P.G.M. Van Kollenburg

EP-1630: Automated iterative plan optimisation widens therapeutic window for prostate cancer arc therapy

ESTRO 35 2016 _____________________________________________________________________________________________________ EP-1630 Automated iterative plan optimisation widens therapeutic window for prostate cancer arc therapy E.J.L. Brunenberg, J.M.A.M. Kusters, P.G.M. Van Kollenburg, C.M. Verhagen, P.M.W. Van Herpen, M. Wendling Radboud UMC, Radiation Oncology, Nijmegen, The Netherlands , R.J. Smeenk, P.M. Poortmans

SU‐E‐T‐590: Automate IMRT Planning in Pinnacle: A Study in Head‐And‐Neck Cancer

PURPOSE We investigated whether the auto-planning prototype included in a research version of Pinnacle 9.700 (Philips Healthcare) is able to create treatment plans with consistent quality, independent of the experience of the planner using a single template. METHODS The auto-planning module requires the user to define a template with prioritized optimization goals for PTV-coverage and dose constraints for organ at risks (OARs). Prioritized optimization goals are used by the auto-planning engine to formulate optimization objectives. Multiple optimization loops iteratively reformulate and adjust the optimization objectives to meet the goals and further lower dose to OAR with minimal compromise to the target coverage. Dose conformality and uniformity to the target(s) are also controlled automatically. The quality of ten oropharynx IMRT auto-planned plans was evaluated by calculating the target coverage (V95) and conformity index (CI) of the PTVs (prescribed dose to PTV> was 50.3 Gy and 68 Gy to PTV<), the maximum dose to the cord, and mean dose to parotids and oral cavity. Efficiency was evaluated by measuring the total planning time. RESULTS All auto-planned plans fulfilled the clinical dose criteria for OARs and PTV coverage. The average V95 and CI to PTV> were 99.1% + /- 1.6% and 0.8 + /- 0.1, respectively and to PTV< 96.2% + /- 1.5% and 0.6 +- 0.1, respectively. The average maximum dose to the cord was 44.9 + /- 2.0 Gy, average mean dose to the parotids was 28.4 + /- 4.5 Gy and 33.7 + /- 7.0 Gy to the oral cavity. Total planning time could be reduced from about 4 hours to less than 30 minutes. CONCLUSION The auto-planning module generates plans with consistent quality and reduces total planning time significantly. The tool is designed to automatically perform many of the manual operations in the current IMRT process, any further optimization for an individual patient has to be done outside auto-plan.

SU‐E‐T‐580: Does Arc Therapy Have the Potential to Improve Radiation Treatment of Hodgkin's Lymphoma Patients?

PURPOSE To evaluate whether arc therapy (helical Tomotherapy and volumetric arc therapy; VMAT) is superior to step and shoot IMRT regarding sparing of lungs while maintaining adequate planning target volume (PTV) coverage in Hodgkins lymphoma patients . METHODS Radiation treatment plans for eleven Hodgkins lymphoma patients were created employing the following techniques: coplanar and noncoplanar Step & Shoot IMRT, VMAT and Tomotherapy, i.e., for every patient 4 different treatment plans were created. The IMRT and VMAT planning was performed with Pinnacle software (v. 8 and 9, Philips) suitable for delivery with an Elekta linear accelerator, Tomotherapy plans were calculated with Tomotherapy planning software (v. 3.4). Four patients received a single prescription dose of 30 or 36 Gy, and 7 patients received a simultaneous integrated boost (30 Gy/36 Gy). Treatment plans were optimized such that the normal tissue constraints for the lung [volume receiving more than 20 Gy (V20) is less than 30% and mean lung dose (MLD) is less than 14 Gy] were met, even if PTV coverage (V95%=99%) had to be sacrificed. RESULTS All 4 techniques delivered clinically acceptable treatment plans. Tomotherapy achieved the highest dose homogeneity in the PTV and highest dose coverage of the boost volume (on average 98% versus 96% for the other 3 techniques). Since lung sparing was the first planning objective, all techniques scored equally well for V20 en MLD. CONCLUSIONS The strength of arc therapy lies in the large number of beamlets entering the patient from a high number of angles. For Hodgkins lymphoma patients this does not automatically translate into a superior treatment due to the high weight on the lung objectives limiting the number of beamlets allowed to pass through the lung. This means that for Hodgkins lymphoma arc therapy has no added value for sparing of the lungs.