Limiting treatment plan complexity by applying a novel commercial tool

Abstract

Purpose: A recently introduced commercial tool is tested to assess whether it is able to reduce the complexity of a treatment plan and improve deliverability without compromising overall quality. Methods: Ten prostate and ten oropharynx plans of previously treated patients were reoptimized using the aperture shape controller (ASC) tool recently introduced in Eclipse TPS (Varian Medical Systems, Palo Alto, CA). The performance of ASC was assessed in terms of the overall plan quality using a plan quality metric, the reduction in plan complexity through the analysis of 14 of the most common plan complexity metrics, and the change in plan deliverability through 3D dosimetric measurements. Similarly, plans optimized limiting the total number of delivered monitor units was assessed and compared. The two strategies were also combined to assess their potential combination. Results: The plans optimized by exploiting the ASC generally show a reduced number of total Monitor Units, a more constant gantry rotation and a MLC modulation characterized by larger and less complicated shapes with leaves traveling shorter overall lengths. Conclusions: This first experience suggests that the ASC is an effective tool to reduce the unnecessary complexity of a plan. This turns into an increased plan deliverability with no loss of plan quality. K E Y W O R D S aperture shape controller, complexity metrics, MLC, plan complexity, plan quality metric, treatment planning 1 | INTRODUCTION Volumetric modulated arc therapy (VMAT) is nowadays the standard treatment technique in high-quality radiation therapy delivered with clinical LINACs. The rapid dose fall-off outside target boundaries grants highly conformed dose distributions and near-optimal sparing of surrounding critical structures. Volumetric modulated arc therapy has generally replaced intensity-modulated radiation therapy (IMRT) because of the shorter treatment time obtained through the simultaneous variation of gantry speed, dose rate and MLC position. 1,2 Moreover, VMAT tends to use fewer monitor units (MU) per fraction than IMRT and thus reduces the burden of second malignancies. 3-5

What is plan quality in radiotherapy? The importance of evaluating dose metrics, complexity, and robustness of treatment plans

“…Some TPSs incorporate methods to restrict complexity during optimization, e.g. the aperture shape controller (ASC) tool in the Eclipse TPS [94] and the modulation factor (MF) in the TomoTherapy Hi-Art treatment system [95][96][97], but most TPSs still do not directly incorporate advanced complexity metrics [77]. Thus, unnecessary plan complexity is sometimes a consequence of inverse planning and better tools are needed to handle plan complexity [98].…”

Dosimetric evaluation of simplified knowledge-based plan with an extensive stepping validation approach in volumetric-modulated arc therapy-stereotactic body radiotherapy for lung cancer

“…[ 14 42 ] On the other hand, the reduced MU ensures plan deliverability. [ 43 ] Thus, the increase of MU should be noted carefully when using KBP.…”

Automation and integration of a novel restricted single‐isocenter stereotactic body radiotherapy (a‐RESIST) method for synchronous two lung lesions

“…Collimator angles were offset by 30° to reduce leakage dose in the same plane and were chosen to ensure that the MLCs can travel to the PTV locations. The new aperture shape controller (ACS) feature in the PO MLC algorithm was set to “very high” in order to reduce the total number of monitor units, reduce plan complexity, and improve plan quality as demonstrated by the previous researchers 16,17 . Briefly, m‐RESIST plans were created by fitting the MLCs to PTV1 and then calculating the dynamic conformal arc (DCA) dose for the respective plan.…”

“…Next, standard manual VMAT optimization began for PTV1 and GTV1 coverage. The jaw tracking option was employed to reduce leakage dose to normal lung as described above 16 . Once dose calculation was complete, the plan for PTV1 was used as a base‐dose plan before VMAT optimization in the plan for PTV2.…”

“…The new aperture shape controller (ACS) feature in the PO MLC algorithm was set to "very high" in order to reduce the total number of monitor units, reduce plan complexity, and improve plan quality as demonstrated by the previous researchers. 16,17 Briefly, m-RESIST plans were created by fitting the MLCs to PTV1 and then calculating the dynamic conformal arc (DCA) dose for the respective plan. Next, standard manual VMAT optimization began for PTV1 and GTV1 coverage.…”