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WE‐AB‐202‐10: Modelling Individual Tumor‐Specific Control Probability for Hypoxia in Rectal Cancer
Author(s) -
Warren S,
Warren DR,
Wilson JM,
Muirhead R,
Hawkins MA,
Maughan T,
Partridge M
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957751
Subject(s) - medicine , anus , radiation therapy , nuclear medicine , hypoxia (environmental) , rectum , colorectal cancer , dosimetry , radiology , cancer , surgery , chemistry , organic chemistry , oxygen
Purpose: To investigate hypoxia‐guided dose‐boosting for increased tumour control and improved normal tissue sparing using FMISO‐PET images Methods: Individual tumor‐specific control probability (iTSCP) was calculated using a modified linear‐quadratic model with rectal‐specific radiosensitivity parameters for three limiting‐case assumptions of the hypoxia / FMISO uptake relationship. 18 FMISO‐PET images from 2 patients (T3N0M0) from the RHYTHM trial (Investigating Hypoxia in Rectal Tumours NCT02157246) were chosen to delineate a hypoxic region (GTV_MISO defined as tumor‐to‐muscle ratio > 1.3) within the anatomical GTV. Three VMAT treatment plans were created in Eclipse (Varian): STANDARD (45Gy / 25 fractions to PTV4500); BOOST_GTV (simultaneous integrated boost of 60Gy / 25fr to GTV +0.5cm) and BOOST_MISO (60Gy / 25fr to GTV_MISO+0.5cm). GTV mean dose (in EQD2), iTSCP and normal tissue dose‐volume metrics (small bowel, bladder, anus, and femoral heads) were recorded. Results: Patient A showed small hypoxic volume (15.8% of GTV) and Patient B moderate hypoxic volume (40.2% of GTV). Dose escalation to 60Gy was achievable, and doses to femoral heads and small bowel in BOOST plans were comparable to STANDARD plans. For patient A, a reduced maximum bladder dose was observed in BOOST_MISO compared to BOOST_GTV (D0.1cc 49.2Gy vs 54.0Gy). For patient B, a smaller high dose volume was observed for the anus region in BOOST_MISO compared to BOOST_GTV (V55Gy 19.9% vs 100%), which could potentially reduce symptoms of fecal incontinence. For BOOST_MISO, the largest iTSCPs (A: 95.5% / B: 90.0%) assumed local correlation between FMISO uptake and hypoxia, and approached iTSCP values seen for BOOST_GTV (A: 96.1% / B: 90.5%). Conclusion: Hypoxia‐guided dose‐boosting is predicted to improve local control in rectal tumors when FMISO is spatially correlated to hypoxia, and to reduce dose to organs‐at‐risk compared to boosting the whole GTV. This could lead to organ‐preserving treatment strategies for locally‐advanced rectal cancer, thereby improving quality of life. Oxford Cancer Imaging Centre (OCIC); Cancer Research UK (CRUK); Medical Research Council (MRC)