ESTRO 37 Abstract book

S1078

ESTRO 37

should only be used as a supplement to T2W for contouring target volumes and the plan should always be done on the T2W imaging as recommended by GEC ESTRO EP-1978 Lung SABR: New optimisation techniques S. Currie 1 , G. Currie 1 , P. Houston 1 1 NHS greater glasgow and clyde, RT Physics, glasgow, United Kingdom Purpose or Objective To investigate whether utilising Eclipse TPS v15.5 [Varian Medical Systems, Palo Alto, CA, USA] multi-criteria optimisation (MCO) can produce improved treatment plans, in terms of reduction in dose to organs at risk and/or improved planning target volume coverage, for VMAT radiotherapy treatment of Lung SABR when compared with a plan generated using RapidPlan TM alone. Material and Methods A retrospective planning study was performed for ten lung SABR patients. Each patient treatment was planned as standard using RapidPlan TM . The plans were then re- optimised within the Eclipse Treatment Planning v15.5 MCO tool (E-MCO). Both plans were normalised to ensure that 95% of the target received 100% of the prescribed dose and the resulting plans were then compared. Differences in dose volume histogram parameters were calculated to assess plan quality. Significance was assessed by two-tailed t-test (p<0.01). Results The E-MCO generated plans exhibited significant organ at risk (OAR) reductions for the dose at 2cm from PTV (mean: 12.9%; range: 9.6% - 24.0%), the maximum spinal cord dose (mean: 3.2 Gy; range: 0.3 Gy – 6.7 Gy), the dose to 1cc of oesophagus (mean: 1.2 Gy; range: 0.3 Gy – 3.2 Gy) and percentage of lung minus GTV to receive 20Gy (mean: 12.8%; range: 0.0% - 25.0%). There was no significant difference observed for the remaining organs at risk. As the plans were normalised to achieve the same target coverage, there was no significant difference in PTV coverage. The plans generated by both RapidPlan TM and RapidPlan TM with E-MCO were all clinically acceptable and met local OAR and PTV dosimetric objectives. Conclusion Using E-MCO to re-optimise RapidPlan TM generated plans was shown to decrease significantly the dose to organs at risk without adverse affect on tumour coverage. E-MCO demonstrated the ability to further enhance plans that were already of a high standard. EP-1979 Automated non-inferiority validation of knowledge-based planning across multiple disease sites R. Kaderka 1 , R. Mundt 1 , N. Li 1 , B. Ziemer 1 , T. Atwood 1 , M. Cornell 1 , K. Moore 1 1 University of California San Diego, Radiation Medicine and Applied Sciences, San Diego, USA Purpose or Objective Knowledge-based planning (KBP) studies seek to demonstrate potential quality and efficiency gains, yet broad clinical implementation of KBP necessitates significant up-front effort even within a single disease. In this study, patient plans treated just before multi-site implementation of KBP were batch re-planned using an automated workflow to (a) assess the non-inferiority of KBP and (b) estimate potential clinical gains post- implementation. Material and Methods We identified 51 prostate, 24 prostatic fossa, 54 hypo- fractionated lung (27 left, 27 right) and 30 head-and-neck patients treated in the year directly preceding broad clinical adoption of KBP at our clinic. Within these disease sites, we presently have clinical KBP models developed in Varian RapidPlan (Varian Medical Systems, Palo Alto, CA, USA). Using the v15.1 Eclipse Scripting API

(ESAPI), we developed a program that automatically batch processes multiple patients and generates KBP plans, taking as input a list of patients to be re-planned, then performs semi-automated structure matching and fully-automated treatment planning. For equivalence, all plans were normalized to PTV D95%=100%. Dose metric differences were computed for standard parameters across the disease sites; two-tailed paired t-test quantified statistical significance (p<0.01). Results An excerpt of the results is shown in Table 1 (dose metrics relative to PTV prescription). Statistically significant OAR improvements were observed in all disease sites: rectum and bladder in prostate/prostatic fossa; total and ipsilateral lung in left lung; larynx, cochlea, pharynx, and cricopharyngeus in head-and-neck (Fig. 1). The prostatic fossa ∆D1%=1.2% was deemed acceptable given OAR sparing gains. The PTV ∆D1% and ITV ∆D99% increase for hypo-fractionated lung was by design (at physician request) due to ITV dose variance in the pre-KBP lung sample.

Right Lung (48 Gy) PTV ∆D1% 18.7% (p<0.01) ITV ∆D99% 6.9% (p<0.01) Total Lung ∆V50% 0.0% (p=0.45) Right Lung ∆V50% 0.1% (p=0.41) Right Lung ∆Dmean 0.1% (p=0.65)

Prostatic fossa (70.2 Gy) PTV ∆D1% 1.2% (p<0.01)

Left Lung (48 Gy) PTV ∆D1% 14.0% (p<0.01) ITV ∆D99% 5.0% (p<0.01) Total Lung ∆V50% -0.1% (p<0.01) Left Lung ∆V50% -0.2% (p<0.01) Left Lung ∆Dmean -0.1% (p=0.39)

Head and neck (70 Gy)

Prostate (81 Gy)

Structure Dose parameter Percentage difference p-value Structure Dose parameter Percentage difference p-value Structure Dose parameter Percentage difference p-value Structure Dose parameter Percentage difference p-value Structure Dose parameter Percentage difference p-value

PTV

High

PTV ∆D1% 0.3% (p=0.05)

∆D1% 0.1% (p=0.84)

Rectum ∆V40Gy -4.3% (p<0.01)

Rectum ∆V40Gy -3.3% (p<0.01)

Larynx ∆Dmean -10.5% (p<0.01)

Rectum ∆V65Gy -1.1% (p<0.01)

Rectum ∆V65Gy -1.8% (p<0.01)

Pharynx ∆Dmean -3.4% (p<0.01)

Rectum ∆V75Gy -0.8% (p<0.01)

Rectum ∆V70.2Gy -3.3% (p<0.01)

Cochlea ∆Dmean -7.8% (p<0.01)

Bladder ∆V40Gy -2.0% (p<0.01)

Bladder ∆V40Gy -2.9% (p<0.01)

Cricopharyngeus ∆Dmean -24.3% (p<0.01)

Conclusion Multi-patient analysis showed KBP to be non-inferior with expected post-implementation OAR sparing gains in all observed disease sites. EP-1980 Influence of different DVH algorithms on dose constraints evaluation for SBRT M. Zani 1 , M. Esposito 1 , C. Carbonini 1 , S. Clemente 1 , C. Fiandra 1 , M. Fusella 1 , C. Garibaldi 1 , F. Giglioli 1 , C. Marino 1 , E. Moretti 1 , S. Russo 1 , A. Savini 1 , L. Strigari 1 , S. Strolin 1 , C. Talamonti 1 , E. Villaggi 1 , M. Stasi 1 , P. Mancosu 1 1 SBRT Working Group, AIFM- Italian Association of Medical Physics, Italy, Italy