Risk-adjusted chemoradiation according to human papilloma viral status for anal cancer: a pilot study.

Background and purpose: HPV-associated or positive (HPV+) anal cancer patients may have better outcome compared to those with HPV negative (HPV-) disease. We report a planned interim analysis of a prospective registry study that tailors chemoradiation (CRT) for anal cancer according to HPV status. Materials and methods: HPV+ patients received de-escalated radiation doses of 45, 50.4 and 55.8 Gy, while HPV- received 50.4, 55.8 and 63 Gy for T1, T2 and T3/T4 disease respectively. Chemotherapy consisted of a single dose of mitomycin-C and oral capecitabine on days of RT. All patients were planned by VMAT following CT, PET/CT and MR simulation. This cohort (n = 24) had a minimum 24-month follow-up. Disease free survival (DFS) and local failure rates (LFR) were compared with 180 patients managed by standard CRT (2 cycles of mitomycin-C and 5-fluorouracil, radiation doses 50.4-63 Gy based on T-category) from 2011-2018. Propensity score comparison was performed using a retrospective to prospective 2 to 1 match based on tumor size and N-category. Results: In the HPV+ cohort (n = 20), there were 2 local failures. Two of 4 HPV- patients failed locally. The 30-month DFS and LFR were 79% and 17% respectively. Similar DFS and LFR were observed in the retrospective (80% and 15% respectively) and matched patients (76% and 16% respectively). No grade ≥3 neutropenia and febrile neutropenia were observed in the registry cohort whereas 19% and 14% respectively were seen in the retrospective patients. Conclusion: De-escalation of CRT for HPV+ anal cancer may result in decreased acute toxicities and similar cancer outcomes compared to standard CRT.

The effect of prone and supine treatment positions for the pre-operative treatment of rectal cancer on organ-at-risk sparing and setup reproducibility using volumetric modulated arc therapy.

BACKGROUND AND PURPOSE: To compare organ-at-risk doses and setup reproducibility using the prone and supine orientations in volumetric modulated arc therapy (VMAT) for rectal cancer. MATERIALS AND METHODS: Seventeen consecutive rectal cancer patients undergoing preoperative radiation were selected and setup in either the prone (N = 8) or supine (N = 9) position. All patients were treated using posteriorly-applied VMAT. Bladder and small bowel dose and cone beam CT (CBCT) reproducibility metrics were retrospectively collected. RESULTS: Dose metrics for bladder and small bowel did not show significant differences between the prone and supine orientations. The prone data had a trend for smaller irradiated volumes than supine for the small bowel at lower doses-V20 (prone: 135 ± 99 cm3; supine: 201 ± 162 cm3) and V30 (prone: 78 ± 71 cm3; supine: 105 ± 106 cm3). At higher doses, the trend reversed as exemplified by the small bowel V50.4 (prone: 20 ± 28 cm3; supine: 10 ± 14 cm3). CBCT data showed that rotational errors in pitch and roll were significantly larger for the prone vs. supine orientation (pitch: 2.0° ± 1.3° vs. 0.8° ± 1.1° p < 0.001; roll: 1.0° ± 0.9° vs. 0.3° ± 0.5°, p < 0.001). CONCLUSIONS: Bladder and small bowel doses were not significantly different when comparing VMAT plans developed for the prone and supine orientations. The supine orientation demonstrated improved setup reproducibility.

Intermediate energy photons (1 MV) to improve dose gradient, conformality, and homogeneity: potential benefits for small field intracranial radiosurgery.

A previously conceived and demonstrated principle of reducing penumbra for small radiosurgical dose fields is here now applied to a multiple beam arrangement in a stereotactic head phantom. In this work it is found that the fourfold reduction in radiological penumbra of small, single 1 MV x-ray fields translates to a more conformal, homogeneous dose distribution in the more complex beam arrangements. The film dosimetry is conducted with a high resolution digital microscope to quantify the sharp dose gradients. Further, the Gafchromic EBT film measurements in phantom are compared to calculations using the Xknife RT3 (Radionics, Burlington, MA) treatment planning software (TPS) with modeled 1 MV beam data. An orthogonal pair of coplanar beams and an 18-beam coplanar arc irradiation both yielded agreement between the modeling within the TPS and the film work. Conventional 6 MV modality is compared alongside 1 MV throughout. The 90%-50% and 90%-10% dose gradients at the intersection of the orthogonal beam pair were 1.7 and 4.7 mm for 6 MV versus 0.5 and 1.3 mm for 1 MV for an identical setup. The 18-beam coplanar arc plan yielded 90%-80% and 90%-50% dose gradients of 0.84 and 2.2 mm for 6 MV versus gradients of 0.29 and 1.36 mm for 1 MV for the midaxial slice coplanar with all beamlet axes. Uncertainties in gradient measurements were +/- 0.15 mm. The 18-beam coplanar beam arrangement represented a worst case scenario for penumbra overlap deteriorating the dose distribution. In brief, 1 MV x-rays provided superior homogeneity, conformality, and dose fall-off to 6 MV for the irradiations examined.