BackgroundMultiple clinical trials had proven that endovascular brachytherapy can reduce the risk of restenosis from 30–60% to 5–15% if radiotherapy is planned and performed correctly. One of the most important parameter for the treatment planning is reference isodose length (RIL) define...
BackgroundMultiple clinical trials had proven that endovascular brachytherapy can reduce the risk of restenosis from 30–60% to 5–15% if radiotherapy is planned and performed correctly. One of the most important parameter for the treatment planning is reference isodose length (RIL) defined as a vessel length at the reference depth (RD) covered by 90 % isodose. RIL depends on the source configuration – active source length (ASL), step times and reference depth. The reference isodose length must be greater or equal to planning target length (PTL) therefore the maximum intervention length (IL) must be smaller then RIL – 10 mm for safety margin.Material and MethodThe MicroSelectron HDR with Ir-192 source and the 5F catheter was used for treatment delivery. The dose distributions were calculated at Plato ver. 14.1.3, and then optimised by internal algorithm for active source length of 10 cm (21 step positions) and reference depths of 5, 7 and 10 mm. TLD chips LIF 100 were used as the detectors after calibration in Co-60 photon beam and Harshaw 3500 as a reader. The catheter and TLD chips were placed in a wax-parafin phantom assuring the distance from the catheter to detectors equal to the reference depth (5, 7 and 10 mm). The measurements were preformed twice for every depth – for the non optimised treatment plan and for the plan with optimisation algorithm applied. The dose delivered at the reference distance was 10 Gy.ResultsThe treatment plan was calculated for the active source length (ASL) of 10 cm. The RIL values calculated without optimisation of the step times, were: 8.9 cm, 9.28 cm and 8.96 cm. The measured RIL were: 8.64 cm, 9.6 cm, 8.32 cm (+/− 0.32 cm), for the RD = 5, 7 and 10 cm, respectively. For the optimised treatment plan, the calculated RIL were: 10.24 cm, 10.56 cm and 10.56 cm while the measured RIL were 10.24 cm, 10.56 cm and 9.92 cm (+/− 0.32 cm), for the RD = 5, 7 and 10 cm, respectively. The RIL measured during the treatment carried according to the optimised plan were by 1.60 cm, 0.96 cm and 1.60 cm longer then those for the treatment made without optimisation at the reference depths. The increase of the dose measured at the last distal and proximal position of the application were 35, 38 and 37% for RD = 5, 7 and 10 cm, respectively.ConclusionOptimisation of the treatment plan is the main tool for the accurate treatment delivery in endovascular brachytherapy. The TLD dosimeters showed the increase of the dose at distal and proximal parts of the active length (AL), and thus optimisation algorithm built in Plato ver. 14.1.3 has been proven to be correct for the above clinical situation.
BackgroundMultiple clinical trials had proven that endovascular brachytherapy can reduce the risk of restenosis from 30–60% to 5–15% if radiotherapy is planned and performed correctly. One of the most important parameter for the treatment planning is reference isodose length (RIL) defined as a vessel length at the reference depth (RD) covered by 90 % isodose. RIL depends on the source configuration – active source length (ASL), step times and reference depth. The reference isodose length must be greater or equal to planning target length (PTL) therefore the maximum intervention length (IL) must be smaller then RIL – 10 mm for safety margin.Material and MethodThe MicroSelectron HDR with Ir-192 source and the 5F catheter was used for treatment delivery. The dose distributions were calculated at Plato ver. 14.1.3, and then optimised by internal algorithm for active source length of 10 cm (21 step positions) and reference depths of 5, 7 and 10 mm. TLD chips LIF 100 were used as the detectors after calibration in Co-60 photon beam and Harshaw 3500 as a reader. The catheter and TLD chips were placed in a wax-parafin phantom assuring the distance from the catheter to detectors equal to the reference depth (5, 7 and 10 mm). The measurements were preformed twice for every depth – for the non optimised treatment plan and for the plan with optimisation algorithm applied. The dose delivered at the reference distance was 10 Gy.ResultsThe treatment plan was calculated for the active source length (ASL) of 10 cm. The RIL values calculated without optimisation of the step times, were: 8.9 cm, 9.28 cm and 8.96 cm. The measured RIL were: 8.64 cm, 9.6 cm, 8.32 cm (+/− 0.32 cm), for the RD = 5, 7 and 10 cm, respectively. For the optimised treatment plan, the calculated RIL were: 10.24 cm, 10.56 cm and 10.56 cm while the measured RIL were 10.24 cm, 10.56 cm and 9.92 cm (+/− 0.32 cm), for the RD = 5, 7 and 10 cm, respectively. The RIL measured during the treatment carried according to the optimised plan were by 1.60 cm, 0.96 cm and 1.60 cm longer then those for the treatment made without optimisation at the reference depths. The increase of the dose measured at the last distal and proximal position of the application were 35, 38 and 37% for RD = 5, 7 and 10 cm, respectively.ConclusionOptimisation of the treatment plan is the main tool for the accurate treatment delivery in endovascular brachytherapy. The TLD dosimeters showed the increase of the dose at distal and proximal parts of the active length (AL), and thus optimisation algorithm built in Plato ver. 14.1.3 has been proven to be correct for the above clinical situation.
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