Accuracy of prostate radiation therapy using a fiducial point‐pair registration technique based on the computer‐assisted portal imaging quality assurance program PIPSpro

Abstract

The aim of this study was to assess portal imaging for quality assurance of patient positioning in external beam radiotherapy. We present a retrospective study of the variability of patient position in the treatment of 34 prostate cancer patients who were treated with whole pelvic irradiation followed by arc therapy or boost field (Series I) and 25 patients treated by 'small' pelvic 4-field box technique (Series II). Weekly anteroposterior-posteranterior (AP-PA) and left-lateral portal images were compared to simulation films by using a fiducial point-pair registration technique based on the computer-assisted portal imaging quality assurance program PIPSpro, developed specifically for the verification of treatment positioning in radiation therapy. Series I consisted of 34 patients and 194 portal films (97 AP-PA and 97 left-lateral). Overirradiated (OA) and underirradiated (UA) areas were computed in terms of percentage of the reference field size. For the AP-PA portals, the average OA was 2.75% and average UA was 2.74%. For left-lateral portals, an average OA of 2.49% and UA of 2.78% were measured. Series II consisted of 25 patients and 194 portal films (98 AP-PA and 96 left-lateral). The average OA was 0.88% and average UA was 0.86% in AP-PA portals, and 1.03 and 0.82% for left-lateral portals, respectively. The accuracy of patient positioning in irradiation of prostate cancer in our institution is in the range of 2.69% for whole pelvic fields and 1.0% for small fields. We conclude that PIPSpro is an effective and useful tool for quality assurance in radiotherapy.

Quality Assurance of Image Registration Using Combinatorial Rigid Registration Optimization (CORRO)

“…Table 1 shows 10 of the 58 cases included with our reference data set. The number of landmark pairs created for each case, the number of unique kcombination set generated for all k-values are shown in columns 5…”

“…This results in inter-and intra-fractional motion which can lead to over-orunder-dosing the intended target and the organs at risk (OAR) [2,3,4]. For these reasons, several methods have been developed to validate and characterize the quality of image registration [5].…”

“…Fiducial markers strategically placed in/on internal targets or OARs have also been used to find the ground truth of a rigid image registration [5] Due to the poor contrast of the prostate relative to the surrounding soft tissue and the increased visibility of gold fiducial markers in kV or MV X-ray imaging, intra-prostatic gold markers are used to improve targeting for surgical procedures and radiotherapy treatment to the prostate and to estimate registration error [9][10][11][12].Though fixed to the target anatomy, the fiducials are known to drift from their original fixed point either due to anatomy changes over time or detachment of the fiducial. The effect of fiducial relocation may lead to inter-observer error associated with the registration [13][14][15].…”

A feasibility study to estimate optimal rigid‐body registration using combinatorial rigid registration optimization (CORRO)

“…Fiducial markers on phantoms and patients have also been used to find the ground truth of a rigid image registration 6 . Due to the visibility of gold markers placed in the prostate in kV or MV x‐ray imaging, they are used to improve targeting for surgical procedures and radiotherapy treatment to the prostate and to estimate registration error 7,8–10 .…”