IFM_201606 v1.indd

120 downloads 0 Views 2MB Size Report
A brachytherapy applicator (Rotherham system – ovoids, ring applicator, VSA) is placed in the uterus/vagina during a theatre procedure. The images from these ...
radiologia / radiology

artykuł / article

Implementation of an independent radiation detector actively monitoring delivery of radiation pulses during gynaecological PDR brachytherapy treatment Tervinder Matharu 1, Dominika Oborska-Kumaszynska1 , Tim Allen1, Christina Stewart 2, Rose Cox1, Erine Dalton1 1

The Royal Wolverhampton NHS Trust New Cross hospital Wednesfield, Wolverhampton WV10 0QP, United Kingdom, e-mail: [email protected]

2

Royal Infirmary of Edinburgh NHS Lothian, Edinburgh, United Kingdom

INTRODUCTION

PDR uses an Iridium-192 radiation source. The main advantage of PDR is a modern afterloading system offering over in-

PDR (Pulsed Dose Rate) brachytherapy treatment is a radiothe-

terstitial or intracavitary insertion of separate needles, tubes,

rapy modality combining physical advantages of HDR brachy-

seeds or wires. A dose distribution can be modulated flexibly to

therapy (dose distribution optimization as well as radiation

fit it to the treated volume (HRV/IRV) as well as OARs’ (organ at

safety) with radiobiological equivalency of LDR (Low Dose Rate)

risk) constraints. This can be realised by setting dwell positions

brachytherapy. At the beginning of the 90’s, a  new technique

of a radioactive source, adjusting dwell times and by a combina-

was developed in order to mimic the radiobiological effect of

tion of positioning of catheters, applicators and another types

continuous LDR, while taking advantage of the same stepping

of interest. PDR brachytherapy and “pulse scheme” of building

source technology developed for HDR (High Dose Rate) brachy-

a dose distribution allows only for incomplete repair, aiming at

therapy. Source strength was reduced from about 1 Ci (instead

achieving a radiobiological effect similar to low dose rate over

of 10 Ci). The total dose delivered is approximately the same as

the same treatment time, typically a few days. The radiation so-

with continuous LDR. It is provided with a large number of small

urce is removed into a shielded safe after completing the each

fractions (or pulses), lasting usually 10 to 30 minutes, typically

pulse what eliminates “environmental” radiation exposures and

one per hour, up to one per 4 hours (Fig. 1).

decreases a risk of delivery of an unintended dose to staff and visitors.

PDR TREATMENT – CERVICAL CANCER Brachytherapy is an integral part of radical therapy for cervical cancer. While image-based planning has gained wide acceptance in external beam radiotherapy, the integration of image-based planning for brachytherapy has lagged significantly. More recently advances in planning software/hardware have a lead to increased use of image-based brachytherapy. In NX Hospital, it is currently based on CT and MRI 3D images

Fig. 1 The PDR treatment idea Source: [4].

taken for a patient with inserted applicator/catheter/BT inserts

Inżynier i Fizyk Medyczny

5/2016

vol. 5

341

radiologia \ radiology

artykuł \ article

. A brachytherapy applicator (Rotherham system – ovoids, ring

placed in the treatment room and the applicator is connected

applicator, VSA) is placed in the uterus/vagina during a theatre

via a  transfer tube to the Flexitron treatment delivery unit

procedure. The images from these two modalities are fused to

(TDU). Radiation dose is delivered via a single source (Ir-192) wel-

provide needed image information to mark up the treated volu-

ded at the end of a steel cable, driven to the number of planned

mes (GTV, HRV, IRV) and OARs (rectum, sigmoid, bowels, blad-

dwell positions and dwell times within the applicator for a pe-

der). 3D planning additionally confirms of applicator placement,

riod about 10-15 minutes creating desired dose distribution.

gives possibilities to decrease OARs dose for patients with

The source then moves into the TDU safe for about 1 hour. The

a small cervix, accounting for sigmoid colon dose, and improves

planned number of repetitions is 26-35 pulses and prescribed

coverage for large volume disease (wide infiltration of disease

dose per pulse is 0.8-1.0 Gy. The patient remains a  bed bound

into a  tissue) while maintaining OARs’ dosimetry. At the time

for all treatment. The patient is nursed or visited during a period

of brachytherapy application, tandem placement can result in

interval. It is very important to manage correctly that kind of

unsuspected uterine perforation despite the clinical impression

situations in relation to appearing next pulse. The members of

of adequate tandem placement. Additionally, introducing MRI

staff have been trained to manage the patient needs and provi-

has given optimization to maintain tumour coverage and reduce

ded treatment to don’t disrupt the schedule of it. It is very im-

the dose to the normal tissues, especially in patients with small

portant in terms a number of pulses as well as interval time kept

cervix where the target volume treated.

between them and finally in relation to a radiobiological effect

The EMBRACE, RCR and GEC-ESTRO guides recommenda-

of the treatment.

tions are used on contouring of tumour targets and OARs as well as dose volume parameters to be reported for IGBT (Image Guided Brachytherapy) for locally advanced cervix cancer. The dose reported to the target volume (90% of volume GTV, HRV, IRV – D90)as well as the OARs’ volumes (0.1cc, 1.0cc, 2.0cc of OAR volume) is calculated using EQD2 to combine the ERT dose and BT dose. EQD2 is also reported to A-points to collect evidences to compare an “old” techniques prescription (dose normalisation to A-points) and a  volumetric optimisation technique. The optimisation dose distribution is very difficult in terms of getting the recommended doses prescriptions with keeping constraints for OARs. When the treatment plan is accepted by a  consultant and checked independently by a  second physicist, the patient is

Fig. 3 The control unit of the PDR system Source: Own materials.

MISSING TREATMENT PULSE The TDU has an internal system to control a number of pulses delivered as well as time of delivery and completing of these pulses. The unit has two independent data bases where the treatments are recorded:

––the user data base (it is also printed off after completing a whole treatment and kept in the patient records),

––engineering logs which are accessible for an administrator/ service user login. Both of them should confirm all events (eg. all breaks generated by staff because of the patient service, any deviations from a standard schedule, any breakdowns and missed treatments) as well realisation of the treatment. The issue of those recording systems was detected when Fig. 2 The PDR treatment system and treatment room Source: [4] and own materials.

342

the user data base showed the one missed pulse (27 pulses instead 28 – the pulse no 12 was missed from that record).

vol. 5

5/2016

Inżynier i Fizyk Medyczny

artykuł / article

radiologia / radiology

Unfortunately, for the Flexitron system the pulse record can only be reviewed on completion. It means that verification of the treatment provided could be verified after completing of it (verification off-line). The records didn’t give full information about the reason which caused missing the pulse. The user logs showed only lack of 12th pulse and time of that event (Fig. 4). The engineers logs didn’t contain clear information about technical or not technical reasons the issue – that record uses the specific codes and labelling, completely impossible to understand by the user or to define the issues or events appeared (Fig. 5). Also, the time of the recorded issues/events was different in the user logs and engineering logs. The issue was reported to the producer of the TDU and system. The PDR treatment was suspended till getting the results of the investigation completed by the manufacturer. That incident never has found full explanation. Finally the system was updated and fully tested by the user (acceptance tests and commissioning). The update didn’t

Fig. 4 The user logs showing the 12 th missed pulse Source: [4].

change the facilities of the user and engineering logs. An idea of an independent detector/control system was created because of:

––the Flexitrion TDU control system doesn’t ensure the user that treatment provided is as planned,

––the Felxitron TDU control system provides records off-line what causes lack of possibilities to compensate the lost pulse or to stop treatment when the additional pulse would happen,

––the user logs and engineers logs don’t pro-

Fig. 5 The engineers log file – the missed pulse detected but not clear which one (different format of recording logs for the machine and different time than in the user log) Source: [4].

vide clear information about the events and issues,

––the engineers logs use coded system of description of the events/issues, what doesn’t provide clear information to the user,

––time of the user logs and engineering logs is different.

PATIENT DOSE EVALUATION AFTER MISSING THE PULSE As it is regulated, when mistreatment appears, the patient dose has to be calculated and compared to dose of intent (planned dose). When difference between prescribed dose and planned dose is bigger than 10% of total treatment it has to be reported to the external authority bodies and the reasons have to be investigated/audited.

Inżynier i Fizyk Medyczny

Fig. 6 The table – EQD2 calculations for intended treatment and delivered treatment Source: [4].

5/2016

vol. 5

343

radiologia \ radiology

artykuł \ article

The calculations completed for the patient showed that final dose was different by 1.2% than planned dose (Fig. 6). The incident didn’t have to be reported externally but was reported internally (the local system of the incidents/adverse events record) and the adequate action was taken (as described above).

INDEPENDENT DOSE/PULSES MONITORING SYSTEM The independent dose/pulse monitoring system was implemented before putting the PDR system back to clinic. That system detects on-line and actively monitors dose/ pulses delivered during a treatment. The radiation doserate monitoring system was installed in the treatment

Fig. 7 The doserate monitoring system – the electrometer installed in the control room Source: Own material.

room connected via network to PC running their Mevis Lite 2.2 software (Fig. 7). The doserate probe is placed in the treatment room far away (the opposite corner next to the celling) from the patient bad to avoid saturation of it during measurements. The LG6500 probe is a Geiger Muller Dose Rate Probe with high dose rate and energy range – adequate to the application (Fig. 8). The system time resolution is 1 minute – it means that the monitoring systems collects data for every 1 minute. It is enough to an intended aim. The system is connected by network to PC and delivered treatment can be monitored on-line.

ADVANTAGES The doserate monitoring system brought a  few advantages to clinical practice. The most important is that the system is totally independent on the PDR system, It provides active monitoring of the treatment remotely and the user can get data on-line and action when it is

Fig. 8 The GM-probe – the probe installed in the treatment room Source [4].

needed. The system presents data numerically as well as the user can get graphical presentation of provided treatment. It means that user can very quickly verify number and time schedule of the pulses. The system appeared extremely reliable. It is not depended on a number of counts and more than one consecutive patients treatments can be recorded. All recorded data is exportable to Excel. The hardware is very simple and easy to install and integrate with network as well as it is very simple to use.

DISADVANTAGES As an each technical solution, the monitoring system has some disadvantages. The installed system has a  large number configurable parameters before an each treatment. It is a time consuming process. To avoid saturation

Fig. 9 The attempt of the recorded pulses Source: [4].

344

of the detector, it has to be placed far away from the

vol. 5

5/2016

Inżynier i Fizyk Medyczny

artykuł / article

radiologia / radiology

patient. It was a  reason of placing the detector in the opposi-

calibration process. It adds confidence to the radiation delive-

te corner next to the celling in the treatment rom. That setup

ry system and patient treatment. The future work is to Intro-

was also beneficial in terms of avoiding additional shielding of

duce a warning system when expected pulses not detected or

the probe. The sampling frequency limited to 1 min. Finally, that

unexpected pulses happened.

technical limit didn’t cause any problems in an implementation

REFERENCES

of the doserate monitor to the clinical practice. But it may not be suitable for treatment pulse width less than 1 min long (generally not an issue in our clinical practice). The system requires

1. http://www.wco.pl/zb/files/publication/fc5fde.pdf

a  very careful verification of setting parameter to local GMT.

2. http://www.estro.org/binaries/content/assets/estro/about/

The dosemeter is synchronised to PC time what can interfere

gec-estro/handbook-of-brachytherapy/e-4-23072002-radio-

with pulse recording times. It can cause a disruption of pulse re-

biology-print_proc.pdf

cording. It is very important to verify a number of the recorded

3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4259954/

pulses. The sync only happens midnight and the system is sen-

4. https://www.rcr.ac.uk/system/files/publication/field_publica-

sitive on that disruption when time zone is changed to GMT/BST.

CONCLUSION

tion_files/BFCO(09)1_Cervix.pdf 5. https://www.researchgate.net/publication/308350045_Im-

pelementation_of_an_independent_radiation_detector_actively_monitoring_radiation_pulses_during_PDR_pulse_dose_

The monitoring Berthold system appaered extremely reliable for independently monitoring of delivery of PDR treatment remotely from a  PC. It appeared Easy to install, setup, imple-

rate_gyneacological_traeatment 6. http://w w w.nrls.npsa.nhs.uk /EasySiteWeb/getresource.

axd?AssetID=75031

ment and use. The system requires a very little maintenance and

Inżynier i Fizyk Medyczny

5/2016

vol. 5

345