RBE-weighted dose conversions for carbon ionradiotherapy between microdosimetric kinetic model and local effect model for the targets and organs at risk in prostate carcinoma

et al. 2020

Radiat Oncol

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Background We sought to establish a conversion curve to convert the RBE-weighted doses calculated by local effect model I (LEM) (LEM RBE-weighted doses) in patients with locally recurrent nasopharyngeal carcinoma (rNPC) to the RBE-weighted doses calculated by microdosimetric kinetic model (MKM) (MKM RBE-weighted doses). We also converted the LEM dose constraints (RBE-weighted dose constraints in LEM plans) for the brain stem, spinal cord, and optic nerve based on this curve. Methods Data from 20 patients with rNPC receiving carbon-ion radiotherapy (CIRT) in our hospital were collected. LEM in Raystation (V8A, Raystation, Sweden) was used to generate treatment plans. The clinical target volume CTV1 (GTV + 5 mm) was given 3 Gy (RBE) per fraction. Ninety-nine percent of target volumes should be covered by 95% of the prescriptions; the maximum doses of the brainstem and spinal cord were < 45 Gy (RBE) and < 30 Gy (RBE), respectively. The doses covering 20% volumes of optical nerves/chiasms D20 were < 30 Gy (RBE). Then physical doses of the LEM plans were recalculated by using MKM in Raystation to generate MKM plans. A series of conversion factors (i.e., the ratio of LEM RBE-weighted dose to MKM RBE-weighted dose) was then obtained by using an isovolumetric dose method. The LEM plan prescriptions (LEM prescription) and dose constraints of the organs at risk (OARs) (OAR constraints) were converted to the corresponding MKM prescriptions and dose constraints using this conversion curve. Results For the CTV1 fractional RBE-weighted dose prescription of 3.00 Gy (RBE) and CTV2 of 2.70 Gy (RBE) in LEM plans, the conversion factors (LEM RBE-weighted dose/MKM RBE-weighted dose) were 1.37 (CI 95% 1.35–1.39) and 1.46 (1.41–1.51), respectively. The average conversion factors from 1.37 (CI 95% 1.33–1.41) to 3.09 (2.94–3.24) corresponded to the LEM fractionated doses from 2.86 Gy (RBE) to 0.24 Gy (RBE), including the doses constraining upon OARs. LEM RBE-weighted doses of 30 Gy (RBE) and 45 Gy (RBE) in 21 fractions were converted to MKM RBE-weighted doses of 16.64 Gy (RBE) and 30.72 Gy (RBE) in 16 fractions. Conclusions This conversion curve could be used to convert LEM RBE-weighted doses to MKM RBE-weighted doses for patients with rNPC receiving CIRT, providing dose references for re-irradiation therapy.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

RBE-weighted dose conversions for patients with recurrent nasopharyngeal carcinoma receiving carbon-ion radiotherapy from the local effect model to the microdosimetric kinetic model

et al. 2020

Radiat Oncol

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“…Wang (18) has analyzed the feasibility of RBE-weighted dose conversion from MKM to LEM. Hence, if the physical dose and fragment spectrum are exactly the same, the LEM isodose can be transformed into a de ned MKM isodose.…”

Section: Isovolumetric Dose Methodsmentioning

confidence: 99%

“…Adaptation of the OAR constraints was absolutely necessary. So far, only LEM constraints of the optical nerve (16) and rectum (17,18) have been reformulated; no studies have been carried for recurrent tumors (e.g., rNPC). Since the OARs of patients with rNPC (e.g., optical nerve, spinal cord, and brain stem) have already exposed to a su cient amount of radiation, stricter dose constraints should be discussed.…”

Section: Introductionmentioning

confidence: 99%

RBE-weighted dose conversions for patients with recurrent nasopharyngeal carcinoma receiving carbon-ion radiotherapy from the local effect model to the microdosimetric kinetic model

et al. 2020

Preprint

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Background We sought to establish a conversion curve to convert the local effect model I (LEM) based RBE-weighted doses (LEM doses) in patients with locally recurrent nasopharyngeal carcinoma (rNPC) to the microdosimetric kinetic model (MKM) based RBE-weighted dose (MKM doses) model. We also converted the relevant organ at risk (OAR) constraints based on this curve. Methods Data from 13 patients with rNPC receiving carbon-ion radiotherapy (CIRT) in our hospital were collected. LEM in Raystation (V8A, Raystation, Sweden) was used to generate treatment plans. Clinical target volume CTV1(GTV+5mm)was given 63 Gy (RBE) in 21 fractions. Ninety-nine percent of target volumes should be covered by 95% of the prescriptions; the maximum doses of the brainstem and spinal cord were < 45 Gy (RBE) and < 30 Gy (RBE), respectively. The doses covering 20% volumes of optical nerves/chiasms D20 were < 30 Gy (RBE). Then physical doses of the LEM plans were recalculated by using MKM in Raystation to generate MKM plans. A series of the ratio of LEM dose to MKM dose was obtained as the conversion factor to obtain the conversion curve by using an isovolumetric dose method. Using prescriptions and OAR, constraints were converted to MKM doses with this curve. Results Conversion factors (LEM dose/MKM dose) from 1.37±0.02 to 3.09±0.09 corresponded to the LEM fractionated doses from 0.24 Gy (RBE) to 2.86 Gy (RBE), including the doses constraining upon OARs. LEM doses of 30 Gy (RBE) and 45 Gy (RBE) in 21 fractions were converted to MKM doses of 16.64 Gy (RBE) and 30.98 Gy (RBE) in 16 fractions. Conclusions This conversion curve could be used to convert LEM doses to MKM doses for patients with rNPC receiving CIRT, providing dose references for re-irradiation therapy.

“…Adaptation of the OAR constraints was absolutely necessary. So far, only LEM dose constraints of the optical nerve (16) and rectum (17,18) have been reformulated; no studies have been carried for recurrent tumors (e.g., rNPC). Since the OARs of patients with rNPC (e.g., optical nerve, spinal cord, and brain stem) have already exposed to a su cient amount of radiation, stricter OAR constraints should be discussed.…”

Section: Introductionmentioning

confidence: 99%

RBE-weighted dose conversions for patients with recurrent nasopharyngeal carcinoma receiving carbon-ion radiotherapy from the local effect model to the microdosimetric kinetic model

et al. 2020

Preprint

Self Cite

Background: We sought to establish a conversion curve to convert the RBE-weighted doses calculated by local effect model I (LEM) (LEM RBE-weighted doses) in patients with locally recurrent nasopharyngeal carcinoma (rNPC) to the RBE-weighted doses calculated by microdosimetric kinetic model (MKM) (MKM RBE-weighted doses). We also converted the LEM dose constraints (RBE-weighted dose constraints in LEM plans) for the brain stem, spinal cord, and optic nerve based on this curve.Methods: Data from 20 patients with rNPC receiving carbon-ion radiotherapy (CIRT) in our hospital were collected. LEM in Raystation (V8A, Raystation, Sweden) was used to generate treatment plans. The clinical target volume CTV1（GTV+5mm）was given 3 Gy (RBE) per fraction. Ninety-nine percent of target volumes should be covered by 95% of the prescriptions; the maximum doses of the brainstem and spinal cord were < 45 Gy (RBE) and < 30 Gy (RBE), respectively. The doses covering 20% volumes of optical nerves/chiasms D20 were < 30 Gy (RBE). Then physical doses of the LEM plans were recalculated by using MKM in Raystation to generate MKM plans. A series of conversion factors (i.e., the ratio of LEM RBE-weighted dose to MKM RBE-weighted dose) was then obtained by using an isovolumetric dose method. The LEM plan prescriptions (LEM prescription) and dose constraints of the organs at risk (OARs) (OAR constraints) were converted to the corresponding MKM prescriptions and dose constraints using this conversion curve. Results: For the CTV1 fractional RBE-weighted dose prescription of 3.00 Gy (RBE) and CTV2 of 2.70 Gy (RBE) in LEM plans, the conversion factors (LEM RBE-weighted dose/MKM RBE-weighted dose) were 1.37 (CI 95％ 1.35–1.39) and 1.46 (1.41–1.51), respectively. The average conversion factors from 1.37(CI 95％ 1.33–1.41) to 3.09 (2.94–3.24) corresponded to the LEM fractionated doses from 2.86 Gy (RBE) to 0.24 Gy (RBE), including the doses constraining upon OARs. LEM RBE-weighted doses of 30 Gy (RBE) and 45 Gy (RBE) in 21 fractions were converted to MKM RBE-weighted doses of 16.64 Gy (RBE) and 30.72 Gy (RBE) in 16 fractions. Conclusions: This conversion curve could be used to convert LEM RBE-weighted doses to MKM RBE-weighted doses for patients with rNPC receiving CIRT, providing dose references for re-irradiation therapy.