Target Volume Delineation in Intensity-Modulated Radiation Therapy (IMRT) for Head and Neck Cancer and Correlation With Patterns of Failure
Presenter: Lee, Nancy
Presenter's Affiliation: Dept of Radiation Oncology, Univ of California-San Francisco Medical Center, San Francisco, CA
Type of Session: Scientific
- IMRT delivers highly focused radiation that closely conforms to the three-dimensional shape of the tumor being treated.
- Accurate delineation of the diseased tissues is essential for effective targeting of IMRT in patients with cancers of the head and neck.
- This study compares the volume defined as the target tissues with the patterns of recurrence in patients with cancers of the head and neck treated with IMRT.
- One hundred fifty one patients with histologically confirmed cancer of the head and neck underwent definitive IMRT between April 1995 and July 2001 at the University of California-San Francisco Medical Center.
- Thirty-four patients (28%) received IMRT after complete surgical resection, 7 of which also received cisplatin-based chemotherapy. Most of the post-operative cases were squamous cell carcinomas of the paranasal sinuses.
- Overall, 92 (74%) patients received cisplatin-based chemotherapy.
- During the time interval studied three different techniques of IMRT were used: 1) manually cut partial transmission blocks, 2) computer controlled auto-sequencing segmental multileaf collimator (SMLC), and 3) sequential tomotherapy using dynamic multivane intensity modulating collimator. The most frequently used technique was the SMLC ?stop and shoot? technique.
- The gross target volume (GTV) was defined as any gross tumor visible on imaging studies (magnetic resonance imaging or computed tomography scan) or evident on physical examination. For the treated after resection, GTV was defined as the preoperative gross tumor volume based on imaging studies.
- In both definitive and post-operative cases, the clinical target volume (CTV) included all potential areas of microscopic disease at risk for tumor involvement. The CTV also included a margin for patient motion and set-up errors.
- The average prescription dose to the GTV on definitive cases was 70 Gy. The corresponding dose for post-operative cases was 66 Gy.
- A diagnostic radiologist determined whether the location of a recurrence was either within the GTV or the CTV by comparing the treatment planning CT with post-treatment imaging studies.
- The median follow-up of the group as a whole was 22.0 months (range, 6.1-78.0).
- Overall, 6 patients had recurrences within the GTV.
- Five of the six GTV recurrences were in post-operative cases.
- One patient failed in the CTV.
- No marginal failures were observed.
- The 2-year local control for the group as a whole was 95%, decreasing slightly to 91% at 3 years.
- There was only one recurrence in the patients treated definitively and it was located within the GTV.
- The local control for the group of patients treated definitively was 100% at 2 years and 98% at 3 years.
- Six patients in the post-operative setting recurred of which five were within the GTV.
- The local control for the group of patients treated in the post-operative setting was 76% at 2 years and 64% at 3 years.
- Meticulous delineation of the target volume for successful IMRT treatment of head and neck cancer is crucial.
- A multidisciplinary approach with input from expert neuroradiologist and otorhinolaringologist to the target volume definition is highly recommended.
- The use of this approach in the present series resulted in few recurrences and no marginal failures.
- Most recurrences occurred in the post-operative setting and within the GTV, suggesting that there may be subpopulations of radioresistent tumor cells.
- The accurate definition of target volumes may allow the evaluation of higher doses and their impact on the local control rates. Studies are ongoing to evaluate the roles or CT, MRI, and PET imaging in the deliniation of target volumes. This early study is encouraging for the low rate of local-regional failures with the use of IMRT since this technique typically utilizes tighter margins then are used with standard external beam radiation therapy.
Oncolink's ASTRO Coverage made possible by an unrestricted Educational Grant from Ortho Biotech.