and co-VMAT plans were compared. The output monitor unit (MU) and delivery time obtained for each set of plans were also investigated. In terms of target coverage, the DWA plans provided an average D_95% of 75.5 Gy, which was comparable to the co-VMAT-plan D_95% of 75.2 Gy (p < 0.05). The HI was significantly better with the DWA. As for the DWA plans, the bladder-wall volume receiving 10, 20, 30, and 40 Gy (V_{10–40 Gy}) was significantly smaller than that of the co-VMAT plans, and the volume of the rectal wall receiving 10 Gy (V_10Gy) was significantly larger than that of the co-VMAT plans. The DWA plans yielded a reduced dose to the bilateral femoral heads compared with the co-VMAT plans (p < 0.05). The values of the CI and MU, and the delivery time exhibited no significant differences between the DWA and co-VMAT plans. The DWA plan is a feasible treatment option for prostate cancer radiotherapy.

View all citing articles on Scopus

: Conflict of interest: Memorial Sloan-Kettering Cancer Center has a research agreement with Varian Medical Systems.

View full text

Clinical InvestigationVolumetric Modulated Arc Therapy: Planning and Evaluation for Prostate Cancer Cases

Purpose

Methods and Materials

Results

Conclusion

Introduction

Section snippets

Optimization algorithm

Results

Discussion

Conclusion

Acknowledgment

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Ooncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Ooncol Biol Phys

Int J Radiat Oncol Biol Phys

Volumetric modulated arc therapy: IMRT in a single gantry arc

Med Phys

Clinical Investigation
Volumetric Modulated Arc Therapy: Planning and Evaluation for Prostate Cancer Cases