Implementation of an intraoperative electron radiotherapy in vivo dosimetry program

Background: Intraoperative electron radiotherapy (IOERT) is a highly selective radiotherapy technique which aims to treat restricted anatomic volumes during oncological surgery and is now the subject of intense re-evaluation. In vivo dosimetry has been recommended for IOERT and has been identified as a risk-reduction intervention in the context of an IOERT risk analysis. Despite reports of fruitful experiences, information about in vivo dosimetry in intraoperative radiotherapy is somewhat scarce. Therefore, the aim of this paper is to report our experience in developing a program of in vivo dosimetry for IOERT, from both multidisciplinary and practical approaches, in a consistent patient series. We also report several current weaknesses. Methods: Reinforced TN-502RDM-H mobile metal oxide semico nductor field effect tran sistors (MOSFETs) and Gafchromic MD-55-2 films were used as a redundant in vivo treatment verification system with an Elekta Precise fixed linear accelerator for calibrations and tre atments. In vivo dosimetry was performed in 45 patients in cases involving primary tumors or relapses. The m ost frequent primary tumors were breast (37 %) and colorectal (29 %), and local recurrences among relapses was 83 %. We made 50 attempts to measure with MOSFETs and 48 attempts to measure with films in th e treatment zones. The surgical team placed both detectors with supervision from the radiation oncologist and following their instructions. Results: The program was considered an overall success by the different professionals involved. The absorbed doses measured with MOSFETs and films were 93.8 ± 6.7 % and 97.9 ± 9.0 % (mean ± SD ) respectively using a scale in which 90 % is the prescribed dose and 100 % is the maximum absorbed dose delivered by the beam. However, in 10 % of cases we experienced dosimetric problems due to detector misalignment, a situation which might be avoided with additional checks. The useful MOSFET lifetime length and the film sterilization procedure should also be controlled. Conclusions: It is feasible to establish an in vivo dosimetry program for a wide set of locations treated with IOERT using a multidisciplinary approach according to the skills of the professionals present and the detectors used; oncological surgeons ’ commitment is key to success in this context. Films are more unstable and show higher uncertainty than MOSFETs but are cheaper and are useful and convenient if real-time treatment monitoring is not necessary.This work was supported by grants IPT-300000-2010-3 and PI11/01659 from the Spanish Government and ERDF funds

Valoración e impacto del tiempo quirúrgico tras el tratamiento neoadyuvante en cáncer rectal avanzado

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Medicina, Departamento de Radiología y Medicina Física (Radiología), leída el 03-03-2014Depto. de Radiología, Rehabilitación y FisioterapiaFac. de MedicinaTRUEunpu

Practical issues regarding angular and energy response in in vivo intraoperative electron radiotherapy dosimetry

AimTo estimate angular response deviation of MOSFETs in the realm of intraoperative electron radiotherapy (IOERT), review their energy dependence, and propose unambiguous names for detector rotations.BackgroundMOSFETs have been used in IOERT. Movement of the detector, namely rotations, can spoil results.Materials and methodsWe propose yaw, pitch, and roll to name the three possible rotations in space, as these unequivocally name aircraft rotations. Reinforced mobile MOSFETs (model TN-502RDM-H) and an Elekta Precise linear accelerator were used. Two detectors were placed in air for the angular response study and the whole set of five detectors was calibrated as usual to evaluate energy dependence.ResultsThe maximum readout was obtained with a roll of 90° and 4[[ce:hsp sp="0.25"/]]MeV. With regard to pitch movement, a substantial drop in readout was achieved at 90°. Significant overresponse was measured at 315° with 4[[ce:hsp sp="0.25"/]]MeV and at 45° with 15[[ce:hsp sp="0.25"/]]MeV. Energy response is not different for the following groups of energies: 4, 6, and 9[[ce:hsp sp="0.25"/]]MeV; and 12[[ce:hsp sp="0.25"/]]MeV, 15[[ce:hsp sp="0.25"/]]MeV, and 18[[ce:hsp sp="0.25"/]]MeV.ConclusionsOur proposal to name MOSFET rotations solves the problem of defining sensor orientations. Angular response could explain lower than expected results when the tip of the detector is lifted due to inadvertent movements. MOSFETs energy response is independent of several energies and differs by a maximum of 3.4% when dependent. This can limit dosimetry errors and makes it possible to calibrate the detectors only once for each group of energies, which saves time and optimizes lifespan of MOSFETs

The Usefulness of Adaptative Radiotherapy in Prostate Cancer: How, When, and Who?

The aim of this study was to develop a deformable image registration (DIR)-based offline ART protocol capable of identifying significant dosimetric changes in the first treatment fractions to determine when adaptive replanning is needed. A total of 240 images (24 planning CT (pCT) and 216 kilovoltage cone-beam CT (CBCT)) were prospectively acquired from 24 patients with prostate adenocarcinoma during the first three weeks of their treatment (76 Gy in 38 fractions). This set of images was used to plan a hypofractionated virtual treatment (57.3 Gy in 15 fractions); correlation with the DIR of pCT and each CBCT allowed to translate planned doses to each CBCT, and finally mapped back to the pCT to compare with those actually administered. In 37.5% of patients, doses administered in 50% of the rectum (D50) would have exceeded the dose limitation to 50% of the rectum (R50). We first observed a significant variation of the planned rectal volume in the CBCTs of fractions 1, 3, and 5. Then, we found a significant relationship between the D50 accumulated in fractions 1, 3, and 5 and the lack of compliance with the R50. Finally, we found that a D50 variation rate [100 × (administered D50 − planned D50/planned D50)] > 1% in fraction three can reliably identify variations in administered doses that will lead to exceeding rectal dose constraint

Failure mode and effect analysis oriented to risk-reduction interventions in intraoperative electron radiation therapy: The specific impact of patient transportation, automation, and treatment planning availability

Background and purpose: Industrial companies use failure mode and effect analysis (FMEA) to improve quality. Our objective was to describe an FMEA and subsequent interventions for an automated intraoperative electron radiotherapy (IOERT) procedure with computed tomography simulation, pre-planning, and a fixed conventional linear accelerator. Material and methods: A process map, an FMEA, and a fault tree analysis are reported. The equipment considered was the radiance treatment planning system (TPS), the Elekta Precise linac, and TN-502RDM-H metal–oxide-semiconductor-field-effect transistor in vivo dosimeters. Computerized order-entry and treatment-automation were also analyzed. Results: Fifty-seven potential modes and effects were identified and classified into ‘treatment cancellation’ and ‘delivering an unintended dose’. They were graded from ‘inconvenience’ or ‘suboptimal treatment’ to ‘total cancellation’ or ‘potentially wrong’ or ‘very wrong administered dose’, although these latter effects were never experienced. Risk priority numbers (RPNs) ranged from 3 to 324 and totaled 4804. After interventions such as double checking, interlocking, automation, and structural changes the final total RPN was reduced to 1320. Conclusions: FMEA is crucial for prioritizing risk-reduction interventions. In a semi-surgical procedure like IOERT double checking has the potential to reduce risk and improve quality. Interlocks and automation should also be implemented to increase the safety of the procedure

Failure mode and effect analysis oriented to risk-reduction interventions in intraoperative electron radiation therapy: The specific impact of patient transportation, automation, and treatment planning availability

Background and purpose: Industrial companies use failure mode and effect analysis (FMEA) to improve quality. Our objective was to describe an FMEA and subsequent interventions for an automated intraoperative electron radiotherapy (IOERT) procedure with computed tomography simulation, pre-planning, and a fixed conventional linear accelerator. Material and methods: A process map, an FMEA, and a fault tree analysis are reported. The equipment considered was the radiance treatment planning system (TPS), the Elekta Precise linac, and TN-502RDM-H metal–oxide-semiconductor-field-effect transistor in vivo dosimeters. Computerized order-entry and treatment-automation were also analyzed. Results: Fifty-seven potential modes and effects were identified and classified into ‘treatment cancellation’ and ‘delivering an unintended dose’. They were graded from ‘inconvenience’ or ‘suboptimal treatment’ to ‘total cancellation’ or ‘potentially wrong’ or ‘very wrong administered dose’, although these latter effects were never experienced. Risk priority numbers (RPNs) ranged from 3 to 324 and totaled 4804. After interventions such as double checking, interlocking, automation, and structural changes the final total RPN was reduced to 1320. Conclusions: FMEA is crucial for prioritizing risk-reduction interventions. In a semi-surgical procedure like IOERT double checking has the potential to reduce risk and improve quality. Interlocks and automation should also be implemented to increase the safety of the procedure