Simulation CTs of up to ten patients with bulky (\>6cm) tumors will be selected. This will be used for optimization of contouring and planning strategy.

Ten patients with bulky tumors (\>6cm) recommended to receive RT with CT and MRI planning will be accrued. MRI DCE sequence (20-30mins) will be added if not requested for clinical use. They will be treated with standard clinical plans. Every effort will be made to include equal numbers of patients (2-3) from head and neck, thorax, abdomen and pelvis. Planning images will be used for the purpose of dosimetric comparison between SBRT-PATHY and CARBON-PATHY radiation plans.

SBRT-PATHY and CARBON-PATHY planning is performed for study purposes only. Patients will be treated according to standard radiotherapy as per institutional policies.

The planning images (CT, MRI) will be anonymized and used for planning purposes only.

Planning CT, MRI

Slavisa Tubin, M.D.

Rebecca Wong, MBChB, FRCPC, MSc, Prof.

This study uses a novel unconventional radiotherapy technique, consisting of high dose PArtial Tumor irradiation targeting exclusively the HYpoxic segment of unresectable bulky tumors delivered either with photons (SBRT-PATHY) or with carbon-ions (CARBON-PATHY) while sparing the peritumoral immune microenvironment (PIM).

This study will be conducted as a two phase study. Phase A is a retrospective study. Up to 10 patients with bulky (\>6cm tumors) previous planned with planning CT with IV contrast will be selected for planning and dosimetry comparison. This is performed to optimize the contouring and planning procedures. Phase B is a prospective study. Ten patients with bulky (\>6cm tumor) requiring radiotherapy, with planning CT and MR with IV contrast will be accrued. Every effort will be made to include equal numbers of patients (2-3) from head and neck, thorax, abdomen and pelvis. Their images will be used for planning and dosimetry comparison.

Patients will be treated according to clinical plans. The study plans will not be used for treatment. Treatment plans for Photon delivery (SBRT-PATHY) and Carbon delivery (CARBON-PATHY) to deliver 30 Gy in three fractions will be planned to be delivered to the BTV will be performed. SBRT-PATHY plans will be generated at the Princess Margaret Cancer Center (PMCC, Toronto, Canada) while CARBON-PATHY plans will be generated at the MedAustron Center for Particle Therapy and Research (W. Neustadt, Austria).

The objective is to compare the dosimetric profile achievable using SBRT-PATHY (using photons) and CARBON-PATHY (using carbon-ions) for unresectable bulky tumors and surrounding tissues.

Radiotherapy Treatment Planning Comparison Using SBRT-PATHY (Photons) Versus CARBON-PATHY for Unresectable Bulky Tumors

The objective of phase A is to optimize the target delineation, planning strategy and techniques for SBRT-PATHY at Princess Margaret and CARBON-PATHY at MedAustron.

a prospective identification of 10 patients who are recommended to receive radiotherapy fulfilling the inclusion criteria. SBRT-PATHY and CARBON-PATHY planning is perfomed for study purposes only. A planning comparison between SBRT-PATHY (using photons) and CARBON-PATHY (using carbon-ions) based on dosimetric consideration achieved for the targeted BTV, non-targeted surrounding NTV (normoxic tumor segment), PIM, regional metastases (i.e. local regional involved nodes and distant metastases located within 15 cm cranial caudal to GTV), regional uninvolved lymph nodes and surrounding organs at risk (OAR) will be performed.

The normoxic tumor segment (NTV) will be created by subtracting the BTV from the GTV, representing the remaining peripheral tumor segment outside the BTV.

The OAR will be delineated on MRT images at the level of the treated area. Particularly normal structures involved by or in the close proximity to the tumor such as vessels, nerves, or hollow organs will be contoured. Contours will be checked and refined on the co-registered simulation CT images.

Abscopal tumor site(s), corresponding to radiographic evidence of the regional (for ex. lymph nodes) metastases, will be delineated on whichever images that clearly demonstrate their presence, including simulation CT or MRT.

Study title	NCT ID	Conditions	Interventions	Eligibility	Organization	Link
Radiotherapy Treatment Planning Comparison Using SBRT-PATHY (Photons) Versus CARBON-PATHY for Unresectable Bulky Tumors	NCT06390657	Cancer	Planning CT, MR...	18 Years -	EBG MedAustron GmbH
Radiotherapy Treatment Planning Comparison Using SBRT-PATHY (Photons) Versus CARBON-PATHY for Unresectable Bulky Tumors	NCT06390657	Cancer	Planning CT, MR...	18 Years -	EBG MedAustron GmbH

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