Decision‐making models in the analysis of portal films: A clinical pilot study

Abstract

Portal films continue to play an important role in the verification of radiotherapy treatment. There is still some discussion, however, as to what action should be taken after a port film has shown a radiation field deviation from the prescribed volume. It was the aim of the present pilot study to investigate the performance of three decision-making models ('Amsterdam', 'Quebec' and 'Newcastle') and an expert panel basing their decision on intuition rather than formal rules after portal film acquisition in a clinical setting. Portal films were acquired on every day during the first week of treatment for five head and neck and five prostate cancer patients (diagnostic phase). If required, the field position was modified according to our normal practice following the recommendation of the expert panel. In order to analyse the results of the models, however, additional port films were taken in the following 3 treatment weeks with the patient moved as required by the different models (intervention phase). The portal films were taken over 4 consecutive days, positioning the patient according to each of the different models on one day each. None of the models diagnosed a field misplacement in the head and neck patients, while the 'Amsterdam' and 'Quebec' models predicted a move in one prostate patient. The 'Newcastle' model, which is based on Hotelling's T2 statistic, proved to be more sensitive and diagnosed a systematic displacement for three prostate patients. The intervention phase confirmed the diagnosis of the model, even if the three portal films taken with the patient position adjusted as required by the model proved to be insufficient to demonstrate an improvement. The 'Newcastle' model does not rely on assumptions about the random movement of patients and requires five portal films before a decision can be reached. This approach lends itself well to incorporation into electronic portal imaging 'packages', where repeated image acquisitions present no logistical difficulty.

Radiation therapy treatment verification imaging in Australia and New Zealand

“…Several studies recommend that the image review should be carried out on the first few fractions of a patient’s treatment because weekly imaging does not adequately or promptly detect systematic errors 24,30,38–40 . Guidelines published by the Cancer Institute New South Wales recommend that an acceptable imaging protocol for radical radiation therapy is to carry out imaging on days 1–3 of treatment, followed by weekly verification thereafter 37 .…”

Australian and New Zealand three‐dimensional conformal radiation therapy consensus guidelines for prostate cancer

“…Systematic errors may be detected by performing a minimum of three consecutive port films at the start of treatment, and weekly thereafter. Decision‐rule protocols will help distinguish between real systematic error requiring patient position movement and random daily set‐up errors 17,30 .…”

Dosimetrische Auswirkungen der Verwendung eines Rektumhüllen-Volumens für die Bestrahlungsplanung fluenzmodulierter Strahlentherapie von Prostatakrebs

“…Daher ist es mög-lich, die Größe des systematischen Lagerungsfehlers aus wenigen gemessenen Fehlern abzuschätzen und diesen zu korrigieren. In der Literatur sind zahlreiche solcher OfflineKorrekturprotokolle zu finden [5,6,11,12,13,16,24,25,33,34].…”