Session Item

Prostate cancer is the most common cancer in males in the UK and the CHHiP technique continues to be a standard of care. At GenesisCare a scripted CHHiP protocol (class solution) had been setup for treatment planning using volumetric modulated arc therapy (VMAT). It was noticed that the Script produced acceptable target and organs-at-risk (OARs) doses, however, wider quality aspects as Conformity index (CI) and gradient index (GI), varied most among planners and lacked an objective measure within the TPS.

This project describes a quality improvement model to develop an objective, class solution template for CHHiP specific prostate VMAT plans:
1.    Develop an objective scoring tool to benchmark plan quality, considering multiple plan criteria.
2.    Use the top benchmarked plans to create a new class solution that increases treatment plan quality and decreases variability among planners.

50 randomly selected CHHiP plans were picked to form the quality review set. A further 40 patient plans were then selected, post release of the tools, to validate the model.  All plans were created within Pinnacle (v14.0, Philips Medical Systems) with plan scoring, DVH parameters collected and analysed in MS. Excel.
The macro-enabled spreadsheet calculates a combined overall score, for PTV coverage, dose spillage and for doses to all OARs. For every parameter evaluated, an ideal value and associated weight were defined and compared against the plan values during analysis. Plans score more if a DVH value approaches the ideal score, then scores linearly lower as the value deviates.
Ideal scores for OAR sparing were derived for each new plan, based on the performance of the review set relative to the current overlap of Bladder and Rectum to the PTV. Average DVH parameters are derived from the previously achieved doses of the review set. In this way, a sparing predictor model was based on prior experiences and is updated for the anatomy of any future case.
After scoring the review set, the top 15 performers were then selected to update the Scripted class solution and, along with the scoring tool, released for clinical use. Close monitoring of post release plans ensued, with plan score results recorded in the validation set in comparison to the review set.

Prior release, the median scores for the review set were:
•    overall score 72.2%
•    PTVs score 59.8%
•    OARs score 85.1%.

Post release, the median score for the validation set were:
•    overall score is 78.2%
•    PTVs score 63.4%
•    OARs score 93.0%.

The introduction of the updated class solution and plan score tool showed improved plan quality and decreased plan variability (standard deviation reduced by ≈ 3%).
The scoring tools uses data derived from DVH to objectively quantify the quality of dose distribution decreasing the subjectivity associated with plan evaluation.
The tools proved successful in increasing normal tissue sparing, providing effective quality control of the VMAT plan for Prostate cancer patients.