Real-time in vivo rectal wall dosimetry using MOSkin detectors during linac based stereotactic radiotherapy with rectal displacement

Abstract

BackgroundMOSFET dosimetry is a method that has been used to measure in-vivo doses during brachytherapy treatments and during linac based radiotherapy treatment. Rectal displacement devices (RDDs) allow for safe dose escalation for prostate cancer treatment. This study used dual MOSkin detectors to assess real-time in vivo rectal wall dose in patients with an RDD in place during a high dose prostate stereotactic body radiation therapy (SBRT) boost trial.MethodsThe PROMETHEUS study commenced in 2014 and provides a prostate SBRT boost dose with a RDD in place. Twelve patients received two boost fractions of 9.5–10 Gy each delivered to the prostate with a dual arc volumetric modulated arc therapy (VMAT) technique. Two MOSkins in a face-to-face arrangement (dual MOSkin) were used to decrease angular dependence. A dual MOSkin was attached to the anterior surface of the Rectafix and read out at 1 Hz during each treatment. The planned dose at each measurement point was exported from the planning system and compared with the measured dose. The root mean square error normalised to the total planned dose was calculated for each measurement point and treatment arc for the entire course of treatment.ResultsThe average difference between the measured and planned doses over the whole course of treatment for all arcs measured was 9.7% with a standard deviation of 3.6%. The cumulative MOSkin reading was lower than the total planned dose for 64% of the arcs measured. The average difference between the final measured and final planned doses for all arcs measured was 3.4% of the final planned dose, with a standard deviation of 10.3%.ConclusionsMOSkin detectors were an effective tool for measuring dose delivered to the anterior rectal wall in real time during prostate SBRT boost treatments for the purpose of both ensuring the rectal doses remain within acceptable limits during the treatment and for the verification of final rectal doses.

Phase 2 Multicenter Study of Gantry-Based Stereotactic Radiotherapy Boost for Intermediate and High Risk Prostate Cancer (PROMETHEUS)

“…Quality assurance can be automated and performed in real time, reducing the learning curve within centers and clinical networks. Technical sub-studies have validated the real time SBRT radiation dose delivery and treatment accuracy (24, 25). We have shown that a protocol incorporating rectal displacement devices, MRI fusion, margin reduction coupled with intrafraction image guidance and homogenous urethral dosing is associated with a low risk of significant urinary and rectal toxicity with a median follow-up of 24 months.…”

TROG 18.01 phase III randomised clinical trial of the Novel Integration of New prostate radiation schedules with adJuvant Androgen deprivation: NINJA study protocol

“…The next 10 patients will have planning performed on sCT and confirmed on planning CT. Subsequent patients will omit a planning CT, be planned on sCT and have confirmation of accurate dosimetry on treatment using a centrally approved approach, for example, Electronic Portal Imaging Device (EPID) dosimetry38 or in vivo dosimetry 39…”

Advances on inorganic scintillator-based optic fiber dosimeters

“…MOSFETs and diode-based devices have been utilized for clinical real-time in vivo dosimetry [10][11][12] owning to their good sensitivity, small size, and real-time readout capabilities. However, MOSFETs are expensive, incident angle-dependent, and of limited durability.…”