A dosimetric study of volumetric modulated arc therapy planning techniques for treatment of low-risk prostate cancer in patients with bilateral hip prostheses

The impact of metal implants on the dose and clinical outcome of radiotherapy (Review)

Radiotherapy (RT) is one of the most widely used and effective cancer treatments. With the increasing need for organ reconstruction and advancements in material technology, an increasing number of patients with cancer have metallic implants. These implants can affect RT dosage and clinical outcomes, warranting careful consideration by oncologists. The present review discussed the mechanisms by which different types of metallic implants impact various stages of the RT process, examined methods to mitigate these effects during treatment, and discussed the clinical implications of metallic implants on RT outcomes. In summary, when metallic implants are present within the RT field, oncologists should carefully assess their impact on the treatment.

Stereotactic Body Radiation Therapy (SBRT) in prostate cancer in the presence of hip prosthesis - is it a contraindication? A narrative review

Hip replacement is a common orthopedic surgery in the aging population. With the rising incidence of prostate cancer, metallic hip prosthetics can cause considerable beam hardening and streak artifacts, leading to difficulty in identifying the target volumes and planning process for radiation treatment. The growing use of Stereotactic Body Radiation Therapy (SBRT) to treat prostate cancer is now well established. However, the use of this treatment modality in the presence of a hip prosthesis is poorly understood. There is enough literature on planning for external beam radiation treatment without any difficulties in the presence of hip prosthesis with conventional or Hypofractionated treatment. However, there is a shortage of literature on the impact of the prosthesis in SBRT planning, and there is a need for further understanding and measures to mitigate the obstacles in planning for SBRT in the presence of hip prosthesis. We present our review of the intricacies that need to be understood while considering SBRT in the presence of hip prostheses in prostate cancer treatment.

The Role of Proton Therapy for Prostate Cancer in the Setting of Hip Prosthesis

PURPOSE

Given that the current standard of proton therapy (PT) for prostate cancer is through bilateral beams, this modality is typically avoided when it comes to treatment of patients with hip prosthesis. The purpose of this study was to evaluate whether novel PT methods, i.e., anterior proton beams and proton arc therapy (PArc), could be feasible options to treat this patient subpopulation. We evaluate PT methods in the context of dosimetry and robustness and compare with standard of practice volumetric modulated arc therapy (VMAT) to explore any potential benefits.

METHODS

Two PT and one VMAT treatment plans were retrospectively created for 10 patients who participated in a clinical trial with a weekly repeat CT (rCT) imaging component. All plans were robustly optimized and featured: (1) combination anterior oblique and lateral proton beams (AoL), (2) PArc, and (3) VMAT. All patients had hydrogel spacers in place, which enabled safe application of anterior proton beams. The planned dose was 70 Gy (RBE) to the entire prostate gland and 50 Gy (RBE) to the proximal seminal vesicles in 28 fractions. Along with plan dose-volume metrics, robustness to setup and interfractional variations were evaluated using the weekly rCT images. The linear energy transfer (LET)-weighted dose was evaluated for PArc plans to ensure urethra sparing given the typical high-LET region at the end of range.

RESULTS

Both PT methods were dosimetrically feasible and provided reduction of some key OAR metrics compared to VMAT except for penile bulb, while providing equally good target coverage. Significant differences in median rectum V35 (22-25%), penile bulb Dmean (5 Gy), rectum V61 (2%), right femoral head Dmean (5 Gy), and bladder V39 (4%) were found between PT and VMAT. All plans were equally robust to variations. LET-weighted dose in urethra was equivalent to the physical dose for PArc plans and hence no added urethral toxicity was expected.

CONCLUSIONS

PT for treatment of prostate cancer patients with hip prosthesis is feasible and equivalent or potentially superior to VMAT in quality in some cases. The choice of radiotherapy regimen can be personalized based on patient characteristics to achieve the best treatment outcome.

Evaluation of VMAT Planning Strategies for Prostate Patients with Bilateral Hip Prosthesis

Purpose: In this study, we investigate linac volumetric-modulated arc therapy (VMAT) planning strategies for bilateral hip prostheses prostate patients with respect to plan quality and deliverability, while limiting entrance dose to the prostheses. Methods: Three VMAT plans were retrospectively created for 20 patients: (1) partial arcs (PA), (2) 2 full arcs optimized with 500 cGy max prostheses dose (MD), and (3) 2 full arcs optimized with max dose-volume histogram (DVH) constraint of 500 cGy to 10% prostheses volume (MDVH). PA techniques contained 6 PA with beam angles that avoid entering each prosthesis. For each patient, other than prostheses constraints, the same Pinnacle VMAT optimization objectives were used. Plans were normalized with PTV D95% = 79.2 Gy prescription dose. Organ-at-risk DVH metrics, monitor units (MUs), conformality, gradient, and homogeneity indices were evaluated for each plan. Mean entrance prosthesis dose was determined in Pinnacle by converting each arc into static beams and utilizing only control points traversing each prosthesis. Plan deliverability was evaluated with SunNuclear ArcCheck measurements (gamma criteria 3%/2 mm) on an Elekta machine. Results: MD and MDVH had similar dosimetric quality, both improved DVH metrics for rectum and bladder compared to PA. Plan complexities among all plans were similar (average MUs: 441-518). Conformality, homogeneity, and gradient indices were significantly improved in MD and MDVH versus PA (P < .001). Gamma pass rates for MD (99.0 ± 1.2%) and MDVH (99.2 ± 0.99%) were comparable. A significant difference over PA was observed (96.8 ± 1.6%, P < .001). Field-by-field analysis demonstrated 12/20 PA plans resulted in fields with pass rates <95% versus 1/20 plans for MD and none for MDVH. Cumulative mean entrance doses to each prosthesis were 62.9 ± 17.7 cGy for MD plans and 83.4 ± 27.5 cGy for MDVH plans. Conclusion: MD and MDVH plans had improved dosimetric quality and deliverability over PA plans with minimal entrance doses (∼1% of prescription) to each prosthesis and are an improved alternative for bilateral prostheses prostate patients.

Bilateral metallic hip implants: Are avoidance sectors necessary for pelvic VMAT treatments?

PURPOSE

Metallic hip implants (MHI) are common in elderly patients. For pelvic cancers radiotherapy, conventional approaches consist of MHI avoidance during treatment planning, which leads, especially in case of bilateral MHI, to a decreased quality or increased complexity of the treatment plan. The aim of this study is to investigate the necessity of using avoidance sectors (AvSe) using a 2-arcs coplanar pelvic volumetric modulated arc-therapy (VMAT) planning.

METHODS

We evaluated: (1) The dose calculation error of a static 6MV open beam traversing a MHI; (2) The magnitude of an error's decrease within the planning target volume (PTV) for a 360° VMAT treatment without AvSe as compared to the static open beam; (3) The dosimetric influence of MHI misalignment generated by patient's repositioning rolls during image-guided radiotherapy (IGRT).

RESULTS

(1) In the static 6MV beam configuration, for distances between 0.5cm and 6cm from the MHI, the median (maximum, number of points) dose calculation error was -1.55% (-2.5%, 11); (2) Compared to the static open beam, in the 360° VMAT treatment without AvSe a simulated error was decreased by a factor of 4.4/2.4 (median/minimum); (3) MHI anterior-posterior misalignment exceeding 0.6cm, resulted in error at PTV surface of >2%.

CONCLUSIONS

A standard 2 coplanar arcs 360° VMAT treatment, with dedicated artifact reduction algorithms applied, decreased the error of static beam traversing MHI, in patients presenting a bilateral MHI and might be used to treat the pelvic region without MHI avoidance.

The need for a dose constraint in hip prosthesis to minimize later hip dysfunction. A retrospective analysis of relevant cases

Results from a single-institution study support the need of a dose constraint for patients who have previously undergone hip replacement surgery. Our study provides evidence that a dose above 30 Gy to the area of hip prosthesis is significantly correlated with later hip arthroplasty dysfunction as measured by the Harris Hip Score. As total hip arthroplasty becomes more and more common, it is urgent to further look into radiation therapy treatment parameters that can be modified to improve the quality of life of patients who receive pelvic irradiation after hip arthroplasty. Further prospective studies are needed to extract safe conclusions.

The robustness of prostate radiotherapy for patients with hip prosthesis

The aim of this study was to investigate prostate radiotherapy techniques for the patients with hip prosthesis in 4 different field setups. Volumetric Modulated Arc Therapy (VMAT) technique was used in 4 different cases: (1) using full VMAT arcs (VMAT_F); (2) same arcs as in case 1 but with avoidance sectors (VMAT_ASEC); (3) as case 2 but with the addition of a lateral static field through the prosthesis (VMAT_ASEC+STAT); (4) as in case 1 but with an automated structure avoidance option to avoid irradiation through the prosthesis (VMAT_ASTR). Fifteen previously treated prostate patients were retrospectively selected to this study. Treatment plans were created for all patients using all 4 techniques. The potential prosthesis misalignment in the treatment setup was modeled by moving the prosthesis 0.5, 1.0, and 1.5 cm ventrally and dorsally and recalculating the plans in each case. For VMAT_ASEC, the dose parameters for organs at risk were the highest and the dose coverage of the target volume was the poorest when compared to the other techniques. For VMAT_ASEC+STAT, the movement of the prosthesis changed the target dose distribution the most. VMAT_F and VMAT_ASTR fulfilled the planning criteria the best, even when the prosthesis was misaligned. VMAT_F radiated through the prosthesis more than VMAT_ASTR and increased the dose near the prosthesis surface when compared to VMAT_ASTR. VMAT_ASTR and VMAT_F were the most robust techniques for the patients with the hip prosthesis considering plan quality and the effect of positioning errors. The increased prosthesis surface dose with VMAT_F and possible dose calculation uncertainties favors the use of VMAT_ASTR.

VMAT Optimization and Dose Calculation in the Presence of Metallic Hip Prostheses

INTRODUCTION

This research quantifies and compares the effect of hip prostheses on dose distributions calculated using collapsed cone convolution superposition and Monte Carlo (with and without correcting for the density of the implant and surrounding tissues). The use of full volumetric modulated arc therapy arcs versus volumetric modulated arc therapy arcs avoiding the hip implants (skip arcs) was also studied.

MATERIALS AND METHODS

Six prostate patients with hip prostheses were included in this study. The hip prostheses and the streaking artifacts on the computed tomography images were contoured by a single physician, and full volumetric modulated arc therapy arcs were created in the Pinnacle3 TPS. Copies of each plan were made, and the doses were recalculated with the densities of the prostheses and surrounding tissues overridden. The plans were then exported to Monaco and recalculated using a Monte Carlo dose calculation algorithm, with and without densities of the prosthesis and surrounding tissues overridden.

RESULTS

With density overrides, Pinnacle3 had a 4.4% error for ion chamber measurements. Monaco was within 0.2% of ion chamber measurement when density overrides were used. On average, when density overrides were used in Pinnacle3 for patient dose calculations, the planning target volume D95 value dropped from 99.3% to 82.7%. Monaco also showed decreased planning target volume coverage when plans were recalculated with correct density information. Full arc plans (with density overrides) for the patient with a bilateral prosthesis provided significant bladder sparing and some rectal sparing compared to skip arc plans.

CONCLUSION

When planning for prostate patients with hip prostheses, correct density information for implants and surrounding tissues should be used to optimize the plan and ensure optimal accuracy. If available, a Monte Carlo algorithm should be used as a second check. Full arcs could be used to spare dose to organs at risk, while maintaining adequate planning target volume coverage, when using a Monte Carlo dose calculation algorithm.

Dosimetry Effects Caused by Unilateral and Bilateral Hip Prostheses: A Monte Carlo Case Study in Megavoltage Photon Radiotherapy for Computed Tomography Data without Metal Artifacts

Background:

Hip prostheses (HPs) are routinely used in hip augmentation to replace painful or dysfunctional hip joints. However, high-density and high-atomic-number (Z) inserts may cause dose perturbations in the target volume and interface regions.

Aim:

To evaluate the dosimetric influence of various HPs during megavoltage conformal radiotherapy (RT) of the prostate using Monte Carlo (MC) simulations.

Materials and Methods:

BEAMnrc and DOSXYZnrc MC user-codes were respectively used to simulate the linac head and to calculate 3D absorbed dose distributions in a computed tomography (CT)-based phantom. A novel technique was used to synthetically introduce HPs into the raw patient CT dataset. The prosthesis materials evaluated were stainless steel (SS316L), titanium (Ti6Al4V), and ultra-high-molecular-weight polyethylene (UHMWPE). Four, five, and six conformal photon fields of 6–20 MV were used.

Results:

The absorbed dose within and beyond metallic prostheses dropped significantly due to beam attenuation. For bilateral HPs, the target dose reduction ranged up to 23% and 17% for SS316L and Ti6Al4V, respectively. For unilateral HP, the respective dose reductions were 19% and 12%. Dose enhancement was always <1% for UHMWPE. The 6-field plan produced the best target coverage. Up to 38% dose increase was found at the bone–SS316L proximal interface.

Conclusions:

The novel technique used enabled the complete exclusion of metal artifacts in the CT dataset. High-energy plans with more oblique beams can help minimize dose attenuation through HPs. Shadowing and interface effects are density dependent and greatest for SS316L, while UHMWPE poses negligible dose perturbation.

ACR Appropriateness Criteria for external beam radiation therapy treatment planning for clinically localized prostate cancer, part II of II

PURPOSE

To present the most updated American College of Radiology (ACR) Appropriateness Criteria formed by an expert panel on the appropriate delivery of external beam radiation to manage stage T1 and T2 prostate cancer (in the definitive setting and post-prostatectomy) and to provide clinical variants with expert recommendations based on accompanying Appropriateness Criteria for target volumes and treatment planning.

METHODS AND MATERIALS

The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a panel of multidisciplinary experts. The guideline development and revision process includes an extensive analysis of current medical literature from peer-reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In instances in which evidence is lacking or equivocal, expert opinion may supplement available evidence to recommend imaging or treatment.

RESULTS

The panel summarizes the most recent and relevant literature on the topic, including organ motion and localization methods, image guidance, and delivery techniques (eg, 3-dimensional conformal intensity modulation). The panel presents 7 clinical variants, including (1) a standard case and cases with (2) a distended rectum, (3) a large-volume prostate, (4) bilateral hip implants, (5) inflammatory bowel disease, (6) prior prostatectomy, and (7) a pannus extending into the radiation field. Each case outlines the appropriate techniques for simulation, treatment planning, image guidance, dose, and fractionation. Numerical rating and commentary is given for each treatment approach in each variant.

CONCLUSIONS

External beam radiation is a key component of the curative management of T1 and T2 prostate cancer. By combining the most recent medical literature, these Appropriateness Criteria can aid clinicians in determining the appropriate treatment delivery and personalized approaches for individual patients.