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Forward versus inverse planning in oropharyngeal cancer: A comparative study using physical and biological indices
T Sundaram1, M Nagarajan, V Nagarajan
1Department of Radiation Oncology, Valavadi Narayanaswamy Cancer Centre, G. Kuppuswamy Naidu Memorial Hospital, Coimbatore, India.
Context:
Possible benefits of inverse planning.
Aims:
To analyze possible benefits of inverse planning intensity modulated radiation therapy (IMRT) over field-in-field 3D conformal radiation therapy (FIF-3DCRT) and to evaluate the differences if any, between low (6 Million Volts) and high energy (15 Million Volts) IMRT plans.
Materials And Methods:
Ten patients with squamous cell carcinoma of oropharynx, previously treated with 6 MV step and shoot IMRT were studied. V100, V33, V66 , mean dose and normal tissue complication probabilities (NTCP) were evaluated for parotid glands. Maximum dose and NTCP were the parameters for spinal cord.
Statistical Analysis Used:
A two-tailed t-test was applied to analyze statistical significance between the different techniques.
Results:
For combined parotid gland, a reduction of 4.374 Gy, 9.343 Gy and 7.883 Gy were achieved for D100, D66 and D33, respectively in 6 MV-IMRT when compared with FIF-3DCRT. Spinal cord sparing was better in 6 MV-IMRT (40.963 ± 2.650), with an average reduction of maximum spinal cord dose by 7.355 Gy from that using the FIF-3DCRT technique. The uncomplicated tumor control probabilities values were higher in IMRT plans thus leading to a possibility of dose escalation.
Conclusions:
Though low-energy IMRT is the preferred choice for treatment of oropharyngeal cancers, FIF-3DCRT must be given due consideration as a second choice for its well established advantages over traditional conventioan technique.
