AAPM WGTG51 Report 385: Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy electron beams.

An Addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water is presented for electron beams with energies between 4 MeV and 22 MeV ( ). This updated formalism allows simplified calibration procedures, including the use of calibrated cylindrical ionization chambers in all electron beams without the use of a gradient correction. New data are provided for electron beams based on Monte Carlo simulations.

Divergent Clinical Equivalence Findings from DVH and NTCP Metrics for Alternative OAR Delineations with Increasing Setup Variability in Head-and-Neck Radiotherapy.

Purpose: This study quantifies the variation in dose-volume histogram (DVH) and normal tissue complication probability (NTCP) metrics for head-and-neck (HN) cancer patients when alternative organ-at-risk (OAR) delineations are used for treatment planning and for treatment plan evaluation. We particularly focus on the effects of daily patient positioning/setup variations (SV) in relation to treatment technique and delineation variability.

Materials And Methods: We generated two-arc VMAT, 5-beam IMRT, and 9-beam IMRT treatment plans for a cohort of 209 HN patients.

OpenKBP-Opt: an international and reproducible evaluation of 76 knowledge-based planning pipelines.

To establish an open framework for developing plan optimization models for knowledge-based planning (KBP).Our framework includes radiotherapy treatment data (i.e.

AAPM WGTG51 Report 374: Guidance for TG-51 reference dosimetry.

Practical guidelines that are not explicit in the TG-51 protocol and its Addendum for photon beam dosimetry are presented for the implementation of the TG-51 protocol for reference dosimetry of external high-energy photon and electron beams. These guidelines pertain to: (i) measurement of depth-ionization curves required to obtain beam quality specifiers for the selection of beam quality conversion factors, (ii) considerations for the dosimetry system and specifications of a reference-class ionization chamber, (iii) commissioning a dosimetry system and frequency of measurements, (iv) positioning/aligning the water tank and ionization chamber for depth ionization and reference dose measurements, (v) requirements for ancillary equipment needed to measure charge (triaxial cables and electrometers) and to correct for environmental conditions, and (vi) translation from dose at the reference depth to that at the depth required by the treatment planning system. Procedures are identified to achieve the most accurate results (errors up to 8% have been observed) and, where applicable, a commonly used simplified procedure is described and the impact on reference dosimetry measurements is discussed so that the medical physicist can be informed on where to allocate resources.

Knowledge-based quality control of organ delineations in radiation therapy.

Purpose: To reduce the likelihood of errors in organ delineations used for radiotherapy treatment planning, a knowledge-based quality control (KBQC) system, which discriminates between valid and anomalous delineations is developed.

Method And Materials: The KBQC is comprised of a group-wise inference system and anomaly detection modules trained using historical priors from 296 locally advanced lung and prostate cancer patient computational tomographies (CTs). The inference system discriminates different organs based on shape, relational, and intensity features.

A regression-based approach to compute the pixels sensitivity map of linear accelerator portal imaging devices.

Purpose: To determine the pixel sensitivity map (PSM) for amorphous silicon electronic portal imaging devices (EPIDs) using a single flood field signal.

Method And Materials: A raw EPID signal results from the incident particle energy fluence, the inherent pixels response, and the background signal. In large open fields, particle energy fluence is a slow-varying signal that is locally considered spatially constant.

An error detection method for real-time EPID-based treatment delivery quality assurance.

Purpose: To quantify the error detection power of a new treatment delivery error detection method. The method validates monitor unit (MU) resolved beam apertures using real-time EPID images.

Methods: The on-board EPID imager was used to measure cine-EPID (~10 Hz) images for 27 beams from 15 VMAT/SBRT clinical treatment plans and five nonclinical plans.

An Automated Workflow to Improve Efficiency in Radiation Therapy Treatment Planning by Prioritizing Organs at Risk.

Purpose: Manual delineation (MD) of organs at risk (OAR) is time and labor intensive. Auto-delineation (AD) can reduce the need for MD, but because current algorithms are imperfect, manual review and modification is still typically used. Recognizing that many OARs are sufficiently far from important dose levels that they do not pose a realistic risk, we hypothesize that some OARs can be excluded from MD and manual review with no clinical effect.

Impact of patients' refusal to undergo adjuvant treatment measures on survival.

Purpose: Breast cancer patients receive treatment recommendations from multidisciplinary tumour boards. To determine the consequences of patients' refusal of such recommendations, we analysed the database of the Centre for Breast Cancer at the Ortenau Clinic in Offenburg, Germany.

Methods: A total of 4315 patients with non-metastatic primary breast cancer, treated between 1997 and 2019, were analysed with descriptive analyses, Kaplan-Meier survival analyses, and Cox regression analyses regarding the effects of their refusal.

Multiobjective, Multidelivery Optimization for Radiation Therapy Treatment Planning.

Purpose: To introduce multiobjective, multidelivery optimization (MODO), which generates alternative patient-specific plans emphasizing dosimetric trade-offs and conformance to quasi-constrained (QC) conditions for multiple delivery techniques.

Methods And Materials: For delivery techniques and organs at risk (OARs), MODO generates ( + 1) alternative treatment plans per patient. For 30 locally advanced lung cancer cases, the algorithm was investigated based on dosimetric trade-offs to 4 OARs: each lung, heart, and esophagus (N = 4) and 4 delivery techniques (4-field coplanar intensity modulated radiation therapy [IMRT], 9-field coplanar IMRT, 27-field noncoplanar IMRT, and noncoplanar arc IMRT) and conformance to QC conditions, including dose to 95% (D95) of the planning target volume (PTV), maximum dose (Dmax) to PTV (PTV-Dmax), and spinal cord Dmax.

Dose escalation in the definite target volume.

Purpose: To introduce the definite target volume (DTV) and evaluate dosimetric consequences of boosting dose to this region of high clinical target volume (CTV)- and low organs at risk (OAR)-probability.

Methods: This work defines the DTV via occupancy probability and via contraction of the CTV by margin M less any planning risk volume (PRV) volumes. The equivalence to within varying occupancy probability of the two methods is established for spherical target volumes.

Beam modeling and beam model commissioning for Monte Carlo dose calculation-based radiation therapy treatment planning: Report of AAPM Task Group 157.

Dose calculation plays an important role in the accuracy of radiotherapy treatment planning and beam delivery. The Monte Carlo (MC) method is capable of achieving the highest accuracy in radiotherapy dose calculation and has been implemented in many commercial systems for radiotherapy treatment planning. The objective of this task group was to assist clinical physicists with the potentially complex task of acceptance testing and commissioning MC-based treatment planning systems (TPS) for photon and electron beam dose calculations.

Influence of patient and tumor characteristics on therapy persistence with letrozole in postmenopausal women with advanced breast cancer: results of the prospective observational EvAluate-TM study.

Background: Treatment of postmenopausal, hormone receptor-positive metastatic breast cancer (MBC) patients varies despite clear therapy guidelines, favoring endocrine treatment (ET). Aim of this study was to analyze persistence of palliative aromatase inhibitor (AI) monotherapy in MBC patients.

Methods: EvAluate-TM is a prospective, multicenter, noninterventional study to evaluate treatment with letrozole in postmenopausal women with hormone receptor-positive breast cancer.

Quantifying the dosimetric impact of organ-at-risk delineation variability in head and neck radiation therapy in the context of patient setup uncertainty.

The purpose of this study was to quantify the potential dosimetric impact of delineation variability (DV) in head and neck radiation therapy (RT) when inherent patient setup variability (SV) is also considered. The impact of DV was assessed by generating plans with multiple structure sets, cross-evaluating them, including SV, across sets, and determining P : the probability of achieving organ-specific plan quality metrics (PQM). DV was incorporated by: (1) using multiple organ at risk (OAR) structure sets delineated by independent manual observers; and (2) randomly perturbing manually generated OARs to generate alternatives with varying levels of uncertainty (low, medium, and high DV).

Robust radiotherapy planning.

Motion and uncertainty in radiotherapy is traditionally handled via margins. The clinical target volume (CTV) is expanded to a larger planning target volume (PTV), which is irradiated to the prescribed dose. However, the PTV concept has several limitations, especially in proton therapy.

Influence of side-effects on early therapy persistence with letrozole in post-menopausal patients with early breast cancer: Results of the prospective EvAluate-TM study.

Background: Endocrine treatment (ET) with an aromatase inhibitor (AI) is the treatment of choice in post-menopausal patients with hormone receptor-positive early breast cancer (EBC). However, adverse events (AEs) often lead to treatment discontinuation. This analysis aimed to identify side-effects that lead to patients failing to persist with letrozole treatment.

Quality assurance tool for organ at risk delineation in radiation therapy using a parametric statistical approach.

Purpose: To develop a quality assurance (QA) tool that identifies inaccurate organ at risk (OAR) delineations.

Methods: The QA tool computed volumetric features from prior OAR delineation data from 73 thoracic patients to construct a reference database. All volumetric features of the OAR delineation are computed in three-dimensional space.

Influence of patient and tumor characteristics on early therapy persistence with letrozole in postmenopausal women with early breast cancer: results of the prospective Evaluate-TM study with 3941 patients.

Background: Patients' compliance and persistence with endocrine treatment has a significant effect on the prognosis in early breast cancer (EBC). The purpose of this analysis was to identify possible reasons for non-persistence, defined as premature cessation of therapy, on the basis of patient and tumor characteristics in individuals receiving adjuvant treatment with letrozole.

Patients And Methods: The EvAluate-TM study is a prospective, multicenter, noninterventional study in which treatment with the aromatase inhibitor letrozole was evaluated in postmenopausal women with hormone receptor-positive EBC in the early therapy phase.

Dose to mass for evaluation and optimization of lung cancer radiation therapy.

Purpose: To evaluate potential organ at risk dose-sparing by using dose-mass-histogram (DMH) objective functions compared with dose-volume-histogram (DVH) objective functions.

Methods: Treatment plans were retrospectively optimized for 10 locally advanced non-small cell lung cancer patients based on DVH and DMH objectives. DMH-objectives were the same as DVH objectives, but with mass replacing volume.

Beyond the margin recipe: the probability of correct target dosage and tumor control in the presence of a dose limiting structure.

In the past, hypothetical spherical target volumes and ideally conformal dose distributions were analyzed to establish the safety of planning target volume (PTV) margins. In this work we extended these models to estimate how alternative methods of shaping dose distributions could lead to clinical improvements. Based on a spherical clinical target volume (CTV) and Gaussian distributions of systematic and random geometrical uncertainties, idealized 3D dose distributions were optimized to exhibit specific stochastic properties.

Quantitative ionization chamber alignment to a water surface: Performance of multiple chambers.

Purpose: The purpose of this study was to experimentally examine the reliability of the gradient chamber alignment point (gCAP) determination method for accurately identifying water surface location with a range of ionization chambers (ICs).

Materials And Methods: Twelve cylindrical ICs were scanned from depth through a water surface into air using a customized high-accuracy scanning system which allows for accurate alignment of the IC with respect to the true water surface. Thirteen other cylindrical ICs and five parallel-plate ICs were scanned using a standard commercially available scanning system.

Quantitative ionization chamber alignment to a water surface: Theory and simulation.

Purpose: To examine the response properties of cylindrical cavity ionization chambers (ICs) in the depth-ionization buildup region so as to obtain a robust chamber-signal - based method for definitive water surface identification, hence absolute ionization chamber depth localization.

Method & Materials: An analytical model with simplistic physics and geometry is developed to explore the theoretical aspects of ionization chamber response near a phantom water surface. Monte Carlo simulations with full physics and ionization chamber geometry are utilized to extend the model's findings to realistic ion chambers in realistic beams and to study the effects of IC design parameters on the entrance dose response.

Insight gained from responses to surveys on reference dosimetry practices.

Purpose: To present the results and discuss potential insights gained through surveys on reference dosimetry practices.

Methods: Two surveys were sent to medical physicists to learn about the current state of reference dosimetry practices at radiation oncology clinics worldwide. A short survey designed to maximize response rate was made publicly available and distributed via the AAPM website and a medical physics list server.

Clinical adequacy assessment of autocontours for prostate IMRT with meaningful endpoints.

Purpose: To determine if radiation treatment plans created based on autosegmented (AS) regions-of-interest (ROI)s are clinically equivalent to plans created based on manually segmented ROIs, where equivalence is evaluated using probabilistic dosimetric metrics and probabilistic biological endpoints for prostate IMRT.

Method And Materials: Manually drawn contours and autosegmented ROIs were created for 167 CT image sets acquired from 19 prostate patients. Autosegmentation was performed utilizing Pinnacle's Smart Probabilistic Image Contouring Engine.