A treatment planning comparison of photon stereotactic ablative radiotherapy and proton beam therapy for the re-irradiation of pelvic cancer recurrence.

BACKGROUND: Patients who experience a pelvic cancer recurrence in or near a region that received initial radiotherapy, typically have few options for treatment. Organs at risk (OAR) have often reached their dose constraint limits leaving minimal dose remaining for standard re-irradiation (reRT). However, photon based stereotactic ablative radiotherapy (SABR) has been utilised for reRT with promising initial results although meeting OAR constraints can be challenging. Proton beam therapy (PBT) could offer an advantage. MATERIALS AND METHODS: SABR plans used for treatment for ten pelvic reRT patients were dosimetrically compared to PBT plans retrospectively planned using the same CT and contour data. PBT plans were created to match the CTV dose coverage of SABR treatment plans with V100% ≥95%. An 'as low as reasonably achievable' approach was taken to OAR tolerances with consideration of OAR dose from the initial radiation (using equivalent dose in 2 Gy fractions). RESULTS: Dosimetric comparison of relevant OAR statistics showed a decrease in OAR dose using PBT over SABR in all patients, with equivalent target coverage. The largest statistically significant reduction was seen for the colon D0.5 cm3 with a median reduction from 13.1 Gy to 5.9 Gy. There were statistically significant dose reductions in the median dose to small bowel, sacral plexus and cauda equina. CONCLUSION: PBT has the potential for significant dose reductions for OARs in the pelvic reRT setting compared to SABR. However, it remains unclear if the magnitude of these OAR dose reductions will translate into clinical benefit.

Postoperative (Chemo)Radiotherapy for Oral Cavity Squamous Cell Carcinomas: Outcomes and Patterns of Failure.

AIMS: To determine outcomes after adjuvant radiotherapy for squamous cell carcinoma of the oral cavity and to correlate locoregional recurrence patterns with radiotherapy target volumes. MATERIALS AND METHODS: All patients receiving adjuvant radiotherapy±chemotherapy after surgery with curative intent for oral cavity squamous cell carcinoma between 2007 and 2012 were retrospectively analysed. Locoregional recurrences were reconstructed on the planning computed tomography scan by both deformable image co-registration and by visual assessment. Recurrences were categorised as in-field, marginal or out-of-field if >95%, 20-95%, and <20% of the recurrence volume was encompassed by 95% of the prescription isodose, respectively. RESULTS: In total, 106 patients with a median follow-up of 42 months were included. Oral cavity subsites included oral tongue (54%) and floor of mouth (32%). Thirty (28%) patients received concurrent chemotherapy. Fifty-five (52%) patients received bilateral neck radiotherapy. Two year overall, disease-free, local disease-free, regional disease-free and distant metastases-free survival were 72, 83, 92, 89, 94%, respectively. On multivariate analysis, extracapsular nodal spread was the only factor significantly associated with inferior overall survival. Fourteen (13%) patients have experienced locoregional failure. Of the eight local recurrences at the primary tumour site, four, three and one were classified as in-field, marginal and out-of-field, respectively. Of 10 regional recurrences, one, one and eight were in-field, marginal and out-of-field. There were 7/21 (33%) contralateral regional recurrences in patients with pN2a/b disease who did not receive contralateral neck irradiation; there were 0/21 (0%) and 0/9 (0%) contralateral regional recurrences in patients with pN0 or pN1 disease, respectively, who did not receive contralateral neck irradiation. CONCLUSION: Marginal recurrences highlight the need for generous target volume delineation. Based upon rates of contralateral regional recurrences, a comprehensive approach to target volume selection should be advised for tumour subsites with bilateral lymphatic drainage in the presence of pN2a/b disease.

Patterns of failure after intensity-modulated radiotherapy in head and neck squamous cell carcinoma using compartmental clinical target volume delineation.

AIMS: To determine the pattern of disease recurrence in non-nasopharyngeal head and neck squamous cell carcinoma (HNSCC) patients treated with radical intensity-modulated radiotherapy (IMRT) with or without chemotherapy, and to correlate the sites of locoregional recurrence with radiotherapy target volumes. MATERIALS AND METHODS: In total, 136 patients treated with radical IMRT with or without chemotherapy between 2008 and 2011 for non-nasopharyngeal HNSCC were retrospectively identified. A compartmental approach to clinical target volume (CTV) delineation was routinely utilised during this period and IMRT was delivered using a 5-7 angle step and shoot technique. Locoregional recurrences were reconstructed on the planning computed tomography scan by both deformable image coregistration and by visual assessment, and were analysed in relation to target volumes and dosimetry. RESULTS: The median follow-up was 31 (range 3-53) months. Two year local control, regional control, disease-free survival, distant metastasis-free survival and overall survival were 86, 93, 78, 89 and 79%, respectively. One hundred and twenty of 136 (88%) patients achieved a complete response to treatment and 7/120 (6%) have subsequently had a locoregional recurrence. Analysis of these recurrences revealed five to be infield; one to be marginal to the high-dose CTV; one to be out-of-field. Overall the marginal/out-of-field recurrence rate was 2/136 (1.5%). CONCLUSIONS: IMRT utilising a compartmental approach to CTV delineation was associated with a low rate of marginal/out-of-field recurrence.