Performance of a knowledge-based planning model for optimizing intensity-modulated radiotherapy plans for partial breast irradiation

Purpose

To evaluate a knowledge‐based (KB) planning model for RapidPlan, generated using a five‐field intensity‐modulated radiotherapy (IMRT) class solution beam strategy and rigorous dosimetric constraints for accelerated partial breast irradiation (APBI).

Materials and methods

The RapidPlan model was configured using 64 APBI treatment plans and validated for 120 APBI patients who were not included in the training dataset. KB plan dosimetry was compared to clinical plan dosimetry, the clinical planning constraints, and the constraints used in phase III APBI trials. Dosimetric differences between clinical and KB plans were evaluated using paired two‐tailed Wilcoxon signed‐rank tests.

Results

KB planning was able to produce IMRT‐based APBI plans in a single optimization without manual intervention that are comparable or better than the conventionally optimized, clinical plans. Comparing KB plans to clinical plans, differences in PTV, heart, contralateral breast, and ipsilateral lung dose–volume metrics were not clinically significant. The ipsilateral breast volume receiving at least 50% of the prescription dose was statistically and clinically significantly lower in the KB plans.

Conclusion

KB planning for IMRT‐based APBI provides equivalent or better dosimetry compared to conventional inverse planning. This model may be reliably applied in clinical practice and could be used to transfer planning expertise to ensure consistency in APBI plan quality.

Clinical Outcomes from Dose-Reduced Radiotherapy to the Prostate in Elderly Patients with Localized Prostate Cancer

Radical treatment of localized prostate cancer in elderly patients may lead to unacceptable treatment-associated toxicities that adversely impact quality of life without improving survival outcomes. This study reports on a cohort of 54 elderly (>70 years) patients that received 4000–5000 cGy of palliative external beam radiotherapy (EBRT) as an alternative to androgen deprivation therapy (ADT). The primary outcome of interest was the period of ADT-free survival, and secondary outcomes included overall survival (OS) and metastases-free survival (MFS). Kaplan–Meier regression was used to estimate survival outcomes. Thirty-six (67%) patients achieved a break in ADT post-radiotherapy, with a median time to ADT reinitiation of 20 months. Common Terminology Criteria for Adverse Events (CTCAE) were limited to low-grade gastrointestinal (GI) or genitourinary (GU) toxicities, with no skin toxicities observed. Grade 1 GI toxicity was observed in 9 (17%) patients, and grades 1 and 2 GU toxicities were observed in 13 (24%) and 3 (6%) patients, respectively, with no higher-grade toxicities reported. Five-year MFS and OS were 56% and 78%, respectively. In summary, the treatment regimen was well-tolerated and achieved durable ADT-free survival in most patients. Dose-reduced EBRT appears to be a viable alternative to ADT in elderly patients with localized prostate cancer.

Increasing Demand on Human Capital and Resource Utilization in Radiation Therapy: The Past Decade

PURPOSE

To quantify the change resource utilization in radiation therapy in the context of advancing technologies and techniques over the last decade.

METHODS AND MATERIALS

Prospectively, the time to complete radiation therapy workflow tasks was captured between January 1, 2020, and December 31, 2020. The institutional task workflows are specific to each technique and broadly organized into 4 categories: 3-dimenstional conformal radiation therapy, intensity modulated radiation therapy, volumetric modulated arc therapy simple, and volumetric modulated arc therapy complex. These discipline-specific task times were used to quantify a resource utilization factor, which is the median time taken to complete all tasks for each category divided by the median time for 3-dimensional conformal radiation therapy treatments. Retrospectively, all plans treated between January 1, 2012, and December 31, 2019, were quantified and categorized. The resource factor was applied to determine resource utilization. For context, institutional staffing levels were captured across the same decade for medical dosimetrists, medical physicists, and radiation oncologists.

RESULTS

This analysis includes 30,229 patient plans in the retrospective data set and 4747 patient plans in the prospective data set. This analysis demonstrates that over this period, patient numbers increased by approximately 45%, whereas time-based human resources increased by almost 150%. The resource allocation factors for 3-dimenstional conformal radiation therapy, intensity modulated radiation therapy, volumetric modulated arc therapy simple, and volumetric arc therapy complex were 1.0, 2.4, 2.9, and 4.3, respectively. Across the 3 disciplines, staffing levels increased from 15 to 17 (13%) for medical dosimetrists, from 10 to 13 (30%) for medical physicists, and from 16 to 23 (44%) for radiation oncologists.

CONCLUSIONS

This work demonstrates the increase in resource utilization due to the introduction of advanced technologies and changes in radiation therapy techniques over the past decade. Human resource utilization is the predominant factor and should be considered with increasing patient volume for operational planning.

Technical Note: A standardized automation framework for monitoring institutional radiotherapy protocol compliance

PURPOSE

To establish a framework for the standardization of monitoring radiotherapy protocol compliance.

METHODS

An automated protocol compliance tool was developed using best practice in software design and a flexible framework to easily adapt to changing institutional standards. The Eclipse scripting environment was used to develop the application with the scripting application programing interface (API) and direct data extraction from ARIA. For each institutional protocol, external validation was specified in a JavaScript Object Notation (JSON) file that stores protocol specific constraints and evaluates compliance of the data from Eclipse and Aria. This tool was applied prospectively to a cohort of prostate cancer patients undergoing radiotherapy with a prescription regimen of 60 Gy in 20 fractions.

RESULTS

The prospective evaluation was performed on 58 prostate cancer patients. For this cohort, the mean (standard deviation) pass rate is 92.3% (6.1%). The overall fail rate is 6.0% (5.8%); the percentage of these failures is in 2.6% in Patient Assessment, 0% in Simulation, and 97.4% in Treatment Planning.

CONCLUSIONS

A protocol compliance application is developed and implemented in a standard radiotherapy information system. The application functionality is demonstrated on a cohort of 58 patients undergoing prostate radiotherapy, which highlights the utility of assessing adherence to institutional protocols. A unified method must be available for the community to ensure consistency in compliance reporting.

Dosimetric consequences of seed placement accuracy in permanent breast seed implant brachytherapy

PURPOSE

This study quantifies the dosimetric impact of implant accuracy and derives a quantitative relationship relating implant accuracy to target dosimetry.

METHODS AND MATERIALS

A framework was developed to simulate multiple implants for error combinations. Spherical clinical target volumes (CTVs) were modeled with volumes 1.4 cm³, 9.2 cm³, and 20.6 cm³, representing the range seen clinically. Each CTV was expanded 10 mm isotropically to create a planning target volume (PTV).. Random and systematic seed placement errors were simulated by shifting needles from their planned positions. Implant errors were simulated over the range of clinically practical errors in permanent breast seed implant. The relative effect on target coverage was evaluated. Regression analysis was performed to derive relationships between CTV dosimetry and the magnitude of implant accuracy. The validity of the clinically used 10 mm PTV margin for each of the CTVs was assessed.

RESULTS

Introducing practical implant errors resulted in CTV V_90% median (10th and 90th percentile) of 97.7% (85.9% and 100%), 96.2% (86.8% and 99.7%), and 100% (77.8% and 100%) for the typical, large, and small CTV, respectively. All CTVs show similar trends in target coverage. Polynomials were derived relating seed placement accuracy to median (R² = 0.82) and 10th percentile (R² = 0.78) CTV V_90%._. CONCLUSIONS: This work quantitatively describes the relationship between implant accuracy and CTV coverage. Based on simulations, the 10 mm PTV margin is adequate to maintain target coverage. These equations can be used with institutional seed placement accuracy to estimate coverage.

Establishing a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy: Building validation evidence

PURPOSE

The purpose of this study was to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy. The first step in formalizing any education program is a validation process that builds evidence-based verification that the learning environment is appropriate.

METHODS AND MATERIALS

The primary education task allowed practitioners to use an anthropomorphic breast phantom to simulate a permanent seed implant brachytherapy delivery. Validation evidence is built by generating data to assess learner and expert cohorts according to their proficiency. Each practitioner's performance during the simulation was evaluated by seed placement accuracy, procedural time-to-complete, and two qualitative evaluation tools-a global rating scale and procedural checklist.

RESULTS

The average seed placement accuracy (±SD) was 8.1 ± 3.5 mm compared to 6.1 ± 2.6 mm for the learner and expert cohort, respectively. The median (range) procedural time-to-complete was 64 (60-77) minutes and 43 (41-50) minutes for the learner and expert cohort, respectively. Seed placement accuracy (student t-test, p < 0.05) and procedural time-to-complete (Mann-Whitney U-test, p < 0.05) were statistically different between the cohorts. In both the global rating scale and procedural checklist, the expert cohort demonstrated improved proficiency compared to the learner cohort.

CONCLUSIONS

This validation evidence supports the utilization of this simulation environment toward appropriately capturing the delivery experience of practitioners. The results demonstrate that, in all areas of evaluation, expert cohort proficiency was superior to learner cohort proficiency. This methodology will be used to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy.

What Conditions Make Proton Beam Therapy Financially Viable in Western Canada?

Background

Proton beam therapy (PBT) is available in many western and Asian countries, but there is no clinical, gantry-based PBT facility in Canada.

Methods

A cost analysis was conducted from the Alberta Ministry of Health perspective with a 15-year horizon. Estimated costs were: PBT unit, facility development as part of an ongoing capital project, electricity, maintenance contract, and staffing. Revenues were: savings from stopping USA referrals, avoiding the costs of standard radiation therapy (RT) for Albertans receiving PBT instead, and cost-recovery charges for out-of-province patients.

Results

The Ministry of Health funded 15 Albertans for PBT in the USA in the 2014/15 fiscal year (mean CAD$ 237,348/patient). A single-vault, compact PBT unit operating 10 hours/day could treat 250 patients annually. A 100 Albertans, with accepted indications, such as the curative-intent treatment of chordomas, ocular melanomas, and selected pediatric cancers, would likely benefit annually from PBT’s improved conformality and/or reduced integral dose compared to RT. The estimated capital cost was $40 million for a single beamline built within an ongoing capital project. Operating costs were $4.8 million/year at capacity. With 50% capacity reserved for non-Albertans at a cost recovery of $45,000/patient, a Western Canadian PBT facility would achieve net positive cash flow by year eight of clinical operations, assuming Alberta-to-USA referrals reach 21 patients/year by 2024 and increase at 3%/year thereafter. Sensitivity analysis indicates the lifetime net savings is robust to the assumptions made.

Conclusion

This business case, based on Canadian costing data and estimates, demonstrates the potential for a financially viable PBT facility in Western Canada.