Abstract
BackgroundOn account of extremity wide range of movements and difficulty of reproducibility during irradiation of extremity sarcomas, assorted immobilization strategies are employed to eliminate setup errors. The study purpose was to compare the setup errors of the commonly used immobilization tools and to define planning target volume (PTV) margins for each device.MethodsA retrospective review comparing Vac-Loc™ and thermoplastic cast (Tcast) was conducted. On radiotherapy treatment, portal imaging was matched with the pre-treatment simulation imaging for both fixation tools. The isocenter shifts and total vector error (TVE) were compared. Random (σ) and systemic errors (Σ) were computed and PTV margins were defined.ResultsThree hundred seven shifts in each direction measured in 14 patients. Mean displacements for the Vac-Loc™ and Tcast, respectively, were as follow: vertical; -0.01 cm vs. 0.02 cm, longitudinal; 0.03 cm vs. 0.04; lateral; 0.04 cm vs. 0.00 cm and TVE; 0.15 cm vs. 0.17 cm with no significant statistical difference. Random and systemic errors were comparable for both devices. The lateral displacement and rotational random errors were higher Vac-Loc™ compared to Tcast. Overall measured PTV margins were marginally lower for Tcast compared to Vac-Loc™.ConclusionVac-Loc™ and Tcast are valid options for immobilization with no clear superiority of either device. The marginal advantage of Tcast warrants further prospective studies.
Highlights
On account of extremity wide range of movements and difficulty of reproducibility during irradiation of extremity sarcomas, assorted immobilization strategies are employed to eliminate setup errors
Mohamed et al J Egypt Natl Canc Inst (2021) 33:27 (CTV); most of the centers agree upon 0.5– 1.5 cm clinical target volume to planning target volume (CTV-PTV) margins [7, 8], which mainly depends on the fixation methods and availability of image guided radiation therapy (IGRT)
We aimed to compare the differences between the two methods in terms of the setup errors and appropriate Clinical target volumes (CTV)-PTV margins required for each method
Summary
On account of extremity wide range of movements and difficulty of reproducibility during irradiation of extremity sarcomas, assorted immobilization strategies are employed to eliminate setup errors. The study purpose was to compare the setup errors of the commonly used immobilization tools and to define planning target volume (PTV) margins for each device. Methods: A retrospective review comparing Vac-LocTM and thermoplastic cast (Tcast) was conducted. The lateral displacement and rotational random errors were higher Vac-LocTM compared to Tcast. Overall measured PTV margins were marginally lower for Tcast compared to Vac-LocTM. There is no standard tool established for extremities immobilization; the most common techniques used include; the negative pressure vacuum air cushions (Vac-LocTM), alpha cradles and thermoplastic casts. The high probability of limbs rotations and diversity of joint movements warrants the use of proper fixation methods in addition to IGRT to achieve least CTV-PTV margins
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