Dirk Van Gestel, M.D., Ph.D., Institut Jules Bordet, Brussels
The last few years, in radiotherapy there has been a growing focus on speed of treatment delivery (largely driven by economical and commercial interests). This study investigates the influence of treatment time on plan quality for helical tomotherapy (HT), using delivery times with Volumetric Modulated Arc Therapy (VMAT; Rapid Arc [RA]) as reference.
In a previous study, double arc RA (Eclipse) and standard HT plans (TomoHD™) were created for five oropharyngeal cancer patients and reported according to ICRU 83 guidelines. By modifying the beam width from 2.5 to 5.0 cm, elevating the pitch and lowering the modulation factor, “TomoFast” (TF) plans were generated with treatment times equal to RA plans. To quantify the impact of TF’s craniocaudal gradient, similar plans were generated on TomoEdge(TM) (TomoEdgeFast;TEF). The homogeneity index (HI), conformity index (CI), mean dose, Dnear-max (D2) and Dnear-min (D98) of the PTVs were analyzed as well as the mean dose, specific critical doses and volumes of 26 organs at risk (OARs). Data were analyzed using repeated measures ANOVA.
With a mean treatment time of 3.05 min (RA), 2.89 min (TF) and 2.95 min (TEF), PTVtherapeutic coverage was more homogeneous with TF (HI.07;SE.01) and TEF (HI.08;SE.01) compared to RA (HI.10;SE.01), while PTVprophylactic was most homogeneous with RA. Mean doses to parotid glands were comparable for RA, TF, TEF: 25.62, 25.34, 23.09 Gy for contralateral and 32.02, 31.96, 30.01 Gy for ipsilateral glands, respectively. OARs’ mean doses varied between different approaches not favoring a particular technique. TF’s higher dose to OARs at the cranial-caudal edges of the PTVs and its higher integral dose, both due to the extended cranial-caudal gradient, seems to be solved by the new TomoEdge™ software. However, all these faster techniques lose part of standard TomoHD’s OAR sparing capacity.
It is possible to treat oropharyngeal cancer patients using HT (TF/TEF) within time-frames observed for RA maintaining comparable target coverage and sparing of OARs. This study indicates that treatment time is not technology specific, rather an operator’s decision on balancing efficiency and quality.
RADIAT ONCOL. 2015, 10:261.