Accuracy of field alignment in radiotherapy of head and neck cancer utilizing individualized face mask immobilization: a retrospective analysis of clinical practice

doi:10.1016/0167-8140(94)01497-Q

Radiotherapy and Oncology

Volume 34, Issue 1, January 1995, Pages 69-72

https://doi.org/10.1016/0167-8140(94)01497-Q Get rights and content

Abstract

Deviations between simulation and first check films were quantitatively assessed for 95 unselected head and neck cancer patients. All measured deviations — calculated on the basis of a total of 190 simulation and 380 verification films — were normally distributed, with mean values of 0–3 mm and standard deviations of 3–5 mm. Of the absolute deviations, 50% and 95% were within 3 mm and 9 mm, respectively. These results should be considered in clinical practice when prescribing safety margins and adequate cut off doses for sparing critical organs in head and neck cancer.

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Cited by (68)

Novel modified patient immobilisation device with an integrated coil support system for MR-guided online adaptive radiotherapy in the management of brain and head-and-neck tumours
2021, Technical Innovations and Patient Support in Radiation Oncology
Magnetic resonance imaging (MR)-guided online adaptive radiotherapy is a promising technique in the field of radiation oncology providing excellent visualisation of soft-tissues, and allowing for online plan adaptation and tumour tracking. In order to facilitate the accurate dose delivery to the target volume while sparing healthy surrounding normal tissue in the brain or head-and-neck (H&N) region, precise patient immobilisation with good image quality is pertinent. Herein, we present a customised thermoplastic mask holder with an integrated anterior MR receiver coil support system for MR-guided online adaptive radiotherapy in the brain and head-and-neck region. The approved medical product was developed by Innovative Technologie Voelp (IT-V), Innsbruck, Austria. MR image uniformity measurements demonstrated improved image uniformity at the expense of decreased signal-to-noise ratio due to a more defined and larger distance between the anterior receiver coil and the phantom or patient. This integrated coil support system represents a practical solution facilitating stable and reproducible anterior coil placement while maintaining the thermoplastic mask holder functionality, a widely established immobilisation technique.
Evaluation of set-up errors in head and neck radiotherapy using electronic portalimaging
2013, Physica Medica
Citation Excerpt :
The range of the errors we reported is comparable to the analogous results of other studies given in Table 3. In those studies, standard deviations of the systematic and random set-up errors varied between 0.02–3.2 mm and 0.4–2.9 mm respectively, whereas CTV-PTV margin ranged from 3 mm to 9 mm [18,21]. In our institution margin approach is used to improve patient positioning and perform regular position correction.
The aim of this study was to evaluate three-dimensional (3D) set-up errors and propose optimum margins for planning target volume (PTV) coverage in head and neck radiotherapy.
Thirty-five patients were included in the study. The total number of portal images studied was 632. Population systematic (Σ) and random (σ) errors for the patients with head and neck cancer were evaluated based on the portal images in the caudocranial longitudinal (CC) and left-right lateral (LR) direction measured in the anterior-posterior (AP) field, as well as from the images in the caudocranial longitudinal (CC) and dorsoventral lateral (DV) direction measured in the lateral (LAT) field. The values for the clinical-to-planning target volume (CTV-PTV) margins were calculated using ICRU Report 62 recommendations, along with Stroom's and van Herk's formulae.
The standard deviations of systematic set-up errors (Σ) ranged from 1.51 to 1.93 mm while the standard deviations of random set-up (σ) errors fell in between 1.77 and 1.86 mm. The mean 3D vector length of displacement was 2.66 mm. PTV margins calculated according to ICRU, Stroom's and van Herk's models were comprised between 1.95 and 6.16 mm in the three acquisition directions.
Based on our results we can conclude that a 6-mm extension of CTV to PTV margin, as the lower limit, is enough to ensure that 90% of the patients treated for head and neck cancer will receive a minimum cumulative CTV dose greater than or equal to 95% of the prescribed dose.
What are the problems when matching photon and electron beams?
2013, Zeitschrift fur Medizinische Physik
Trotz zunehmender IMRT-Bestrahlungstechniken gibt es im klinischen Alltag der Strahlentherapie immer noch in Einzelfällen die Notwendigkeit zum Anschluss von Photonenfeldern an Photonen- oder Elektronenfelder. Derartige Feldanschlüsse werden in dieser Arbeit untersucht, indem in mehreren Tiefen gemessene Dosisquerverteilungen durch systematische relative Verschiebungen zueinander rechnerisch überlagert werden und die dabei entstehenden Dosisüberhöhungen und Dosiseinbrüche dargestellt werden. Es zeigt sich, dass „optimale“ Feldanschlüsse nur in seltenen Fällen zu erreichen sind. Aber die Ergebnisse können dazu dienen, die Größenordnung der zu erwartenden Dosisänderungen abzuschätzen.
Despite increasing IMRT techniques in the clinical routine of radiotherapy there is still the need of matching photon beams with either photon or electron beams in some particular cases. Such matched beams are investigated in this paper by mathematical adding of measured transverse dose profiles in different depths and shifting them systematically relative to each other. The resulting hot and cold spots are shown. As demonstrated, an “optimal” field matching is only rarely achieved. However, the results can help to estimate the order of magnitude of the expected dose variation.
Achieving the Relocation Accuracy of Stereotactic Frame-based Cranial Radiotherapy in a Three-point Thermoplastic Shell
2013, Clinical Oncology
To compare the accuracy of fractionated cranial radiotherapy in a standard three-point thermoplastic shell using daily online correction with accuracy in a Gill–Thomas–Cosman relocatable stereotactic frame.
All patients undergoing fractionated radiotherapy for benign intracranial tumours between March 2009 and August 2010 were included. Patients were immobilised in the frame with those unable to tolerate it immobilised in the shell. The ExacTrac imaging system was used for verification/correction. Daily online imaging before and after correction was carried out for shell patients and systematic and random population set-up errors calculated. These were compared with frame patients who underwent standard departmental imaging/correction with fractions 1–3 and weekly thereafter. Set-up margins were calculated from population errors.
Systematic and random errors were 0.3–0.7 mm/° before correction and 0.1–0.2 mm/° after correction in all axes in the frame, and 0.6–1.5 mm/° before correction and 0.1–0.4 mm/° after correction in the shell. Isotropic margins required for patient set-up could be reduced from 2 mm to <1 mm in the frame and from 5 mm to <1 mm in the shell.
Similar set-up accuracy can be achieved in the standard thermoplastic shell as in a relocatable frame despite less precise immobilisation. The use of daily online correction precludes the need for larger set-up margins.
Evaluation of the radiobiological impact of anatomic modifications during radiation therapy for head and neck cancer: Can we simply summate the dose?
2010, Radiotherapy and Oncology
Adaptive strategies in radiotherapy (RT) require the knowledge of the total dose given to every organ of the body. Because of anatomical changes and setup errors non-rigid registration is necessary to map the different dose fractions to a common reference. This study evaluates practically if the accumulation of all of these registered dose fractions must take radiobiology into account in a classical clinical setting.
Ten patients with head and neck tumors treated by chemo-RT were used. Contrast-enhanced CT scans were acquired prior and during RT following delivery of mean doses of 14.2, 24.5, 35.0 and 44.9 Gy and the planned pre-treatment helical tomotherapy sinograms were applied on the per-treatment CTs to create a series of per-treatment dose distributions corresponding to each per-treatment CT image. In order to calculate the cumulative dose distribution, the per-treatment dose maps were non-rigidly deformed by using the deformation map computed by a non-rigid registration. The deformed dose maps were then summed in two ways: one while taking radiobiology into account and one without. These two strategies were compared using clinical surrogates in the target volumes (TV) and in surrounding organs at risk (OAR).
The differences between the strategies, while statistically significant (p < 0.05), are clinically irrelevant. In the OARs, the mean differences stay in the 0.01–0.07 Gy range for the total dose. In the targets, all mean differences stay in the 0.001–0.012 Gy range. However, some local high difference spots appear leading to punctual errors as high as 2.5 Gy.
If using current radiotherapy practices and clinical recommendations based on dose surrogates computed globally on OARs and TVs, one does not need to take radiobiological effects into account while accumulating total dose as these lead to very small differences compared to a simple accumulation technique consisting of a linear sum of the dose fractions. However, care must be taken if other adaptive strategies, based on local rather than global information, are used.
The clinical feasibility and effect of online cone beam computer tomography-guided intensity-modulated radiotherapy for nasopharyngeal cancer
2009, Radiotherapy and Oncology
Online adaptive correction in image-guided intensity-modulated radiotherapy appeared to be a promising approach for precision radiation treatment in head and neck tumors. This protocol was designed to evaluate the clinical feasibility and effect of online cone beam computed tomography (CBCT) guidance in IMRT of nasopharyngeal cancer (NPC).
The Elekta Synergy system, which integrates an X-ray volumetric imager (XVI), was used to deliver radiation treatment for 22 cases of NPC. The acquired CBCT was registered to the planning CT for online and offline analysis. The systematic and random setup errors, as well as planning target volume (PTV) margin, were calculated at different correction threshold levels. The impact of online setup correction on dosimetry was evaluated by simulation of pre-correction errors.
The correction-of-setup-errors frequencies for 1, 2 and 3 mm thresholds were 41.3–53.9%, 12.7–21.2% and 6.3–10.3%, respectively. Online correction was effective at the 2 mm threshold level for all three axes. The pre-correction systematic errors for the whole group ranged 1.1–1.3 mm, and the random errors were also 1.1–1.3 mm. After online correction, the systematic and random errors ranged 0.4–0.5 mm and 0.7–0.8 mm, respectively, in the three directions. The PTV margins for the pre-correction, pretreatment and post-treatment positions were 3.5–4.2 mm, 1.6–1.8 mm and 2.5–3.2 mm, respectively, in three directions. Analysis of hypothetical dosimetric change due to a translational isocenter shift of 3 mm showed that if no correction was applied, the mean maximum dose to both the brain stem and spinal cord would be increased by 10 Gy, the mean dose to the left and right parotids would be increased by 7.8 and 8.5 Gy, respectively, and the dose to target volumes would be decreased: 4 Gy for 95% GTV and 5.6 Gy for 95% CTV_60.
CBCT-based online correction increased the accuracy of IMRT for NPC and reduced irradiated margins, by decreasing both the systematic and random errors. Online CBCT correction reduces the radiation dose to normal tissue and creates room for further dose escalation of tumors.

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Technical noteAccuracy of field alignment in radiotherapy of head and neck cancer utilizing individualized face mask immobilization: a retrospective analysis of clinical practice

Abstract

Int. J. Radiat. Oncol. Phys.

Int. J. Radiat. Oncol. Phys.

Int. J. Radiat. Oncol. Phys.

Radiother. Oncol.

Int. J. Radiat. Oncol. Phys.

Radiother. Oncol.

Int. J. Radiat. Oncol. Phys.

Radiother. Oncol.

Int. J. Radiat. Oncol., Biol. Phys.

Int. J. Radiat. Oncol., Biol. Phys.

Technical note
Accuracy of field alignment in radiotherapy of head and neck cancer utilizing individualized face mask immobilization: a retrospective analysis of clinical practice