- Email: [email protected]
EP-1554: Partially ablative VMAT for large tumors using simultaneous integrated boost: a proof of concept
S837 ESTRO 36 _______________________________________________________________________________________________
Conclusion Although DWA increased the V10-40 of bladder wall, beam-on time, and MU, DWA significantly reduced the mean doses and D1cc of the bilateral femoral heads. DWA also significantly reduced the V10, V20 and V70 of rectal wall. DWA seems to be a promising irradiation technique for prostate cancer. EP-1554 Partially ablative VMAT for large tumors using simultaneous integrated boost: a proof of concept S. Cilla1, F. Deodato2, A. Ianiro1, G. Macchia2, V. Picardi2, M. Ferro2, M. Boccardi2, M. Ferro2, S. Cammelli3, A. Arcelli3, E. Farina3, L. Giaccherini3, G.P. Frezza4, V. Valentini5, A.G. Morganti3 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy 2 Fondazione di Ricerca e Cura "Giovanni Paolo II"Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy 3 Università di Bologna, Radiation Oncology CenterDepartment of Experimental- Diagnostic and Specialty Medicine - DIMES, Bologna, Italy 4 Ospedale Bellaria, Radiation Oncology Department, Bologna, Italy 5 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy Purpose or Objective The aim of this study was to assess the feasibility in the delivery of highly heterogeneous doses to symptomatic large tumor using VMAT technique and simultaneous integrated boost during a short course palliative accelerated radiotherapy. Material and Methods For this dosimetric analysis we selected a patient with a large symptomatic sarcoma. A Planning Target Volume (PTV) and a Boost Target Volume (BTV) were defined as the GTV plus and minus 1cm, respectively. Two different doses were simultaneously delivered to the PTV and BTV according to a dose-escalation protocol in 4 fractions. Five dose levels were planned: Level 1 (basal plan: PTV: 20Gy/5Gy), Level 2 (PTV: 20Gy/5Gy; BTV: 25Gy/6.25Gy), Level 3 (PTV: 20Gy/5Gy; BTV: 30Gy/7.5Gy), Level 4 (PTV: 20Gy/5Gy; BTV: 35Gy/8.75Gy) and Level 5 (PTV: 20Gy/5Gy; BTV: 40Gy/10Gy). The aim was to irradiate the central part of the tumor up to 10Gy/fraction while maintaining the border area of the tumor and the surrounding healthy tissues with <5Gy/fraction. SIB-VMAT plans were generated using Oncentra Masterplan TPS, in the dual-arc modality. The mean dose, D98%, D95% and D2% doses were scored for each target. A conformity index, PTV_CI, defined as the volume encompassed by the PTV 95% isodose divided by the PTV volume, was calculated. A dose contrast index (DCI) was defined as the mean dose to the BTV divided by the mean dose to the PTV (excluding BTV). For healthy tissue, an integral dose, Dint, was defined as the product of mean dose and volume of normal tissue, excluding the PTV. This was reported together with the irradiated volumes at the dose levels of 5, 10, 15 and 20Gy (V5, V10, V15 and V20). Results Overall results are reported in Table 1. When BTV dose escalated up to 200% of PTV prescription, the PTV_CI increase was <8% (from 1.11 to 1.20), proving that SIB strategy was able to reduce the dose to the BTV surrounding volume despite the major dose escalation. Similarly the percentage increase of ID to normal tissues was 11%. The increase in healthy tissues receiving more than 5, 10 ,15 and 20 Gy was about 2%. Deviation from the ideal contrast dose slightly increased with increased BTV dose.
Conclusion We quantified the capability of SIB-VMAT to deliver highly heterogeneous doses in the treatment of large tumors. Despite the major dose escalation in the BTV, the dose conformity to PTV and the integral dose to the normal tissue minimally increased, with a slow increase of dose spillage from PTV to normal tissue. The safe delivery of ablative dose in the central part of the tumor has the potential to greatly improve the palliative effect. EP-1555 Improving inter-planner variability in head and neck (H&N) VMAT H. James1, C. Scrase2, K. Yip2 1 Suffolk Oncology Centre The Ipswich Hospital, Radiotherapy Physics, Ipswich Suffolk, United Kingdom 2 Suffolk Oncology Centre The Ipswich Hospital, Clinical Oncology, Ipswich Suffolk, United Kingdom Purpose or ObjectiveInverse plan optimisation for H&N VMAT is resource intensive. Variation exists between planners when determining optimal solutions. Reoptimisation of sub-optimal plans impacts upon the patient pathway. In our institution class solutions and dose assessment criteria improve consistency in prostate VMAT planning. In this study inter-planner variability was assessed for H&N VMAT. Analysis of plans and shared learning informed the development of optimisation templates to improve consistency and meet clinician expectations.Material and MethodsVMAT plans for a radical tonsil treatment were created by 10 individuals with varying levels of experience. Plans were expected to meet or exceed pre-defined PTV and PORV dose requirements. Planners used their own judgement to determine optimisation objectives and priorities, define dummy structures and assess whether an optimal plan had been produced. Quantitative dosimetric analysis of the plans covered 3 areas – PTV coverage (conformity index (CI), homogeneity index (HI)), PORV doses and dose spill. Parameters were scored against a gold standard and ranked. Plans were independently reviewed by 2 clinicians
Conclusion Although DWA increased the V10-40 of bladder wall, beam-on time, and MU, DWA significantly reduced the mean doses and D1cc of the bilateral femoral heads. DWA also significantly reduced the V10, V20 and V70 of rectal wall. DWA seems to be a promising irradiation technique for prostate cancer. EP-1554 Partially ablative VMAT for large tumors using simultaneous integrated boost: a proof of concept S. Cilla1, F. Deodato2, A. Ianiro1, G. Macchia2, V. Picardi2, M. Ferro2, M. Boccardi2, M. Ferro2, S. Cammelli3, A. Arcelli3, E. Farina3, L. Giaccherini3, G.P. Frezza4, V. Valentini5, A.G. Morganti3 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy 2 Fondazione di Ricerca e Cura "Giovanni Paolo II"Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy 3 Università di Bologna, Radiation Oncology CenterDepartment of Experimental- Diagnostic and Specialty Medicine - DIMES, Bologna, Italy 4 Ospedale Bellaria, Radiation Oncology Department, Bologna, Italy 5 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy Purpose or Objective The aim of this study was to assess the feasibility in the delivery of highly heterogeneous doses to symptomatic large tumor using VMAT technique and simultaneous integrated boost during a short course palliative accelerated radiotherapy. Material and Methods For this dosimetric analysis we selected a patient with a large symptomatic sarcoma. A Planning Target Volume (PTV) and a Boost Target Volume (BTV) were defined as the GTV plus and minus 1cm, respectively. Two different doses were simultaneously delivered to the PTV and BTV according to a dose-escalation protocol in 4 fractions. Five dose levels were planned: Level 1 (basal plan: PTV: 20Gy/5Gy), Level 2 (PTV: 20Gy/5Gy; BTV: 25Gy/6.25Gy), Level 3 (PTV: 20Gy/5Gy; BTV: 30Gy/7.5Gy), Level 4 (PTV: 20Gy/5Gy; BTV: 35Gy/8.75Gy) and Level 5 (PTV: 20Gy/5Gy; BTV: 40Gy/10Gy). The aim was to irradiate the central part of the tumor up to 10Gy/fraction while maintaining the border area of the tumor and the surrounding healthy tissues with <5Gy/fraction. SIB-VMAT plans were generated using Oncentra Masterplan TPS, in the dual-arc modality. The mean dose, D98%, D95% and D2% doses were scored for each target. A conformity index, PTV_CI, defined as the volume encompassed by the PTV 95% isodose divided by the PTV volume, was calculated. A dose contrast index (DCI) was defined as the mean dose to the BTV divided by the mean dose to the PTV (excluding BTV). For healthy tissue, an integral dose, Dint, was defined as the product of mean dose and volume of normal tissue, excluding the PTV. This was reported together with the irradiated volumes at the dose levels of 5, 10, 15 and 20Gy (V5, V10, V15 and V20). Results Overall results are reported in Table 1. When BTV dose escalated up to 200% of PTV prescription, the PTV_CI increase was <8% (from 1.11 to 1.20), proving that SIB strategy was able to reduce the dose to the BTV surrounding volume despite the major dose escalation. Similarly the percentage increase of ID to normal tissues was 11%. The increase in healthy tissues receiving more than 5, 10 ,15 and 20 Gy was about 2%. Deviation from the ideal contrast dose slightly increased with increased BTV dose.
Conclusion We quantified the capability of SIB-VMAT to deliver highly heterogeneous doses in the treatment of large tumors. Despite the major dose escalation in the BTV, the dose conformity to PTV and the integral dose to the normal tissue minimally increased, with a slow increase of dose spillage from PTV to normal tissue. The safe delivery of ablative dose in the central part of the tumor has the potential to greatly improve the palliative effect. EP-1555 Improving inter-planner variability in head and neck (H&N) VMAT H. James1, C. Scrase2, K. Yip2 1 Suffolk Oncology Centre The Ipswich Hospital, Radiotherapy Physics, Ipswich Suffolk, United Kingdom 2 Suffolk Oncology Centre The Ipswich Hospital, Clinical Oncology, Ipswich Suffolk, United Kingdom Purpose or ObjectiveInverse plan optimisation for H&N VMAT is resource intensive. Variation exists between planners when determining optimal solutions. Reoptimisation of sub-optimal plans impacts upon the patient pathway. In our institution class solutions and dose assessment criteria improve consistency in prostate VMAT planning. In this study inter-planner variability was assessed for H&N VMAT. Analysis of plans and shared learning informed the development of optimisation templates to improve consistency and meet clinician expectations.Material and MethodsVMAT plans for a radical tonsil treatment were created by 10 individuals with varying levels of experience. Plans were expected to meet or exceed pre-defined PTV and PORV dose requirements. Planners used their own judgement to determine optimisation objectives and priorities, define dummy structures and assess whether an optimal plan had been produced. Quantitative dosimetric analysis of the plans covered 3 areas – PTV coverage (conformity index (CI), homogeneity index (HI)), PORV doses and dose spill. Parameters were scored against a gold standard and ranked. Plans were independently reviewed by 2 clinicians