A Practical Method of Adaptive Radiotherapy for Prostate Cancer using Real-time Electromagnetic Tracking

Abstract

Purpose/Objectives-We have created an automated process utilizing real-time tracking data to evaluate adequacy of PTV margins in prostate cancer, allowing for a process of adaptive radiotherapy with minimal physician workload. We present an analysis of PTV adequacy and a proposed adaptive process.Materials/Methods-Tracking data was analyzed for 15 patients who underwent SMLC IMRT with uniform 5mm PTV margins for prostate cancer utilizing the Calypso® Localization System. Additional plans were generated with 0 and 3 mm margins. A custom software application utilizing the planned dose distribution and structure location from CT simulation was developed to evaluate the dosimetric impact to the target due to motion. The dose delivered to the prostate was calculated for the initial 3, 5, and 10 fractions, and for the entire treatment. Treatment was accepted as adequate if minimum delivered prostate dose (D min ) was at least 98% of the planned D min . Conclusions-Our adaptive process successfully utilized real-time tracking data to predict the need for PTV modifications, without the added burden of physician contouring and image analysis. Our methods are applicable to other utilizations of real-time tracking, including hypofractionated treatment. Results-For

Geographical miss of the prostate during image-guided radiotherapy with a 6-mm posterior expansion margin

“…22 One paper which accounts for rotations and translations proposed a uniform margin of 5 mm when used with a 3-mm online correction protocol and <10 degree rotation allowance. 23 This is in agreement with our findings that prostate geographical miss may not be represented by all fiducial translations (Table 1).…”

Changes in prostate orientation due to removal of a Foley catheter

“…[13][14][15] Other studies have measured inter-and intrafraction prostate rotations [16][17][18] and the dosimetric impact of rotations. 19 Many strategies have been investigated to manage prostate rotations through appropriate PTV margins, [20][21][22] motion management devices, 23 rotation compensations with the table, collimator or gantry, 24,25 and adaptive replanning. 21,26,27 Given the risks of catheter placement, including urinary tract infections and discomfort, we utilized data from a multiinstitutional prostate SBRT study conducted from 2011 to 2013 to better determine the impact and benefit of the Foley catheter placement.…”

“…19 Many strategies have been investigated to manage prostate rotations through appropriate PTV margins, [20][21][22] motion management devices, 23 rotation compensations with the table, collimator or gantry, 24,25 and adaptive replanning. 21,26,27 Given the risks of catheter placement, including urinary tract infections and discomfort, we utilized data from a multiinstitutional prostate SBRT study conducted from 2011 to 2013 to better determine the impact and benefit of the Foley catheter placement. The goal of the project was to investigate whether two CT simulation scans were necessary and if treatment planning could be performed on the FCT alone, or on the TPCT without a Foley at all.…”

Motion-compensated estimation of delivered dose during external beam radiation therapy: Implementation in Philips’ Pinnacle3treatment planning system

“…Previous work performed by Olsen et al using the SWIFTER application found considerable variation in motion-compensated dosimetry for prostate cancer patients displaying the same general characteristics and treatment schemes. 24 The authors concluded that different margins were appropriate for different patients, and that SWIFTER was important in indentifying individualized margin adequacy. A basic comparison between the plan dose parameters and estimated delivered dose parameters (Table I) indicates that the 0 mm margin treatment plan is more susceptible to motion than the 3 and 5 mm margin treatment plans.…”