Radiation Therapy Treatment Plan Illustration

Decoding Radiation Therapy: Is Your Treatment Plan as Precise as You Think?

Theo Raines in Health & Wellness December 2025 • 4 min read.

"A closer look at the accuracy of biological effective dose calculations in multiphase cancer treatments."

For over two decades, the biological effective dose (BED) has been a cornerstone in radiation therapy, offering a way to relate treatment outcomes more closely to the actual radiation delivered. Despite its benefits, BED hasn't become universally adopted due to uncertainties in its calculation and application.

BED, extrapolated from the linear-quadratic (LQ) model, helps compare different fractionation schemes, ensuring they have the same clinical effect—like killing the same percentage of cells. Ideally, BED helps determine the best fractionation and dose for a given clinical outcome. However, BED is typically used in single-phase treatment plans, where the treatment configuration and dose per fraction remain constant.

Modern radiation therapy often involves multiple sequential phases, such as a boost phase, with different doses per fraction or varying numbers of fractions compared to the primary phase. Calculating BED in these multiphase treatments introduces complexities, and this article explores the accuracy of an approximate BED calculation method in such scenarios.

Unpacking the Science: How Accurate Are Multiphase BED Calculations?

Radiation Therapy Treatment Plan Illustration

A recent study published in Medical Dosimetry (2017) delves into the accuracy of an approximate biological effective dose (BEDA) equation in multiphase treatment plans. This equation was introduced because many treatment planning systems (TPS) cannot calculate the true BED (BEDT). The research investigates how closely BEDA matches BEDT in real-world clinical cases involving patients with head and neck cancer and prostate cancer.

Researchers analyzed treatment plans from twenty patients—ten with head and neck cancer and ten with prostate cancer—using Pinnacle³ 9.2 TPS. They focused on organs at risk (OARs) such as the normal brain, optic nerves, spinal cord, brainstem, bladder, and rectum. BEDA and BEDT distributions were calculated using MATLAB 2010b, and the data were analyzed voxel by voxel to determine percent error, correlation coefficients, and other statistical measures.

The Underestimation Factor: BEDA consistently underestimated BEDT.
Organ-Specific Accuracy: The accuracy of BEDA varied across different organs. For example, in the optic chiasm and brainstem, 50% of patients had an overall BEDA percent error of less than 1%.
Error Range: Maximum errors in BEDA distributions ranged from 2% to 11%, with the highest error observed in the bladder.
Maximum BED Values: BEDA produced more accurate maximum BED values in adjacent organs like the normal brain, bladder, and rectum.

The study highlights that while BEDA can calculate BED distributions with acceptable accuracy under specific conditions, its consistency and accuracy depend heavily on the dose distributions across different treatment phases. Therefore, caution is advised when using BEDA in multiphase treatment planning.

The Future of Precision in Radiation Therapy

This research underscores the need for enhanced precision in radiation therapy planning, particularly in multiphase treatments. While BEDA offers a practical approach, its limitations call for more sophisticated methods that accurately reflect the true biological effective dose. By improving the precision of BED calculations, clinicians can optimize treatment plans, minimize risks to organs at risk, and ultimately improve patient outcomes. Further studies are essential to reduce uncertainties in BED calculations and develop more reliable models for clinical application.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

What is the primary purpose of the biological effective dose (BED) in radiation therapy?

The biological effective dose (BED) is used to relate treatment outcomes more closely to the actual radiation delivered, offering a way to compare different fractionation schemes, such as single-phase and multiphase treatments. Its primary function is to help determine the best fractionation and dose for a given clinical outcome, ensuring that different treatment plans have the same clinical effect on the targeted cancer cells. The BED is based on the linear-quadratic (LQ) model, which is an extrapolation method used to understand the effects of radiation on cells.

Why isn't the biological effective dose (BED) universally adopted in radiation therapy, and what challenges does it present?

The biological effective dose (BED) hasn't been universally adopted due to uncertainties in its calculation and application. The article specifically highlights complexities arising in multiphase treatments, where the treatment configuration and dose per fraction vary. Calculating BED in these scenarios can be challenging. An additional challenge is that BED is typically used in single-phase treatment plans. This presents a problem, as modern radiation therapy frequently involves multiple sequential phases. The study investigates the accuracy of an approximate BED calculation method (BEDA) in these complex scenarios.

What are the key findings of the Medical Dosimetry (2017) study regarding the accuracy of the approximate biological effective dose (BEDA) in multiphase treatment plans?

The *Medical Dosimetry* (2017) study revealed several key findings. Firstly, BEDA consistently underestimated the true biological effective dose (BEDT). Secondly, the accuracy of BEDA varied across different organs at risk (OARs). For instance, in the optic chiasm and brainstem, the BEDA percent error was less than 1% for 50% of patients. The maximum errors in BEDA distributions ranged from 2% to 11%, with the highest error observed in the bladder. Furthermore, BEDA produced more accurate maximum BED values in adjacent organs like the normal brain, bladder, and rectum.

What are the implications of using approximate biological effective dose (BEDA) in radiation therapy planning, and what precautions should clinicians take?

While the approximate biological effective dose (BEDA) can calculate BED distributions with acceptable accuracy under specific conditions, its consistency and accuracy are highly dependent on the dose distributions across different treatment phases. The research emphasizes that clinicians should exercise caution when using BEDA in multiphase treatment planning. The underestimation of BEDT by BEDA and the varying accuracy across different organs highlight the potential for inaccuracies. Clinicians must be aware of these limitations to ensure accurate treatment planning and minimize risks to organs at risk.

How can the precision of radiation therapy planning be improved, and what role does future research play in enhancing the accuracy of biological effective dose (BED) calculations?

Improving the precision of radiation therapy planning requires more sophisticated methods that accurately reflect the true biological effective dose (BED). This involves developing and utilizing models that minimize the uncertainties in BED calculations. Future research is essential to reduce these uncertainties and create more reliable models for clinical application. Such advancements will enable clinicians to optimize treatment plans, reduce risks to organs at risk, and ultimately improve patient outcomes. Continuous studies are vital to refine the accuracy of BED calculations and enhance the effectiveness of radiation therapy.