<abstract xmlns="http://www.w3.org/1999/xhtml"><sec id="j_raon-2020-0036_s_006_w2aab3b7c20b1b6b1aab1c16b1Aa"><h3>Background</h3><p>The aim of the study was to (a) compare the accuracy of two different immobilization strategies for patients with head and neck tumors, and (b) compare the set-up errors on treatment units with different portal imaging systems.</p></sec><sec id="j_raon-2020-0036_s_007_w2aab3b7c20b1b6b1aab1c16b2Aa"><h3>Patients and methods</h3><p>Variations in the position of the isocenter (IC) relative to the reference point determined on the computed tomography simulator were measured in a vertical (anterior-posterior), longitudinal (superior-inferior), and lateral (medial-lateral) direction in 120 head and neck cancer patients irradiated with curative intent. Depending on the treatment unit (unit A - 2D/2D image previews; unit B- 2D image previews) and the time of irradiation, patients were divided into 6 groups of 20 patients. In patients irradiated in 2014, standard head supports were used (groups 1 and 2), whereas in those treated in 2015 and 2017 (groups 3–6) individual head supports were employed. The clinical-to-planning target volume safety margin was calculated according to the formula proposed by Van Herk.</p></sec><sec id="j_raon-2020-0036_s_008_w2aab3b7c20b1b6b1aab1c16b3Aa"><h3>Results</h3><p>In total, 2,454 portal images and 3,681 set-up errors were analysed. Implementation of individual head supports in 2015 resulted in a statistically significant reduction in the average inter-fraction displacement in the vertical direction and in decreased number of IC displacements in the vertical and longitudinal direction (applies to both treatment units). The largest reduction of the safety margin was calculated in the longitudinal direction and the safety margins were larger for unit B than for unit A.</p></sec><sec id="j_raon-2020-0036_s_009_w2aab3b7c20b1b6b1aab1c16b4Aa"><h3>Conclusions</h3><p>The use of individual head supports and a more advanced imaging system were found to increase set-up precision.</p></sec></abstract>

BackgroundThe aim of the study was to (a) compare the accuracy of two different immobilization strategies for patients with head and neck tumors, and (b) compare the set-up errors on treatment units with different portal imaging systems.Patients and methodsVariations in the position of the isocenter (IC) relative to the reference point determined on the computed tomography simulator were measured in a vertical (anterior-posterior), longitudinal (superior-inferior), and lateral (medial-lateral) direction in 120 head and neck cancer patients irradiated with curative intent. Depending on the treatment unit (unit A - 2D/2D image previews; unit B- 2D image previews) and the time of irradiation, patients were divided into 6 groups of 20 patients. In patients irradiated in 2014, standard head supports were used (groups 1 and 2), whereas in those treated in 2015 and 2017 (groups 3–6) individual head supports were employed. The clinical-to-planning target volume safety margin was calculated according to the formula proposed by Van Herk.ResultsIn total, 2,454 portal images and 3,681 set-up errors were analysed. Implementation of individual head supports in 2015 resulted in a statistically significant reduction in the average inter-fraction displacement in the vertical direction and in decreased number of IC displacements in the vertical and longitudinal direction (applies to both treatment units). The largest reduction of the safety margin was calculated in the longitudinal direction and the safety margins were larger for unit B than for unit A.ConclusionsThe use of individual head supports and a more advanced imaging system were found to increase set-up precision.

Assessment of set-up errors in the radiotherapy of patients with head and neck cancer: standard vs. individual head support

Radiology and Oncology

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

BackgroundThe aim of the study was to (a) compare the accuracy of two different immobilization strategies for patients with head and neck tumors, and (b)...

	2014 Standard head support			2015 Individual support			2017 Individual support
	VRT	LNG	LAT	VRT	LNG	LAT	VRT	LNG	LAT
UNIT A
Average displacement – M [mm]	- 0.86	0.05	0.05	- 0.47*	- 0.24*	- 0.05	- 0.16*	0.88	0.18
Systematic error – Σ [mm]	0.66	1.04	0.88	0.91	0.79	0.95	0.82	0.59	0.83
Random error – σ [mm]	1.49	1.21	1.37	1.56	1.28	1.38	1.28	1.14	1.2
UNIT B
Average displacement – M [mm]	- 0.60	0.46	- 0.43	- 0.02*	0.51	0.25	- 0.18*	0.46	- 0.02
Systematic error – Σ [mm]	1.09	0.80	0.82	0.92	0.74	0.94	0.93	0.69	0.88
Random error – σ [mm]	1.77	1.83	1.47	1.77	1.22	1.41	1.71	1.56	1.44

	CTV-PTV safety margin [mm]

	VRT	LNG	LAT
UNIT A
2014 – standard head support	2.7	3.4	3.2
2015 – individual head support	3.4	2.9	3.3
2017 – individual head support	2.9	2.3	2.9
UNIT B
2014 – standard head support	4.0	3.3	3.1
2015 – individual head support	3.5	2.7	3.3
2017 – individual head support	3.5	2.8	3.2

	Isocenter movements

	VRT	LNG	LAT	Gross errors
	Regression errors
	Unit A / unit B (direction)	Unit A / unit B (direction)	Unit A / unit B (direction)
2014 – standard head support	11 / 15 (P)	5 / 15 (I)	4 / 5 (L)	2 / 5
2015 – individual head support	12 / 13 (P)	3 / 6 (I)	9 / 8 (R)	0 / 1
2017 – individual head support	5 / 14 (P)	7 / 10 (I)	6 / 7 (L)	0 / 1

Assessment of set-up errors in the radiotherapy of patients with head and neck cancer: standard vs. individual head support

Article Category: Research Article

Publié en ligne: 06 juin 2020

Pages: 364 - 370

Reçu: 17 févr. 2020

Accepté: 03 mai 2020

DOI: https://doi.org/10.2478/raon-2020-0036

© 2020 Sabina Androjna, Valerija Zager Marcius, Primoz Peterlin, Primoz Strojan, published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Figure 2

Inter-fraction displacements recorded on units A and B at different periods

Clinical target volume - planning target volume (CTV-PTV) safety margins for units A and B at different periods (calculated according to van Herk8)

Number of IC displacements and of gross errors at treatment units in relation to time for both units. In the brackets, the most prevalent direction of applied movements is indicated