Abstract
PurposeFirst, this experimental study aims at comparing out‐of‐field doses delivered by three radiotherapy techniques (3DCRT, VMAT (two different accelerators), and tomotherapy) for a pediatric renal treatment. Secondly, the accuracy of treatment planning systems (TPS) for out‐of‐field calculation is evaluated.MethodsEBT3 films were positioned in pediatric phantoms (5 and 10 yr old). They were irradiated according to four plans: 3DCRT (Clinac 2100CS, Varian), VMAT (Clinac 2100CS and Halcyon, Varian), and tomotherapy for a same target volume. 3D dose determination was performed with an in‐house Matlab tool using linear interpolation of film measurements. 1D and 3D comparisons were made between techniques. Finally, measurements were compared to the Eclipse (Varian) and Tomotherapy (Accuray) TPS calculations.ResultsAdvanced radiotherapy techniques (VMATs and tomotherapy) deliver higher out‐of‐field doses compared to 3DCRT due to increased beam‐on time triggered by intensity modulation. Differences increase with distance to target and reach a factor of 3 between VMAT and 3DCRT. Besides, tomotherapy delivers lower doses than VMAT: although tomotherapy beam‐on time is higher than in VMAT, the additional shielding of the Hi‐Art system reduces out‐of‐field doses. The latest generation Halcyon system proves to deliver lower peripheral doses than conventional accelerators. Regarding TPS calculation, tomotherapy proves to be suitable for out‐of‐field dose determination up to 30 cm from field edge whereas Eclipse (AAA and AXB) largely underestimates those doses.ConclusionThis study shows that the high dose conformation allowed by advanced radiotherapy is done at the cost of higher peripheral doses. In the context of treatment‐related risk estimation, the consequence of this increase might be significative. Modern systems require adapted head shielding and a particular attention has to be taken regarding on‐board imaging dose. Finally, TPS advanced dose calculation algorithms do not certify dose accuracy beyond field edges, and thus, those doses are not suitable for risk assessment.
Highlights
Early diagnosis and improvements in treatment techniques and therapeutic strategies have led to an increasing success of cancer treatments.[1]
Away from planning treatment volumes (PTV), that is, beyond approximatively 2.5 cm from field edge, the delivered doses decrease with distance and the discrepancies between techniques increase. 3DCRT better spares normal tissues in comparison with modern radiotherapy techniques and the highest doses were obtained with volumetric arc therapy (VMAT)
Out‐of‐field doses delivered by four radiotherapy techniques have been evaluated by means of film measurements in pediatric anthropomorphic phantoms
Summary
Early diagnosis and improvements in treatment techniques and therapeutic strategies have led to an increasing success of cancer treatments.[1]. Among the different techniques involved, radiation therapy is nowadays used in more than 50% of cancer treatments[2,3] and its efficacy has been largely acknowledged. The most advanced techniques enable conformal dose distribution to the tumor volume reducing adjacent organs doses. This precision in dose delivery is carried out thanks to multiple beam incidences, beams’ intensity modulation, and a precise patient positioning using on‐board imaging systems. Modern radiotherapy inevitably increases the volume of normal tissue exposed to ionizing radiation from treatment beams themselves, from out‐of‐field radiation,[4] and from daily imaging.[5]
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