A Dosimetric Comparison of Tomotherapy and Volumetric Modulated Arc Therapy in the Treatment of High-Risk Prostate Cancer With Pelvic Nodal Radiation Therapy

doi:10.1016/j.ijrobp.2012.03.046

International Journal of Radiation OncologyBiologyPhysics

Volume 85, Issue 2, 1 February 2013, Pages 549-554

https://doi.org/10.1016/j.ijrobp.2012.03.046 Get rights and content

Purpose

To compare the dosimetric results of volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of high-risk prostate cancer with pelvic nodal radiation therapy.

Methods and Materials

Plans were generated for 10 consecutive patients treated for high-risk prostate cancer with prophylactic whole pelvic radiation therapy (WPRT) using VMAT and HT. After WPRT, a sequential boost was delivered to the prostate. Plan quality was assessed according to the criteria of the International Commission on Radiation Units and Measurements 83 report: the near-minimal (D98%), near-maximal (D2%), and median (D50%) doses; the homogeneity index (HI); and the Dice similarity coefficient (DSC). Beam-on time, integral dose, and several organs at risk (OAR) dosimetric indexes were also compared.

Results

For WPRT, HT was able to provide a higher D98% than VMAT (44.3 ± 0.3 Gy and 43.9 ± 0.5 Gy, respectively; P=.032) and a lower D2% than VMAT (47.3 ± 0.3 Gy and 49.1 ± 0.7 Gy, respectively; P=.005), leading to a better HI. The DSC was better for WPRT with HT (0.89 ± 0.009) than with VMAT (0.80 ± 0.02; P=.002). The dosimetric indexes for the prostate boost did not differ significantly. VMAT provided better rectum wall sparing at higher doses (V70, V75, D2%). Conversely, HT provided better bladder wall sparing (V50, V60, V70), except at lower doses (V20). The beam-on times for WPRT and prostate boost were shorter with VMAT than with HT (3.1 ± 0.1 vs 7.4 ± 0.6 min, respectively; P=.002, and 1.5 ± 0.05 vs 3.7 ± 0.3 min, respectively; P=.002). The integral dose was slightly lower for VMAT.

Conclusion

VMAT and HT provided very similar and highly conformal plans that complied well with OAR dose-volume constraints. Although some dosimetric differences were statistically significant, they remained small. HT provided a more homogeneous dose distribution, whereas VMAT enabled a shorter delivery time.

Introduction

Intensity modulated radiation therapy (IMRT) is emerging as a standard of care for prostate cancer radiation therapy. Advanced techniques for creating conformal dose distributions include static fields (“step-and-shoot” IMRT), dynamic fields (sliding-window IMRT), and, more recently, volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT). However, there is no consensus in the literature on the superiority of any one technique.

The aim of the present study was to compare target coverage and organ at risk (OAR) sparing obtained with HT and VMAT in high-risk prostate cancer treated with prophylactic, whole pelvic nodal radiation therapy (WPRT). The latter treatment approach is still controversial but was mandatory in the prospective, randomized trials that established the value of hormone therapy and radiation therapy in these patients 1, 2. In a recent review, Morikawa and Roach (3) emphasized the roles of WPRT, volume delineation, and, in particular, the upper border of the clinical target volume (CTV). In 2009, the Radiation Therapy Oncology Group (RTOG) published the consensus guidelines on pelvic lymph node delineation for high-risk prostate cancer (4). These guidelines were applied in the present study.

Dosimetric comparisons of HT and VMAT have been published for organs other than the prostate 5, 6 and for low-risk and intermediate-risk prostate cancer not treated with WPRT 5, 7, 8, 9, 10. Data on WPRT in prostate cancer are very scarce 11, 12. In the present study, we compared the dosimetric results of HT and VMAT for WPRT in 10 consecutive, high-risk prostate cancer patients. We used the guidelines of the International Commission on Radiation Units and Measurements 83 to prescribe, record, and report the target volumes and OAR doses (13).

Section snippets

Patient population

We studied 10 consecutive, high-risk prostate cancer patients. The estimated high risk of microscopic pelvic node invasion (according to Partin's tables and the Roach equation) had prompted the prescription of WPRT 14, 15. Specific instructions were given to the patient regarding preparation for treatment: a comfortably full bladder (ingestion of 250 mL of water 90 minutes beforehand) and an empty rectum. Patients underwent a planning computed tomograpy scan, with a contiguous 3-mm slice

Results

For PTV1, HT provided a higher D98% (44.3 ± 0.3 Gy) than did VMAT (43.9 ± 0.5 Gy; P=.032), with a lower D2% (47.3 ± 0.3 Gy vs 49.1 ± 0.7 Gy, respectively; P=.005) (Table 3 and Fig. 2a). Hence, for PTV1, the HI was better with HT than with VMAT (0.07 ± 0.01 vs 0.11 ± 0.02, respectively; P=.005). The DSC was also significantly better with HT than with VMAT (Table 3). For PTV2, the techniques' respective D98%, D2%, D50%, HI, and DSC values did not differ significantly (Table 3 and Fig. 2b).

Discussion

As mentioned in the Introduction, there are very few literature data on dosimetric comparisons between VMAT and HT in the treatment of high-risk prostate cancer with WPRT 11, 12. Some authors have compared VMAT with IMRT or VMAT with HT for the treatment of low-risk and intermediate-risk prostate cancer not treated with WPRT 5, 7, 8, 9, 10, 18. Hence, the present study is one of the first to report dose-to-target volumes and OAR and to calculate the HI and DSC, as recommended in the ICRU report

Conclusion

Our study was one of the first to statistically compare VMAT and HT for the treatment of high-risk prostate cancer with WPRT. The 2 planning techniques provided highly conformal plans that easily complied with OAR dose-volume constraints. As has been seen for the treatment of other body sites, HT provided a more homogeneous dose distribution, and OAR sparing was very similar for the 2 techniques. Although some dosimetric differences were statistically significant, they remained small and

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There are limited long-term data on patients treated with image guided intensity modulated radiation therapy (IG-IMRT) for prostate cancer recurrence or high-risk disease features after radical prostatectomy. We report single-institution results for patients treated with IG-IMRT and identify variables associated with outcome.
This is a retrospective chart review consisting of 313 consecutive patients who were treated with adjuvant or salvage IG-IMRT from 2004 to 2013. Cox proportional hazards analysis was used to identify factors related to survival and toxicity. Toxicity was graded using the Common Terminology Criteria for Adverse Events Version 4.0.
The median follow-up was 55 months (range, 6-131 months). The median pre-radiation therapy (RT) prostate-specific antigen (PSA) was 0.3 ng/mL (range, <0.01-55.4). The vast majority of patients (87%) received elective pelvic nodal irradiation (median dose: 45 Gy). Androgen deprivation therapy (ADT) was given to 39% of patients for a median of 9 months. Five-year biochemical progression-free survival and distant metastasis-free survival were 59% (95% confidence interval, 53%-66%) and 89% (95% confidence interval, 85%-93%), respectively. On multivariate analysis, higher pre-RT PSA (>0.2 ng/mL), biopsy Gleason score (≥7 [4+3]), and duration of ADT (>6 months) were significantly associated (P < .05) with biochemical progression-free survival. Actuarial late grade 3 genitourinary and gastrointestinal toxicities at 5 years were 10% and 2%, respectively.
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Citation Excerpt :
Volumetric-modulated arc therapy (VMAT) is an intensity-modulated, arc delivery technique that uses inverse planning including degrees of freedom for gantry rotation, aperture shape, and dose rate in radiation optimization and delivery. VMAT has been shown to be effective in reducing delivery time, achieving target coverage,1-3 and reducing dose to organs at risk (OARs) over intensity-modulated radiation therapy (IMRT) and 3-dimensional conformal therapy techniques in a variety of clinical studies.4,5 In many cases, VMAT performs as well as or better dosimetrically than IMRT, but for complex target volumes, like for head and neck cancers, IMRT can be slightly superior to VMAT in terms of OAR sparing.6
The purpose of this study was to evaluate the dosimetric and practical effects of the Monaco treatment planning system “max arcs-per-beam” optimization parameter in pelvic radiotherapy treatments. We selected for this study a total of 17 previously treated patients with a range of pelvic disease sites including prostate (9), bladder (1), uterus (3), rectum (3), and cervix (1). For each patient, 2 plans were generated, one using an arc-per-beam setting of “1” and another with an arc-per-beam setting of “2” using the volumes and constraints established from the initial clinical treatments. All constraints and dose coverage objects were kept the same between plans, and all plans were normalized to 99.7% to ensure 100% of the planning target volume (PTV) received 95% of the prescription dose. Plans were evaluated for PTV conformity, homogeneity, number of monitor units, number of control points, and overall plan acceptability. Treatment delivery time, patient-specific quality assurance procedures, and the impact on clinical workflow were also assessed. We found that for complex-shaped target volumes (small central volumes with extending arms to cover nodal regions), the use of 2 arc-per-beam (2APB) parameter setting achieved significantly lower average dose-volume histogram values for the rectum V₂₀ (p = 0.0012) and bladder V₃₀ (p = 0.0036) while meeting the high dose target constraints. For simple PTV shapes, we found reduced monitor units (13.47%, p = 0.0009) and control points (8.77%, p = 0.0004) using 2APB planning. In addition, we found a beam delivery time reduction of approximately 25%. In summary, the dosimetric benefit, although moderate, was improved over a 1APB setting for complex PTV, and equivalent in other cases. The overall reduced delivery time suggests that the use of mulitple arcs per beam could lead to reduced patient-on-table time, increased clinical throughput, and reduced medical physics quality assurance effort.
Prostate cancer: What treatment techniques for which tumors? Ethical and methodological issues
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L’identification de la technique optimale d’irradiation prostatique repose principalement sur des données méthodologiques correspondant à des études dosimétriques et cliniques, bien que les études de phase III comparant différentes techniques soient cependant quasi inexistantes. La faisabilité des techniques innovantes dépend aussi des ressources humaines et techniques des services de radiothérapie, du coût des traitements à la fois du point de vue de la société, du patient et du thérapeute, et finalement du choix du patient informé objectivement. L’histoire naturelle très lente du cancer de prostate conduit à considérer un critère de jugement principal de récidive biochimique discutable. Un suivi important est nécessaire pour évaluer la toxicité urinaire, potentiellement de survenue très tardive. La radiothérapie conformationnelle avec modulation d’intensité (RCMI) guidée par l’image est recommandée en cas de haute dose dans la prostate (76 Gy et plus), d’irradiation des aires ganglionnaires ou d’irradiation hypofractionnée. Pour les tumeurs de bas risque, la stratégie thérapeutique vise prioritairement à préserver la qualité de vie et minimiser les coûts. La radiothérapie stéréotaxique proposant un hypofractionnement extrême montre des résultats prometteurs avec un recul limité. Elle est en cours d’évaluation dans des essais de phase III. L’irradiation focale est à un stade de faisabilité. Pour les tumeurs de risque intermédiaire et de haut risque, l’objectif est d’augmenter le taux de contrôle locorégional en limitant la toxicité. La RCMI guidée par l’image permet pour ces tumeurs ainsi, soit une stratégie d’escalade de dose bien validée pour les tumeurs de risque intermédiaire, soit un hypofractionnement modéré, qui n’est cependant pas encore un standard thérapeutique. Ces techniques conjuguées permettent aussi l’irradiation de larges volumes ganglionnaires à dose élevée ou un complément d’irradiation dans la tumeur intra-prostatique, éventuellement dans le cadre d’une irradiation avec boost intégré, dont la faisabilité est démontrée.
The identification of the optimal radiation technique in prostate cancer is based on the results of dosimetric and clinical studies, although there are almost no randomized studies comparing different radiation techniques. The feasibility of the techniques depends also on the technical and human resources of the radiation department, on the cost of the treatment from the points of view of the society, the patient and the radiation oncologist, and finally on the choice of the patient. The slow evolution of prostate cancer leads to consider the biochemical failure as the main judgment criteria in the majority of the studies. A proper urinary radio-induced toxicity evaluation implies a long follow-up. Intensity-modulated radiotherapy (IMRT) combined with image-guided radiotherapy (IGRT) is recommended in case of high dose (≥ 76 Gy) to the prostate, pelvic lymph nodes irradiation and hypofractionation schedules. For low-risk tumors, the aim of the treatment is to preserve quality of life, while limiting costs. Stereotactic body radiotherapy shows promising results, although the follow-up is still limited and phase III trials are ongoing. Focal radiation techniques are in the step of feasibility. For intermediate and high-risk tumors, the objective of the treatment is to increase the locoregional control, while limiting the toxicity. IMRT combined with IGRT leads to either a well-validated dose escalation strategy for intermediate risk tumors, or to a strategy of moderate hypofractionated schedules, which cannot be yet considered as a standard treatment. These combined radiation techniques allow finally large lymph node target volume irradiation and dose escalation potentially in the dominant intraprostatic lesion. The feasibility of simultaneous integrated boost approaches is demonstrated.
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The purpose of new radiotherapy techniques is to better deliver dose conformation in the tumour volume while diminishing organs at risk exposition. Their development is soaring in the breast cancer field in the adjuvant setting with intensity-modulated radiation therapy but also in cerebral and extracerebral oligometastastic presentation. Their usage is still being debated for breast cancer care. The objective of this narrative review is to list and discuss clinical data at our disposal for these news technologies.
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Citation Excerpt :
High-risk patients with prostate and rectal cancer treated with whole-pelvic nodal radiotherapy (WPRT) represent a higher challenging planning task because of large and irregularly shaped target volumes (as pelvic lymph nodes), which may lead to inadequate target coverage or inacceptable irradiation to OARs or both. Data on the application of VMAT to WPRT are nowadays emerging, with29-31 or without32-34 the SIB strategy, showing an overall equivalent dosimetric quality as fixed-field IMRT but with a significant improvement in efficiency in treatment delivery. Most of these comparative planning dosimetric studies have been performed almost exclusively for RapidArc technique, and only 1 research group focused on the commercial solution of Oncentra MasterPlan treatment planning system (TPS) with Elekta linacs,35,36 but without using the SIB strategy.
Intensity-modulated radiotherapy (IMRT) allowed the simultaneous delivery of different doses to different target volumes within a single fraction, an approach called simultaneous integrated boost (SIB). As consequence, the fraction dose to the boost volume can be increased while keeping low doses to the elective volumes, and the number of fractions and overall treatment time will be reduced, translating into better radiobiological effectiveness. In recent years, volumetric-modulated arc therapy (VMAT) has been shown to provide similar plan quality with respect to fixed-field IMRT but with large reduction in treatment time and monitor units (MUs) number. However, the feasibility of VMAT when used with SIB strategy has few investigations to date. We explored the potential of VMAT in a SIB strategy for complex cancer sites. A total of 15 patients were selected, including 5 head-and-neck, 5 high-risk prostate, and 5 rectal cancer cases. Both a double-arc VMAT and a 7-field IMRT plan were generated for each case using Oncentra MasterPlan treatment planning system for an Elekta Precise linac. Dosimetric indexes for targets and organs at risk (OARs) were compared based on dose-volume histograms. Conformity index, homogeneity index, and dose-contrast index were used for target analyses. The equivalent uniform doses and the normal tissue complication probabilities were calculated for main OARs. MUs number and treatment time were analyzed to score treatment efficiency. Pretreatment dosimetry was performed using 2-dimensional (2D)-array dosimeter. SIB-VMAT plans showed a high level of fluence modulation needed for SIB treatments, high conformal dose distribution, similar target coverage, and a tendency to improve OARs sparing compared with the benchmark SIB-IMRT plans. The median treatment times reduced from 13 to 20 minutes to approximately 5 minutes for all cases with SIB-VMAT, with a MUs reduction up to 22.5%. The 2D-array ion-chambers' measurements reported an agreement of more than 95% for a criterion of 3% to 3 mm. SIB-VMAT was able to combine the advantages of conventional SIB-IMRT with its highly conformal dose distribution and OARs sparing and the advantages of 3D-conformal radiotherapy with its fast delivery.

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Physics ContributionA Dosimetric Comparison of Tomotherapy and Volumetric Modulated Arc Therapy in the Treatment of High-Risk Prostate Cancer With Pelvic Nodal Radiation Therapy

Purpose

Methods and Materials

Results

Conclusion

Introduction

Section snippets

Patient population

Results

Discussion

Conclusion

Lancet 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

Radiother Oncol

Radiother Oncol

Med Dosim

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Physics Contribution
A Dosimetric Comparison of Tomotherapy and Volumetric Modulated Arc Therapy in the Treatment of High-Risk Prostate Cancer With Pelvic Nodal Radiation Therapy